waterway valves are essential components the water sector. These valves form part of water and wastewater treatment plants, bulk water supply, reticulation, commercial and residential plumbing systems. They regulate, direct, or control the flow of water to ensure efficient operation and safety. Various types of water valves are available, each designed for specific applications. Understanding their differences can help you choose the right valve for your needs.

What is a valve?

A valve is a mechanical device used in fluid systems to control, direct, isolate, mix, or regulate the flow or pressure of a fluid, by modifying the passageway through the pipe. When a valve is in the open position, the passageway is unobstructed and the fluid flows in a direction from higher pressure to lower pressure. By partially or fully obstructing the passageway through the valve, the flow can be reduced or completely stopped.

What are the different types of valves?

The table below lists the different types of valves and their corresponding P&ID symbols. The most commonly used types of valves are gate valves, globe valves, check valves and ball valves.

Overview of piping instrumentation diagram symbols of different valve types.

Gate Valve

Gate valves are the most common type of valves found in process plants. The closing gate moves along a linear path to block or allow fluid flow. Gate valves provide good shutoff and are considered suitable for almost all fluid services including air, fuel gas, feedwater, steam, slurries and viscous liquids.

Globe Valve

A globe valve generally has a spherical body that contains a movable plug element and a stationary ring seat. The two halves of the body are separated by an internal baffle. The plug element is connected to an operating hand wheel through a stem. As the wheel is turned, the screw action moves the plug towards or away from the ring seat. Globe valves can be used for stop/start function as well as to regulate fluid flow. They are useful in applications where good flow control is desired and leak tightness is important such as cooling water systems, feedwater and chemical feed systems, and fuel/lubricating oil systems.

Ball Valve

A ball valve uses a hollow ball to stop or allow fluid flow. The perforated ball can be pivoted using the valve handle. When the hole in the ball faces the flow inlet, the fluid flows through. A quarter-turn rotary motion of the valve handle turns the ball by 90° blocking the flow.

Check Valve/Non-return Valve

A check valve is used to prevent backflow in piping systems. The valve opens due to the pressure of the fluid passing through the pipeline. Reverse flow closes the valve and prevents the fluid from moving in the opposite direction. Check valves do not require external control. They work automatically and hence do not have an operating handle or stem. The simplest check valves are designed with a one-way flap mechanism.

Plug Valve

Plug valves use a cylindrical or conically tapered plug to allow or restrict fluid flow. The plug has one or more hollow passageways that allow the fluid to pass through when the passage is aligned with the flow direction. A quarter-turn rotary motion is required to turn the plug and block the fluid flow. Plug valves perform well in slurry applications. The wiping action of the plug does not allow suspended particles to accumulate and form an obstruction. Typical applications of plug valves include gaseous, and vapor services, natural gas piping systems, oil piping systems, coal, mineral and sewage applications. They are also suitable for vacuum and high-pressure applications.

Butterfly Valve

The “butterfly” refers to a rotatable metal disc mounted on a rod. A quarter turn of the disc is required to open or shut-off the valve. In the closed position, the disk completely blocks off the passageway. In the open position, the face of the disc is parallel to the flow direction and allows nearly unrestricted fluid flow. Butterfly valves find applications in cooling water systems, compressed air or gas applications, fire protection, slurry services, vacuum service, and high-pressure / high-temperature water and steam services.

Needle Valve

Needle valves are similar in design to globe valves. The plugging element in these valves is a long, tapered, needle-like plunger which fits into a matching seat to stop the flow. A stem is turned to insert or retracted the plunger, opening or restricting the flow path. The finely-threaded stem requires many turns to fully retract the plunger; this feature allows precise regulation of the flow rate. Needle valves are typically used in small diameter piping systems where very fine control of flow is desired. Needle valves are generally suitable for systems with low viscosity fluids flowing at low flow rates. The most common application is to regulate flow to fragile gauges in order to protect them from damage caused by an abrupt pressure surge. They are also used as bleed valves to relieve pressure or to drain off the fluid for analysis or for maintenance.

Pinch Valve

Pinch valves employ an elastic tubing and a pinching device that directly restricts the flow through the tubing. The pinching mechanism flattens the tubing to create a seal.

Diaphragm Valve

A diaphragm valve, also known as a membrane valve, consists of an elastomeric diaphragm, and a saddle/seat upon which the diaphragm closes. A linear compressor is used to push the thin, flexible diaphragm into contact with the seat/saddle to close the valve. Diaphragm valves also allow partial closure of the passageway making them suitable for throttling applications. They are suitable for viscous fluids and fluids containing solid materials as the solids are not trapped in the valve mechanism. Diaphragm valves are commonly used in water treatment facilities, pharmaceutical, food and chemical plants, vacuum services and corrosive applications.

How are valves in piping systems classified?

There are several different ways in which valves can be classified. They can be grouped based on their function, type of operating mechanism, end connections, mechanical motion, construction material, pressure and temperature ratings and port size. When choosing a valve, it is important to consider each of these classifications to ensure that the valve is suitable for the desired application.

( A ) Valve function

Valves are incorporated in a process to perform different functions. They may be used to start/stop the flow or to regulate flow and pressure. They may be required to control the direction of flow, or for improving process safety. Based on flow control, valves are classified as either isolation valves or regulation valves.

-Isolation valves

Isolation valves are designed to either completely restrict fluid flow or allow it without obstruction. These valves are not recommended for continuous use in the partially open state as they may provide poor flow control or suffer wear damage over time.

-Regulation valves

Regulation valves are used for regulation of pressure and fluid flow with suitable precision. These valves can be safely and efficiently used in processes that require partial open or closed state.

( B ) Mode of operation

Valves can be classified as manual, actuated or automatic based on how they are operated.

-Manual valves

Manual valves are typically operated by hand with the help of wheels, levers, pedals, knobs, or chains. These valves can be geared mechanically to change the direction of movement and/or to increase the operation speed or torque.

-Actuated valves

In high-precision or large-scale applications, valves are often connected to electric motors, pneumatic systems, hydraulic systems, or solenoids, to enable remote operation and automation of valve function.

-Electric motor actuators

Electric motor actuators use reversible electric motors to rotate the valve stem through a gear system that increases torque and reduces rotational speed.

-Pneumatic actuators

Pneumatic actuators use air pressure to provide the force needed to operate the valve.

-Hydraulic actuators

Hydraulic actuators use a pressurized liquid and a piston to deliver the force required to operate the valve.

-Solenoid actuators

Solenoid actuators employ the magnetic attraction between a slug attached to the valve stem and the coil of an electromagnet to operate the valve.

-Automatic valves

Some valves are automatically activated when a specific flow condition is met. For examples, check valves close without any need for outside intervention during backflow. Similarly, pressure release valves are activated automatically when an over-pressure condition is detected.

( C ) End connections

Valves are connected to pipes through joints; these joints can be screwed, flanged or welded. Some common types of valve ends are listed below:

-Flanged end valves

A flange is a plate or ring that forms a rim at the end of a pipe or valve; two flanges are bolted together to form a joint.

-Screwed end valves

Screwed end valves have threaded joints, to which the end of a pipe or another fitting is screwed.

-Socket welded valves

The pipe is inserted into a socket and welded.

-Butt weld valve

The butt weld valves have beveled ends that match a similar bevel on the pipe.

Valves provide several functions, including:

-Starting or stopping flow based on the valve state

-Regulating flow and pressure within a piping system

-Controlling the direction of flow within a piping system

-Throttling flow rates within a piping system

-Improving safety through relieving pressure or vacuum in a piping system

Conclusion

waterway valves are available in a large variety of designs and configurations. The large number of available options make valve selection a difficult task. Choosing the best valve for an application requires consideration of the required function, fluid service conditions and characteristics, frequency of operation, isolation or regulation requirements, maintenance needs, and the desired level of safety and reliability.

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