What is a piston check valve?
A piston check valve is a type of valve that is used to prevent reverse fluid flow. This type of valve is mechanically automatic and thus it does not need an actuator or valve operator. Piston check valve manufacturers design this valve to allow fluid flow in one direction only. A piston check valve is designed with a dash-pot that consists of a cylinder and a piston for providing cushioning effect when the valve is operating. There are guides in the piston type check valve that help to enhance the proper alignment of the disc and seat configuration when the piston closes. The fluid flows through the valve from below the valve disc. This design helps the fluid flow rate and pressure to force the valve disc to float on the seat which then allows fluid to pass through the valve. The piston check valve closes when the fluid tries to reverse the direction of flow in which the disc is assisted by its weight and gravity. Piston check valve manufacturers produce different varieties of these valves for use in different applications such as in high and low temperature. Piston type check valves used in low temperatures have the seats made of soft materials like rubber and plastics. Those used for high temperature applications have the seats made of metallic materials like brass, bronze, and steel.
Figure: Piston-type check valve.
Components of a piston type check valve
This is the part of the piston check valve that contains the internal parts of the valve. The valve body is made of strong materials such as ductile iron, cast iron, stainless steel, and carbon steel among others. The body also serves as the main pressure barrier to ensure fluid pressure is not lost. The body contains the inlet and outlet valve ports where fluid passes through the valve to the piping system.
This is top part of a piston check valve. The bonnet is placed on top of the valve body and the two are connected using various methods such as bolts and nuts, threads, or welds. The weld and bolt connections are suitable for use in high-pressure applications as they offer a tight seal. The screwed or threaded connection involves connecting the body and the bonnet through threads. The welding connection guarantees a very tight seal despite high pressure. However, the welding connection makes it hard to open the valve while in the field for inspection, cleaning or repair.
This is the part of a piston check valve that is used to close and open the valve.
The spring is used to help in closing the valve immediately suction pressure starts reducing.
This part acts as a seal between the valve body and the disc to prevent fluid leakage.
Figure: Components of a piston type check valve.
How does a piston check valve work?
A piston check valve works by employing the principle of pressure difference. To open a piston check valve, the fluid pressure must be greater than the outlet pressure. In this case, the fluid pressure energy becomes high enough to lift the valve disc off the valve seat. When the disc moves upwards, it leaves space for the fluid to pass through the valve. The fluid keeps flowing through the piston check valve until a time when the suction pressure drops. At that instance, the fluid starts reversing the direction of flow from the outlet side to the suction side due to low inlet pressure. However, piston check valve manufacturers design these valves with high sensitivity to pressure so that the valve closes immediately before significant fluid starts flowing backward. Fluid reversing backward causes damage to equipment like boilers or pumps. It can also bring losses due to unnecessary contamination. So the use of piston check valves is inevitable in certain industrial applications.
Figure: Working of a piston check valve in open state (left side) and closed state (right side).
Types of piston check valves
Z-shaped piston check valve
This is a piston check valve that has a z-shaped partition inside the valve. The Z-shape is where the valve seat is mounted. This is one of the most famous and simplest piston check valves. Piston check valve manufacturers make the seat with a horizontal arrangement. This type of design allows the disc to move perpendicular to the axis of the pipeline. Z-shaped piston type check valve is easier to do maintenance, installation, and cleaning.
Figure: Z-shaped piston check valve.
Y-loaded piston check valve
This is a piston check valve in which the disc and the horizontal axis are at an angle of around 45o degrees. This design makes it possible to inspect and clean the valve without disconnecting it from the piping system. The working principle of this piston type check valve is the same as the Z-shaped piston check valve. The only difference is that in the Y-loaded type the piston moves up and down at an angle of around 45o. The y-loaded piston check valve is heavy and it occupies more space for installation.
Figure: Y piston check valve.
Flanged end piston check valve
This is a piston-type check valve that is connected to the pipeline using bolts and nuts. Piston check valve manufacturers design these valves with flanged ends that have holes. Also, the pipe end to be connected to the piston type check valve has a flanged end with holes to allow for an effective connection between the pipe and the valve. A gasket is used between the piston-type check valve and the pipe to enhance a tight connection free from fluid leakage. There are three types of flange faces which are ring type, raised face, and flat face. The ring type of flanged end is used in piston-type check valves meant for use in high-pressure applications. Most piston-type check valves are designed with flanged ends. This design is easy to install and it makes the piston check valve easy to remove from the piping system for repair and maintenance or replacement. Flanged end piston check valves use several bolts and nuts to connect it to the pipeline which means they need less torque to tighten relative to other types of valves. Because of the several bolts and nuts used, these valves have a tight connection with the pipe which makes them free from fluid leakage. Flanged end piston check valves are heavier due to the bolts, nuts, and flanged ends when compared to other types of piston check valve types.
Flanged end piston type check valve.
Threaded end piston check valve
This is a piston check valve that is connected to the pipe using threads. Piston check valve manufacturers design this type of valve with either female or male threads. A piston-type check valve that has male threads is connected to a pipe that has female threads. Threaded end piston valves are mostly small in size relative to the flanged end type. Piston check valve manufacturers design these valves for use in low and medium pressure applications. These valves are easy and quick to install and assemble.
Figure: Threaded end piston type check valve.
Welded end piston check valve
This is a piston-type check valve that is connected to the pipe using the welding method. Both the valve and pipe are made of compatible material to help in enhancing high strength after they are welded together. Welded end piston-type check valves are suitable for use in high-pressure applications. This is because the welding method provides a very tight seal and because the valve and pipe become one unit after weld it is not possible to experience fluid leakage. However, it is not possible to open the piston-type check valve for inspection, repair, and cleaning while it is in the field. Piston check valve manufacturers design these valves for use in applications that do not need frequent repair and maintenance and or where the media to be controlled is hazardous such as acids and or combustibles such as oil and gas. Welded end piston-type check valves are lighter in weight relative to the flanged end types. These valves can be of different sizes from small to large depending on where they will be used.
Applications of piston type check valves
- Piston check valves are used in the oil and gas industries.
- Piston-type check valves are used in the freshwater supply.
- They are used in wastewater treatment plants.
- They are used in feed water control in steam power generation plants.
- These valves are used in the manufacturing of pharmaceutical products.
- They are used in the manufacturing of chemicals.
- Piston type check valves are used in foods and beverages processing.
- These valves are used in air-conditioning systems to prevent the reverse flow of cooling media.
Advantages of piston check valves
- Piston-type check valves are durable since they can be used for a long period without being replaced. Also, these valves are repairable which makes them suitable for use after being repaired when they break down.
- Piston check valves are versatile because they can be used in different industrial applications.
- These valves do not allow fluid flow in the reverse direction which helps to prevent fluid contamination as well as prevent damage to piping equipment such as boilers and pumps.
- Piston check valves are automatic which relieves the owner of the additional cost of hiring a valve operator or including a valve actuator.
- These valves are suitable for use in both high-pressure and high-temperature applications.
- These valves have low-pressure drop which enhances pumping efficiency thus saving on energy.
- Piston check valves operate fast with zero fluid leakage.
- These valves can maintain pressure levels required through the piping system.
- They are easy to install, repair, and do maintenance.
Disadvantages of piston check valves
- Piston type check valves allow fluid flow in one direction only.
- These valves are not suitable for use in pulsation fluid flow applications.
- These valves tend to produce water hammer problems.
Troubleshooting a piston check valve
Fluid leakage from the valve-pipe connection
- The connection that is bolts or screws is loose. Tight the connection.
- Worn out gasket. Replace the gasket.
- Damaged or worn-out O-rings. Replace the O-rings.
No fluid flow through the piston check valve
- The valve has been installed in the wrong direction. Remove the valve from the piping system and connect it according to the piston check valve manufacturer’s instructions.
- The pipe connecting the piston check valve is blocked. Check the pipe for blockage and remove any foreign material blocking fluid flow.
Fluid leakage when the valve is fully closed
- There are solid particles lodged in the piston check valve. Clean the valve of the solid particles causing blockage.
- O-rings are damaged. Replace the O-rings.
- The valve seat is damaged. Replace the valve seat or the valve.
A piston check valve is a valve used to prevent reverse fluid flow. A piston-type check valve operates automatically using the principle of pressure difference. Using this principle, the piston check valve opens when the suction pressure is more than the outlet pressure. The high-pressure results in high-pressure energy used to open the valve. If the suction pressure becomes lower than the outlet pressure or when the pump stops, fluid attempts to flow backward but the valve closes immediately. As such, this type of valve does not need a valve actuator or valve operator. There are various types of piston check valves which include Z-shaped piston check valves, Y-loaded piston check valves, flanged end piston check valves, threaded end piston check valves, and welded end piston check valves. Applications of these valves include oil and gas industries, pharmaceuticals, chemical production, foods and beverages processing, water supply, air-conditioning, and steam power generation applications among others. Advantages of using piston check valves are durable, versatile, no reverse fluid flow, automatic operation, ability to maintain pressure, low-pressure drop, and they have zero fluid leakage. However, piston check valves allow fluid flow in one direction only and they are prone to water hammer problems.