Pulsating Pump-Possible Leak?

[NCRhodes]

Here is my problem: When my pool is running from the skimmer, the pump seems to be running fine; a few air bubbles at the pump lid. The pressure holds pretty steady at 12-13 P.S.I. and the suction feels like it's normal. When I attach the Hayward Pool Vac to the skimmer inlet the pump just pulsates/chugs and the pressure varies wildly from 2-5 P.S.I. and the Vac is barely moving.

Things I've done so far:
1. Took the Sta-Rite 1 hp motor off, checked the impeller. Looks fine.
2. Lube the Pump lid O-ring. (Could be an invisible crack on lid)
3. Snaked the inlet pipe for debris. Seems clear.
4. Closed off the skimmer inlet; filled pump inlet with water. No air bubbles observed and pump filled with water so hopefully the inlet pipe isn't leaking.
(Note: my main drain is blocked and inoperable in order for the pool vac to work properly-old style pool with one diverter valve in the skimmer).
5. Checked the Pool Vac/hoses- seem fine, no obstructions.

I'm kind of at a loss as to what the problem is. Is it the pump inlet pipe/fittings that have a small leak causing this. That's my only guess right now.
Any help would be appreciated.
Thanks

 

[Richard320]

Sounds normal to me... I don't know whether it's good or bad, but my pump starves when I hook up the vacuum. Face it, sucking 5' through 2" pipe is lots easier than sucking through 35' of 1¼" hose and 5' of 2" pipe.

 

[NCRhodes]

Actually I think the inlet is 1-1/2" and runs about 10' from skimmer to pump. Not that it matters.
This hasn't done this before with the Pool Vac attached, so I know that this isn't normal.
My local pool service will be out Monday to take a look at it.

 

[Bama Rambler]

It's most probably an air leak. You can run a water hose over the suction side of the pump and plumbing while it's running and if the air bubbles go away you've found you're leak.

 

[NCRhodes]

Dave J,
Yep I did that this morning. No luck. Like I said, this only seems to be a problem when the Pool Vac is hooked up. I have even taken just a few hoses and connected them to the skimmer-no change, the pump pulsates intermittently like it has air in the system. I'm kind of at a loss here.

 

[cubbybeave08]

Dave J,
Yep I did that this morning. No luck. Like I said, this only seems to be a problem when the Pool Vac is hooked up. I have even taken just a few hoses and connected them to the skimmer-no change, the pump pulsates intermittently like it has air in the system. I'm kind of at a loss here.

When you attach the pool vac to the skimmer does the attachment fit right. Could it be getting air when you attached it?

 

[NCRhodes]

Dave J,
Yep I did that this morning. No luck. Like I said, this only seems to be a problem when the Pool Vac is hooked up. I have even taken just a few hoses and connected them to the skimmer-no change, the pump pulsates intermittently like it has air in the system. I'm kind of at a loss here.

When you attach the pool vac to the skimmer does the attachment fit right. Could it be getting air when you attached it?

There might be a small amount of air when attaching it to the skimmer, but normally will 'clear out' and start suctioning properly after a few seconds.

 

[cubbybeave08]

Dave J,
Yep I did that this morning. No luck. Like I said, this only seems to be a problem when the Pool Vac is hooked up. I have even taken just a few hoses and connected them to the skimmer-no change, the pump pulsates intermittently like it has air in the system. I'm kind of at a loss here.

When you attach the pool vac to the skimmer does the attachment fit right. Could it be getting air when you attached it?

There might be a small amount of air when attaching it to the skimmer, but normally will 'clear out' and start suctioning properly after a few seconds.

NC...I have a 2 HP pump and my auto cleaner does that...In fact usually what happens is that when I put it in the skimmer it will almost completely drain the pump basket than it reprimes, but after that it only primes up to just below the plastic window...never fully primes while running. I don't think mine ever fully primed again.

 

[NCRhodes]

Just to update: my neighbor came over and we replaced the pipe, elbows, and new union from the pump to the 1st elbow underground that leads to the skimmer and letting everything dry for awhile. The straight piece of vertical pipe that goes underground basically came right off the joint. This PVC pipe was the thinnest walled stuff I've ever seen. Probably 35 year old pipe, elbows and glue (what's left of any).........in other words good places for an air leak. I'll let this dry and try tomorrow, but I'm afraid there is probably a leak elsewhere like the skimmer box or the pipe itself. Since the main drain is blocked off, there could even be an air leak at the pipe from the main drain to the skimmer box (tee).

 

[NCRhodes]

Another update on this problem:
I set up a temporary 1-1/2" PVC suction line from the pump to the pool (pipe layed above ground) to see if I can eliminate the air in the pump. I replaced the pump lid o-ring as well as the the pump drain plug o-ring on the suction side. Still no luck.. air in the pump. Had a pool tech with 30 yrs. experience come out to look at it; tested the the temporary suction line - no leaks, said, "I'm stumped". If anybody else has any suggestions as to what this problem could be I'd appreciate it.

 

[Bama Rambler]

Have you resealed the drain plug(s) on the pump? There may be more than one.

 

[NCRhodes]

Yep, there's two. Done that already.

 

[Bama Rambler]

Have you ran water over everything on the suction side wheil it's pulsating?