▶ A valve is a devices which control the amount and direction of fluid flow in piping systems
▶ Valves are technically pipe fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction
from higher pressure to lower pressure.
▶ Valves are used in a variety of contexts, including industrial, commercial, residential, and transport. The industries in which
the majority of valves are used are oil and gas, power generation, mining, water reticulation, sewage and chemical manufacturing
▶ Valves may be operated manually, either by a handle, lever or pedal. Valves may also be automatic, driven by changes
in pressure, temperature, or flow. These changes may act upon a diaphragm or a piston which in turn activates the valve,
examples of this type of valve found commonly are safety valves fitted to hot water systems or boilers.
▶ Typically made of bronze, brass, iron, or steel alloy
▶ Components : Valve body, Packing, Disc, Packing gland/nut, Seat, Stem, Bonnet, Wheel
(Valves of Water Treatment Plant)
Type of Valve
• Stop valves (used to shut off or partially shut off the flow of fluid) : globe, gate, plug, needle, butterfly, etc
• Check Valves (used to permit flow in only one direction) : ball-check, swing-check, lift-check, etc
• Special types : Relief valves, Pressure-reducing valves, Remote-operated valves, etc
Classified by Valve
• Globe Valve
- A globe valve is a type of valve used for regulating flow in a pipeline, consisting of a movable disk-type element and a
stationary ring seat in a generally spherical body
- Most common type of stop valve
- Used in steam, air, water, & oil lines
- Disc attached to valve stem rests against seat to shut off flow of fluid
- Advantage : Used for throttling
- Disadvantage : flow resistance
• Gate Valve
- The gate valve(= sluice valve) is a valve that opens by lifting a round or rectangular gate/wedge out of the path of the fluid.
- Gate valve should be either all the way open or all the way closed
- Gate usually wedge-shaped or a vertical disc
- Advantage : No flow restrictions
- Disadvantage : poor throttling
• Butterfly Valve
- A butterfly valve is a valve which can be used for isolating or regulating flow. The closing mechanism takes the form of a disk. Operation is similar to that of a ball valve, which allows for quick shut off. Butterfly valves are generally favored because
they are lower in cost to other valve designs as well as being lighter in weight, meaning less support is required.
- Used in water, fuel, and ventilation systems
- Advantage : small, light-weight, & quick-acting
- Disadvantage : leaks early & only low-flow throttle
• Ball Valve
- A ball valve is a valve with a spherical disc, the part of the valve which controls the flow through it. The sphere has a hole,
or port, through the middle so that when the port is in line with both ends of the valve, flow will occur. When the valve is closed,
the hole is perpendicular to the ends of the valve, and flow is blocked.
- Similar to butterfly valves
- Normally found in seawater, sanitary, trim and drain, and hydraulic systems
• Check Valve
- A check valve, clack valve, non-return valve or one-way valve is a mechanical device, a valve, which normally allows fluid
(liquid or gas) to flow through it in only one direction.
- Controls direction of flow
- Operated by flow of fluid in pipe
- Types :
Swing check : disc moves through an arc
Lift check : disc moves up and down
Ball check : ball is located at end of stem and lifts to allow flow
• Relief Valve
- Used to protect piping system from excessive pressure
- Opens automatically when fluid pressure becomes too high (pressure acts against spring pressure)
- Relieving pressure set by an adjusting screw
• Safety Valve
- A safety valve is a valve mechanism for the automatic release of a substance from a boiler, pressure vessel, or other system
when the pressure or temperature exceeds preset limits.
• Pressure-reducing Valves
- Used to automatically provide a steady, lower pressure to a system from a higher pressure source
- Used in air, lube-oil, seawater, and other systems
Control Valve (Auctuator)
▶ The opening or closing of control valves is usually done automatically by electrical, hydraulic or pneumatic actuators.
Positioners are used to control the opening or closing of the actuator based on electric, or pneumatic signals.
▶ A handle is used to manually control a valve from outside the valve body. Automatically controlled valves often do not have
handles, but some may have a handle (or something similar) anyway to manually override automatic control, such as
a stop-check valve. An actuator is a mechanism or device to automatically or remotely control a valve from outside the body.
Some valves have neither handle nor actuator because they automatically control themselves from inside
▶ Actuators are used for the automation of industrial valves and can be found in all kinds of technical process plants:
they are used in waste water treatment plants, power plants and even refineries. This is where they play a major
part in automating process control. The valves to be automated vary both in design and dimension. The diameters
of the valves range from a few inches to a few meters.
▶ Valves may also be classified by how they are actuated; Manual, Hydraulic actuator, Pneumatic actuator, Solenoid actuator,
Motor actuator, etc
• Pneumatic Actuator Valve (AIR-OPERATED)
- A pneumatic actuator converts energy (typically in the form of compressed air) into motion. The motion can be rotary or
linear, depending on the type of actuator.
- Pneumatic actuators are commonly used to actuate control valves and are available in two main forms; piston actuators and
♦ Piston actuators
Piston actuators are generally used where the stroke of a diaphragm actuator would be too short or the thrust is
too small. The compressed air is applied to a solid piston contained within a solid cylinder. Piston actuators can
double acting, can withstand higher input pressures and can offer smaller cylinder volumes, which can act at high
♦ Diaphragm actuators
Diaphragm actuators have compressed air applied to a flexible membrane called the diaphragm. Figure 6.6.2 shows
a rolling diaphragm where the effective diaphragm area is virtually constant throughout the actuator stroke.
These types of actuators are single acting, in that air is only supplied to one side of the diaphragm, and they
can be either direct acting (spring-to-retract) or reverse acting (spring-to-extend).
(Pneumatic Actuator & Motor Operation Valve)
• Motor Operation Valve (MOTOR-OPERATED)
- Motor operated valve (MOV) is an ordinary ball valve or any other valve that operated by an electric actuator. In general,
the MOV is used as isolation valves for equipment which requires regular access. The MOV is also used on any valve
that the total energy required to open or close the valve manually is large.
- The typical MOV construction consist of electric motor actuator, gear box, and the valve it self. First of all, the motor is
tated by applied an AC voltage to it. The motor rotation then transferred through a gear mechanism to the output thrust part.
he output thrust is then transferred to the gear mechanism in the gear box to rotate the valve stem
• Hydraulic actuator Valve (HYDRAULIC-OPERATED)
- Slow but very powerful, used for moving or transferring heavy loads. Liquids used are virtually uncompressible so they
provide precise control of position, limited only by the flexibility of hoses etc.
• Solenoid Valve (SOLENOID-OPERATED)
- A solenoid valve is an electromagnetic valve for use with liquid or gas controlled by running or stopping an electrical
current through a solenoid, which is a coil of wire, thus changing the state of the valve.
- The operation of a solenoid valve is similar to that of a light switch, but typically controls the flow of air or water, whereas a
light switch typically controls the flow of electricity. A solenoid valve has two main parts: the solenoid and the valve.
- The solenoid converts electrical energy into mechanical energy which, in turn, opens or closes the valve mechanically.
- Solenoid valves may use metal seals or rubber seals, and may also have electrical interfaces to allow for easy control.
- A spring may be used to hold the valve opened or closed while the valve is not activated.
- Solenoid valves are also used in industry to control the flow of all sorts of fluids.