I have two skimmers, one has two holes and the other only one. Why are there two holes at the bottom of a pool skimmer was one of the earliest questions I had when I first got my inground pool and started to clean it.
There are two holes at the bottom of a pool skimmer because the first one sends water to the pool pump and the second, known as a pool equalizer line, is there to prevent the pump from running dry should the pool level drop below the bottom of the skimmer by drawing water from the pool main drain.
Where there is more than one inground pool skimmer, the second usually has one hole blanked off with a screw-in blanking plate as only one equalizer is required per pool.
Why does my skimmer have two holes?
What are the 2 holes in my pool skimmer? Well, there are two holes for a reason – one hole at the bottom of the pool skimmer takes water to the pool filter, via the pool pump, to allow it to be cleaned and then returned to the pool by the return line/s.
The second hole, called an equalizer line, connects to either the main drain inlet at the bottom of the pool (sometimes called a bottom skimmer) or to a separate inlet a few feet below the surface of the water in the pool wall.
If the water level in the pool falls below the water entrance at the top of the skimmer, so no more water is running in over the weir door, or if the skimmer basket becomes clogged so water cannot pass through, then water will start to be drawn from the pool via the second hole. But this only happens if you have a diverter valve installed (see below).
If this didn’t happen then the pump would continue to operate but would start to run dry. Prolonged dry running would cause the pool pump to overheat and fail. This would mean a costly repair that no-one wants.
Why is one skimmer hole plugged?
If you have more than one skimmer you will probably find that only one has both holes open (normally the skimmer closest to the pool pump).
While the other skimmer will still have two holes in the skimmer bottom, only one will have both holes open with the hole closest to the pool being plugged.
This is because only one is required to have two holes at the bottom of a pool skimmer open in case the water level drops to prevent the pump from running dry.
The other skimmer/s may actually have two holes but the one closest to the pool is likely to be closed with a blanking plate.
Pool float valve assembly
None of the above will actually happen, should the water level drop in the pool, if your pool does not have a pool float valve assembly installed in the skimmer. These are sometimes called a diverter valve.
Many pools may be designed to use these (which is why there are two holes) but over time people either don’t put them back in after cleaning or they break (or perhaps don’t even know what they are).
Pool skimmer float valve operation
A float valve assembly, also known as an equalizer assembly, sits over the 2 holes at the bottom of the skimmer.
It does very little under normal circumstances when there is water in the skimmer by allowing water through it and into the pool pump line.
However, if either the pool level drops to below the skimmer opening, or if the skimmer basket becomes so full that no water can be drawn through it (so no water goes to the pump) then the float in the valve is sucked down forming a seal.
This causes water to be drawn from the pool drain pipe (equalizer) which then flows down the pool pump line.
These diverter valves prevent the pump from running dry and becoming damaged.
If you do not have one I suggest you buy one to fit your particular skimmer. The most common float valve assemblies are:
- Hayward SP1070FV Float Valve Assembly
- Pentair 08650-0079 Float Assembly
- Southeastern New Pool Skimmer Float Valve Assembly
- Waterway Plastics 806105099358 Renegade Skimmer Float Valve
- Custom 25140-000-700 Generic Skimmer Float Valve
If your pool has an automatic water top up, as mine does, then there isn’t really a need for a float valve as the water level in the pool should never actually drop below the skimmer opening as the water level gets topped up whenever the level drops.
Which hole in skimmer for vacuum?
When vacuuming your pool you should insert one end of the vacuum hose into the hole that goes to the pool pump and filter.
If there are two pool skimmer holes at the bottom of your pool skimmer then this is always the one furthest away from the pool you plug the vacuum hose into. The hole nearest the pool is the one that draws water from the pool main drain if the water level drops and you have diverter valve fitted.
If you were to plug the vacuum hose into the other hole at the bottom of the skimmer it would do no harm as frankly, nothing would happen as there is no suction from that hole. You could try vacuuming all day and get nowhere!
If you use a skimmer plate into which you attach the vacuum hose so that any debris is caught in the skimmer basket then you do not need to worry about which hole to use.
You can buy skimmer plates very cheaply should you wish to try one such as this Hayward model but they are available for all makes of skimmer.
If you have a dedicated pool vacuum port in the side of the pool then you should use this to vacuum the pool.
Pool Care Handbook and Video Course
When I bought my house with a swimming pool, I knew absolutely nothing about pool care. I just winged it for a while, making many mistakes along the way.
Fortunately, I was recommended Swim University’s Pool Care Handbook and Video Course. I bought it and it was an absolute game-changer.
It was the best money I spent that year. I learned everything from basic cleaning to advanced troubleshooting. Swim University offers a no-quibble refund policy too so what do you have to lose?
Should pool skimmers be on all the time?
Pool skimmers should be used at all times the pump is running in order to remove any debris such as leaves, bugs, pollen and even sun oil that may be floating on the surface of the pool. By used, I mean that the valve or valves controlling the flow of water from the skimmers to the pump should be open.
Depending on how strong the suction you have then you may also have the valve to the main drain at the bottom of the pool open, at least part way.
Why might the water level in the pool drop?
For the second hole at the bottom of a pool skimmer to come into play then the water level must drop below the level of the skimmer.
There are a number of possible reasons why your pool is losing water:
- All pools lose water through evaporation. The rate of evaporation can be quite significant, particularly on warm and windy days with low humidity. I found it quite amazing when I discovered that a pool can lose between 2-4 inches per week due to evaporation alone.
You can significantly reduce this water loss by using a solar pool cover. These will not only help to keep your pool water warm but also will drastically reduce the rate of evaporation since there will be little water surface exposed to the air.
- If you have an automatic top up system then check that the float is not stuck in the up position which will prevent water from flowing into the pool to top up the level.
- When you backwash a pool the water is pumped out into the garden or the sewer system so the water level will drop due to that. It would be normal practice to top up with a hose (unless you have an automatic top up in 2 above). See my article “How to backwash a pool – step by step“
- If your pool is very dirty then you may need to vacuum to waste with the filter multiport valve in the waste position. When you do the water level will lower quickly as all the vacuumed water will be going to the garden or the sewer.
- If none of the above seem to be the reason then unfortunately it may be that you have a leak either in your pool lining or in your pool pipework.
See my post – Why is my pool losing water? for more information.
Why is one skimmer hole plugged?
If you have two skimmers it is likely that one will have two holes open and the other skimmer will have one closed with a plug and the other open.
That is because the skimmer nearest the pump, as well as having an opening to the pool pump, will also have a pipe (equalizer) from the main drain to ensure the pump does not run dry if the water level drops below the skimmer.
Should both holes in my skimmer be open?
Only one skimmer should have both holes open., if you have more than one simmer. The hole nearest the pool is the equalizer to prevent the pool pump from running dry if the water level in the pool drops below the skimmer opening.
Why does my pool have two skimmers?
Many pools have more than one skimmer as this helps to create a good flow of water in order to pull in any floating debris on the surface of the pool.
Should pool skimmers be on all the time?
Pool skimmers should generally be left on in order to operate whenever the pool pump is running. The pool pump doesn’t need to run 24/7 though, just enough normally to filter the volume of water in the pool once per day..
Does a pool need two skimmers?
It is not normally necessary for a small pool to have two skimmers. The larger a pool is then the more it is likely to have. The shape of the pool can also determine the number needed to create a surface flow to capture floating debris.
I have had hot tubs for over 20 years and a pool for the last 10 years. I had to learn how to clean, maintain and fix them the hard way. Since then I have helped many friends and neighbors with their pools and now I want to share everything I have learned with you. About Me