Check valves are automatic flow-control devices used to limit fluid movement to one direction. They are also known as non-return valves, reflux valves, retention valves, foot valves, and one-way valves.
This reference explains the basic check valve terminology used in piping documentation and introduces the accompanying DWG resource. Use it alongside related references for pipe fittings, flanges, and piping terminology when reviewing or drafting a piping system.
check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) 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, or 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. The bodies (external shells) of most check valves are made of plastic or metal.
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How a check valve works
A check valve has two openings: one through which fluid enters and another through which it leaves. Its operating principle is automatic. Fluid movement in the intended direction allows passage, while reverse movement causes the valve to prevent or restrict backflow.
Unlike many manually operated valves, check valves generally do not use a handle or stem operated by a person or an external control system. Their action depends on the fluid flow condition and the valve’s internal design. The exact behavior during installation and operation should be confirmed from the applicable valve documentation and project requirements.
Check valve terminology
The names used for check valves can vary by industry, application, or reference source. The terms below describe the terminology associated with this page rather than separate guarantees of construction or performance.
- Check valve: the general term for a valve intended to permit flow in one direction.
- Non-return valve: a term emphasizing prevention of reverse flow.
- Reflux or retention valve: alternative terminology used in some piping references.
- One-way valve: a plain-language description of directional flow behavior.
- Foot valve: a related term that may identify a particular check valve arrangement; confirm the intended design before specifying it.
At-a-glance reference
- Valve category: automatic, two-port valve.
- Flow function: normally permits flow in one direction.
- External control: most examples do not have a handle or stem.
- Common body materials: plastic or metal.
- Drawing resource: a DWG file is provided with this reference for CAD and drafting workflows.
Using the DWG reference
The downloadable DWG can support piping layout, drafting, and symbol or component reference work. Treat the file as a drawing resource, not as a substitute for project specifications, manufacturer documentation, installation requirements, or engineering review. When connecting this topic to other site content, useful related references include pipe dimensions and schedules, fittings, flanges, and CAD/DWG drafting resources.
Check valve FAQ
What is another name for a check valve?
Common alternatives include non-return valve, reflux valve, retention valve, foot valve, and one-way valve.
How many openings does a check valve have?
Check valves are two-port valves, with one opening for fluid to enter and another for fluid to leave.
Are check valves manually operated?
Most check valves operate automatically and do not use a handle or stem controlled by a person or an external control system.
What materials are check valve bodies made from?
The source description identifies plastic and metal as common body materials. The correct material for a particular installation must be verified from the applicable product and project documentation.