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Common check valve problems are noise, water hammer, vibration, reverse flow, sticking, leakage, and component wear/damage.

A check valve requires a minimum pressure differential between the inlet and outlet to open, allowing media to flow through it. This minimum upstream pressure at which the valve opens is called the check valve's cracking pressure. The specific cracking pressure changes based on the valve design and size, so ensure that the system's pressure can generate the cracking pressure of the chosen check valve(s).

A check valve is a unidirectional valve that passes fluid in one direction but prevents any flow in the opposite direction.

Stainless steel check valves are available in various grades, with 304 and 316 being the most common. Grade 316 stainless steel offers enhanced resistance to chlorides and other corrosive substances, making it suitable for marine and coastal applications.

Stainless steel check valves are renowned for their superior resistance to corrosion, heat, and low temperatures, making them ideal for demanding environments. They exhibit excellent mechanical properties, including high strength and durability, contributing to their long service life. These valves are well-suited for applications involving high temperatures and pressures, such as in industrial processing, chemical plants, and oil and gas industries.

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Check valves operate differently depending on their design. The most common check valve is a spring-loaded in-line check valve.

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A pneumatic check valve, or air check valve, allows airflow and prevents it from going out. They are often simply called one-way air valves. The most common application is for an air compressor. A pneumatic check valve allows the compressor to keep certain parts pressurized and other parts de-pressurized. They can be located on an air receiver, discharge pipe, or as a piston check valve on the piston compressor's inlet and outlet sides.

A check valve can prevent water hammer if it is fast-acting like a spring-actuated check valve. This prevents pressure surges, which create shock waves throughout the media.

A foot valve is a check valve combined with a strainer on the inlet side. The strainer prevents debris that could clog or damage something downstream from entering the check valve. This valve is installed at the end of a section of piping as its input doesn't have a connection point. Common check valve types included in a foot valve are in-line spring assisted or an in-line ball check valve. They are typically installed at the end of a pump suction line of a water well, fuel tank, or any other application where the suction line is situated below the pump. They can keep pumps primed, prevent liquid from siphoning back, and keep debris out of the line. Figure 6 shows an example of a foot valve.

If the upstream pressure falls below the cracking pressure or there is back pressure (flow attempting to move from the outlet to the inlet), the one way check valve will close. Typically, check valves have a gate, ball, diaphragm, or disc pressed against a seal to close the valve and block flow. Gravity or a spring can assist in the closing process.

Brass check valves are excellent for air, water, oil, or fuel applications. However, they are not resistant to seawater, purified water, or chlorinated water. Compared to stainless steel, brass is less resistant to heat and corrosion and is typically used for applications with low pressure.

In-line spring-loaded check valves are common, easy to understand, and have a simple design. Figure 2 shows a spring-loaded in-line check valve in the open and closed positions. The arrows indicate flow direction. When flow enters the input port of the valve, it should have enough pressure (force) to overcome the cracking pressure and the spring force. The pressure pushes the disc (Figure 2 labeled B), opening the orifice and allowing flow through the valve. When the input pressure is no longer high enough, or there is enough back pressure, the back pressure and spring (Figure 2 labeled C) push the disc against the orifice and seal the valve shut. The spring and the short travel distance for the disc allow for a quick reaction time for closing. The spring check valve design also prevents pressure surges in the line, preventing water hammer.

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Figure 2: Spring-loaded in-line check valve open (left) and closed (right). The working components are the valve body (A), disc (B), spring (C), and guide (D).

Spring-loaded y-check valves operate similarly to in-line spring-loaded check valves. The difference is that the spring and movable disc are positioned at an angle. This creates a ‘y’ shape, hence the name of the valve. It works the same way as an in-line valve, but since the moveable components are at an angle, they can be inspected and serviced while the valve is connected to the system. These valves are larger and take up more room within the system.

As a one-way valve only allows flow in one direction, knowing the correct installation orientation is crucial. Typically, an arrow on the valve's housing (Figure 3) indicates the flow direction. If there isn't an arrow, examine the valve to ensure it is installed in the intended flow direction. If the valve is installed backward, the media cannot move through the system, and the resulting pressure build-up can cause damage.

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The main purpose of a check valve in a system is to prevent backflow, which could damage equipment or contaminate media upstream.

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A normally open check valve allows the medium to flow freely but shuts off the flow in case of backflow. A normally closed check valve prevents the flow of media through it until the cracking pressure builds up, at which point the valve opens.

Swing check valves are called ‘tilting-disc’ or ‘flapper’ check valves. They have a disc on a hinge (or trunnion) that swings open with an inlet pressure. The disc swings shut as the inlet pressure decreases or if there is backflow. If there is no spring to assist in closing, mounting orientation is important to consider to ensure that the disc swings shut with gravity. Figure 5 shows an example of a swing check valve. Read our article on swing check valves for more information.

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PVC check valves are frequently used in irrigation and water management systems. They are corrosion-resistant to most corrosive media like seawater, acids, bases, chloride solutions, and organic solvents. However, they are not immune to aromatic and chlorinated hydrocarbons and typically have a max temperature resistance of around 60 °C.

Due to their function, they are used in almost every industry. They are used on common household appliances, like dishwashers, washing machines, and wastewater lines. For industrial purposes, they are used on boilers, furnaces, gas systems, pumping applications, or vacuum systems. They are also frequently used as aquarium check valves on water and CO2 lines. Also, a miniature check valve is a popular choice where the space is limited, yet a reliable operation is essential. Two of the most common check valve applications are for water and air, which are discussed in more depth below.

While stainless steel check valves provide exceptional performance, they may not be the most cost-effective solution for applications that do not require such high durability or resistance. In such cases, alternative materials like PVC or brass may be more economical.

A water check valve is used in numerous water applications, like drinking water and wastewater. These valves are simply called one-way water valves. Plumbing check valves for drinking water applications ensure that no environmental media (outlet side of the valve) can enter the system with the safe, clean drinking water and contaminate it. For wastewater applications, they ensure that the wastewater cannot re-enter the system and cause an overflow or additional contamination. For water pumping applications, a foot valve is often used to ensure no debris enters the line and keep internal pressure for priming purposes. Sump pump check valves ensure that the discharged water does not come back into the sump pump with gravity when the pump is turned off.

A check valve allows liquid and air to flow in only one direction. The primary purpose of a check valve is to prevent backflow in the system. Check valves are inexpensive, effective, and easy solutions to the potential issue backflow. Backflow can cause a problem if the flow is contaminated because it can contaminate upstream media. For example, a sewer line will have a non-return valve to ensure that waste can leave a system (e.g., residential plumbing system) but cannot re-enter.

Figure 4: Spring-loaded ball check valve in the open position allowing flow (A), and in the closed position preventing backflow (B)

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Figure 7: The check valve P&ID symbol points in the orientation that it allows the flow with a vertical line showing it doesn’t allow backflow.

A ball check valve uses a free-floating or spring-loaded ball that rests on the sealing seat to close the orifice. The sealing seat is normally conically tapered to guide the ball into the seat and create a positive seal, thereby stopping reverse flow. When the pressure of the fluid in the inlet side exceeds the cracking pressure, the ball is dislodged from its seat, which permits flow. When the inlet pressure doesn’t exceed the cracking pressure, or there is back pressure, the ball will close with the back pressure or via the spring, effectively closing the orifice. True union ball check valves allow for easy removal and replacement of balls, eliminating the need to buy a new valve. Read our article on ball check valves for more information.