Check Valves

Check Valves

Check Valves

A check valve is a one-way flow valve, with a purpose to keep water from flowing backwards or to prevent cycling of water in solar systems or bypass loops. Check valves are used in pool, spa and fountain plumbing to keep water flowing in only one direction.

When are Pool Check Valves Used?

The purpose of a check valve 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’.

Solar Pool Heaters

Solar pool heater panels that are roof mounted may use check valves on the supply and return pipes. A check valve placed on the pipe that leads to the solar panels will prevent drain down of the solar system, when the pump shuts off. A second check valve may be placed on the pipe that returns from the solar system, to prevent water from cycling backwards through the solar panels, when the solar system is turned off.

For pools that winterize their system during winter, you can place PVC unions on either side of the check valves to allow for system drain down and/or blowing out the solar panels with air more confidently. New style check valves from Jandy, Pentair and Waterway are serviceable, and can be opened to allow for solar system drain down, and to be sure no water is trapped on top of the flapper, after winterizing.


Pool chlorinators can potentially damage a pool heater or filter, if they are installed too close to other equipment. A check valve can be installed just before the in-line chlorinator or just before an off-line chlorinator injection point, to keep high concentrations of chlorine from backing up into heaters, filters or other nearby pool equipment.

Raised Spas

Remember that water seeks its own level, and when a spa, fountain or water feature is placed at a higher level than the pool water, it will naturally gravity drain (into the pool), when the pump shuts off. Check valves are used on spa return lines, and/or spa overflow lines, to keep attached spas on shared systems from losing gravity draining when the pump shuts off. Similarly, check valves can also be used for wall fountains, deck jets and waterfalls, to prevent draining when they are not being used.

Spa Blowers

For pools with attached spas, a blower line is often attached to add forced air into the spa jets. Many builders place the blower on top of a tall pipe, several feet above the pump level, to keep water from entering the blower motor. As added insurance, may builders install a check valve on the blower pipe, to keep water from backing into the blower motor.


Ozonators use small ball check valves on the ozone feed tube that carries the ozone gas to the injection fitting (another type of small ball check valve). Manufacturers recommend regular replacement of the ozone tubing and check valve, to keep the gas flowing in one direction only, and to prevent water from backing into the ozone production chamber.

Spa Overflow Lines

For pools with attached spas with a controller, a spa overflow line or spa make-up line (bypass line) is often used to send enough filtered water to the spa returns to keep it clean and circulated, as the spa drain and spa return valves are normally closed. When the valves are opened to Spa Mode, a check valve is used on the spa over-flow line to keep water from looping backwards through the overflow pipe.

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. Jandy check valves are available to fit pipe sizes of 1.5” to 3”.

Waterway has redesigned the original Jandy check valve into their own version, the Waterway Truseal Serviceable check valve, by securing the lid with a quick opening lock ring, rather than the 8 screws used on Jandy check valves.

Pentair also has a line of inline check valves available, based on the Pac-Fab Compool line, another Jandy valve redesign, and also continues to make Ortega spring loaded check valves.

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.

Installing Pool Check Valves

The most important thing to remember is to install the check valve with the printed arrow pointing in the direction of the water flow.

Most check valves are glued into place with heavy duty PVC or ABS cement, after the pipe and valve surfaces are cleaned and primed. Be careful not to use too much glue on the diverter end, to avoid gluing the check valve permanently closed.

Horizontal installation of pool check valves is preferred, to reduce the pressure on the valve, but a vertical installation can also be made, with the flow running upwards.

Jandy check valves and others allow a plumbing flexibility of 1.5” or 2” pipe fitting inside of the check valve, or you can glue on a 2” or 2.5” coupling around the outside of both ports, and attach the larger pipe diameter into the couplings. This allows you use a check valve size that is one size larger than your pipe size, to reduce resistance and clogging potential. You’ll find these valves listed sizes as 1.5”/2”, 2”/2.5”, and 2.5”/3”, which means the check valve will accommodate both pipe sizes.

NOTE: Before installing a check valve to correct a previously non-existent drain-down problem, check first for any air leaks on the system (pump, filter, valves, air bleeders – anything with an o-ring) that may be allowing air to be drawn into the system, contributing to a gravity drain down. Water will stay in the pipes, pump and filter as long as it is air-tight, like the finger on the end of a straw. Small air leaks if found, can be fixed, negating the perceived need for inline check valves.

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