I have a inground pool and my problem is when I switch the valve to skimmer only the pressure drops from 30 to 10 and will build back-up to 15 psi and some times jumps to 22/24 psi and back to 15 psi.
I blew out the line using my air compressor maybe a blockage no change. I want to do a pressure test but don't know how to. Can you help me how to do set up this test.

I don't recommend a pressure test on pool lines. They are not usually made to withstand it. But, it does sound like you have a leak in that skimmer line.

Does the skimmer housing appear to be in good shape? Do you have any bubbles in the skimmer? If that all seems okay, check the pump housing and suction pipe at the pump. That is usually where the suction leaks are due to the vibration of the pump. Replace the pump strainer o-ring on the lid if it appears to be cracked or deteriorated at all. Always grease them with silicone grease when you take them apart and reassemble.

Soap up the fittings with some real sudsy water to see if you can see it being sucked in during pump operation. I always install pumps with unions on suction and discharge so that I can take them loose, re-tape fittings and reinstall on pump housing. Over time they will vibrate loose. One other thing to check is for a crack in the strainer lid on the pump. A hairline crack can cause suction leaks.

A couple of more things to check... the 3-way valve may be mal-functioning or leaking air around the stem. Also, if you have a spider-valve on your filter, that could be the problem.

If all of these prove to be fruit-less, it is probably the pipe at the bottom of the pool skimmer. You may want to use your 3-way valve set to partial drain/ skimmer at that point. It will be a major job to dig that up.

Hope that helps.
Al

I don't recommend a pressure test on pool lines. They are not usually made to withstand it. But, it does sound like you have a leak in that skimmer line.

Does the skimmer housing appear to be in good shape? Do you have any bubbles in the skimmer? If that all seems okay, check the pump housing and suction pipe at the pump. That is usually where the suction leaks are due to the vibration of the pump. Replace the pump strainer o-ring on the lid if it appears to be cracked or deteriorated at all. Always grease them with silicone grease when you take them apart and reassemble.

Soap up the fittings with some real sudsy water to see if you can see it being sucked in during pump operation. I always install pumps with unions on suction and discharge so that I can take them loose, re-tape fittings and reinstall on pump housing. Over time they will vibrate loose. One other thing to check is for a crack in the strainer lid on the pump. A hairline crack can cause suction leaks.

A couple of more things to check...the 3-way valve may be mal-functioning or leaking air around the stem. Also, if you have a spider-valve on your filter, that could be the problem.

If all of these prove to be fruit-less, it is probably the pipe at the bottom of the pool skimmer. You may want to use your 3-way valve set to partial drain/ skimmer at that point. It will be a major job to dig that up.

Hope that helps.
Al

:confused:
Thanks AL
Question is if there was air leak in the suction skimmer line wouldn't there be sand or dirt in the pump?

Not necessarily. Air takes a lot less opening than sand or dirt to come into the line. It can be as simple as a crack in the pipe glue. As I said earlier, the line is the least likely out of all of the possible causes.

I would be looking around the pump first. That is usually where you will find the problem. The suction line coming into the front of the pump is a frequent problem. The strainer lid on the pump or the o-ring on the lid is #1. If equipped, the gasket between the strainer housing and the pump is also a problem. You can snug the bolts. If the gasket looks cracked and dried out, replace it.
Al