the correct check valve to ensure proper functionality during system operation: Non-return check valve: These allow flow
direction while preventing reverse flow in the opposite direction. The direction in which the fluid or gas can flow is called the free flow direction; the direction in which fluid is prevented from flowing is the checked or non-return direction. Check valves are found in common household
items. For example, when a raft or air mattress is inflated, the check valve allows air in and prevents its escape until a release is activated. Irrigation systems also use check valves – they allow water to spray out of the sprinkler head and prevent mud and rainwater from flowing back into pipes. The purpose of a check valve in an application
will determine some design parameters. Generally, check valve functions can be divided into three categories, and it is important to select
check valve, also known as a non-return or one-way valve, is a mechanical device that allows a gas or liquid to flow freely in one
in one direction with minimal pressure loss and prevent flow in the opposite direction, with a common application being in pump inlet and outlet ports. One check valve placed at the pump inlet allows fluid to flow from the desired source; and a second located at the outlet allows the pump to dispense fluid. Vent check valve: These are designed to open
and prevent pressure build-up in a system, while preventing flow in the checked, or non-return, direction. In a vehicle fuel tank, for example, gasoline volume expands as it warms and contracts as it cools. As the volume of gasoline increases, air must exit the tank to alleviate the change in pressure. A check valve vents air when pressure increases, preventing damage within the tank and to connected components. It also prevents debris and moisture from getting into the tank. Fill and drain valve: These permit fluid to flow
into a system and prevent it escaping once filled. Fill and drain valves are commonly found near the tank of any hydraulic or pneumatic system. If the system needs maintenance or will be retired, safety precautions may require depressurisation of the charged system. The check valves used to
fill the system may be piloted open, mechanically or manually, to drain the system fluid.
Check valves are available in a variety of configurations, with common configurations featuring a ball bearing, poppet, disc, or other seal held against a seat when pressure is in the checked direction; and in many cases, a lightly loaded, compressed spring, is used. The combination of these components creates the internal seal used to prevent flow in the checked direction. If the application requires flow in the checked
direction under certain conditions, the check valve may include additional features to force it open against pressure. Some check valves may include a feature that allows them to be manually piloted. Alternatively, one common configuration for hydraulic systems is a pilot-operated check valve. There are several factors that must be
considered to ensure the proper operation of a check valve within a system: system pressures, flow rate; leakage; cracking pressure; materials; and envelope. In addition, a number of environmental factors will impact the design of a check valve – such as operating fluid, operating life, temperature, external pressures, etc.
The full guide is available in PDF format from The Lee Company:
www.theleeco.com/resources/ebooks/an-engineers-guide-to-selecting-a-check-valve/
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