A check valve, non-return valve, or one-way valve is a valve that normally allows fluid to flow through it in only one direction.
Check valves are two-port valves, meaning they have two openings in the body, one for fluid to enter and the other for fluid to leave. There are various types of check valves used in a wide variety of applications. Check valves are often part of common household items. Although they are available in a wide range of sizes and costs, check valves generally are very small, simple, and inexpensive. Check valves work automatically and most are not controlled by a person or any external control; accordingly, most do not have any valve handle or stem.
There are several concepts which should be considered when selecting a check valve ; cracking pressure, pressure drop, valve capacity, critical velocity, closing acceleration, water hammer, material selection , flow characteristics ; Laminar or Turbulent, installation requirements.
Cracking Pressure:
- This is the minimum pressure difference required to open the valve.
- A lower cracking pressure is desirable for applications where low pressure differentials are common.
- However, a lower cracking pressure may also result in more frequent valve operation and wear.
- In some applications, a check valve can be used as a pressure/vacuum relief valve by carefully selecting and setting the cracking pressure which is in fact the set pressure of this.
Pressure Drop:
- The pressure drop across the valve is the difference in pressure between the inlet and outlet sides.
- A higher pressure drop can lead to energy loss and increased operating costs.
- Valve design and size can significantly impact pressure drop.
Valve Capacity:
- This refers to the maximum flow rate that the valve can handle without causing excessive pressure drop or damaging the valve.
- Valve capacity is influenced by factors like valve size, design, and operating conditions.
Critical Velocity:
The velocity in which the valve operate at fully open condition. Not being able to meet the required critical velocity, can lead to chattering of the valve and leads to declining the lifespan of the valve. Moreover, operating the valve at lower velocities than critical velocity, causes the turbulent flow inside our at the down stream of the valve.
Closing Acceleration:
- This is the rate at which the valve closes when the flow reverses.
- A rapid closing acceleration can cause water hammer, which can damage the valve or other components in the system.
- Some check valves have features to mitigate water hammer, such as slow-closing mechanisms or internal dampers.
Water Hammer:
- This is a pressure surge that occurs when a fluid is suddenly stopped or its flow direction is reversed.
- Water hammer can cause damage to the valve, pipes, and other components.
- Proper valve selection and installation, along with measures to mitigate water hammer, are essential.
Material Selection:
- The materials used for the valve body, disc, seals, and other components should be compatible with the fluid being handled.
- Spring Materials not only should be compatible with the flow, but also should be designed properly for the required number of cycles that the valves undergoes in its lifespan.
- Factors to consider include corrosion resistance, erosion resistance, temperature tolerance, component function, and pressure rating.
Seat leakage:
Is a critical factor to consider when selecting a check valve. It refers to the leakage of fluid or gas past the sealing surface between the valve seat and the valve disc in close position. Soft seat valve or metal to metal seat valves can be a suitable option for a wide range of applications. At low back pressures it is very difficult to prevent the leakage even with a soft seat, that’s why seating angle also plays an important role in the design of a check valve to reduce the leakage rate.
Flow Characteristics:
- The flow characteristics of the fluid can influence valve performance.
- Laminar or turbulent flow, as well as the presence of solids or gases in the fluid, can affect valve selection and operation.
Installation Requirements:
- Proper installation is crucial for the correct functioning of a check valve.
- Factors to consider include Orientation, piping configuration (Upstream / Down stream length) .
- Incorrect installation can lead to valve malfunction, leakage, or damage.
By carefully considering these factors, we can select a reliable check valve that is suitable for your specific application and provides reliable protection against backflow.
At Kara we supply swing type, dual plate, ball check valve, insert type, non slam check valves in Carbon Steel, Stainless Steels and high alloy steels. We can check your applications and based on your system requirements we offer the best product which suits your design.