A check valve closes automatically when the forward fluid pressure drops below the valve's cracking pressure, or when reverse flow occurs. Without external controls, it relies on internal mechanisms, back pressure, and gravity to force a disc, ball, or diaphragm against its seat to block reverse flow.
Diaphragm check valves consist of a rubber diaphragm clapper that flexes open when the pressure on the upstream side is greater than the pressure on the downstream side and closes when this pressure is equalized or lowered below a set pressure differential.
Check Valves: Let Flow Direction Guide You
Check valves (one-way flow) don't have handles, but you can test them: Open (Normal Flow): Fluid flows freely in the direction of the arrow on the valve body. Closed (Reverse Flow): The internal flap/disc blocks flow—you'll hear a “clacking” sound if reverse flow is attempted.
Check valves:Check valves permit flow in one direction and prevent backflow. They are always "on" in the intended flow direction. Check valves are fluid-operated; unlike manually operated valves such as gate or ball valves, the status of a check valve automatically responds to the conditions within the pipeline.
The height to install a check valve on a sump pump is 6 to 12 inches above the pump on the vertical discharge pipe. This specific placement stops water from falling back into the sump pit when the pump shuts off. That action, called “backflow,” causes the pump to short-cycle and wear out too quickly.
To test a check valve, verify it allows flow in only one direction and prevents backflow. For a removed valve, perform the "breath/blow test"—air should flow freely in the direction of the flow arrow, but you shouldn't be able to blow air backward. For an installed valve, perform a pressure or bubble test.
Identification mainly relies on the number of handwheel turns. It is necessary to know how many turns are required to move the valve from fully closed to fully open. Typically, when fully closed, the handwheel cannot be turned further clockwise; when fully open, it cannot be turned further counterclockwise.
To instantly tell if a standard valve is open, check the handle's alignment: if the lever is parallel to the pipe, the valve is open. If it is perpendicular (forming a T-shape across the pipe), the valve is closed.
A check valve that is normally open allows a medium to flow through it freely from one direction to another. However, when there is backflow, the valve will shut due to the pressure on that end of the valve.
To fix a stuck check valve, safely shut down the system and relieve pressure. Remove the valve or open its housing to clean out internal debris or mineral scale. Gently tap the valve to break up rust, and if the internal spring or seal is corroded, replace the part.
However, like any mechanical component, a check valve can sometimes become stuck due to debris, mineral buildup, or prolonged wear. When this happens, it can compromise system performance, reduce efficiency, and even cause equipment damage.
Pilot-to-close check valves operate as standard check valves, but block flow completely when a pilot signal is supplied; capable of flows up to 38 lpm (10 gpm) and pressures up to 240 bar (3,500 psi).
Installing the valve in the wrong direction
The valve must allow water to flow forward only. Installing it backwards means it won't stop backflow and can cause leaks or damage.
What a closed valve looks like depends entirely on its type and handle, but in most cases, a closed position means the handle is turned 90∘90 raised to the composed with power90∘ across the pipe, or a wheel is turned as far clockwise as it can go.
Diseased valves can become prolapsed where they don't completely close; this is called regurgitation. If this happens, blood leaks back into the chamber and not enough blood can be pushed forward through the heart (Figure 2).
How to Identify Normally Open vs. Normally Closed
In a normally operating internal combustion engine, the intake and exhaust valves are opened by the camshaft (or cam lobes) and closed by the action of valve springs. The camshaft lobe pushes the valve open against spring pressure, and when the cam lobe moves away, the spring snaps the valve shut.
For the vast majority of valves, the closing direction is clockwise (to the right). A helpful rule of thumb is "righty-tighty, lefty-loosey". However, the exact closing action depends on the type of handle your valve has:
4 Common Problems With Valves You Need To Be Aware Of
Check valve failure symptoms include backflow (reverse fluid movement), pressure drops, "water hammer" (banging noises), and vibrating or chattering pipes. If a check valve sticks or fails to seal properly, it can lead to frequent equipment cycling, pump strain, visible leaks, and increased energy consumption.
Causes of Failure:
If there are loose parts, then you may be able to repair or replace just those components. If the valve itself is ill-suited to the current use case because it requires a higher PSI to crack (i.e. your flow is too low), then you'll need to replace the valve entirely with the right match.