World's Number 1 Air Spring.

TABLE OF CONTENTS

PLEASE NOTE The information contained in this publication is intended to provide a general guide to the characteristics and applications of these products. The material, herein, was through engineering design and development, testing and actual applications and is believed to be reliable and accurate. However, Firestone makes no warranty, express or implied, of this information. Anyone making use of this material does so at his own risk and assumes all liability resulting from such use. It is suggested that competent professional assistance be employed for

1 Advantages
2 Terms Air Springs & Suspensions
3 Types Of Air Springs

develol0ed

specific applications.

4 How To Use The Product Data Sheets

23

Application Considerations
6 Basic Principles (Derivation of Formulas)

33
37

7 Sample CalculationsAir Springs & Suspensions

8 Sample CalculaUons: Using A Personal Computer 9 Warranty Considerations

49 63

71

HISTORY
In the early 1930's, the Firestone Tire and Rubber Company began experiments to develop the potential of pneumatic springs. Between 1935 and 1939, several makes of U.S. automobiles were equipped with air springs and extensively tested to prove the potential of automotive air suspension systems. They were never put into production, however, because significant developments in steel spring design gave an improved ride at much lower cost than the air spring system at that time. In 1938, the country's largest manufacturer of motor coaches became interested in using air springs on a new design bus they were developing. Working with Firestone engineers, the first busses were tested in 1944 and the inherent ride superiority of air suspensions was clearly
documented.

In the early 1950's, after several years of intensive product development, the air sprung bus finally went into production. That was the beginning of the Airide(R) air spring success story. The success of air springs in bus applications spurred new interest in truck and trailer applications as well as industrial shock and vibration isolation uses. Consequently, almost all of the busses, most of the Class 8 trucks and many of the trailers on the road today now ride on air springs, and significant advances inthe design of control systems have opened the door to automotive applications as well.

TERMS AIR SPRINGS & SUSPENSIONS

PRESSURE 8 PROCESS TERMS

Absolute Pressure. The pressure in a vessel located in a complete vacuum. Usually determined by adding 14.7 to the gauge pressure. Absolute pressure gauge pressure + atmospheric pressure.
Adiabatic Process. All the calculation variables, volume, pressure, and temperature, change without any heat transfer (not often a real life situation).

perature, change with heat transfer to the air spring structure. To account for this, air spring dynamic operation is calculated by the use of what is known as the polytropic exponent (n). n 1.38 is the 9enerally accepted value for air springs.

AIR SPRING COMPONENT TERMS

Bead. A part of the flexible member that locks the cord structure to an inside reinforcing metal ring and provides a means of sealing the joint between the flexible member and the adjacent structure. Bead Plate. A metal plate closing the top end of the flexible member. It is attached to the flexible member by crimping. It has studs, blind nuts, brackets, or pins to facilitate its attachment to the vehicle structure. A means of supplying air to the assembly is provided as a separate fitting or in combination with an attachment stud. Convoluted type springs incorporate a second bead plate on the bottom to create an air tight unit and to provide a means of fastening the unit to the suspension.
Bead Ring. A metal ring incorporating a shaped cross-section that grips the bead of the flexible member and provides a means of attaching and sealing the bead to a plate or other structure.

Atmospheric Pressure. The average atmospheric air pressure measured at sea level. Normally accepted to be 14.7 pounds per square inch (psi).

Constant Volume With Airflow Process. Volume and temperature constant, pressure changes. This condition applies when load is added or removed from above the air spring over a period of time.

Gauge Pressure. Gas or liquid pressure in a vessel, which is higher than atmospheric pressure. Usually measured by a Bourdon tube gauge in pounds per square inch (psi).
Polytropic Process. All the calculation variables, volume, pressure, and tem-

Bumper. Usually, these are made of rubber, plastic, or rubber and fabric materials. They are used to support the vehicle when there is no air in the air springs, when the vehicle is not in use, or when there is a system failure on the road. They will also, to some degree, cushion the shock of very severe axle force inputs to prevent damage to both the Airide(R) spring assembly and to the vehicle.
Clamp Ring. A metal band placed near the end of a beadless flexible member. It is swaged tightly in place to secure the beadless flexible member to the upper end cap and piston.

Piston. A metal or plastic component of the air spring assembly usually placed at the lower end of the flexible member and used to both support and provide a surface for the flexible member to roll on. It also provides a means for attaching the assembly to the mounting surface. Pistons with tailored contours may be used to obtain air spring characteristics to meet special performance requirements.

Upper End Cap. A plastic or metal component containing an air entrance and a means of fastening or positioning the air spring assembly to the adjacent mounting surface. The air entrance may be combined with a mounting stud.

Flexible Member. The fabric-reinforced rubber component of the air spring assembly.
Lower End Closure. Usually a metal
cup-shaped component used to close off and seal the lower end of reversible sleeve type air springs. It is frequently molded to the flexible member. It generally has a blind nut which allows it to be secured to the piston and/or lower mounting surface by the use of a long bolt. Larger diameter end closures may have mtfltiple studs allowing them to be bolted directly to the piston.

Assembly. This includes the flexible member, which may include an end closure, upper bead plate, piston, or lower bead plate with an internal bumper. See illustration on page 11.

Assembly Volume. The internal working air volume, exclusive of any external working volume.

Bumper Volume. The space taken up

inside the air spring assembly by the bumper. See Bumper Volume Chart on page 36.

Compression Stroke (Jounce). The reduction in heioht from the normal desion heioht of the sprino as it cycles in dynamic operation.
Curb Load. The normal minimum static load the air spring is expected to support. It is a zero payload condition, but includes that portion of the unloaded vehicle that is supported by the axle. It is this axle load divided by the number of air springs working with the axle and adjusted according to any lever arm ratio incorporated in the suspension.

Dynamic Force. The instantaneous supporting force developed by the air spring during vehicle motion. It is this constantly changing force that creates the spring rate, suspension rate, and in combination with the normal vehicle load on the spring, creates the suspension system's natural frequency.
Effective Area. The actual working area perpendicular to the output force of the spring. It is not the diameter of the spring. This working area, when multiplied by the gauge pressure in the spring, produces the correct output force. Conversely, dividing the measured output force of the spring by the measured internal gauge pressure obtains the correct effective area. In many cases, this is the only practical way to obtain it. Extension Stroke (Rebound). The increase in height from the normal design height of the spring as it cycles in dynamic operation. Reservoir Volume. Any working air volume located externally from the air spring assembly, but functioning with the spring.

Design Load. This is the normal maximum static load the air spring suspension is expected to support. It is the rated axle load divided by the number of air springs working with the axle and adjusted according to any suspension lever arm ratio incorporated.
Design Height. The overall height of the air spring as selected from the characteristics chart design position range. The air spring selected should provide for adequate jounce and rebound travel for the proposed suspension. The design height would be the starting position for calculating the spring and suspension dynamic characteristics.

SUSPENSION RELATED TERMS

Height Sensor. An electronic device that senses the position of a suspension or other mechanical device. The output signal from this device is sent to a control circuit which then exhausts or adds air to the air spring through a solenoid valve. Leveling Valve. A pneumatic valve that senses the distance between the vehicle frame and the axle via a mechanical linkage which adds or exhausts air pressure to maintain a constant vehicle height.

Sprung Mass Natural Frequency. The speed of vertical oscillations of the suspended vehicle sprung mass. Can be expressed in cycles per minute (cpm) or cycles per second (hertz). Sprung Mass (Weight). That part of the vehicle structure and cargo that is supported by the suspension.

Unsprung Mass. That part of the suspension that is not supported by the spring (e.g., trailing arm, axle & wheels, air spring, etc.).

OUTER COVER

(R)

Inner Liner. An inner liner of

calendered rubber.

An air spring is a carefully designed

rubber and fabric flexible member which contains a column of compressed air. The flexible member itself does not provide force or support load; these functions are performed by the column of air. Firestone air springs are highly engineered elastomeric flexible members with specifically designed metal end closures. The standard two-ply version is made up of four layers:

Frst Ply. One ply of fabricreinforced rubber with the cords at a specific bias angle.

Second Ply. A second ply of fabricreinforced rubber with the same bias angle laid opposite that of the first ply.

Outer Cover. An outer cover of

calendered rubber.

Although the two-ply air spring is standard, many of our air springs are also available in fourJply rated construction for use at higher pressures. Each air spring's flexible member is identified by a style number, which is molded in during the curing (vulcanization) process. Examples would be 16, 22, 313, 1T15M-6, etc. Ths identfies only the
rubber/fabric flexible member.., not the

complete assembly.

10

IEVERSIBLE SLEEVE STYLE AIR SPRING WITH CRIMPED BEAD PLATE

Stud. Mounting stud. Usually
1/2"-13 UNC.

Combination Stud. Combination UNF mounting stud with NPT internal air entrance.
3/4"-16

9 gauge (.49") carbon Bead Plate. for corrosion resistance.

steel, plated Permanently crimped to the flexible member to form an airtight assembly which allows for leak testing before the unit leaves the factory.

B approximately
system.

Flexible Member. Wall gauge is .25 inches. See page 9 for detailed information.

Bumper (Optional). An internal device to prevent damage to the air spring during times when no air is in the

U End Closure. made of steel and permanently molded to the flexible

This is is member (except for 1T19 series air springs).

SERVICE ASSEMBLY
On Firestone's reversible sleeve style Airide (R) air springs, the flexible member, with cured-in end closure and bead plate, is a separate sealed unit. This unit is called a Service Assembly, and may be purchased without the piston as an economical replacement for existing air springs in truck and trailer suspensions.

composites. The threaded holes in the piston are used to secure the assembly to the mounting surface.
Piston Bolt. Attaches the piston to the flexible member end closure. For mounting, a long bolt may be used coming up through the mounting surface and attaching to the end closure. Or, a short bolt may be used to attach the piston to the end closure.

1 Piston. May be made of aluminum, steel, or engineered

NOTE: There are several different mounting options available for most air springs. Therefore, always specify both the style number and the complete Assembly Order Number (AON). For example, T15M-6, Assembly Order Number W01-358-9082. Both numbers are published on the Product Data Sheets for individual air springs.

12

Bead Plate. 9 gauge (.149") carbon

steel. Plated for corrosion resistance. Permanently crimped to the flexible member to form an airtight assembly which allows for leak testing before the unit leaves the factory.

0 Fleble Member. Wall gauge is .25 inches. See 9 for

approximately detailed information.

page

Bumper (Optional). An internal device to prevent damage to the air spring during times when no air is in the system.
Flush Air Inlet. 1/4" NPT is standard. 3/4" NPT is also available for most parts.

|3

Blind Nut. 3/8"-16 UNC thread x 5/8" deep (two or four per plate, depending upon the part size). Used for mounting the part.

D stranded

Girdle Hoop. A solid steel ring or wire ring cured to the flexible member between the convolutions.

NOTE: There are several different mounting options available for most air springs. Therefore, always specify both the style number and the complete Assembly Order Number (AON). For example, Style #22, Assembly Order Number W01-358-7410. Both numbers are published on the Product Data Sheets for individual air springs.

14

The larger convoluted parts are available with bead rings or permanently attached plates called, "rolled plates." Rolled plate assemblies may offer an advantage over the bead ring parts because installation is much easier (they attach the same way as the bead plate parts). When installing the rolled plate parts, a backup plate as large in diameter as the bead plate must be used. This plate should be a minimum of 1/2" thick. The blind nut and air entrance locations of rolled plate assemblies are available from Firestone.

Ar
l

Inlet. 3/4" NPT is standard.

Blind Nut. 1/2"-13 UNC thread x 3/4"

deep is standard.

B Upper Bead plated

Plate. 6-gauge (. 194') for corrosion resiscarbon steel, tance. Permanently attached to the flexible member with a clamp ring (D) to form an airtight assembly. Allows for leak testing before the assembly leaves the factory.

Clamp Ring. This ring is crimped to the bead plate to permanently attach it to the flexible member. It is also plated for rust protection.
Girdle Hoop. Solid steel type cured to the flexible member between the convolutions

Fllexible Member. Wall gauge is approximately .25 inches (see page 9 for construction).

Lower Bead Plate. Usually the same as the upper bead plate, except without the air inlet.

16

Mounting Plate. Not included. See page 21 for material, machining recommendations and installation instructions.

Bead Ring Bolt. May be one of four varieties included with air spring assemblies. See chart on page 21.

17

Nuts &

Lock Washers. Included with air spring assembly.

Flexible Member. Wall gauge is approximately .25 inches.

D Girdle Hoop. Wire wound type shown, molded into the flexible member.
Bead Rng. Steel countersunk type shown. May also be of
a second stamped steel variety or made of aluminum (see page 2:l).

The flexible member is available separately as a replacement on convoluted bead ring assembfies.

REVERSIBLE SLEEVE AIR SPRINGS BEAD RING ASSEMBLIES

Mounting Plate. Not included. See page 21 for material, machining recommendations and installation instructions.

D Bead Ring Bolt. May

with air

be one of four varieties included with the air spring assembly (see chart on page 21).

Nutsspring & Lock Washers. Included assembly.

Flexible Member. Wall gauge is approximately .25 inches.

End Closure. This is made of steel and is permanently molded into the flexible member (except for the 1T19 style air spring).

'

D Piston. May be made of aluminum, steel, or engineered

Bead Ring. Steel countersunk type shown. also

composites. The threaded holes in the piston are used to secure the assembly to the mounting surface.

May be of a second stamped steel variety or made of aluminum. (See page 21).

The flexible member with cured-in end closure is available separately as a replacement.

20

STEEL BUTTON HEAD BEAD RING

STEEL COUNTER SUNK BEAD RING

ALUMINUM RIBBED NECK BEAD RING

ALUMINUM ALLEN HEAD BEAD RING

J
Length

Use

1/4"

Cap

Screws
cluded)

Custom_er
Supplies

Supplies

Pate

r-

Length

Plate

Optional Shoer Length Ribbed Neck Bolt

Optional Bolt Length (in)
1%

Standard Bolt Length (in)

17/8

Standard Bolt Length (in)

1%

Standard Bolt Length (in)

(il/4)

Standard Effective Length (in) Standard Effective Length (in) Standard Effective Length (in) Optional Effective Length (in) (.66) 1.28 1.22 1,28 Standard Order Number (bolt only) W01-358-3607 Thread %6-24UNF
Standard Order Number (bolt only) W01-358-3625 Standard Order Number (bolt only) W01-358-3620

Optional Order Number (bolt only)

(W01-358-3618)
Thread %-24 UNF

Thread %6-24UNF

Thread %-24UNF
Tightening Torque (ft-lb) 28 to 32

Tightening Torque (ft-lb) 17 to 22

Tightening Torque (ft-lb) 17 to 22

Tightening Torque (ft-lb) 28 to 32

WITH BEAD RINGS

When using bead rings, you will need to fabricate your own mounting plates. Hot or cold rolled steel provides satisfactory mounting surfaces with finishes of 250 micro inches, if machined in a circular fashion, or 32 micro inches when ground (side-to-side). The thickness of

mounting plates depends upon the application. The plates must be strong enough and backed by structural members to prevent bowing of the plates when subjected to the forces or loads involved. The flexible member provides its own seal, so "O" rings or other sealants are not required.

iNSTALLATION

3
Follow this technique for assembling a bead ring style flexible member to the mounting plate: Make certain that the flexible member bead is properly seated under the bead ring. Please note that uniform successive tightening of the nuts is important to seat the rubber bead properly to the mounting plate around its full circumference.

Insert the bolts into the bead ring, which has already been attached to the flexible member.
2
Slip all of the bolts, which protrude through the bead ring, into the mating holes of the mounting plate and attach the lock washers and nuts. Finger tighten all nuts to produce a uniform gap between the bead ring and mounting plate all the way around. The bolts will be pulled into place by the action of tightening the nuts. When using aluminum bead rings, it may be necessary to lightly tap the ribbed neck bolts with a small hammer to engage the splined portion into the bead ring.

4
Tighten all nuts one turn each, moving around the circle until continuous contact is made between the bead ring and mounting plate.

5 Torque all nuts to the torque specifications shown in the chart on the previous page, going at least two complete turns around the bolt circle.

NOTE: Consult Firestone for proper selection of bead ring type.

22

1T15M-11

The part description is shown in the

upper right hand corner. The standard piston is used unless noted below the part description.

Mounting arrangement of the piston's threaded holes or stud(s).

Piston base diameter.

D Bead plate diameter.

Bead plate mounting arrangement
and air inlet location and size.

The last four digits of the Assembly Order Number, W01-358-9320.

H Approximate weight of the assembly.

Piston height.

Alignment: the relationship of the bead plate mounting to the piston mounting.

D Maximum psig
100

rubber part diameter at and minimum height.

Piston body diameter.

Bumper and reference number.

"B" dimension. The distance from the mounting surface to the rubber loop at 100 psig.

STATIC DATA
Recommended Design Position Stalic Pressure 10-100 Psig

The Maximum Rebound Height is the maximum extended position of the air spring before the flexible member is put in tension. Some means of preventing the suspension extending the air spring past this height must be provided to prevent damage to the air spring. Shock absorbers are typically used, however chains, straps, and positive stops may also be used.

The Volume Curve is a plot of the data points obtained by measuring the volume of exhausted liquid as the part is compressed from maximum to minimum height while maintaining a regulated pressure of 100 psig in the air spring. (This is the volume without a bumper). The Shaded Area (24" to 28") on the left side of the chart is a range of heights in which the air spring is not normally used except during unloading as the axle goes in rebound. Do not use in ths range of heights for applying a force. The number, B-0689, is the Test

D The Design Position Range shows the recommended operating range of

static heights. This range is 16 to 20 inches for the 1T15M-11, as shown on the chart. Use outside this range may be possible, however, Firestone should be consulted.

Request Reference Number.

The Constant Pressure Curve is the

Load trace obtained as the part is compressed from the maximum height to the minimum height while maintaining a regulated constant pressure in the part. A series of constant pressure curves, 20 psig through 120 psig are shown at 20 psi increments. The 120 psig curve is shown for reference only, as most parts are limited to static design pressure of 100 psig.

Height

100 Psig Data Load Volume

B-Dim

(In)

(Lbs)

(Cu In)

(In)

Dynamic Characteristics at Various Design Heights

Pressure
Height(In)

(Lbs)

(Psig)

Rate Natural Frequency (Lbs/In)

Dynamic Load vs Deflection

APPLICATION CONSIDERATIONS

Obtaining the maximum performance and life from Airide(R) air springs requires proper application.

AIR SPRING CHOICE CONSIDERATIONS

The air spring design height should be kept within the recommended range to get optimum performance and durability. Select a spring that carries the suspension rated load in the range of 80-90 psig. This gives you an air spring that has the optimum characteristics for your application (i.e., natural frequency, size, cost, etc.). The compressed height of the air spring in the suspension must not be less than the minimum height of the air spring chosen, as shown on the Product Data Sheet. Conversely, the extended height of the air spring in the suspension must not be greater than the maximum extended height of the air spring chosen (refer to the Product Data Sheet).

with the centers of both bead plates aligned. The bead plates can be angled so that a good relationship between compression and extension travel can be achieved with appropriate bumper contact. The maximum extended height should never be exceeded. Under normal conditions, the included angle between the bead plates should not be greater than 20 however with Firestone's approval, angles of up to 30 may be acceptable on some models.

INSTALLATION CONCERNS (CONVOLUTED

AIR SPRIHGS)
To achieve the maximum lifting force, and produce a minimum of horizontal forces, convoluted air springs should be positioned at the normal design height

Reversible sleeve air springs incorporating internal bumpers should have the bead plate and piston parallel within 3 to 5 at bumper contact height. Normally, the piston is angled at the design position so that a good relationship between compressed and extended travel can be achieved. Reversible sleeve air springs which do not have an internal bumper may have the piston angled to allow full compression stroke without the flexible member being pinched between the piston and the bead plate.

Flexible member

must

not

against

rub itself

Reversible sleeve type air springs may stroke through an arc, but care must be taken to prevent the flexible member from rubbing internally against itself where it rolls over the piston.

Plastic pistons should normally be fully supported over the entire base surface. Exceptions should be reviewed by

Frestone.
Metal pistons used with 1T15 size or smaller assemblies may be mounted on a flat beam surface at least three inches wide which extends the full diameter of the piston base. Bead plates should be supported by a back-up plate the size of the bead plate. Under certain circumstances, the bead plate may be supported by a minimum three-inch wide beam. These mountings should also be reviewed by Firestone. If a single long fastening bolt is used to clamp the air spring end closure and the piston to the trailing arm, it should be grade 5 or above, and tightened according to the appropriate value shown in the chart on page 35. If the piston is tipped more than 5 degrees, some means should be provided to locate the piston.
34

:ASTENER ''IGHTENING SPECIFICATIONS

Description
Bead ring nuts on bolts

OPERATIONAl. CAUTIONS
Air spring failure can be caused by a variety of situations, including internal or external rubbing, excessive heat and overextension. For further details, refer to Section 9, Warranty Considerations. Bead plates are normally fully supported, however, mounting the bead plate directly to the frame raft, or other mounting surface with less than full support, may be possible.

Size
5/16-24

Torque
(Ib-ft)

17-22
28-32
15-20

Bead ring bolts and nuts

Bolts in blind nuts in bead plates
End of adapter studs in blind nut

3/8-24
3/8-16

3/8-16
1/2-13

15-20 25-30 25-30 25-30

Nut on end of adapter studs

Studs on bead plates or blind nuts
Bolt to attach piston base to lower mounting surface

1/2-13 or 1/2-20
1/2-13

The normal ambient operating temperature range for standard vehicular air springs is -65F to +135F.

Nut on air entrance

stud

UMPERS
3/4-16
1/4

40-45

NPT air supply fitting

Nut on end closure lower mounting

& up

17-22
45-50

3/4-10

In general, bumpers are used to support the vehicle weight to prevent damage to the flexible member during times when no air is in the system. They are also used as stops when the axle is raised by a lift unit. In applications that require frequent bumper contact, consult Firestone.

35

Nurnr
3073 3136 3147 3155 3157 3159 3162 3209 3285 3294 3350 3386 3404 3604 3691 3777 4457 4518 4519 4964 7725

48.5 8.8 28.5 70.3 93.0 41.0 40.4 65.3 43.4 33.9 19.7 9.4 34.6 37.7 11.3 31.0 48.0 22.1 28.2 1.6 32.2

CAUTION: Contact Firestone for specific

bumper applications

36

BASIC PRINCIPLES

iNTRODUCTION
The fundamental concept of an air spring is a mass of air under pressure in a vessel arranged so that the pressure exerts a force. The amount of static force developed by the air spring is dependent on the internal pressure and the size and configuration of the vessel. The vessel is defined in this manual as the Airide(R) spring by Firestone or air spring. Dynamic force is the result of internal pressure changes and air spring effective area changes as height decreases (compresses) or increases (extends). The amount of pressure change for a stroke depends on volume change compared to total volume at equilibrium position. For the convoluted type, effective area change for a stroke depends on where in the total travel range the motion takes place. For the reversible sleeve type, the shape of the piston, size of the piston related to the flexible member diameter, and cord angle built into the flexible member all have an influence on effective area. The effective area can be arrived at by taking the longitudinal static force developed at a specified assembly height and dividing this force by the internal pressure (psig) existing in the air spring at that height. This method is used to develop the static effective areas used in dynamic rate and frequency calculations.

EFFECTIVE AREA
Effective area is the load carrying area of the air spring. Its diameter is determined by the distance between the centers of the radius of curvature of the air spring loop. The loop always approximates a circle because the internal air pressure is acting uniformly in all directions, so that only the area inside the centers is vertically effective. For a convoluted air spring, the effective area increases in compression and decreases on extension. For a reversible sleeve air spring, the effective area is constant while operating on the straight side of the piston, increases when working on the flare of the piston in compression, and decreases when the rubber part lifts off the piston in extension. When a vehicle having air springs in its suspension is at rest, and then load is added or removed, the height control valve operates to add or remove sufficient air in the air spring to maintain the set air spring overall height. This then increases or decreases the pressure in the air spring the amount needed to provide the required lifting force to match the current downward force created by the new load condition, and equilibrium is again reached.

"
+

EFFECTIVE DIAMETER

EFFECTIVE DIAMETER

EFFECTIVE DIAMETER

Convoluted
Air Spring

Reversible Sleeve Air Spring

Change In Effective Diameter

Change in
Effective Diameter

..

Pressure Load (supporting force) Pressure x Area

Effective area

Load

38

SPECIAL

CNANG|S

SAT|

Constant Temperature (Isothermal)

Non-flow process, specific heats assumed constant. Subscripts 1 and 2 refer to the initial and final states, respectively.

P P

V V

This requires very slow movements not normally applicable to air spring operation.

P T V

Absolute Pressure Absolute Temperature Total Volume

Q Reversible Adiabatic (Isentropic)

PVk pava

Constant Volume (Isochoric)

This is an unattainable process due to the nature of the flexible member, however, at static conditions, the change in pressure may be calculated for a change in temperature.

This is defined as a process with no heat transferred to or from the working fluid. This is a theoretical process not attainable with pneumatic springs, however, for rapid deflections, it is closely approached, k=1.404 for air.

U Constant Pressure (Isobaric)

Dynamically, the only way to maintain constant pressure is in combination with infinite volume and is generally not useful.

39

Polytropic

PV n- Constant
This process usually represents actual expansion and compression curves for pressures up to a few hundred pounds. By giving "n" different values and assuming specific heats constant, the preceding changes may be made special cases of the polytropic change. Thus for:

and

T2

(VI/n-1 -)

(n-1)

P)

n nn-n-

I, PV Const. (Isothermal) k, pvk= Const. (Isentropic) Const. (Constant Pressure) 0, P Const. (Constant Volume) 0% V

The principal formulas for air compression up to a few hundred pounds pressure where lnk are:

During air spring dynamic operation, the pressure, volume and temperature change instantaneously. The air spring flexible member structure also changes depending upon the specific configuration. As a result, air springs operate in the range lnk, however, a generally acceptable value for "n" is 1.38 for normal vehicle operation.

Note: Shadow boxes

are

used to designate important formulas.

40

U
E
"5

L Po (A) L Po (AD
Pg Pge
Gauge Pressure at L Gauge Pressure at Le
Effective area at Lc Effective area at Le

Where:

: Lc
o

A Ae
ALe
k
e

',- Ah e- Ah c-'
Deflection

setting Ahc

Ahe- .5 inch

Extension Compression

U
D

K- Po(A)- Poe(Ae)

Rate is the slope of the tangent at the equilibrium position. For small increments of deflection, rate equals the load change per unit deflection. (The slope of the chord line through Lc and Le is parallel to the tangent at L for small deflections.)

Po -Pa-14.7 Poe Pae-- 14.7

P Pe
14.7

Where:

Absolute Pressure at Lc Absolute Pressure at Le Atmospheric Pressure

K U Where:
K

(Lc- Le)/(Ahc + Ahe)

Rate (Load per unit deflection)
Load at compression travel Load at extension travel Height change, compression Height change, extension

!i

now using the polytropic gas law and n- 1.38

L Le
Ahc Ahe
41

Where:

Pal
V V V

Absolute pressure at equilibrium position Volume at equilibrium position Volume at Lc Volume at

substituting

in

Pge

PalkTT
Il
K

-14.7

now substitute

in

Pgc(Ac)- Pe(Ae)

Then, grouping terms, this becomes the general rate formula for air springs.
.38

Ae/TTe

14.7(A Ae)

ATURAE.

REQU|NCY

Where-

W- Weight, pounds
Since the air spring has a variable rate and essentially a constant frequency, it is helpful to calculate the natural frequency when evaluating characteristics. When considering a single-degree-offreedom system (undamped), the classical definition of frequency s as follows:
Note: The period of free vibration (which is the reciprocal of frequency,) is the same as the period of a mathematical pendulum, tle length of which is equal to the static deflection of the spring under the action of load W.
f_

Acceleration of gravity, 386 inches per second

Substituting:

cpm

co 2

ands02= K

cpm
This is normally rounded to.

Where: Frequency, cycles per second f Circular frequency, c0 radians per second K Rate, pounds per inch m- Mass, pound seconds per inch
Then:

Where.

K- Rate W- Weight (load)

Also since:

Also.

W
g

W K

de (effective deflection)
cpm

188 =

43

Effective deflection (dE) has no physical significance, however, has mathematical meaning. It is defined as load divided by rate and is graphically explained below.
Variable Rate Spring

vs. the spring located fore or aft of the wheel. Note the distance to the spring is always 'A" whether located forward or aft of the axle.
Schematic representation of a trailing arm suspension:
Wheel
1111///I//

Load Deflection Curve

Tangent

Spring
ZZ4/l/ll//

Lw

Ls

Deflection

Rate Load- Rate x de

Note: For a constant rate spring, d e and the deflection from free height are equal.

de

Load

Where:

Lever Arm Ratio LAR

LAR- Distance to spring

Distance to wheel

A B

And:

SPRING MASS SYSTEM WITH LEVER ARM

The rate and frequency at the wheel (axle) are the same as that of the spring only if the centerline of the spring is located on the centerline of the wheel. The following is a derivation of the rate and frequency relationship at the wheel

I Ls
Zs

Rate at spring
Load at spring Deflection at spring

For an equivalent spring at the wheel: Kw Rate at wheel

L
Zw

Load at wheel Deflection at wheel

T| R|IT|ONSH|P

Solving for Lw

Balancing moments about the pivot

LA- LwB
LW

Lw
LAR

Also.

Kw
Load

Rate x de

So.

FREQUENCY

R|T|ONSH|P

Solving for Kw

Lw
And:

cpm

D
D
L KZ

fw 188

cpm

substitutingU in D

from the natural frequency derivation where f Frequency at spring fw Frequency at wheel Also: LsA- LwB from

Solving for Ls

now using

Kw-Ks

and substitute in

from

L
now substitute fs from

Or':

fw fs(LAR)
So"

F'ecen,

w- F,'equen t in x LA/

/
,46

Polytropic Gas Law

Dynamic Air Spring Rate

K Pal Ac

Ae

"J[4

7(Ac Ae)

Natural Frequency

Lever Arm Considerations

LAR_Distancetospring_A
Rate

at wheel

Rate at sprin x (LA)

Frequency at wheel

Frequency at spring x (LAR)I/

48

SAMPLE CALCULATIONS: AiR SPRINGS & SUSPENSIONS

CA[.CUET|NG DYNAH|C

AND :REQUENCY
The dynamic rate of an air spring over a plus and minus 1/ inch stroke is calculated using Formula 8 on page 42, substituting values as follows:

For example, find the air spring rate of the 1T15M-11, W01-358-9320 at an 18 inch design height and a load of 7000 pounds. See the Product Data Sheet for the necessary information.
The effective area on the 100 psig curve is calculated:

Where.

Rate (lb/in)
Absolute pressure (psia) at design position Gauge pressure (psig) at design position plus 14.7- Pgl / 14.7
Effective area (ins) at design position Load (lb) / Pressure (lb/in s)

Pal-

A1-

Load

7146
100

Pressure

71.46 in

Also calculate A and A.

Ac AeV1

Effective area (in s) at 1/ff inch below design position Load (lb) / Pressure (lb/in s) Effective area (in s) at / inch above design position Load (lb) / Pressure (lb/in s)

A 7146 100 A
7146 100

71.46 in

71.46 in

Internal volume at design position (in

Internal volume at / inch below design position (in

Then calculate the pressure at 7000 pounds:

Vc

7000 71.46

97.96 psig

Ve
49

Internal volume at /ff inch above design position (in

Then calculate the rate:

K-Pal Ac

c -Ae)

-14.7(Ac-Ae) -14.7(71 46-71 46)

1170.2

-71.46

1244.46

677

lb/in

Now calculate the frequency:

f-188K-1881677
W
f- 58.5 cpm

7000

Note: These are the same values shown in the Dynamic Characteristics Chart on the Product Data Sheet at 18 inches and 7000 pounds.
50

The curves on the Dynamic Load vs. Deflection Chart (Section 4) can be calculated using the formulas developed in Section 6. It is helpful to construct a table of values as shown below.

Static

Height
(in)

Load

(lb)

Volume (cu in)

Effective Area (sq in)

Absolute
Pressure (psia)

Pressure (psig)

Gauge

Dynamic

Load

OrS

(Ib)

Line

21

Line Line

"15

The 1T15M-11 on an M-9 piston is used for this example (W01-358-9320). Refer to that Product Data Sheet.
Conditions selected: 4000 lb Air spring load 18 inches Design height

Line
Line

Line

U D D

is the selected design condition. is the data for 3 inch compression.

is the data for 3 inch extension.

Find:

Dynamic load at + 3 inch compression Dynamic load at- 3 inch extension

Note: For loads between constant pressure curves, calculate the effective area By using the load on the closest constant pressure curve. Then calculate the pressure By dividing the design load By the effective area.

Line

entries are determined as follows (Design).

Static Load, This value is obtained on the closest constant pressure curve, 60 psig in this case, at the 18 inch design height. Refer to the Static Load Deflection Curve.

L- 4200
Volume, This value is taken from the 100 psig Data Table at 18 inch height

V1

1207.89 cu in

Effective Area, Calculated at 60 psig and 18 inch height.

Load

Pressure

4200 60

70 in

Gauge Pressure, The Design Load divided by the effective area.

j1

L A

4000 70

57.14 psig

Absolute Pressure, Gauge pressure / 14.7.

Pal Pgl + 14.7

57.14 + 14.7

71.84 psia

Dynamic Load at point 1, equals the Design Load

4000 lb.

Enter these values in the data chart constructed.

52

Now calculate the values for Line

(3 inch compression):

Static Load, From the 60 psig constant pressure curve and 15 inch design height. L- 4200 lb

Volume, From the 100 psig Data Table at 15 inch height. V2 981.62 cu in
Effective Area, At 60 psig and 15 inch height. 4200 Load 70 in A2 60 Pressure

Absolute Pressure, Use the polytropic gas law.

P2-PI

-71.84

9-B-

P2

95.65 psia

Gauge Pressure, Absolute pressure- 14.7.

P, Pa

14.7

95.65

14.7

80.94 psig

Dynamic Load, Effective area x pressure. D L2 P, x A- 80.94 x 70- 5666 lb

G's, The ratio of Dynamic Load to Design Load.

DL2 L

5666 4000

1.42

Enter these values in the data chart constructed.

Now calculate the values for Line

(3 inch extension):

Static Load, From the 60 psig constant pressure curve and 21 inch design height.

L- 4000 lb
Volume, From the 100 psig Data Table and 21 inch height.

V:- 1419.72 cu in
Effective Area, At 60 psig and 21 inch height.

A3

Load

Pressure

4000 60

66.67

Absolute Pressure, Use the polytropic gas law.

P,

(Vl/n
z-:-.

V3

71.84

1207"89 1419.72

138

57.48 psia

Gauge Pressure, Absolute pressure- 14.7.

P. P- 14.7
DL

57.48- 14.7

42.78 psig

Dynamic Load, Effective area x pressure.

P., x A,

42.78 x 70

2852 lb

G's, The ratio of Dynamic Load to Design Load.

DL
L

2852 4000

.71

A plot of the dynamic load points vs. height will give the curve shown on the Product Data Sheet, Dynamic Load vs. Deflection Chart with a starting point of 18 inch height and 60 psig.
The completed table of values is shown below.
Static

Height
(in)

Load (Ib)

Volume (cu in)

Effective Area (sq in)

Absolute Pressure
(psia)

Gauge
Pressure (psig)

Dynamic

Load (Ib)

a's

Line
Line Line

21

4000

1419.72

66.67
70

57.48 71.84 95.65

42.78

2852 4000
5666

0.71 1.0 1.42

D 18
Q
15

4200 4200

1207.89 981.62

57.14 80.94

70

55

TRAILING ARM SUSPENSION

CALCULAT|ONS

The trailing arm design is a common truck and trailer air suspension. The air spring does not carry the same load that is applied at the wheel (axle). The formulas developed in Section 6 are used. One method of obtaining a trial suspension design follows for a 20,000 lb axle, using a 1T15M-6 reversible sleeve air spring at 13 inch height. Determine the necessary trailing arm ratio needed to support the axle design load within the air spring maximum allowed static pressure of 100 psig which creates a lifting force of 7,045 lb at a 13 inch height. See Product Data Sheet (W01-358-9082).

FRAME

WHEEL

Assume an unsprung weight of 800 lb

Load at wheel Lw

(20,000- 800) + 2

9600 lb.

LAR

Lw Ls

9600 7045

1.36 using the M-6 at 100 psig

For this example a 90 psig operating pressure will be used.

LAR

9600 Lw ---1.52 using the M-6 Ls 6340

at 90 psig

Note, the 6340 lb at 90 psig is calculated by multiplying the pressure ratio times the load at 100 psig, or:
90 --x 7045- 6340 lb 100

56

Now using the maximum OD of the M-6, 12.6 inches, and an assumed axle diameter of 5 inches plus a minimum clearance of one inch, calculate the dimension "C" shown in the illustration on page 56:
C
(1/2 x OD air spring / 1/2 x axle diameter)
--//

clearance

/1-9.8inch

Calculating dimension "C" in this manner places the air spring as close to the axle as possible, which provides-the lowest rate and frequency at the wheel (with the air spring aft of the axle).

Now calculate dimensions "A" and "B" with LAR- 1.52 and C -9.8.

LAR-A-1.52-B/C-B/9"8 B B B
1.52B- B- 9.8

9.8 .52

18.85 inch

Then determine A.

A- B / C

18.85

9.8- 28.65 inch

Note that with a given "B" dimension (e.g., 21 inches) determined by other
factors, proceed as follows:

LAR 1.52

A B
1.52 x 21 31.9

A- 1.52 B

Then check for clearance at the axle:

A- B- 31.9- 21

10.9 which is greater than 9.8

The following is now known for the sample situation:

20,000 lb axle rating

Load at wheel

9600 lb 6340 lb

Load at the spring

LAR- 1.52
Distance from pivot to spring

28.65 inch

Distance from pivot to axle- 18.85 inch

Design height

13 inch

58

The system characteristics may now be calculated using the preceding results with data from the Product Data Sheet 1T15M-6 (W01-358-9082).

7045 100

70.45 in. (at 13 inch height) 70.5 in

7O5O IO0

(at 1_2.5 inch height)

Ae

7042 100

70.42 in (at 13.5 inch height)

Va

917.41 cu in (at 13 inch height) 879.31 cu in (at 12.5 inch height) 955.30 cu in (at 13.5 inch height)

Vc
Ve

Now calculate the pressure at the 13 inch height:

6340 70.45 90 psig

Air Spring Rate:

Ks

104.7 [74.75- 66.591

Ks

854.35

1.176

853.2 lb/in

Air Spring Frequency:

fs-188K--5-W 18 1853"26340

68.97 cpm

6O

Wheel Rate:

K,,, K, (LAR)
853.2 (1.52)2= 1971 lb/in

Wheel Frequency:

f,, f, (LAR) /e
68.97 (1.52)
/e

85 cpm

Other factors that must be considered include, but are not limited to: Maximum extension Minimum height Stroke at the axle
(R) (R) (R)

61

SAMPLE CALCULATIONS USING A P|RSONAI COMPUTER

Carmel,

piston Design Height

NSTRUCTONS

In this example you will calculate the static rate and frequency of the ITI5M-11
(W01-358-9320) reversible sleeve style air spring on an M-9 piston at an 18 inch design height.
(ib)
(psig)

(lb/in)

U Load *Lotus spreadsheet.

59. 59.

i-2-3 or file compatible

Load the file named STATCALC.WKL Save from the

Enter the information: Date Part Number Test Request #
Design Height Bumper Volume Bumper Number Load start Load increment

disk provided. the file with a new name (for example MIDH18) on a separate data disk.

(Sample File STATSPL.WKI)

(Label.) (Label) (Label) (Value) (Value) (Label) (Value) (Value)

*Lotus 1-2-3 is

registered trademark of Lotus Development Corp.

63

D Enter(cu
volumes
(R) (R) (R)

the areas (sq in) and in):

A1 is the effective area at the design height. Ac is the effective area at 1/2 inch below design height. Ae s the effective area at 1/2 nch above design height. VI s the internal volume at the design height. Vc is the volume at I/2 nch below the design height. Ve is the volume at 1/2 nch above the design height. Note: All entries are values. If a bumper is used, subtract the bumper volume from V1, Vc, and Ve. Refer to the Bumper Volume Chart on page 36.
(R) (R) (R)

The pressure, rate and frequency

are automatically calculated for the loads selected.

Save the File with the new file name selected in Step 2.

64

NSTRUCTIONS
piston

In this example you will calculate the wheel frequency of the 1T15M-11 (W01-358-9320) reversible sleeve style air spring on an M-9 piston at an 18 inch design position.
(ib)

(psig)

(ib/in)

spring

*Lotus B spreadsheet.
Load

1-2-3 or file compatible

Load the file named WHFREQ.WK

from the disk provided. Save the file with a new name (for example MllWFREQ) on a separate data disk.

D Enter
(Sample File WHFRQSPL.WK1)

the information:

Date Part Number Test Request #

Design Height Bumper Volume Bumper Number

(Label) (Label) (Label) (Value) (Value) (Label)

*Lotus 1-2-3 is

registered trademark of Lotus Development Corp.

65

Enter the areas (sq D (cu

in) and volumes in): (R) A1 is the effective area at the design height. (R) Ac is the effective area at 1/2 inch below the design height. (R) Ae is the effective area at 1/2 inch above the design height. (R) V1 is the internal volume at the design height. (R) Vc is the volume at 1/2 inch below the design height. (R) Ve is the volume at 1/2 inch above the design height.

Enter the suspension dimensions. Dimension A is the distance from the pivot to the spring center line. Dimension B is the distance from the pivot to the axle center line.

The lever arm ratio, its square and

square root are calculated and used in the calculations for loads, rates and frequencies.

D The air spring loads, rates and frequencies are repeated.

The wheel (axle) loads, rates, and frequencies are calculated. Change the loads in step 5 to obtain any desired wheel loads.

Note: All entries are values. If a bum]aer is used, subtract the bumper volume from V1, Vc, and Ve. Refer to the Bumper Volume Chart on page 36.

Enter four air spring loads that might be of interest to you. The air spring pressure, rate, and frequency are automatically calculated for the loads you selected.

Save the file with the new name you

selected in Step 2.

66

INSTRUCTIONS
piston

Design Height Design

In this example you will calculate the

Dynamic psig (ib) psig

Height

(in)

in)

in)

(psia)

(psig)

dynamic load for the 1T15M-11 358-9320) reversible sleeve style air spring on an M-9 piston at an 18 inch design position and a load of

design

spreadsheet.
from the disk provided. Save the file with a new name (for example, on a separate data disk.

(Sample File DYNSPLI.WK1)

Date Part Number Test Request #

Design Height Design Load Pressure (Which constant pressure curve used)

(Label) (Label) (Label) (Value) (Value) (Value)

*Lotus 1-2-3 is

registered trademark of Lotus Development Corp.

67

each height, enter the load from the constant pressure curve closest to the design load. Take this information from the Product Data Sheet. In this example, the design load selected was that at 100 psig. In general, volume data is available only at 100 psig, and is used for all loads. Enter the volume data from the 100 psig static data chart on the Product Data Sheet at each height. Subtract the bumper volume if applicable.

At

Save the file with the new file name selected in Step 2.

The following are automatically

calculated at each height:
Air spring effective area (sq in) Air spring absolute pressure (psia) Air spring gauge pressure (psig) Air spring dynamic load (lb) G's for compression heights (a ratio of dynamic load to design load)

A dynamic load vs. height plot will give the results of the Dynamic Load vs. Deflection Chart on the 1T15M-11 Data Sheet, part number 9320.

68

DYNAMIC LOAD
INSTRUCTIONS
piston Design Height Design

In this example you will calculate the

Dynamic psig psig in)

Height

(in)

in)

(psia)

(psig)

(ib)

-2.0

dynamic load for the 1T15M-11 (WO1358-9320) reversible sleeve style air spring on an M-9 piston at an 18 inch design position and a load of 4,000 lb.

design

U Load *Lotus 1-2-3 spreadsheet.

or file compatible

Load the file named Save DYNAMIC.WK1

Enter the information: Date Part Number Test Request #
Design Height Design Load Pressure (Which constant pressure curve used)

the file with from the disk provided. a new name (for example, M11DYN2) on a separate data disk.

(Sample File DYNSPL2.WK1)

(Label) (Label) (Label) (Value) (Value) (Value)

*Lotus 1-2-3 is

registered trademark of Lotus Development Corp.

69

D At

each height, enter the load from the constant pressure curve closest to the design load. Take this information from the Product Data Sheet. In this example, the design load of 4,000 lb is closest to the 60 psig curve. In general, volume data is available only at 100 psig and is used for all loads. Enter the volume data from the 100 psig static data chart on the Product Data Sheet at each height. Subtract the bumper volume if applicable.

Save the file with the new file name selected in Step 2.

The following are automatically each

calculated at
height:
Air spring effective area (sq in) Air spring absolute pressure (psia) Air spring gauge pressure (psig) Air spring dynamic load (lb) G's for compression heights (a ratio of dynamic load to design load)

A dynamic load vs height plot will give the results of the Dynamic Load vs. Deflection Chart on the 1T15M-11 Data Sheet, part number 9320.

70

WARRANTY CONSIDERATIONS

iNTRODUCTiON
Firestone air springs are designed to provide years and thousands of miles of trouble-free service. The durability of Firestone air springs is such that they will often outlast other maintenance items on your suspension, such as bushings, shocks, leveling valves or regulators. Airide (R) springs by Firestone are *warranted to be free of material defects and/or workmanship for various periods of time, depending upon the application. Replacements may be provided by the original suspension manufacturer, manufacturer's representative or dealer, or by any Firestone air spring distributor. All labor and incidental costs associated with replacing the defective air spring are the responsibility of the purchaser, or end user. Firestone Industrial Products Company offers a complete line of Airide springs, with replacement springs available for virtually every vehicular air suspension system.

Since each individual air spring is closely examined and pressure tested at the factory, the vast majority of premature failures and consequent warranty returns are found not to be defective, but fail because of abuse caused by other problems associated wth the suspension. Before you nstall a new ar sprng, you should carefully examine the old one to determine what caused t to fail. if t was due to a defect in the suspension system,, then the new air sprng will also fail unless you correct the problem. The information that follows was developed to illustrate the types of failures that may occur, and to assist you in determining the cause and corrective action required.

Firestone Airide air spring distributor

*Complete warranty information may be obtained from any by calling 1-800-247-4337.

71

Most air spring failures are caused by a lack of suspension maintenance or improper application. This is a guide to common failures that are not covered by warranty.

Appearance Or Condition
Off-center bumper contact

Possible Causes
Worn bushing

Same as bottoming out or abrasion (See pages 74 and 75)

Improper installation

72

LOOSE GIRDLE HOOP

Appearance Or Condition
Flexible member distorted and girdle hoop torn loose

Possible Causes
Running at extended positions with low air pressure

73

BOTTOMING OUT

Appearance or Condition
Bead plate concave Internal bumper loose

Possible Causes
Broken or defective shock absorber
Defective leveling valve

Hole in girdle hoop area (convoluted) Hole in bead plate junction area
Leaking around blind nuts

Overloaded vehicle

Pressure regulator set too low

Wrong air spring (too tall)

74

Appearance Or Condition
Hole rubbed into side of flexible member Hole in flexible member area that rolls over piston (reversible sleeve style air springs)

Possible Causes
Structural interference such as: broken shock misalignment loose air line worn bushings

No air pressure (reversible sleeve style)

Foreign material (sand, rocks, etc.)

Wrong air spring

75

CiRCUMFERENTiAL CUTS

Appearance Or Condition
Flexible member cut in circle at bead plate

Possible Causes
High pressure, fully extended for long periods of time

junction
Flexible member cut in circle at piston junction (reversible sleeve style)

Impact in compressed position

76

OVER-EXTENSION

Appearance Or Condition
Bead plate convex, especially around blind nuts or studs
Flexible member separated from bead plate

Possible Causes
Broken or wrong shock absorber
Defective leveling valve Ride position too high

Leaking at blind nuts or studs

Defective upper stop (lift)

Leaking at end closure (reversible sleeve type)

Wrong air spring (too short)

Loose girdle hoop on convoluted style

77

PREVENTIVE MAINTENANCE CHECKLIST

The following items should be checked when the vehicle is in for periodic maintenance.

5 Correct ride height should be

maintained. All vehicles with air springs have a specified ride height established by the O.E.M. manufacturer. This height, which is found in your service manual, should be maintained within 1/4". This dimension can be checked with the vehicle loaded or empty.

WARNING: Never attempt to service an air suspension with the air springs inflated.

Inspect the O.D. of the air spring.

Check for signs of irregular wear or heat cracking.

2 Inspect air lines to make sure contact

doesn't exist between the air line and the O.D. of the air spring. Air lines can rub a hole in an air spring very quickly.

Leveling valves (or height control valves) play a large part in ensuring that the total air spring system works as required. Clean, inspect and replace, if necessary.

7
Make sure you have the proper shock absorbers and check for leaking hydraulic oil and worn or broken end connectors. If a broken shock is found, replace it immediately. The shock absorber will normally limit the rebound of an air spring and keep it from overextending.

3
Check to see that there is sufficient clearance around the complete circumference of the air spring while it is at its maximum diameter.

4 Inspect the O.D. of the piston for

buildup of foreign materials. (On a reversible sleeve style air spring, the piston is the bottom component of the air spring).

8
Check the tightness of all mounting hardware (nuts and bolts). If loose, re-torque to the manufacturer's specifications. Do not over-tighten.

78

CLEANING
APPROVED METHODS

Approved cleaning media are soap and water, methyl alcohol, ethyl alcohol and isopropyl alcohol.
NON-APPROVED METHODS

Non-approved cleaning media include all organic solvents, open flames, abrasives and direct pressurized steam
cleaning.

PLEASE NOTE: The total inspection process of the air springs on your vehicle can be performed in a matter of minutes. If any of the conditions described on the previous page exists, please take corrective action to ensure that your air springs will perform properly. It will save you both time and money in the long run.

79

80

SUGGESTED READING
SAE Information Report, First Edition, June 1988, SAE HS 1576, Manual for Incorporating Pneumatic Springs in Vehicle Suspension Designs (Warrendale, PA: Society of Automotive Engineers, Inc., 1988).
Thomas D. Gillespie, Fundamentals of Vehicle Dynamics (Warrendale, PA: Society of Automotive Engineers, Inc., 1992).

Robert K. Vierck, Vibration Analysis, 2nd ed. (New York: Harper & Row, 1979).

HISTORY

In the early 1930's, the Firestone Tire and Rubber Company began experiments to develop the potential of pneumatic springs. Between 1935 and 1939, several makes of U.S. automobiles were equipped with air springs and extensively tested to prove the potential of automotive air suspension systems. They were never put into production, however, because significant developments in steel spring design gave an improved ride at much lower cost than the ar spring system at that time. In 1938, the country's largest manufacturer of motor coaches became interested in using air springs on a new design bus they were developing. Working with Firestone engineers, the first busses were tested in 1944 and the inherent ride superiority of air suspensions was clearly documented.

In the early 1950"s, after several years of intensive product development, the air sprung bus finally went into production. That was the beginning of the Airide(R) air spring success story. The success of air springs in bus applcations spurred new interest n truck and trailer applications as well as ndustral shock and vbrafion solaton uses. Consequently, almost all of the busses, most of the Class 8 trucks and many of the trailers on the road today now rde on ar springs, and sgnficant advances n the design of control systems have opened the door to automotive applications as well.