Typically, check valves have a gate, ball, diaphragm, or disc that is pressed against a seal to close the check 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 check valve will close. 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). How does a check valve work? Cracking pressureĪ check valve requires a minimum upstream pressure (pressure differential between inlet and outlet) to open the valve and pass the media through it. Double check valves and dual check valves.An arrow on its bonnet indicates the check valve flow direction. The atmospheric vent allows the disposal of purged water into an existing drain. Check valves with vents are used as three-way check valves to protect the incoming water supply from contamination caused by backflow. There are various sizes, designs, and materials to ensure there is a check valve for every application. Figure 1 shows an example of a check valve. For example, a sewer line will have a non-return valve to ensure that waste can leave but not re-enter the system it came from. Backflow can cause a problem if the flow is contaminated and, therefore, contaminates the media upstream. Check valves are cheap, effective, and easy solutions to a potential issue. The primary purpose of a check valve is to prevent backflow in the system. A check valve, also called a one-way valve, is a device that allows the flow of fluids to move only in one direction.
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