Loosing prime when using vacuum

[wipple]

I hate to vacuum, and hate it even more when having issues. I have a 2 speed pump on a Hayward EC50 earth filter. I setup for the season yesterday, went to vacuum and what ever I do I loose prime in the pump basket.
I took the whole filter apart and realized that the union between the pump and filter was cracked. Replaced that, removed all shut-offs, cleaned lubed and new teflon tape on the threads, and replaced the basket cover on the pump for good measure, (31.00 dollars, the insanity). Put it all back together, recharged the filter, tried to vacuum again, same results. I was able to vacuum in 5 minute intervals before having to reprime the pump again, and that is only on the slow speed. High speed there is no way.
I am hoping that someone out there has seen this and resolved it.

Thank in advance.

 

[Thinkly]

So you are losing prime only when vacuuming? If so i would say you are getting air in the vac hose etc.

 

[wipple]

Thinkly, I tested that hose and it is ok. Not only that I have a kreepy krawly that has that sectioned hose, and I get that same results with that.
Also I always fill the vacuum hose with water from the return before connecting it up.

 

[KNIGHTCAP]

I have the same problem, with both the vacuum and the Kreepy. I hook them up in one skimmer, then I adjust the other skimmer until I can keep the prime. Basically, I slowly close the other skimmer until I just start to lose prime, then open it a bit. So most suction is coming through the vacuum, and a little through the partially open other skimmer. I cannot run the vacuum or Kreepy with the other skimmer fully closed. (I also close the main drain completely). I am certain there are no air leaks, and it works the same way from either skimmer hook up -- I have to leave the other skimmer partially open. It seems like it just can't get enough water through the vacuum hose.