Spring Check Valve
Figure 1: Spring check valve
A spring check valve utilizes a spring and disc to close the valve and prevent fluid flow reversal. Because of spring-assisted closure, spring-loaded check valves close before any backflow through the valve. These valves are popular because of their versatility and protection against backflow. Spring check valves are the focus of this article. For a more comprehensive understanding, read our article on check valves.
Table of contents
- Spring check valve components
- Spring check valve P&ID symbol
- End connection types
- Selection criteria
- Advantages and disadvantages
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Spring check valve components
The housing (Figure 2 labeled A) of spring-loaded check valves protects the inner components from the environment. The disc (Figure 2 labeled B) opens and closes to allow or prevent flow through the valve. The check valve opens when the system’s pressure through the inlet overcomes the valve’s cracking pressure, which is determined by the spring’s (Figure 2 labeled C) setting. The spring also assists in closing the valve, which occurs when the inlet pressure reduces below the valve’s cracking pressure. Finally, the guide (Figure 2 labeled D) keeps the disc properly aligned to ensure a complete seal when it is closed.
Figure 2: Spring check valve components: body (A), disc (B), spring (C), and guide (D).
Spring check valve P&ID symbol
As seen in figure 3, the spring-loaded check valve's P&ID system has a horizontal Y that opens towards the flow direction. Opposite the horizontal Y is a horizontal line with a zigzag line passing through it. This zigzag line represents the spring.
Figure 3: Spring check valve P&ID symbol.
End connection types
Specific applications require certain end connections. Spring check valves' three common end connection types are threaded, flanged, and welded.
- Threaded: For low-pressure applications, threaded connections are typically iron and brass. For high-pressure applications, stainless steel and carbon threaded connections are adequate. Threaded connections are not suitable for very high-pressure applications.
- Flanged: Flange connections have a gasket between the valve's flanges and the pipe's. Very large valves use flange connections. Flange connections are suitable for applications that require excellent sealing.
- Welded: Welded end connections are suitable for small valves, 2 inches (5 cm) and below. These connections are for permanent installations, withstand high pressures, and are leak free.
The appropriate material for a spring check valve depends on the system’s media, temperature, and pressure. For more information about material chemical resistances, read our chemical resistance guide.
- Stainless steel: Always consider stainless steel's resistance to an application's specifications since most spring check valves have stainless steel internal components. Stainless steel is resistant to corrosion and rust in non-salt water applications.
- Brass: Compared to stainless steel, brass is more cost-effective. Brass is also resistant to high temperatures and pressure.
- Ductile iron: Iron is cost-effective, strong, and pressure resistant. However, it is prone to rust.
- Monel: Monel is a nickel-copper alloy highly resistant to acid and seawater corrosion. It is suitable for underwater applications.
- Bronze: Bronze is strong, cost-effective, and resists rust.
- PVC: PVC is flexible and cost-effective, making it suitable for a wide range of applications. PVC’s limiting factor is its low temperature resistance.
- Inconel: Inconel is a nickel-chromium alloy that is highly resistant to heat and corrosion. It is preferable for extreme environments.
- EPDM: EPDM seals have a working temperature range from -40 °C to 150 °C. Also, these seals are excellent for water applications and not recommended for oil and gas applications.
- FKM: FKM seals have a working temperature range from -20 °C to 230 °C. Also, these seals have high abrasion resistance, age well, and are suitable for petroleum applications.
- FEP: FEP seals have a working temperature range from -250 °C to 204 °C. Also, these seals are resistant to nearly all chemicals.
- NBR: NBR seals have a working temperature range from -35 °C to 120 °C. Also, these seals have excellent abrasion resistance and are resistant to oil.
- Teflon (PTFE): Teflon seals have a working temperature range from -260 °C to 260 °C.These seals are chemical resistant and have a low coefficient of friction. Also, they mate well with metal parts due to their hardness.
- Metal: Metal seats allow for higher operating temperatures than rubber seats. However, leakage through metal seating is more likely.
There are several things to consider when choosing the most suitable spring-loaded check valve for an application:
- Media: Choose a spring-loaded check valve made of the material that best suits media properties and budget.
- System temperature: Temperature is a critical factor when using PVC check valves. However, when using metal check valves, focus on the temperature limitations of the rubber seal.
- System pressure: Ensure that the system's pressure will overcome the valve's cracking pressure and be able to open it fully.
- Closing speed: The spring’s setting impacts how quickly the valve closes. If the valve closes too quickly, water hammer may occur.
Advantages and disadvantages
- Versatility: With correct spring settings, spring check valves can be installed in any orientation. Spring check valves perform well in vertical piping locations. These valves depend on the spring’s potential energy to close the valve. Therefore, the valve closes independently without waiting for the fluid to force its way back into the piping.
- Ease of installation: Because of their versatility, spring-loaded check valves are more likely to fit in the system without rearranging pipe configurations.
- Noise control: If water hammer does occur, spring check valves are more able to diminish any disruptive noises. They are considered silent check valves.
- Sealing: With the spring’s support, check valves can fully seal without backflow.
Spring-loaded check valves are typically more expensive than other check valves (e.g., swing check valves) and have a lower flow capacity.
Spring check valves are suitable for low-risk applications that require zero backflow. For example:
- HVAC systems
- Sprinkler systems
- Sump pumps
High-risk applications that require zero backflow, for example, drinking water systems that connect to public water sources, require backflow preventers.
What is a spring-loaded check valve?
A spring-loaded check valve has a spring that applies pressure and seals the valve’s disc. It allows media flow in one direction and prevents backflow.
What is the difference between a swing check valve and a spring-loaded check valve?
A spring check valve uses a spring to force the valve to close. A swing check valve has a flapper that allows flow passage but returns to its original position when it stops.
How much pressure is needed to open a spring check valve?
It takes 0.07 to 0.3 bar to overcome the valve's cracking pressure.
Is a swing or spring check valve better?
Spring check valves are more versatile than swing check valves and have better sealing properties. However, spring check valves cost more than swing check valves.