What is a hydrostatic relief plug?
Have you ever looked at the bottom of your pool and seen a white ring? They are known as the Hydrostatic Relief Plug, sometimes referred to as "Hydrostats." While typically plastered in place, they are threaded into a piece of piping that runs along the floor of the pool, leading into the gravel pit beneath the pool.
Why does my pool need these?
These openings in the pool floor are strategically placed in order to allow ground water to come into the pool instead of lifting the pool out of the ground because of immense pressure. This hydrostatic pressure could be a problem for pools built in places that are topographically depressed or areas that have a high water table. The plugs are also there in case you need to open them and drain the pool so that you can clean (acid wash), paint your pool, or get rid of pool algae.
In short, hydrostatic relief plugs allow high-pressure underground water to enter the pool rather than having those forces build up under the pool shell and result in costly damage.
Where can I find the hydrostatic relief plugs in my pool?
There are usually several hydrostatic relief plugs in the pool: one in the shallow end, on at mid-depth, and one or two in the deep end. These are all typically along the center of the pool. There is sometimes a plug inside the main drain pot, directly in the bottom.
Is there a hydrostatic relief valve in my vinyl-lined pool?
They are typically not installed in vinyl-lined pools, although you may have one placed inside your main drain pot. If you don’t have one here, the pressure that builds up under the liner may result in some bubbling in the liner.
How do I remove it?
To remove a hydrostatic plug, you’ll need to chisel away the plaster from the inside of the plug in order to get a pair of pliers onto the center ridge. Twist counter-clockwise and the plug will thread out. If you are draining the pool and are leaving it empty for more than one day, you should open at least one of the floor plugs to prevent any pressure related damage.
If water begins to come into the pool (sometimes very forcefully), that’s good. The water flow should stop at some point. Use a sump pump to get the water out of the pool and redirect it to a drain that won’t cycle back beneath the pool. You should only have to open one plug/valve at a time unless you have a large amount of water coming through that won’t stop.
What are automatic hydrostatic relief valves?
Automatic hydrostatic relief valves can be located along the bottom of the main drain pot in the pool. They have a spring loaded mechanization that lets water in automatically when the pool is drained. Automatic hydrostats have an o-ring seal that keeps water from leaking out of the pool, although sometimes the o-ring slips and causes leaks of its own. Automatic valves are mostly used on commercial or high-end home pools and are rarely found in older, plaster pools.