Hydrostatic pressure is an extremely important idea to know and understand as a pool owner. It wasn’t a hard idea to grasp once my father explained it to me. Had I not had this important information, I could have made some expensive mistakes when maintaining my pools and hot tubs in the past.
A Hydrostatic Relief Valve is a metal spring check valve that allows a place for ground-water pressure from underneath a pool to dissipate safely without causing damage to the pool. The valve opens when under pressure to allow water to move which releases the built-up hydrostatic pressure underneath the pool. For pool owners, this most likely happens anytime there is a large storm that places large amounts of water into the ground surrounding your pool.
Most pools will have a Hydrostatic Relief Valve but perhaps you don’t know where it’s located. what it looks like? if it’s working or if it’s leaking? I’ll share that information below.
What you need to know about the Hydrostatic Relief Valve in your Pool
When your pool is built, the area where your main drain will be located will also have a piece of PVC pipe that will be 6 inches into the ground underneath your pool shell. This PCV pipe is filled with holes and it allows for water that collects under your shell to enter into the Hydrostatic Relief Valve.
This handy little valve is the reason your pool doesn’t pop out of the ground anytime it rains or there is an excess of pressure under your pool from groundwater. This valve will activate under pressure and allow for water to come through the valve into your pool to release pressure from below. This valve, when working properly, will only allow water to flow one way into the pool so you do not lose your pool water.
Hydrostatic pressure is exactly the reason that you have heard time and time again not to allow your pool to sit empty. If there isn’t opposite pressure placed on the shell of your pool against the ground-water pressure, you risk the chance of your pool popping out of the ground. This opposite pressure would be the thousands of gallons of water that should normally be in your pool.
That does not mean the Hydrostatic Relief Valve will keep your pool in the ground if you leave the pool empty. The excess pressure from groundwater could easily overwhelm the pressure-releasing mechanism in the valve and pop your pool out of the ground. We do not recommend having your pool empty for long periods of time, it’s an expensive risk to take.
The Valve is rather simple and after your pool is installed you really shouldn’t have to worry about it for quite some time.
Does my pool have a Hydrostatic Relief Valve?
Not all pools require a Hydrostatic Relief Valve. Fiberglass Pools and any custom Shotcrete/Gunite pool will require a hydrostatic relief valve. Vinyl Liner pools will not require a hydrostatic relief valve when they are installed.
The easiest way to think about this is to ask one simple question, “is my pool basically one single piece submerged into the ground?” For example, a fiberglass pool is one single large piece of fiberglass that is inserted into the ground. This is going to require a Hydrostatic Relief Valve to stay where your installers put it. Otherwise, an extreme excess of built-up ground-water pressure could pop the whole fiberglass piece out of the ground.
You also might find that your Hydrostatic Relief Valve isn’t where it should be. The hole for the valve might be plugged. If it is, you can easily have that plug removed and replaced with a Relief Valve if you would like.
Where is the Hydrostatic Relief Valve?
Typically, the hydrostatic relief valve will be located at the bottom of your pool under a small grate that also contains your pool’s main drain. If you would like to know more about that you can check out our article about your pool’s main drain.
Once you pop off the small grate you’ll be able to see your Hydrostatic Relief Valve. Sometimes there are other plugs where the Hydrostatic relief valve should be, you can read more about those in my article here.
Does the Hydrostatic Relieve Valve need to be replaced? How often?
A hydrostatic relief valve will get worn down over time due to various issues like pool chemicals deteriorating the rings and debris build-up. You will need to start considering replacing the Relief Valve after 6-7 years.
Tip: Anytime you have to empty your pool for any type of repair or cleaning. Take that opportunity to replace your Hydrostatic Relief Valve. It could save you hundreds of dollars when compared to having any issue with the valve while your pool is full.
If you do have an issue while your pool is full. There are professionals who will dive down into your pool and replace the relief valve for you. This would be the recommendation from my family and me. I believe that any issues caused by damaging this area of the pool while trying to replace a hydrostatic relief valve aren’t a good risk vs reward situation. Any damage to the underlying main drain or area in this part of the pool would be a major headache to have repaired.
If you decide to replace your valve while your pool is empty, you will need a special tool for this endeavor. You can find the Hydrostatic Relief Valve replacement Tool here. There is another one that I did see but after reading the reviews for it, let’s just say people weren’t happy about its design.
You’ll also need a replacement valve, you can find that here.
Can a Hydrostatic Relief Valve Fail? What happens?
In a likely scenario that a Hydrostatic Relief Valve fails, it will be stuck in an open position. If we were going to have a failure, it would be better to lose pool water from the position being left open rather than a failure that left excess build-up of pressure under the pool.
If your Relief Valve gets stuck in an open position you will notice a significant decrease in the water level of your pool. The likely culprit would be after a storm, there was a lot of movement through the valve and a piece of debris like a small pebble could be stuck. You’ll want to get that valve replaced right away if that is the case or perhaps, unlodge the debris if that is possible.