Check Valves

Check valves (also called non-return valve, one-way valve) are used to allow the flow of fluid in only one direction. They prevent the flow of fluid in the other direction.  Check valves work automatically and do not need to be operated. Most available types have a small spring to close the valve, the medium pressure in the forward direction opens the valve. Note that there is a minimum pressure required to open the valve (usually called cracking pressure). The purpose is to force water in a pipe to flow in one direction only, and also to prevent gravity draining of water in the filter, pump and pipes, when the pump shuts off. They are also used to keep raised spas, fountains or solar heaters full of water, when the pump shuts off, again to prevent gravity draining. There are other uses for pool check valves, see below.

Raised Pool Pumps

The most common use for a check valve is to hold the water in the pump when the motor shuts off. As such, a common location for a check valve is on the incoming suction pipe, in front of the filter pump. For best results with pump priming, especially for pumps lifting more than 24” from the water surface, the check valve should not be installed directly against the pump intake, but 12”-18” in front of the pump. This allows not only a full basket, but also a full pipe of water.

If space is not available for a check valve on the horizontal pipe that comes into the pump, check valves can be installed on the vertical suction lines, or the skimmer and main drain pipes. When doing so however, you will need to install check valves on all vertical suction pipes, unless one pipe normally has a closed valve, like a spa drain pipe.

For pools that winterize their system during winter, placing check valves on vertical suction lines prevents air from being blown backwards through the skimmer and main drain pipes. There also is the concern of water being trapped on top of a vertically mounted check valve. Installing PVC Unions directly beneath a vertical check valve will overcome the problem, and allow full winterization of the suction lines. Another option is to move the pump further back from the incoming valves, and/or reconfigure the suction manifold, to add more horizontal pipe space for mounting a single check valve, between the pump and any suction line valves.

Pump check valves help inground pool pumps to catch prime quickly, by keeping the water in the pump and filter, when the pump shuts off. This ensures fast pump priming for long motor life, and also prevents pool filters from back flowing DE or dirt to the pool, when the pump is off. Check valves are not normally used on aboveground pools, which have their equipment located below water level, in what is called ‘flooded suction’.

Types of Pool Check Valves

In regards to internal operation, there are three basic types, swing check valves, spring check valves and ball check valves. Swing check valves have a flapper door or diverter on a hinge that swings closed when the pump is off, and swings open, in one direction only, when the pump is on and pushing water through the valve. Ball check valves utilize a round ball inside that rolls closed when not under pressure, and rolls open with the water flow.

Spring check valves have a ball cone or disk diverter and a compression spring. As water flow increases, the spring is compressed, separating the disk or cone from the housing and allowing water flow. When the pump is off, or lower than the required cracking pressure of 1 to 3 lbs psi, the spring seals the diverter into the housing, stopping water flow.

Swing check valves are generally preferred over spring valves in pool and spa plumbing, because they don’t clog as easily, and a steel spring can deteriorate in harsh water conditions. And the pressure required to open a spring check valve adds pressure to the overall system.

The preferred pool and spa check valve is the type pioneered by Jandy, an ABS swing check valve with a clear, removable lid for inspection, repair or winterization. They are available in a straight flow-thru 180° design, or also in 90° elbow check valve. 

Valterra has a Swing/Spring Combination check valve that can be installed in any position. Clear housing, union connections and a low 0.5 psi required to open the valve.

Lower cost pool PVC swing check valves are available, with the disadvantage that they are not accessible or serviceable, and don’t have a clear lid for visual inspections, but will function just as well as more expensive check valves, in most cases. Inline check valves are also available with union connections to allow for servicing or for winterizing purposes.

Ball check valves use an internal ball to make a seal on one end of the valve when the pump shuts off. When the pump is turned on, the ball is pushed by water flow to the other end, allowing water to pass through the valve.

Hayward makes a popular series of True Union ball check valves that are fully serviceable and ruggedly designed. Double unions allow for complete disassembly to service or repair.

Ball valves are also used in smaller check valves, like ozonator check valves, or for liquid chemical injection fittings, and the small check valve and injector fittings used on off-line tablet chlorinators.