What does a check valve do?

It allows flow in one direction and automatically prevents it from reversing, protecting pumps, meters, and equipment from backflow, back-siphoning, and contamination.

Which way does a check valve go?

In the direction of the arrow cast into the body. Forward flow opens it; reverse flow closes it. Installing it backward blocks your line.

What is cracking pressure?

The minimum forward pressure needed to open the valve. Spring-loaded checks have a specified cracking pressure; match it to your system so the valve opens fully but still seals against backpressure.

Is a check valve the same as a backflow preventer?

No. A single check valve resists backflow but is not a certified backflow-prevention assembly. Code-required backflow protection uses a double-check or reduced-pressure assembly.

Check Valves: Types, Sizing & Selection Guide

Check Valves: How to Choose the Right One

A check valve (also called a one-way valve or non-return valve) lets fluid flow in one direction and closes automatically to stop it flowing back. That backflow protection sounds simple, but choosing the wrong type, orientation, or cracking pressure is one of the most common and most preventable mistakes in a fluid system. This page is built to help you make the correct choice in a few minutes, then send you straight to the right valve.

If you already know what you need, jump to the collection: swing, spring, inline, ball check, wafer, or Y-pattern check valves. If you are not sure, start below.

The main check valve types, at a glance

Most check valves fall into a handful of families. The differences that matter to you are how they seal, which way they can be mounted, and how much pressure it takes to open them.

Swing check valves

A hinged disc swings open with forward flow and drops closed against a seat when flow stops or reverses. Low pressure drop, good for larger lines and steady flow. Must be installed in the correct orientation (horizontal, or vertical with upward flow). Can slam and cause water hammer on sudden reverse flow. Shop swing check valves →

Spring (in-line spring-loaded) check valves

A spring holds a poppet closed until forward pressure overcomes it, so they open at a defined cracking pressure and can mount in any orientation, including vertical-down. Quiet, fast-closing, and ideal where water hammer is a concern. Shop spring check valves →

Inline / cartridge check valves

Compact spring-and-poppet checks in a small threaded or barbed body, sized from 1/8 in. up. The workhorse of chemical metering and dosing systems, small pumps, and instrumentation. Shop inline check valves →

Ball check valves

A ball lifts off its seat under forward flow and drops back to seal against reverse flow. Compact brass compression sizes for low-pressure lines, instrumentation, and appliance connections. Shop ball check valves →

Wafer (double-door) check valves

Two spring-loaded half-discs fold together against reverse flow inside a thin body that bolts between flanges. Very compact and light for large-diameter lines. Common in fire protection (UL/FM rated), HVAC, and municipal water. Shop wafer check valves →

Y-pattern check valves

A check disc set at an angle in a Y-shaped body, giving low pressure drop and easy in-line servicing without removing the valve. Available threaded or solder-connect in brass. Shop Y-pattern check valves →

Want the full engineering breakdown of each type? See Check Valve Types Explained or the side-by-side types comparison.

Choose by how you will use it

Chemical metering / dosing pump: inline or spring check in 316 stainless or PVC with a Viton seal. See metering pump check valves.
Water treatment / sodium hypochlorite: PVC or 316 stainless with chemically compatible seals. See our sodium hypochlorite piping guide.
Pump discharge where water hammer is a risk: spring-loaded (silent) check, not a swing. See spring check valves and how to stop water hammer.
Large water or HVAC line: wafer check between flanges. See wafer check valves.
General plumbing / threaded line: brass swing or Y-pattern. See swing or Y-pattern.

Choose the material

Material governs chemical compatibility, pressure rating, and cost. The seal (seat) material matters as much as the body. Brass suits water, air, and oil; 316 stainless suits chemicals and higher temperatures; PVC suits water treatment and chlorine; ductile iron suits large water and fire lines. Full help in Check Valve Material Selection and the Valve Seat Material Guide. Shop by material: brass, stainless, PVC.

Size and cracking pressure

Size the valve to the line, not oversized, so forward flow keeps it fully open and stable. And check the cracking pressure, the forward pressure needed to open the valve. See the cracking pressure guide and the pressure and temperature ratings chart.

Install it the right way

Every check valve has a flow-direction arrow on the body; flow must match the arrow. Swing checks need horizontal or vertical-upward flow; spring, inline, and ball checks can run in any orientation. Full rules: Check Valve Installation: Flow Direction & Orientation. Troubleshooting a problem valve? See Check Valve Troubleshooting.