I have two skimmers: one has two open holes, and the other has only one. “What are the two holes in a pool skimmer?” was one of the earliest questions I had when I first got my inground pool and started cleaning it.
Understanding the function of your pool skimmer is essential for maintaining a clean and healthy swimming environment. The holes in the skimmer are critical to its efficiency, yet many pool owners are unaware of their purpose.
Well, we will be going over:
- What each hole in the pool skimmer does.
- Common issues and troubleshooting tips related to skimmer holes.
- How the two holes contribute to overall pool maintenance.
Why does my skimmer have two holes?
Why are there two 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 a separate inlet in the pool wall a few feet below the water’s surface.
If the pool water level 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 a diverter valve is installed (see below).
If this didn’t happen, the pump would continue operating but 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 (usually the skimmer closest to the pool pump).
While the other skimmer will still have two holes in the bottom, only one will open both holes, with the hole closest to the pool 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 have two holes, but the one closest to the pool will likely be closed with a blanking plate.
Pool float valve assembly
None of the above will happen should the pool water level drop if your pool does not have a pool float valve assembly installed in the skimmer. These are sometimes called diverter valves.
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.
Under normal circumstances, it does very little when water is in the skimmer by allowing water to pass 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 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
Suppose your pool has an automatic water top-up, as mine does. In that case, there isn’t a need for a float valve, as the water level in the pool should never actually drop below the skimmer opening, as it gets topped up whenever it drops.
Which hole in the skimmer for the vacuum?
When vacuuming your pool, when the skimmer has two holes, 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, the one furthest away from the pool is always the one you plug the vacuum hose into. The hole nearest the pool draws water from the pool main drain if the water level drops and you have a diverter valve fitted.
If you were to plug the vacuum hose into the other hole at the bottom of the skimmer, it would not harm; 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 to attach the vacuum hose so that any debris is caught in the skimmer basket, you do not need to worry about which hole to use.
You can buy skimmer plates very cheaply if you wish to try a model like this Hayward model, but they are available for all models.
If you have a dedicated pool vacuum port in the side of the pool, you should use this to vacuum the pool.
If you have low suction, then read this article – pool skimmer has no suction
Pool Care Handbook and Video Course
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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 always be used when the pump is running to remove debris, such as leaves, bugs, pollen and even sun oil floating on the pool’s surface. 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 the strength of your suction, 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, the water level must drop below the level of the skimmer.
There are several possible reasons why your pool is losing water:
- All pools lose water through evaporation. The evaporation rate can be significant, particularly on warm and windy days with low humidity. Amazingly, 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 help keep your pool water warm and drastically reduce the evaporation rate since there will be little water surface exposed to the air. - If you have an automatic top-up system, check that the float is not stuck in the up position. This will prevent water from flowing into the pool to raise the level.
- When you backwash a pool, the water is pumped out into the garden or the sewer system, causing the water level to drop. It would be standard 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 go to the garden or the sewer.
- If none of the above seems to be the reason, you may leak into your pool lining or pipework.
See my post – Why is my pool losing water? for more information.
Related posts
Why is my skimmer not skimming?
Do you remove the skimmer basket when vacuuming a pool?
FAQs
Why is one skimmer hole plugged?
If you have two skimmers, one will likely have two holes open, and the other will have one closed with a plug and the other open. That is because the one nearest the pump will have two holes in the pool skimmer open. One hole will be to the pool pump, and the other will 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?
If you have more than one, only one should have two open skimmer holes. The hole nearest the pool is the equalizer, which prevents the pool pump from running dry if the water level drops below the skimmer opening.
Why does my pool have two skimmers?
Many pools have more than one skimmer, which helps create a good water flow to pull in any floating debris on the pool’s surface.
Should pool skimmers be on all the time?
Pool skimmers should generally be left on whenever the pool pump runs. The pump doesn’t need to run 24/7, though; it is usually enough to filter the pool’s water once per day.
Does a pool need two skimmers?
It is not usually necessary for a small pool to have two skimmers. However, the larger the pool, the more likely it is to have them. 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 12 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
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