AALBORG INDUSTRIES KK

File No.
PNP-
O/# -

PRIMAVAC SYSTEM

INSTRUCTION MANUAL

Date : 30-Aug-2004
AALBORG INDUSTRIES KK
ENGINEERING GROUP
In charge Manager G. Manager

AkY
ReV. Alteration Date Sign App'l
AALBORG INDUSTRIES KK
2-2, 4-Chome, Kumoi-dori, Telephon +81 78 271 5736
Chuo-ku, Kobe 651-0096 Japan Telefax +81 78 271 5741

コピー表紙
 TABLE OF CONTENTS PRIMAVAC SYSTEM

Table of contents
General description of Primavac System ....................................................................1
Principle of Operation .................................................................................................3
Components.................................................................................................................6
Installation .................................................................................................................13
Associated equipment................................................................................................13
Operation ...................................................................................................................15
Maintenance ..............................................................................................................19
Life of parts ...............................................................................................................24
Service Network ........................................................................................................25
Discussion on Cavitation...........................................................................................27
Operation precautions................................................................................................29

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 Instruction Manual for Primavac System Rev.0

Instruction Manual for Primavac System

1 General description of Primavac System

The Primavac System is an assembly that is used in conjunction with any centrifugal
pump to provide self-priming capabilities.

The Primavac System as shown in Figure 1 is comprised of a Primavac unit,

Combination Recirculation Tank and Suction Strainer, Air Evacuation Check Valve
and Main Discharge Check Valve. The individual components will be explained in
detail under separate sections in this manual.

The system Function relies on the change in flow rate and its operation is automatic,
thus no additional controls or devices are required.

Figure 1 shows liquid admitted to the pump through the combination recirculation
tank-suction strainer and discharged through the Primavac unit and the main
discharge check valve.

While the main purpose of the Primavac System is to self prime the pump,
additional features are provided by the system such as protection against dry
operation and subsequent over heating, damage to mechanical seals and damage as a
result of operation with suction and/or discharge valves closed. These advantages
will become evident as the operation of the system is explained in detail.

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General arrangement of Primavac System

Figure-1

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2 Principle of operation
Refer to Figure 2.

When the pump is operating normally, the increased fluid velocity through the
venturi throat results in a reduction of pressure in this area. This pressure is
transmitted by the sensing tube to the back side of valve piston. When the flowing
fluid reaches the area of the Primavac valve it regains virtually all of the original
pressure as a result of the decrease in velocity. This pressure is imposed on the front
of the valve piston.
Thus a differential pressure is effected across the piston.

The design of the Primavac valve incorporates a spring whose action results in a
normally-open condition. When sufficient fluid flows through the venturi, the
differential pressure, as described above, will overcome the spring force and close
the valve. A reduction in flow rate to approximately 40% of pump rated capacity
will reduce the differential pressure to a point that the spring will force the poppet
open.

The arrows on Figure 2 show the path of the returning flow through the open
Primavac valves.

Normal pump operation is shown in Figure 3.

Figure 4 through Figure 7 demonstrates the Priming Cycle.

Figure 4: The loss of pump suction results in the no flow rate through the venturi
and activation (opening) of the Primavac valves.

Figure 5: The fluid in the discharge line between the Primavac unit and the main
discharge check valve is permitted to flow through the open Primavac valves and the
recirculation line and is accumulated in the recirculation tank.

As this fluid is moving from the discharge line to the recirculation tank, it is
displaced by gas which moves through the air evacuation line and into the discharge
line.

Figure 6: As soon as the eye of the impeller becomes submerged, priming completes.

Figure 7: The regained suction condition and subsequent pumping forces the
displaced air now in the discharge line beyond the main discharge check valve. At
the same time an equal volume of gas and/ or liquid is drawn into the recirculation
tank from the suction line.

The priming cycle will normally require thirty seconds for completion and will
repeat, each time evacuating the predetermined volume of gas, until normal suction
conditions have been restored.

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Mechanism of Primavac unit

Figure 2

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3 Components

3.1 Recirculation Tank with Suction Strainer

Figure 8 shows the construction of a typical recirculation tank. This recirculation

tank is of welded steel construction with connecting piping for inlet, outlet,
recirculation, air evacuation, drainage, and air vent valve and level indication valve.
A strainer which is designed to be detachable for cleaning and a weir are placed
inside the tank.
The weir prevents “priming liquid” from escaping through the suction inlet pipe
when returning to the recirculation tank, and also forms the tank capacity (shadowed
portion) needed for the operation of the system.

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Recirculation Tank with Suction Strainer

Figure 8

Description for Recirculation Tank with Suction Strainer

No. Description Material
1 Inlet line connection Steel
2 Outlet line connection Steel
3 Drain line connection Steel
4 Recirculation line connection Steel
5 Air evacuation line connection Steel
6 Liquid level indication valve Steel
7 Tank vent valve Steel
8 Strainer Steel
9 Baffle plate Steel

3.2 Primavac Unit

A Primavac unit consists of inlet and outlet flanges, venturi, valve housing,
Primavac valve, and sensing tube as shown in Figure 9. One Primavac unit has 1-6
Primavac valves, each connected to a sensing tube which transmits the pressure at
the venturi throat to the valve body. Figure 10 shows the details of a Primavac valve.

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Primavac Unit

Figure 9

Description for Primavac Unit

No. Description Material
1 Venturi Steel
2 Primavac valve Bronze body/SS trim
3 Sensing tube adapter Bronze
4 Gasket Non-asbestos
5 Gasket Rubber
6 Socket head cap screw Stainless steel
7 Hex head cap screw Stainless steel
8 Sensing tube Copper
9 Valve housing Steel
10 Inspection cover Steel

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 Instruction Manual for Primavac System Rev.0

Primavac Valve

Figure 10

Description for Primavac Valve

No. Description Material
1 Body “G” Bronze
2 Piston Stainless steel 316
3 Stem Stainless steel 316
4 Poppet Nickel-Al Bronze
5 Closure “G” Bronze
6 Bushing Bronze
7 Spring INCONEL
8 Piston Ring Teflon
9 O-Ring Buna-N or VITON
10 O-Ring Buna-N or VITON
11 Retaining Ring Stainless steel 316
12 Nut, Self-Locking Stainless steel 303
13 Gasket Rubber

3.3 Main Discharge Check Valve

The liquid volume between the Primavac unit and the main discharge check valve,
i.e. the volume of “priming liquid” returning to the recirculation tank during priming
cycle is one of the parameters in the system design.
Consequently this valve location in the discharge line becomes critical. Figure 11
shows the detail of the main discharge check valve.

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It should be noted that the Primavac System is a vacuum creating assembly and the
degree of vacuum which may be created is dependent upon the reliability of the
check valves. Therefore a good quality check valve which offers leak tight seating is
recommended. Wafer type dual plate check valves which utilize resilient seals have
been found to be highly satisfactory in this service. The check valve shown in Figure
11 is of this type.

Discharge Check Valve

Figure 11

Description for Primavac Valve

No. Description Material
1 Body FC25 or SC49
2 Plate ALBC3 or SCS13
3 Spring SUS316
4 Hinge Pin SUS316
5 Stop Pin SUS316
6 Pin Retainer SUS304
7 B-Lug Bearing PTFE
8 P-Lug Bearing PTFE
9 Eye Bolt S20C
10 Spring Lug Bearing PTFE
11 Seat VITON or Buna

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3.4 Air Evacuation Check Valve

A PENCO FLEX-TACT type air evacuation check valve shown in Figure 12 is

employed and is installed in the air evacuation line located as close to the main
discharge check valve as possible. This check valve prevents pumped fluid from
circulating through the tank.
The valve opening pressure is designed to be very low (about 0.02 kg/cm2) so that
air evacuation can be effected smoothly during the priming cycle.
A pump vent line check valve, also with a very low required opening pressure
(about 0.01 kg cm2), is employed to facilitate pump venting.
Figure 13 shows the check valve.

Air Evacuation Valve (Flex-Tact Type)

Figure 12

Description for Primavac Valve

No. Description Material
1 Body-Inlet Steel ASTM A216-WCB
2 Body-Outlet Steel ASTM A216-WCB
3 Seat Stainless Steel 17-4PH
4 Poppet Stainless Steel 17-4PH
5 Gasket Compressed ASBESTORS
6 Spring INCONEL
7 Spring Guide Stainless Steel 316
8 Bolt-Hex Steel ASTM A193
9 Nut-Hex Steel ASTM A194
10 Nut-Hex Stainless Steel 303

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Pump Vent Check Valve

Note : Ensure that valve should be installed on a horizontal piping and the shaft
should be kept vertical.
Figure 13

Description for Primavac Valve

No. Description Material
1 Body FC25
2 Plate ALBC3 or SCS13
3 Spring SUS316
4 Hinge Pin SUS316
5 Stop Pin SUS316
6 Pin Retainer SUS304
7 B-Lug Bearing PTFE
8 P-Lug Bearing PTFE
9 Spring Lug Bearing PTFE
10 Seat VITON or Buna

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4 Installation
The accurate located and orientation of the various components is extremely
important to the proper performance of the system. Figure 14 shows an installation
correctly arranged.

5 Associated Equipment
Turbine Governor:
Special attention should be given to speed control on turbine driven pumps. Pump
speed adjustments should be made with the turbine governor rather than by the
steam supply.

During recycling of the Primavac, load fluctuations on the turbine may vary from
full load to virtually no-load in a very short period of time. Special attention should
be paid to the condition of the turbine governor. Where possible, the use of a
Woodward governor is recommended.

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AIR EVACUATION CHECK VALVE IS TO BE INSTALLED : MAIN DISCHARGE CHECK VALVE IS TO BE INSTALLED :

** HOLIZONTALLY ** VERTICALLY
** AS CLOSE AS POSSIBLE TO THE ** AT THE SPECIFIED DISTANCE FROM
MAIN DISCHARGE CHECK VALVE THE PRIMAVAC UNIT
** WITH THE CORRECT FLOW DIRECTION

NEVER CONNECT ANOTHER PIPE TO THIS DISCHARGE

PIPE BETWEEN PRIMAVAC UNIT AND MAIN DISCHARGE
PUMP VENT LINE CHECK VALVE CHECK VALVE WITHOUT PROVIDING A STOP VALVE
IS TO BE INSTALLED : HOLIZONTALLY

** WITH CORRECT FLOW DIRECTION

** HORIZONTALLY
** IN SUCH WAY THAT VALVE SHAFT
IS TO BE KEPT VERTICALLY PRIMAVAC UNIT IS TO BE INSTALLED

** VERTICALLY
THESE PIPES ARE TO BE ARRANGED : ((THE SENSING OPENING OF TUBE INSIDE THE
VENTURI IS TO FACE UPWARD AS SHOWN BELOW)
** AS STRAIGHT AS POSSIBLE

OPENING

BUTTERFLY VALVE OR GATE VALVE IS TO BE EMPLOYED.

DO NOT USE GLOBE VALVE.

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6 Operation

6.1 General Procedure

The following outlines the general operating procedure of the system.

Refer to the below sketch.
Step A: Close recirculation tank drain valve.

Step B: Open recirculation tank vent valve.

Step C: Open valve in recirculation line between Primavac unit and recirculation
tank.

Step D: Open valve in pump vent line between pump and air evacuation line.

Step E: Open pump suction valve to recirculation tank.

Step F: Set all pump discharge piping valves for discharge to the desired point. This
valve operation encompasses normal procedure to be followed regardless of
whether a Primavac System is provided or not.

Step G: When liquid flows from recirculation tank vent valve, close this valve. If
liquid cannot flow into the recirculation tank because the cargo tank level is
too low, this tank must be filled from another source to a level equal to the
level of the weir or baffle which is just higher than the impeller eye top.

1) closed 4) opened

7) closed 3) opened

closed

Step H: Start pump in normal manner, gradually increasing speed to rated PRM.

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6.2 Basic Procedure for Stripping

Step A: Keep an about 3-5 meter trim by the stern for faster stripping.

Step B: Separate suction line completely for each pump during the whole stripping
procedure, and close the valves unnecessary for operation.

Step C: Decrease pump speed to 80 (～75) % of rated RPM when the cargo tank
liquid level has reached approximately one meter from tank bottom, and
keep the 80 (～75) % RPM until the completion of stripping for this tank.

Step D: Open the stripping bellmouth at the previously mentioned one meter liquid
level when it is provided. Below 50cm liquid level of cargo tank, throttle
the main bellmouth to about 2/4 opening and at about 25cm liquid level, to
about 1/4 opening taking care not to make an excessive vacuum. Below
15cm liquid level around the main bellmouth, close the main bellmouth,
using the stripping bellmouth alone. In this condition the Primavac System
will recycle automatically, discharging the accumulated air in the suction
line together with the cargo and will empty the tank.

Step E: The transfer of cargo pump discharge from another tank is accomplished by
appropriate valving, i.e. isolate the empty tank and admit the next tank to be
discharged to the pump suction. This operation can be performed without
stopping the pump. Adjust the pump RPM if necessary, again depending on
liquid level of the new tank. The Primavac System will recycle until all the
air is evacuated from the suction line and normal pumping is restored. As
this liquid level is reduced the stripping action will be again instituted as
before. This entire procedure is repeated until all desired tanks have been
emptied.

6.3 Precautions

Step A: If the pump flow rate is set to be less than 40% of the rated flow, Primavac
valve will be kept open and a short-circuiting will occur (as described later).
As a result, unloading efficiency is reduced or stripping failure is caused in
some cases. From such a viewpoint, low flow operation should be avoided
and previously mentioned pump revolution should be kept.

Step B: If a stripping bellmouth piping is too small in area (i.e. less than 15% of the
area of main bellmouth piping), stripping by only one stripping bellmouth
is not preferable from a viewpoint of keeping a proper flow rate. Until the
liquid level around the main bellmouth has reached around 15cm, use the
main bellmouth with the opening considerably throttled together with the
stripping bellmouth; thereafter, use the stripping bellmouth alone.

• ・If the stripping bellmouth piping is suitable in area, the change-over to the
bellmouth alone can be made at a higher liquid level than the above level.
Step C: Final stripping of each tank should be made for only one tank at a time. If
multiple tanks are finally-stripped simultaneously, some empty tanks (if

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their valves are not closed properly) will continuously provide air to the
suction line and the pump will fail to withdraw liquid from the other
connected tanks. If multiple tanks are simultaneously unloaded and stripped
by one pump, desirable stripping can be accomplished through an operation
with some 50cm level differences between the tanks.

Step D: The Primavac System may be shut-off and its operation eliminated from
cargo pumping by closing the valve in the recirculation line between the
Primavac unit and recirculation tank.

6.4 Example of Stripping Procedure

Unloading procedure varies depending on the condition of cargo, the grouping of

pipe lines, etc. But, some examples are given below for references: For efficient
stripping, it is desirable that the bellmouth is permitted to suck as less air as possible.
From this viewpoint, these instructions adopt adjustment of bellmouth opening,”1
pump: 2 tank method”, etc. as described below. Please note that Item 2 “Basic
Procedure” is needed for every stripping procedure.

6.4.1 Stripping by “1 pump: 1 tank method”

• As shown in the above illustration, carry out unloading to 3-1 meter level for
each tank and then start to strip one tank by one pump.
• When liquid level has lowered to about 50 cm, throttle the main bellmouth to
about 2/4 opening taking care not to make an excessive vacuum. And when the
level has further lowered and air suction from the bellmouth has gradually
increased (vacuum has decreased), further throttle the same valve. When the
liquid level around the main bellmouth has reached about 15cm, close the
bellmouth, using the stripping bellmouth alone.
• For detection the time for completion of stripping, the detection by “sounding”
is most effective, in view of the possible error of level gauge. Just before the
completion of stripping, the bellmouth sucks air almost continuously. The
guidance for completion of stripping will be obtained by recognizing the above
situation ----- for example, vacuum tends to zero, or discharge pressure
decreases, or it periodically cycles within a small amplitude.
• When the liquid level of the next cargo tank is below the suction line, Primavac
System repeats priming cycles until whole air in suction line has been evacuated,
and then the pump delivers liquid from the cargo tank. But, if the liquid level in
the cargo tank is kept a little above the suction line, on the change-over to the
tank the whole air in suction line can be soon evacuated to the discharge side by
the head of cargo oil, so as to shorten the above-mentioned air evacuation time.

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6.4.2 Stripping by “1 pump: 2 tank method”

• Referring to the illustration in previous item, “1 pump: 1 tank method”, carry

out unloading to 3-1 meter level for each tank and then start to strip one tank by
one pump from the foremost tank.
• At about 50cm liquid level, throttle the main bellmouth to 2/4 opening taking
care not to make an excessive vacuum.
• At about 25cm liquid level around the main bellmouth, 1/4 open a main
bellmouth of second tank (1-3 m liquid level) and strip the two tanks by one
pump.
• When air suction from the first tank has gradually increased as the liquid level
lowers, throttle its main bellmouth to about 1/4 opening.
• At around 10cm level, close the main bellmouth, keeping its stripping bellmouth
opened and the second tank main bellmouth 1/4 opened until the completion of
stripping for the first tank.
• After completing it, continue unloading of the second tank, now opening its
main bellmouth to full.
• Thereafter, repeat above procedures.
• When a change-over is made to “1 pump: 2 tank method”, the vortex motion of
liquid around the bellmouth in low liquid level tank is reduced. As a result,
unnecessary air suction is avoided and frequency for suction loss of pump is
reduced.
• Should a reverse flow occur from the high level tank to the tank being stripped,
it is because of such a great difference in suction condition between both the
tanks as described below:
• The level of the higher level tank is too high, say more than 7 - 8 meter.
• (Main bellmouth of this tank should be throttled.)
• The main bellmouth of the higher level tank is too much opened, say full open.
• (The bellmouth should be throttled to roughly 1/4 opening.)

6.5 PRIMAVAC Valve Washing Method

Stop valve with Primavac Unit are installed for cleaning of Primavac Valve in
Primavac Unit.
Step A: Immediately after stopping the pump. connect hot water lines with all ports
of the stop valves. Fully open the stop valve and supply hot water for 5 to
10 minutes. Primavac Valve Cylinder inside can be cleaned by this
procedure.

Step B: During this cleaning procedure, keep recirculation valve open.

Step C: After cleaning, be sure to close the stop valve. Never open this valve except
cleaning time.

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7 Maintenance

7.1 Maintenance Interval

The Primavac System requires little maintenance, due to the relatively few
components in the system. However, it is suggested that periodic checks be made to
the strainer tank for cleanliness and to the Primavac valves for freedom of operation.

Intervals for inspection and cleaning of the valves cannot be sweepingly generalized
because they vary depending on the kind of cargo, the frequency for use of
equipment, etc. Therefore, it is recommended as guidance that inspection and
cleaning be carried out once every 2 voyages provisionally for the initial period, and
then, according to the result, the most suitable intervals are determined for
inspection and cleaning.

Note: Valve Washing Device

The washing device is provided for some ships to clean the valve inside after cargo
unloading for the prevention of valve sticking. However, it must be noted that even
if this device is provided, the valve inspection, disassembly, and cleaning are
necessary, although at some extended intervals.

7.2 Maintenance Procedure

7.2.1 Inspection on valve operation

• Valve operation can be checked by actuating the piston through the port with an
L-shaped wrench (or fingertips).
• The piston should operate smoothly by a weak external force to overcome the
spring force.

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Important: Piston stroke abt. 1cm

Important: Spring force abt. 12kg for 6 inch valve, abt. 6kg for 4 inch valve

• When the external force is taken away, the piston should promptly recover the
original position by spring force.
• If the piston does not operate smoothly, disassemble the valve for cleaning.

7.2.2 Disassembling and cleaning of valve

• Following the above sequence (1)-(5) as illustrated, dismount Primavac valve

and carry out its disassembling and cleaning and, when necessary, parts
replacement. After having cleaned every part, carry out the inspections as per
the instructions in the next page.
• When mounting Primavac valve, tighten all hexagon socket head bolts evenly.
• Make sure that the sensing tube is open and not plugged.

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• After mounting the valve, check the valve operation by means of 7.2.1.
If the valve does not operate smoothly, check valve mounting bolts to insure
that all are secured that evenly and no interference or binding occurs between
the movable and stationary parts.
7.2.3 Inspection after disassembly and cleaning
Inspection on operation of piston-stem-poppet assembly without spring.
After having cleaned every part of the valve, assembly only piston, stem and poppet
to the valve body, support the valve (without spring) vertically by both hands and
check the piston-stem-poppet assembly (called piston assembly hereinafter) to see if
it slides smoothly (freely) by its own weight inside the valve body, while the valve is
speedily turned upside down and upside up.
When the piston assembly does not smoothly slide by its own weight after the
cleaning, the replacement of the piston-rings and O-rings will improve the sliding
operation. If the piston assembly does not still slide smoothly, contact Aalborg
Industries K.K. or Penco Division of Maritime Tanksystems International. Inc. for
the re-conditioning of the valve.
Inspection on bleed hole
There is a small bled hole at the cylinder of valve body.
Check the hole for any clogging.
7.2.4 Inspection on inside of recirculation tank
Procedure for inspection
Step A: The followings should be always confirmed before overhauling the tank.

• The oil in the tank to be completely drained out.

• Empty condition in the air evacuation line and also in the tank to be confirmed.
Step B: The air evacuation line to be dismounted at suitable point so that the top
cover can be hung up.

Step C: The top cover to be dismounted and to be moved to a safe place.

Step D: The followings to be checked in the tank.

• To check if the strainer is blocked with some foreigners, and to clean it if

necessary.
• To check coating condition, and if there are some damages, coating repair to be
made.

Caution: When valves on the tank are opened to check if the tank becomes
empty, sometimes, a liquid can’t flow out even in case that some
liquid remain in the tank because of vacuum condition. Please mind
tat.

Caution: Do not loosen bolts of any connections on the tank until empty
condition of the tank can be confirmed.

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7.3 Problems and Causes

If problems should occur, the following is a list of conditions and probable causes.

CONDITION CAUSES

1. Extended cycle duration a) One or more Primavac valves stuck in

(normal 30-45 sec.) closed position.

b) Air evacuation check valve not

functioning.

c) Pump air vent valve closed, improperly

adjusted or not functioning.

2. System Recirculating * a) Pump discharging at less than 40% of

rated capacity.

b) Primavac valves stuck in open position.

3. High steady vacuum pressure a) Clogged suction strainer.

during recycling
b) Closed suction valve.

4. Low pumping efficiency a) System recirculating.

*… Recirculation is a short circuiting of the system whereby liquid discharged from

the pump flows through the open Primavac valves into the recirculation line
and back to the recirculation tank. To maintain design discharge, this condition
can be corrected temporarily by closing the recirculation valve. Upon
completion of discharge, Primavac valves should be inspected and repaired.

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7.4 Drainage of Primavac System

When the pump is not used, never fail to drain liquid from the vertical pipe of
Primavac Unit.
If the liquid is left in the pipe, it will hinder drainage from inside Primavac valve
and cause sticking of valve.

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Life of parts for Primavac Valve

No. Parts Name Material Life Remarkes

1 Body “G” Bronze Idenfinitely very long Check if contact part is not grooved too much.

2 Piston Stainless Steel 316 Idenfinitely very long Check if contact part is not grooved too much.

3 Stem Stainless Steel 316 Idenfinitely very long Check if threads are in good condition.
Check if contact part with body is not grooved too much.
4 Poppet Nickel A1-Bronze 2 – 4 years
Groove less than 1 mm deep is serviceable.
5 Closure “G” Bronze Idenfinitely very long Do not deform the outside diameter or o-ring groove.

6 Bushing Bronze 2 – 3 years Do not remove from valve body during overhaul.
Normal spring constant is abt.0.87 kg/cm for 6” valve and
7 Spring Inconel 4 years or more
About 1.2 kg/cm for 4” valve.
8 Piston Ring Teflon 1 – 2 years Carefully handle the ring during overhaul.

9 O-Ring BUNA-N or VITON 1 year Do not stretch the ring during overhaul.

10 O-Ring BUNA-N or VITON 1 year Do not stretch or pinch during valve overhaul.

11 Retaining Ring Stainless Steel 316 2 – 4 years

Nylon insert is useable for a hundred successive applications,
12 Self-Locking Nut Stainless Steel 303 2 – 4 years
Though depends on the condition of the stem thread.

Note : 1. Refer to Fig.10 of the Primavac valve drawing.

2. The above life is given as a guidance for replacement of parts in normal service, but does not mean the guarantee period of the parts.

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PENCO AGENTS / LICENCEES

Aries Industrial Y Naval, S.A. AGENTS/LICENSEES
Parque de las Naciones Territory: Spain
Edificio Germania
Gusman el Bueno, 133
Madrid 3, Spain
Contact: Mr. Jose Luis Gutierrez
Mr. Antonio Alvarado
Tel: 253 7104/03/02

Aalborg Industries KK AGENTS / LICENSEES

2-2, 4-chome, Kumoi-dori, Territory:
Chuo-ku, Kobe 651-0086 Japan Exculsive: Japan,Korea, China,
Contact: Mr. H. Tanaka Non-Exclusive: Hong Kong, China,
Telephone: 078-271-5735 Philippines, Malaysia, Singapore,
Telefax: 078-271-5741 Thailand, Indonesia

R. Jumabhoy & Sons (Pte) Ltd. AGENTS

9-B D’Almeiaa Street Territory: Singapore
Singapore 0104
Mailing Address:
P.O. Box 303
Singapore 9006
Singapore
Contact: Mr. A.R. Jumabhoy
Telephone: 911052

B.V. Materiaal Metingen AGENTS

Wilson Walton International Territory: Netherland/Benelux
P.O. Box 10 Countories
Marijkesingel 45
Barendrecht, Holland
Contact: Mr. B. Van Schie/Mr. B. Muller
Tel: 806 15555

Meecon Private Ltd. AGENTS

Nirmal 21st Floor Territory: India
Nariman Point
Bombay 400-021
Contact: Mr. T. M. Sanghavi
Tel: (9122) 230381 230384
Cable: TECHMAR BOMBAY

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PENCO AGENTS / LICENCEES

Polarmarine Ltd. AGENTS/: LICENSEES
34 Ebury Street Territory: Great Britain
London SW1W 0LU
England
P.O. Box 303
Contact: Mr. David H.Idwal Jones
Tel: 730 7158

Technava, S.A. AGENTS

6 Loudovidou Square Territory: Greece
P.O. Box 512
Piraeus, Greece
Contact: Mr. B. Tomazos
Tel: 4413916 473776 422450
Cable: TECHNAVES

Worthington Pump (U.S.A.) LICENSEE to manufacture

270 Sheffield Street PrimaVac System for Deepwell Pumps
Mountainside, New Jersey 07092 using their pumps.
Tel: (201) 654-3300

Penco Division of LICENSOR

Maritime Tanksystems International Inc.
7 Oak Place Montclair
New Jersey 07042 U.S.A.
Tel: 201-509-1106

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 Instruction Manual for Primavac System Rev.0

8 Discussions on Cavitation in Cargo Oil Pump

8.1 General meaning of cavitation

When a liquid flows through a narrow part with high velocity, the static pressure
decreases as explained by Bernoulli’s theorem. If the pressure decreases below the
saturated vapor pressure at the liquid temperature, bubbles of vapor are formed in
the liquid. And, at the same time, liquid dissolved air is separated also as bubbles
from the liquid. Such a phenomenon is generally called cavitation.

The produced bubbles are carried over to the high-pressure zone and, therein, are
crushed out to be again mixed or dissolved into the liquid. At the very time when the
bubbles are smashed down, sound is emitted or vibration is caused by the severe
shock of the smashing down of bubbles. And, it also causes the wall surface to be
eroded.

8.2 Cavitation of pump

In order to prevent the cavitation of a pump, the minimum pressure in the impeller
must not be reduced to so low a level as to generate bubbles. On the assumption that,
at the pump suction port, the pressure head, the velocity head, and the saturated
vapor pressure head are shown as Ps/r (absolute pressure indication), Vs2/2g, and
Pv/r respectively, we consider the following Hsv:

Hsv = Ps/r + Vs2/2g – Pv/r …………… (1)

If the above Hsv is gradually reduced (namely, the total pressure at the pump suction
port, Ps + r ・ Vs2/2g, is made to approach the saturated vapor pressure, Pv),
cavitation occurs at a certain value of Hsv. This lowest Hsv for cavitation varies
depending on the pump characteristics.

The Hsv in the above expression (1) is called Net Positive Suction Head (NPSHav).
And, the lowest limit of Hsv that is determined by the pump characteristics is
expressed as NPSHreq. In order to avoid the cavitation of a pump, NPSHav must be
kept larger than NPSHreq.

These descriptions on the cavitation of a pump are more specifically explained

hereinafter. NPSHav (Hsv) can be transformed as follows:

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 Instruction Manual for Primavac System Rev.0

Pa Vs2 Pv
NPHav = − | Hsg | + − ……… (2)
γ 2⋅g γ

Pa Vs2 Pv
= − Ys − f ⋅ − ……… (3)
γ 2⋅g γ

where Pa = atmospheric pressure (kg/㎡), γ = specific gravity of liquid (kg/m3)

Hsg = vacuum gauge pressure head at pump suction port (m)

Ys = suction lift (m)

Vs 2
f⋅ = loss head on suction tube side (m)
2⋅g

As presumed from the above expression (3), NPSHav generally decreases with the
increase in suction lift Ys or the increase in loss head, f・Vs2/2g.
When NPSHav at last reaches NPSHreq, cavitation occurs.

In the zone where there is a possibility of the occurrence of cavitation, the flow rate
is generally lowered as measures to prevent cavitation. Such action produces the
following processes:
the decrease in flow rate ―→ the decrease in loss head ―→the increase in NPSHav.
On the other hand, with the decrease in flow rate, NPSHreq decreases. Therefore,
the relation, NPSHav > NPSHreq can be kept to effectively prevent cavitation.

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 Instruction Manual for Primavac System Rev.0

8.3 Primavac System does not cause cavitation

Primavac System can provide a pump with automatic self-priming function, but can
never change the pump characteristics which are proper to the pump.
During the priming cycle of the Primavac System, the pump sucks air temporarily
making no-load operation, the pump load increases with priming liquid returning to
the suction side of the pump, and the pump recovers suction. The sound, which is
emitted during the suction recovery, echos loudly through the piping.

Sometimes, these “suction of air“ and “sound emission“ are mistaken as if cavitation
occurred on the pump. However, this is quite a different phenomenon from
cavitation, and has particularly no ill effect on the pump.

Pump suction loss due to air suction is not cavitation. As mentioned in item 2,
cavitation is caused by the pressure decrease of liquid (excessive vacuum) but is not
caused by such a near-atmospheric pressure (slight vacuum) as at the above suction
loss.
This explanation is backed up by the fact that when cavitation has occurred, it is
eased or avoided by making the pump to suck a small amount of air as seen
sometimes in land pump applications.

More than 300 ships use Primavac System at sea for over one year, but they have
until now had no trouble concerning cavitation.

“The prevention of cavitation” must be dealt with as the subject on the proper pump
operation.

9 Operation Precautions for PrimaVac System (PVS)

9.1 Inspection or maintenance before operation

To insure normal-satisfactory operation of PVS, it is indispensable to keep its vital

components (valves and sensing tube) in good working condition.
9.1.1 Primavac Valve
In earlier time, open up and clean this valve once every voyage or two. Thereafter
the interval of inspection or cleaning may be extended depending on the operation
condition.
To check the valve for proper function, remove the spring and turn the valve up side
down, and then adjust the condition so that the piston/stem/poppet assembly slides
down the cylinder by its own weight.
9.1.2 Pump vent line non-return valve and sensing tube
In earlier time, open up and clean these parts once every 3 or 4 voyages. Thereafter
it is desirable to determine a frequency of inspection or cleaning that suits the
circumstances aboard the ship. Be sure that the non-return valve is properly oriented.

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 Instruction Manual for Primavac System Rev.0

Other) Primavac Valve cleaning device

Immediately after stopping the pump, supply hot water to the devices for 5 to 10
minutes.

9.2 Precautions before operation

It is imperative for the normal, satisfactory stripping operation that the individual
valves installed on PVS are held in proper positions as shown below.

Even if PVS is installed, care should be taken to minimize unnecessary air suction.
For this purpose keep the ship 3 to 5 meters trim by the stern throughout unloading
operation. The greater is the inclination, the better the efficiency of PVS. This helps
the gathering of cargo oil and delays the occurrence of air suction. Furthermore, it is
effective to heel the ship about one degree to the bellmouth fitting side.

Note the following points when establishing an unloading plan.

Note: Care should be taken when stripping more than one tank simultaneously
with a single cargo oil pump. For it is possible that the pump sucks air
from an empty tank and fails to draw oil.

Note: Whenever possible, unload oil through the shortest of the routes between
the cargo oil pump and the tank. If oil is guided as shown below, its flow
may be refilled and unloading may be impeded due to the up grade that
intervenes.

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 Instruction Manual for Primavac System Rev.0

9.3 Operation of PVS (important)

The principal duty of PVS is to permit the cargo oil pump to complete stripping in as
short a time as possible, i.e., with as little and interruption of unloading as possible.
This means that (in spite of PVS being installed) the pump must be allowed to keep
operation with a minimum air suction.
If the pump sucks air to such an extent that the main cargo oil line is entirely filled
with air, PVS needs to repeat air venting cycle over again. This will be unnecessarily
extend unloading time.
To prevent the undue air suction, it is recommendable that liquid from other tank be
drawn to replace air in the main line as soon as stripping is completed in a given
tank.

9.4 Efficient unloading by PVS

Step A: Unload other tanks than the slop tank until cargo oil level falls to a level 1.0
to 3.0 meters from the bottom and perform stripping in sequence starting
from the nearest tank to the bow. (Operate one pump for one tank)

Step B: Pump rpm

Note: Reduce pump rpm to about 70% of the rated value when oil level in a
given cargo tank has lowered to, say, 1m deep. This is instrumental in
deterring eddy current in the tank and thus reducing air suction.

Note: When oil level has decreased further (50cm) and air suction seems about
to start, raise pump rpm to a level higher than 80%. Then PVS begins to
operate. Keep pump rpm at this level till stripping is concluded.

Step C: Avoid low-flow operation

In case when the pump is set at less than 40% of the rated capacity, the Primavac
valve is kept open and liquid discharged by the pump returns to the recirculation
tank, a short circuit is formed.
Loss of unloading efficiency or deficient stripping can result.
Step D: Go on to unload two tanks simultaneously with one pump keeping one-
meter ullage difference between them.

Step E: Stripping in the last tank to be unloaded must be carried out with one pump.
It should be done by making the most of PVS. PVS starts as soon as the
pump begins to suck air.

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Step F: State of operation of PVS

In the following graph, mark a show the normal operating condition of the cargo oil
pump. When the suction pressure begins to drop (mark b), close the main bellmouth
valve to its full-closed position. The delivery pressure also falls abruptly (mark C).
Subsequently, a repeat of pump suction and delivery pressure change (so-called
re-cycling) occurs.
In the interim, the pump makes rather loud noise.
But this is not a cause for worry.

Step G: It normally takes about 10 to 30 minutes between time when recirculation

in one tank starts and when stripping in the same tank completes. (Time
depends on ship’s condition, though.)

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 Instruction Manual for Primavac System Rev.0

Step H: 8. In order to operate PVS efficiently, a close watch should be kept on the
openings of the suction and delivery valves.

• The openings of suction valves in the individual cargo oil tanks should be
carefully adjusted so that air suction will be kept as scarce as possible
(especially in case of one pump-two tanks method).

Unloading tank Next tank

Main Strip bellmouth Main
* Level bellmouth valve valve bellmouth valve

more than 50 cm 100% open 100% open close

about 50cm 25% open 100% open close

about 25cm close 100% open 25% open

about 10 cm close 100% open 25% open

finish ** close ** close 100% open

* Liquid (oil) level near the bellmouth

** Check liquid (oil) level after valve closed

Figures in the above table are given as a general guide.

They can not be always applied since piping arrangement, sizes of cargo oil
tanks and gathering of cargo oil vary with ships.
When throttling the suction valves, also throttle the delivery valves in order
not to create excessive vacuum.

• Maintain pump delivery pressure above 3 to 4 kg/c ㎡ while PVS is in operation.

For this purpose, it is necessary to throttle the delivery valve within a range of
25 to 10% opening.
(Optimum opening varies with the shipboard piping arrangement, though.)

9.5 Examples of Practice for Effective Use of PVS

Stripping by one pump-two tanks method

Unload the cargo oil tanks till they come to
be left with 3 to 1 meter of oil. Then carry on
stripping by using one pump-two tanks
method – starting from the nearest tanks to
the bow and switching to the one
immediately aft and so on.

When a further fall of oil level in a given tank results in the main bellmouth being
immersed about 25cm in oil, open the main bellmouth valve in the next tank 25%.
Since pump suction is divided between the two tanks, eddy current around the

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 Instruction Manual for Primavac System Rev.0

bellmouth in the first tank is diminished and the likelihood of suction loss is reduced.
Thus stripping in that tank completes quickly.
In certain instances involving a combined use of one pump-two tanks method with
“6m trim by the stern,” No.1 tank as shown in the sketch was unloaded to virtual
“dryness” without recirculation by the effect similar to an ejector in that tank.

9.6 Short cycle – mechanism and corrective measure

As illustrated below, the pump fails to show cyclic drop in delivery pressure when it
simultaneously sucks air and liquid.
If this condition, called “short cycle,” lasts more than about 20 minutes, the pump
will get overheated. Meanwhile, Primavac valve is left open as it is when the pump
runs at a low flow rate and part of discharged liquid forms a continuous flow in the
recirculation line, creating a pressure balance at about 2 kg/c ㎡.

To break the pressure balance, proceed as follows.

• Fill up the suction side of the pump by drawing liquid from a tank having a
higher liquid level.
• Temporarily close the recirculation valve (manually operated) in the pump room.
With liquid collected at the discharge side of the pump, allow 2 to 3 minutes and
open the valve again. This will cause liquid to return to the suction side
(recirculation tank and pump) and positively restore a liquid recycle.

For more details, consult the operating instruction and maintenance procedure that
accompany every shipment of Primavac System.

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