The swimming pool skimmer box works as the first line of defense to keep the pool water clear of debris and prevent larger items of debris from being pumped to the filter. When the pump is operating the weir flap is drawn open and pool water flows through the skimmer box to the filter.
The use of a skimmer sock enhances the skimmer’s filtering capability and reduces the frequency of filter cleaning. After all it’s easier to empty a skimmer basket and filter sock than clean the filter cartridge or backwash a sand filter.
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How Does a Pool Skimmer Box Work?
A pool skimmer is a plastic box fitting with a rectangular opening built into the side wall of the pool. The box opening is set just below the top of the pool so the water level will be halfway on the skimmer weir flap.
The pool skimmer box works with a weir flap that floats open and closed with the water level. When the pump is off the weir flap floats to the closed position preventing debris drifting back into the pool.
When the pump operates the weir flap is open and pool water flows into the skimmer box. The skimmer box contains a removable plastic filter basket that traps larger items of debris such as leaves, flowers and insects that are floating on the surface.
The pump draws water from the bottom of the skimmer box through the pump to the filter. After the water is filtered it returns to the pool through the outlet jets in the wall of the pool.
You must empty the skimmer basket periodically to keep the filtration system working effectively. Simply open the skimmer box lid and remove the basket. Empty the basket into the trash and replace into the skimmer box. Always keep the lid on the skimmer box as the suction is dangerous to young children and pets.
How high should pool water be on skimmer?
A swimming pool skimmer box works properly when the water level is halfway up the weir flap.
If the water is too high floating debris passes the skimmer box.
If the water is too low the skimmer box may run dry damaging the pump motor.
What happens if pool water is above the skimmer?
The pool skimmer box works incorrectly if the water level is too high and above the top of the skimmer box.
When the pump operates the weir flap will open and water will flow into the skimmer box. However, the skimmer box will not be able to skim the surface of the pool as the water will be drawn from below the surface of the pool.
As a result, any debris floating on the surface will remain floating on the surface. After the pump has switched off the floating debris will sink to the bottom. The debris will decay causing organic stains on the bottom of you pool.
Switching your pump valve to drain and running the pump for a minute will lower the water to the correct level. Remember to switch the pump valve back to filter again.
Some swimming pools are fitting with overflow plumbing to drain excess pool water into the storm water drain. The pool water level will automatically drain off to the midway point on the skimmer box. The pool water level can never rise above the desired level. This is great for pool owners who go on holiday as they don’t have to worry about rain overflowing the pool.
What happens if pool water is below the skimmer?
The pool skimmer box works incorrectly if the water level is too low and below the bottom of the skimmer box.
When the pump operates the weir flap is open and water will not flow into the skimmer box.
If the skimmer box is fitted with an equalizer pipe, water flows from the pool through the equalizer pipe into the skimmer box.
If there is no equalizer pipe fitted, the skimmer box will be sucked dry and air will be drawn into the pump and filter. There will be a gurgling noise from the skimmer. If this is allowed to continue the pump will dry run and overheat. The pump motor may be damaged.
Some swimming pools are fitting with plumbing to add water to the pool when the water drops below a set level. The additional water may come from a rainwater tank or the town water supply. Usually there is a valve set in the plumbing to detect the water level and open when the level drops. The pool water level can never drop below the desired level. This is great for pool owners who go on holiday as they don’t have to worry about water evaporation and the skimmer not working.
Danger of Swimming Pool Skimmer Box
Older-style fibre-glass pools with skimmer boxes molded into the side are highly unlikely to be safe as children can easily lift the cover and sit inside them. These old skimmers require modification to comply with current safety rules.
To a young child, an uncovered skimmer box looks like a potty toilet or seat. If young children sit in a skimmer box when the pump is on it can cause horrific injuries and even death. Young children have been dis-embowelled by the strong pump suction after sitting in a pool skimmer box.
Newer swimming pools have a skimmer box built into the ground where strong suction cannot build up when a child sits in the box. Newer skimmers have a lid that locks into position and cannot be opened by a small child.
These days this problem is less of an issue as all swimming pools must have a safety pool fence to prevent young children accessing the pool area.
How many skimmer boxes does a pool need?
Generally, the average backyard swimming pool has one skimmer box. Larger pools will have extra skimmer boxes based on the surface area of the pool. You may have noticed hotel swimming pools have several skimmer boxes.
Swimming pools are constructed to building standards that specify one skimmer box for every 400 sq. ft. of surface area.
How many return jets should a pool have?
A typical backyard swimming pool has two or three water return jets. Larger pools will have more skimmer boxes and more return jets. Generally, there will be 2 or 3 return jets for every skimmer box.
After water pumps through the filter it returns to the pool through the outlet jets. The outlet jets are built into the side walls of the pool at least half a meter (2 ft.) below the surface. The outlet jets point in different directions to circulate the water around the pool.
Why do skimmers have two holes?
Many skimmer boxes have two holes located at the bottom of the box. The first hole is the pipe connecting to the filtration system. The pool pump draws water from the pool through the skimmer box to the filter.
The second hole is a pipe connecting to the bottom of the pool at the deep end under the drain plate. The hydrostatic valve is also located under the drain plate. Some pools have the second pipe exiting into the pool lower down under the skimmer box.
If the water level ever falls below the skimmer flap the pump cannot draw water into the skimmer box. This will cause the pump to take in air and run dry damaging the pump motor. This second pipe is an equalizer line to prevent the pump sucking air from an empty skimmer box. The pool pump draws water up the equalizer pipe to refill the skimmer box so the pump won’t run dry.
If you ever want to empty the pool you can purchase a connector to join the two holes (pipes) together. When the pump is running water will be drawn from the bottom of the pool through the equalizer pipe into the filter pipe. Set the pump valve to drain and the pump will empty the swimming pool right to the bottom. There is no need to purchase a separate submersible pump or call in the pool service people.
Note that if the equalizer pipe doesn’t go to the bottom of the pool this is not an option.
Do you remove the skimmer basket when vacuuming pool?
No, there is no need to remove the skimmer basket when manually vacuuming the pool. Most skimmer boxes work with a skimmer suction plate inserted into the box to create a vacuum. The vacuum hose connects to the top of the suction plate. When you vacuum the pool the skimmer basket traps larger items of debris protecting the filter from becoming clogged up.
If you are connecting an automatic suction cleaner you still leave in the skimmer basket to protect the filter from debris.
If you are vacuuming the pool to waste (stormwater drain) you can remove the skimmer basket because the debris is not going to the filter.
Does a pool need a bottom drain?
An in-ground swimming pool doesn’t need a bottom drain but I have never seen one without it. I strongly recommend an in-ground pool is fitted with a bottom drain so the pool can be emptied without a separate pump. The plumbing from the bottom drain also acts as an equalizer to the skimmer box. When the water level is low water flows into the skimmer box to prevent the pump running dry.
Use a skimmer basket filter bag
The use of a skimmer basket filter bag helps to extend the life span of your filter cartridge.
Simply place the filter bag into the skimmer basket and capture more dirt and debris than the skimmer basket alone. When the filter bag is full of dirt throw it in the garbage bin and replace with a new filter bag. This prevents the filter from becoming clogged with dirt and reduces the frequency of filter cleaning.
Should pool skimmers be on all the time?
No, the filtration system only needs to be run 8 hours per day. This is enough time to filter all the water in the pool.
I recommend to split the pump running time into two periods of 4 hours each. One period during the day and one during the night. The pool water will remain unfiltered for a maximum time of 8 hours. If you operate the pump once a day for 8 hours the pool water will remain stagnant and unfiltered for 16 hours every day. Running the pump twice a day cleans the pool more effectively as surface debris never gets a chance to sink to the bottom.
Please read our article on How Many Hours to Run the Pool Pump
When your swimming pool pump is running for the normal 8 hours per day the skimmer box will remove and trap all surface debris from the pool. It’s important to keep the skimmer basket clean to keep water running through the system and protect the filter. I highly recommend using a skimmer sock to trap smaller debris and reduce the need to frequently clean the filter. This will extend the life of your filter and filter element.