Vacuum causing pump losing its “prime” - ie air

mjc123

Well-known member
Jul 20, 2018
114
Halifax, NS (Canada)
Pool Size
18500
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-15)
A couple years ago our dual speed pump failed and we had it replaced by a variable speed pump. Ever since, we’ve been having suction issues while vacuuming.

So to start, my process for vacuuming is as follows:
1) set the pump to pull ~50% from the main drain
2) put the vacuum plate & hose into the skimmer but just under the surface- not enough to get sucked down over the filter basket
3) other end of the hose goes over a return jet until all bubbling stops. The goal is to get as much air out of the vac hose as possible
4) once I’m fairly confident as much air is out as possible, I attach the vacuum head and pole entirely underwater, then hook the other end of the handle to a nearby hook so it remains out of the water but with the vac head submerged
5) return to the skimmer, and push the plate down such that it gets suctioned against the filter basket
6) slowly turn the valve to 100% skimmer

As I do step 6, I begin seeing more and more bubbles entering the filter basket of the pump until eventually the pump loses its prime and the rpm’s wind up as it tries to restore suction. At this point it essentially just goes in and out of this state. I’m able to vacuum slowly like this, but I can tell that the suction strengthens and weakens as the pump hits pockets of air, and bubbles come out in “clumps” from the jets.

I’ve tried getting a new vac hose (used) but that didn’t solve the issue. I currently have a brand new one on the way, so fingers crossed that’s it- but I’m not confident. Last season I tried running the hose direct to the hole in the bottom of the skimmer, through the skimmer opening (and therefore keeping the hose fully submerged) and still ran into the same issue.

The only thing I can think of is that the pump is not able to get enough water through the vac hose to meet its intake requirement and that it’s causing its own cavitation - but I find it hard to believe my little 1.5 HP pump has that much force. I guess the way to test that would be a short/wider diameter hose. Idk

Open to any ideas or experiences others might have. Maybe this is normal?
 
the pump is not able to get enough water through the vac hose to meet its intake requirement and that it’s causing its own cavitation

Is there any chance that the new pump is pulling so hard (on 100%) that it's actually causing the vacuum hose to collapse?
It sounds like that's what's happening. Is your vacuum just a standard vacuum head? What speed are you running your pump at? Maybe you should try to start the pump at a low speed, set the valve to 100% vacuum, then slowly increase pump speed until you achieve a good suction without cavitation.
 
It sounds like that's what's happening. Is your vacuum just a standard vacuum head? What speed are you running your pump at? Maybe you should try to start the pump at a low speed, set the valve to 100% vacuum, then slowly increase pump speed until you achieve a good suction without cavitation.
Yeah, standard triangle head. The vacuum hose definitely isn’t collapsing so that’s not the issue.

My pump has a “quick clean” button that runs it at max (3450 rpm) for an hour for vacuuming, so that’s what I’ve always used. I can try lower settings though it’s tricky because I can’t really change it “live”. It seems to need to restart every time the speed is changed. I think I should be able to do it though. If nothing else it will help troubleshoot
 
slowly turn the valve to 100% skimmer
123,

Why do you do that?? If you leave the main drain open about 10% or so, the pump will not run out of water.

I have a robot, so I never vacuum anymore. But, when I did, I always had to have an additional source of water other than the vac hose for my pump to work well.

Thanks,

Jim R.
 
123,

Why do you do that?? If you leave the main drain open about 10% or so, the pump will not run out of water.

I have a robot, so I never vacuum anymore. But, when I did, I always had to have an additional source of water other than the vac hose for my pump to work well.

Thanks,

Jim R.
Because that’s what I was taught from the start. Not a good reason - but it worked without issue on my old pump.

I did try leaving it roughly 10% open to main drain yesterday and worked much better. Suction isn’t near as good as it was with the old pump (there were times it would get “stuck” to the liner despite the bristles), but much better than it was when it was getting airlocks with the new pump.

In any case, my first robot is being delivered tomorrow, so fingers crossed this will be a thing of the past. That said, I suspect my robot will have some issues in my pool since it’s sort of kidney shaped and has concave and convex vertical walls, so I expect at least some manual vacuuming to continue
 
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