CONTROL VALVES

BY G.D.GAWANDE
CONTROL VALVES

Control valves automatically regulate pressure and/or flow rate, and are available for
any pressure.
TYPES OF CONTROL VALVES

• Multi-turn valve (linear motion valves):

• Rotary Motion Valves.
• Quarter Turn Valves.
Multi-turn valve

The closure member has a linear displacement generally by turning its

threaded stem several times.
This operation is slow, but it gives accuracy and stability to position the
closure member, which is necessary in some control valves.

Types of valves: Gate valve, Globe valve, Fixed cone valve, Needle valve
and Pinch valve.
• Rotary Motion Valves. When the valve-closure member travels along an angular or circular path, as
in butterfly, ball, plug, eccentric- and Swing Check Valves, the valves are called rotary motion valves.

• Quarter Turn Valves. Some rotary motion valves require approximately a quarter turn, 0 through
90°, motion of the stem to go to fully open from a fully closed position or vice versa.
THE FUNCTIONALITY OF THE VALVE

• Control: pressure / flow rate regulation.

• Closure at over-speed flow. (i.e. immediate closure if downstream pipeline is

broken by accident).

• Overpressure protection.

• Back flow prevention (check valve).

• On/Off service.
THE NATURE AND PHYSICAL CONDITIONS OF THE FLOW

• Low/High temperatures.

• Low/High pressures.

• Cavitation risk.

• Corrosive or erosive properties of the flow.

• Viscosity: Gas, liquid, solid.

• Hygiene requirements (for the food or pharmacy industry...).

• Explosion and risk of inflammability (chemical, petrochemical industry).

 OTHER FORMS OF VALVE CLASSIFICATION
• Connection to the pipe.

• An unique direction of the flow or bidirectional flow.

• Number of ports: most of the valves have two port, named inlet and outlet port. But for same
applications there are multi-port configured valves. They can be three-way and four-way valves.

• Angle between the inlet and outlet port of the valve.

Some valves are self-operated while others manually or with an actuator or pneumatic or
hydraulic is operated.
 VALVE PARTS
• Valve Body
• The valve body, sometimes called the shell, is the primary boundary of a pressure valve.
• It serves as the main element of a valve assembly because it is the framework that holds
all the parts together.
• It receives inlet and outlet piping through threaded, bolted, or welded joints.
 VALVE BONNET

The cover for the opening in the body is the bonnet, and it is the
second most important boundary of a pressure valve. Like valve
bodies, bonnets are in many designs and models available.

During manufacture of the valve, the internal components,

such as stem, disk etc., are put into the body and then the
bonnet is attached to hold all parts together inside.
VALVE TRIM

• THE REMOVABLE AND REPLACEABLE VALVE INTERNAL

PARTS that come in contact with the flow medium are collectively termed
as VALVE TRIM.
• These parts include valve seat(s), disc, glands, spacers, guides, bushings, and
internal springs. The valve body, bonnet, packing, et cetera that also come in
contact with the flow medium are not considered valve trim.
• Because of the trim, basic motions and flow control are possible
• Valve trim parts may be constructed of assorted materials because of the different properties
needed to withstand different forces and conditions
DISK

• The disc is the part which allows, throttles, or stops flow, depending on
its position.
• In the case of a plug or a ball valve, the disc is called plug or a ball.
• The disk is the third most important primary pressure boundary. With
the valve closed, full system pressure is applied across the disk, and for
this reason, the disk is a pressure related component.
Valve Stem
• The valve stem provides the necessary movement to the disc, plug or the ball for opening
or closing the valve, and is responsible for the proper positioning of the disk.

• It is connected to the valve handwheel, actuator, or the lever at one end and on the other
side to the valve disc.
• In gate or globe valves, linear motion of the disc is needed to open or close the valve,
while in plug, ball and Butterfly valves, the disc is rotated to open or close the valve.
There are five types of valve stems:
• RISING STEM WITH OUTSIDE SCREW AND YOKE
• RISING STEM WITH INSIDE SCREW
• SLIDING STEM
• ROTARY STEM
VALVE ACTUATOR

• There are applications where it is not possible or desirable, to actuate the valve manually by
handwheel or lever.
These applications include:
• Large valves that must be operated against high hydrostatic pressure
• Valves they must be operated from a remote location
• When the time for opening, closing, throttle or manually controlling the valve is longer, than
required by system-design criteria
ACTUATORS

• An actuator is a device that produces linear and rotary motion of a source of power under
the action of a source of control.
• Basic actuators are used to fully open or fully close a valve.
• Actuators for controlling or regulating valves are given a positioning signal to move to
any intermediate position.
• There a many different types of actuators, but the following are some of the commonly
used valve actuators:
• Gear Actuators
• Electric Motor Actuators
• Pneumatic Actuators
• Hydraulic Actuators
• Solenoid Actuators
BALL VALVE
• A Ball valve is a quarter-turn rotary motion valve that uses a ball-shaped disk to stop or
start the flow.
• It resembles a plug valve in many ways.
• When a port in the ball is in line, it allows flow whereas when you rotate the valve 90
degrees, solid part of the ball stop the flow.
APPLICATIONS

• Ball valves are commonly found in flowing systems on ships, fire safe protection
services and chlorine manufacturers.
• They are not recommended for use in pharmaceutical, bioprocessing, or food and
beverage applications because they cannot be cleaned easily.
GLOBE VALVE
GLOBE VALVE
GLOBE VALVE

• The disc is opened and closed with a handwheel on manually operated valves and with
an actuator and sliding shaft on automatic valves
• Globe valves are used for shut-off and regulating
• Globe valves are used in wastewater plants, food processing facilities, and process
plants.
• The most common variety is the Z-style valve, so-called because of the path which the
fluid follows through the valve body.
 GLOBAL VALVE DISC

The plug disc is the best among all three globe valve disk designs and are suitable
for throttling services.
A long tapered metal plug is made into a plug disc that seats into a cone
generating a wide seating surface.
• Although these valves exhibit slightly higher pressure drops than straight through
valves (e.g., gate, plug, ball, etc.)
• They may be used where the pressure drop through the valve is not a controlling
factor.
Rising Stem Gate Valve
 GATE VALVE
▪ The advantage of gate valves is their reduced head loss when open
compared to globe valves

▪ They are not useful for throttling and may not produce the positive
shut-off that globe valves provide.
▪ They are usually designated as rising-stem and non-rising
stem designs.
▪ The advantage of rising-stem valves is that they permit easy
visualization as to whether a valve is open or closed.
▪ The advantage of the Non-Rising Stem, or NRS valves, is
that the stem is protected from exposure to corrosive or
other environmental conditions by the valve bonnet.
▪ Neither design has much impact on the actual valve
function.
• Gate valves are used in
• wastewater plants
• power plants
• process plants for shut-off and for isolating service.
BUTTERFLY VALVE
BUTTERFLY VALVE

• Generally smaller and cheaper than a ball valve of the same capacity, butterfly valves can be difficult to
operate against high pressure and flow.
• They are also more leak-prone than ball valves and subject to higher head losses.

• Operation is similar to that of a ball valve, which allows for quick shut off. The
disc is positioned in the center of the pipe.
• A rod passes through the disc to an actuator on the outside of the valve. Rotating
the actuator turns the disc either parallel or perpendicular to the flow.
• Unlike a ball valve, the disc is always present within the flow,
• Butterfly valves are generally favored because they cost less than other
valve designs, and are lighter weight so they need less support

Valve principle butterfly valve - Bing video

PNEUMATIC DIAPHRAGM CONTROL VALVE

How Diaphragm Valves Work - Bing video

• Diaphragm valves get their name from a flexible disc which comes into contact
with a seat at the top of the valve body to form a seal.
• A diaphragm is a flexible, pressure responsive element that transmits force to
open, close or control a valve.
• Diaphragm valves are related to pinch valves, but use an elastomeric diaphragm
DIAPHRAGM VALVE
Material Of Construction
Diaphragms can be made from a variety of materials. The material choice is based on the
nature of the material handled, temperature, pressure, and frequency of operation. Elastomeric
diaphragm materials are highly resistant to chemicals at high temperatures.
 CHECK VALVES
• Check Valves permit fluid to flow through them in one direction only. Lift-type check valves are
similarly constructed as globe valves and use a ball or piston, often backed by a spring that opens
under a specified pressure but closes as the pressure decreases, thus preventing backflow.
• These valves are often suited for high-pressure applications. A variant is the stop check
valve which doubles as a shut-off valve.

• Swing Check Valve - Bing video

Needle Valves
Needle Valves are used to meter fluid flow through tubing or ports.
Flow is regulated by inserting or withdrawing a tapered stem into or out of a
similarly tapered orifice, creating a very precise way of adjusting fluid flow
through the orifice
There will be one handle wheel, as shown in figure, assembled with stem of
valve and this handle wheel is used to open and close the needle valve.
.
Applications of needle valve
1.Needle valves are basically used for controlling the fluid flow into the delicate
gauges of the system, which might be damaged if high pressure fluid will be delivered
suddenly.

2.Needle valves could also be used in various industrial equipment where motion of
work must stop slowly at the end of operation.

3.Needle valves are usually used for controlling and adjusting the fluid flow precisely.
Needle valves are much in demand where lower flow rate will be required.

4.Needle valves could be used under throttling condition, complete open condition or
in complete closed position.
Variation with other flow control valves
Needle valves are slightly different with other flow control valve because needle
valves are bi-directional valves and could be used for controlling the fluid flow in
both direction, while other flow control valve will control or restrict the fluid flow
in one direction only as there will be one check valve for providing the free flow of
fluid in reverse direction.
Plug Valves are quarter-turn valves used to control fluid flow through a pipe. A plug valve constricts flow
similarly to a ball valve, using a ported plug rather than a ported ball that swivels in the flow stream to constrict
or allow flow.
Relief Valves protect pressurized systems such as boilers or piping from over-pressure conditions, usually by way
of a spring-loaded diaphragm.
They can relieve internal pressure as well as external pressure caused by vacuum formation within a tank, for
example.
What are Spring-and-Diaphragm Actuators for Globe Valves? -
Bing video
Valve symbols for P&ID Drawing
• Actuators
• Manual/hand operated actuators use a hand-wheel or crank to open or
close the valve.
• They are not automatic but offer the user the ability to position the
valve as needed.
• Manual actuators are used in remote systems that may not have
access to power, however they are not practical for applications that
involve large valves.
• Gearheads can be added for additional mechanical advantage and
open/close speed.
• Electric motor actuators permit manual, semi-
automatic, and automatic operation of the valve.

• The high speed motor is usually reversible and

used for open and close functions.

• The actuator is connected through a gear train to

reduce the motor speed and thereby increase the
torque.

• The actuator is operated either by the position of

the valve or by the torque of the motor.

• A limit switch can be included to automatically stop

the motor at fully open and fully closed.
Electric Linear Actuator - How It Works - Progressive
Automations - Bing video
Applications

it is extensively used in various industries like

▪ power generation,
▪ metallurgical
▪ papermaking
▪ petrochemical
▪ environmental protection and light industries.
• Pneumatic operated valves can be
automatic or semi-automatic.

• They function by translating an air signal

into valve stem motion by air pressure
acting on a diaphragm or piston connected
to the stem.

• These actuators also use a spring and can

be programed in a variety of manners, such
as using the air pressure to open the valve
and spring pressure to close the valve or
vice versa.

• Pneumatic actuators are fast-acting for use

in throttle valves and for open-close
positioning.
Hydraulic actuators provide for semi-automatic or automatic positioning of the
valve.
• They are used when a large force is required to open the valve, such as a main
steam valve.

• With no fluid pressure, the spring force holds the valve in the closed position.

• Fluid enters the chamber, changing the pressure. When the force of the
hydraulic fluid is greater than the spring force, the piston moves upward and
valve opens.

• To close the valve, hydraulic fluid (such as water or oil) is fed to either side of the
piston while the other side is drained or bled.

• Hydraulic actuators are available in a wide range of sizes and are economical to
use in a valve system as well as with a single valve.
Hydraulic actuators
Thermally actuated valves
are activated by a change in media temperature.
• A temperature and pressure are preset and the valve will open or close to
adjust to the desired specifications.

• When selecting an actuator it's important to consider the output power, which
is used to overcome resistance and ensure high degree sealing and valve
opening.
Electric actuator
Pneumatic Actuator