valve types

Introduction of types of valves – ball, gate, globe, plug, butterfly and applications

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Introduction of types of valves – ball, gate, globe, plug, butterfly valves and their applications in different industries

Types of valves

Ball Valve

Ball Valve
Ball Valve

Ball valve  is a valve with a quarter turn. The closing part is a spherical plug with a through hole. When the valve is in the open position, the passage hole is in the direction of the fluid flow and through this the fluid passes. The valve is closed by turning the handle by 90 degrees. So that the passage hole is now perpendicular to the flow and hence, the flow stops.

A seat is usually an area made of soft material to create a tight outlet. The seat can be made of plastic or metal. Ball valves are not recommended in a situation where they are to be partially opened. Due to the imbalance between the flow direction and the opening direction of the plug, a large pressure drop will occur in the partially opened condition.

Due to the challenges identified above, ball valves are mostly used in shut off applications. Ball valves are usually used in steam, water, oil, gas, air, corrosive liquids. They can handle dusty liquid and dry liquids. Ball valves are not used with abrasive and fibrous materials, as they cause damage to the seat and surface of the ball plug.

gate valve

gate valve
gate valve

Gate valve is a type of sliding valve. In gate valves, the closing part is a metal gate. Gate lowers the drawer to close the valve.. In fully open conditions, the flow level is equal to the pipe area and hence, there is negligible pressure drop across the valve.

A gate valve should ideally be used as an on-off valve. It is not recommended to use them as throttle valves because in half-open conditions, gate erosion may occur.

In partially open conditions, due to vibrations, the valve is subject to rapid wear and tear. Also, there is a significant amount of friction during closing and opening, and therefore opening and closing these valves quickly and often is not possible.

Gate valves are well used in petrochemical industries due to the fact that they can work with metal-to-metal sealing.

Plug valve

Plug valve
Plug valve

Plug valves, like ball valves, are quarter-turn types. This valve includes a plug that can be cylindrical or conical in shape. The plug has a slot that lines up with the current in the open position. When this plug is turned 90 degrees, this gap is perpendicular to the flow and the valve is closed.

Plastic valves are suitable for managing fluids with suspended solids, liquid, etc.
Plastic plug valves are mainly used for passive applications. When used for reduction purposes, the pressure drop through the valve is higher due to the asymmetry between the flow direction and the opening (gap) direction.

Butterfly valve

butterfly valve
butterfly valve

Butterfly valves are the simplest multipurpose valves. They have quarter-turn valves that are regularly used in various industries for a variety of applications. A quarter turn in turn causes the valve to work quickly.

In the open condition, there is minimal blockage of fluid flow through the valve around the disc aerodynamically, resulting in less pressure drop through the valve.
Due to its unique shape, the butterfly valve can be used easily without the need for high torque and wear and tear. Due to the lack of friction, the use of large actuators can be avoided. Butterfly valve rubber is used for tap water, which is made with different materials according to the needs.

Another advantage offered by butterfly valves is their compact size. The valve is quite compact, it looks like a metal disk. This makes them very easy to install. They can be used for slurries and liquids with suspended solids, because there are no cavities for solid particles to settle inside the valve body.

Globe valve

globe valve
globe valve

Globe valve is a linear movement type valve and is usually used in both on-off and throttling applications.

In globe valves, the fluid flow is through an S path. Due to the fact that the flow path changes twice, the pressure drop increases. Due to their other advantages, these valves are widely used where the pressure drop through the valve is not a control factor.

These valves are generally not used in sizes larger than NPS 12 (DN 300) because of the enormous force exerted on the stem to open or close the valve under fluid pressure. Globe valves require a lot of pressure on the seat to keep it closed when the fluid is pressurized from below the disc.

Globe valves are used for both on-off and throttling applications, but special types of trim are required for ease of use in applications where large pressure drops are involved. These valves can be used in three configurations, depending on the application:

– Tee pattern
– Angle pattern
– Wye pattern

Globe valves can be used as non-return valves when the disc is removed from the stem and allowed to rest on its own weight. Machining seats is easier and cheaper than other types of valves.

Pinch valve

pinch valve
pinch valve

Pinch valves have a plastic tube/sleeve made of reinforced elastomers. The sealing/closing action is achieved by pulling this sheath/tube.

Pinch valves are suitable for moving liquids and liquids with suspended solids. Pinch valves have many advantages over other types of valves. They can be used to handle corrosive liquids because there is no connection between the liquid being transported and the actual valve mechanism. After choosing the right sleeve, this valve can work with all kinds of liquids.

Since the transported liquid is not in contact with metal parts, pinch valves can also be used for food applications.

In general, pinch valves are suitable for low pressure applications. When using abrasive solutions, they should be used as on-off valves; If used for throat purposes, the sleeve is worn out.

Disc check valve

One-way valves – disc check valves, – also called non-return valves – allow flow through them in one direction only and stop flow in the opposite direction. Due to this unique guiding feature, disc check valves are mainly used for some important applications in steam system.

There are four main types of disc check valve as follows:

 1- Lift check valve

disc check valve
disc check valve

These check valves simply work on the principle of gravity. As the fluid moves forward, the disk can be lifted off the sieve by the force of the incoming fluid – against the force of gravity. In this way, the valve allows liquids to pass in this direction.

When the fluid is in the opposite direction, it supports gravity and weight and the disc remains on the seat and keeps the valve closed.
If the back pressure is low, it is difficult to keep the valve completely closed and the liquid will leak out in such conditions.

2- Swing Check Valve

Swing Check Valve
Swing Check Valve

In a check valve, the swing, disc or closing element changes around the point it is attached to.

When the fluid moves in the forward direction, the disc opens in the open position to allow the fluid to pass through. When the fluid flow is in the opposite direction, the disc oscillates and rests on the seat to lose it.

3- Spring loaded Check Valves

Spring loaded Check Valves
Spring loaded Check Valves

In this type of one-way valves, its complete closure is done using a spring. The rear spring holds the disc on the seat. Even under forward flow conditions, the fluid must develop a small pressure, called cracking pressure, to open the disc against the spring pressure.

 

 

4- Diaphragm Type Check Valve

These types of one-way valves use diaphragms that are set to open and allow flow to move only in the forward direction. When the flow is coming from the opposite direction, the diaphragm remains closed.

Common applications in a steam system:

4.1- After a float trap
steam trap
steam trap

Steam traps are passive components and work based on the principle of pressure difference. During operation, the process pressure may drop below the pressure of under pressure trap . In such a situation, due to the negative pressure in the steam trap, the condensate can return to the process equipment through the trap.

Therefore, it is always recommended to check the disc valve or non-return valve after the float trap. This check valve allows liquid to pass through the trap outlet to the liquid recovery or condensate system but ensures that it does not flow in the reverse direction.

4.2- Mixing of liquids

In applications where two or more fluids are mixed, check valves should be installed at the end of each separate line. This prevents contamination of one liquid by another.

4.3- Use as a vacuum breaker

Disc check valves can act as vacuum breakers when installed in reverse.

Under normal operating conditions, the valve remains closed and does not allow steam to pass through. When vacuum formation occurs (during shutdown), the disc opens and allows air to enter, thus avoiding vacuum formation.

 

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