There is an air leak (suction leak) in the underground pipe between the weir (skimmer box) and the pump, causing the swimming pool pump to lose pressure. The connector fitting at the weir or the pump could be loose or perished. The shaft seal in the pump could be cracked and leaking. The filter sand could be clogged.
Rule out the obvious causes of poor vacuum first. Make sure the water level in the pool is sufficient and air is not being sucked in through skimmer inlets. Add water to the pool to submerge the skimmers if necessary. Verify that the pump strainer basket and the skimmers are free of debris that may obstruct water flow.
It could be a clogged pump basket, impeller, pipe, or skimmer basket. It could also be a closed or broken valve before the pump. In some cases, the pump may have an air leak and is drawing in more air than water. This can reduce filter pressure (and filtration ability).
Why does the pool pump loses pressure after a few minutes? This might happen due to a few different reasons. There might be clogs or dirt on the pool filter. Even debris stuck in the draining hose and motor might be the reason.
Clogged Pump and Skimmer Baskets - This is the most common cause of low pressure problems and thankfully the easiest to remedy. Simply clean out your pump or skimmer baskets to restore the flow of water and you should be good to go.
The first thing to do to increase the suction is to check for blockage and air leaks. If one of the skimmers does not suck, it would be necessary to remove the basket from the skimmer. Then check if there isn't a flow control valve at the bottom of the skimmer, which would be almost closed.
Air Leaks. The number one cause of pump surge or pulsing is your classic air leak. The more pressure your pump creates, the easier it is for air to get sucked through even the smallest leaks. And since air poses less resistance than water, it will get sucked by the pump instead of water, causing the pump to pulse.
A suction side air leak shows itself most commonly by bubbles and splashing and frothing in the pump basket This indicates your pump is not getting the water it needs to function smoothly but, instead, air is getting into the system and starving or semi-starving the pump.
Hold the smoking end of the stick directly under or next two (within an inch or two) all the various seams of your suction side plumbing. If an air leak is present, you should see an obvious pulling of the smoke column. Mark any problems areas showing signs of an air leak, address as needed.
One air leak detection method, as odd as it sounds, is to use shaving cream (foam, not gel) to locate the air leaks. Evenly spread shaving cream over the possible leak points on the pump, as well as the plumbing.
You can reverse this process by attaching the end of the hose to a water outlet nozzle. When the hose is completely filled up, slowly begin lifting the hose out of the water always keeping the head submerged. If at any point along the hose you begin to see water spraying, you have found the leak.
Debris blocking the suction strainer or foot valve is the most common cause. A blockage in the intake line can cause the water in the pump casing to overheat and literally boil out of the casing causing the pump to lose prime.
If air is getting in your pool through the skimmer housing, then the pool filters will be starved of water. This will result in poor water filtration and cleaning.
Check the suction side of the system for leaks. Pump seals, pipe fittings and unions are all possible areas for air leaks that allow the system to pull in air and pressurize it. You can find these leaks using an ultrasonic gun or by simply placing a small drop of oil or grease around the suspected leak site.
Check the Water Level
Low water levels in your pool cause the skimmer to suck in air instead of water. If the skimmer sucks in air, you'll see air bubbles burst from the return jets down the line. In general, water levels need to be at least halfway up the skimmer.
You may need to replace the o-ring or simply lubricate it to create a stronger seal. You can also check the pump basket and lid, either of which may be cracked and require replacement. If you feel uncertain that the pump is the source of the air leak, try pouring water over the lid with the pool pump running.
A stream of bubbles is a sign of the unwanted presence of air within our pool's plumbing system. This air is likely the cause of a sucking air leak from a pump, union or diverter gasket. The leaks and the air pockets they form will lower water pressure and greatly decrease the capacity of our filter system.
Do you see air bubbles shooting out of the return jets in your pool? As whimsical as it may look, it's not a good thing. The return jets should be returning water to the pool. It's a common problem, especially when you open your pool in the spring, and it has a simple cause: there's air in the pool pump.
The product of excessive vacuum conditions created at the hydraulic pump's inlet (supply side), cavitation is the formation, and collapse of vapors within a hydraulic pump. High vacuum creates vapor bubbles within the oil, which are carried to the discharge (pressure) side. These bubbles then collapse, thus cavitation.
Cavitation is a common pump problem that is characterised by a high pitched whining sound or, in extreme conditions, a severe rattling sound. This sound is caused by a condition in which a drop in fluid pressure causes cavities to form in the fluid, which rapidly implode (hundreds or thousands of times every minute).