Pump losing prime?

[jmbuys]

Have a new VS Pentair pump. When it ramps up in the morning it primes for a few min at 3000 rpm (about 10 psi at filter), then shifts to 2100 rpm for about 3 hours (about 6 psi at filter), all good so far, then I have it shift down to 1600 for several hours in the cycle, for the first couple of hours at 1600 all seems good, still good water flow at the returns (less then when pump is at 3000 or 2100 obviously but still a good flow and psi about 2)....but I notice after about 4+ hours at 1600 the water flow at the returns has greatly reduced and psi not registered at filter, if I look at the pump basket the water level has really dropped and water flow in is pretty low into the basket.....if I ramp the pressure back up to 2100 flow , flow returns, pump basket fills w/ water and psi and return water flow goes back to normal.
I've triple checked, no leak at pump (though I'm pretty sure I have a leak on the suction side piping (due to modest water loss /more then ambient water evap) that I just haven't been able to deal with yet. Is the lower rpm speed just not enough to keep pump primed w/ the probably suction side leak? until leak fixed should I just keep the rpm's above 2000? Never had a VS pump before so not sure if 1600 is too low or if it's just too low along w/ my prob suction side leak?

Thanks!

 

[Texas Splash]

There could be more than one issue happening, so let's cover them all.
1. Make sure your filter is clean. When my filter gets dirty, I get less flow and my lower speed barely does anything.
2. Water leak? Perhaps. But water doesn't usually leak on the suction side when the pump is on because of the vacuum pressure inward pulling air in. Now when the system is off, sure, you can lose water on the suction side.
3. Leaks underground do happen, but they are not the #1 cause for air leaks. Many times it's something relatively simple around the equipment pad. Also note that with your VSP on high, there is going to be more vacuum (suction) pressure on the clear pump lid which could explain less air on higher rpms, so check there first. Even though it's new, make sure that lid O-ring is lubed well. Drain plugs too. From there, work your way backwards to any joints or 3-way valves. Anything like that can let air in.

 

[jmbuys]

Thanks TS! Can you clarify something for me, is a water leak the same as an air leak?

For example I def get the symptoms of a suction side leak (turbulence in the pump basket etc) and I'm def. losing water (about 3/4 inch more then evap/day). The pump basket is clean, I dbl checked the basket lid and o-ring and the other items around the equipment pad. Reason I don't think it's the equipment is had the same problem w/ old pump. I don't have a water leak when pump not running and/or when pool closed for the season (also went around the pool w/ dye to check for anything).....so it all leads me to something underground?

If air leak is different then water leak and water leak is not common on suction side, could it be air leak on suction side and water leak on returns? Next step is to dig down to first joint near equipment pad....if not there I guess doing line pressure tests?

Thank You

 

[1Sammy]

Easy way to check for suction side leak.
Shut down the pump and take the lid off the basket. Wait for the water to stop draining back. Put your winter plug in the bottom of the skimmer suction line. If the waster in the basket drops you have a leak. Might take a while if the ground around the leak is already soaked but a day will tell you.