Pump Priming Issues

[piku]

Many of you guys know I got a house with a neglected pool with no manuals and it's been a guessing game ever since. Last year on closing I figured out that in addition to a main drain, 2 skimmers and 2 returns, I have a main RETURN. And in fact one jandy valve controls the side returns and another controls the bottom return whereas I thought the two valves controlled each side return independently.

Anyway, all the guides I've read have told me it's easier to get prime using the main drain. Well definitely not in my case. THe only way I can get prime is to close the main drain. Playing around the other day with my new found knowledge I've figured out why

Basically the prime was getting going a little bit from the main drain and then sending air back out to the main return located under the same caps. The main drain was then picking up the air that the main return was sending down and losing prime then immediately. Lather, rinse, repeat. Close the main return and viola, primes instantly.

The moral of the story is... uh.. I dunno, make sure to get labels on your plumbing! On the bright side the main return gives me a dedicated solar return and good dilution when I get solar so that's nifty indeed. Now I understand what the pool inspector meant when he said "oh this is already setup for a heater for you".

 

[mas985]

So they plumbed a return back into the same fixture as the suction for the main drain? While using the main return, I assume that you would normally turn off the main drain suction. Otherwise, this would create a circulation loop which would be counter productive for solar and circulation in general. Kind of an interesting way to do it although I would make sure you only use one or the other and not both at the same time.


A few comments on priming:

The primary factor on how fast a pump will prime, or even if it will, is how high it must pull the water up to basket. An above ground pool will always prime since the pump is always below water level. The higher the pump is relative to the water level, the harder it is for the pump to prime.

Another factor, although less important than relative height, is the amount of head loss in the plumbing. Here is where I would disagree with common convention of using the main drain. Skimmers are usually closer to the pump and sometimes even have the main drain plumbed through it but either way the pipe length is usually less with the skimmer so it should prime a little faster. The only except to this is if the water level is not high enough, the skimmer may add air to the water mixture which will make it very difficult to prime the pump. This is would be similar to what you are seeing but with your main drain. However, the best way to prime a pump should be to have all the suction valves open so that the suction head loss is minimized. This is the way I prime my pump and seems to prime the fastest.

 

[Durk]

Actually, Sylvan makes the loop right at the pad. There is only one line to the twin bottom drain caps. You can feed return water through it while closing off your suction to the drain, or pull water from it, while closing the return connection. If you open both valves, the return water will go right back into the pump without ever visiting the pool. I have pictures of the way mine was built in 2004 if there is any doubt.

The theory is you can optimize solar warming by returning warm water from the skimmers to the cold bottom of the pool, thus lowering surface temperature and increasing heat gain at the surface. It actually seems to work. It's also handy when you vacuum, as it does not disturb the surface as much as the standard returns.

You can't prime with both open because the suction end of the pump is trying to draw water from its discharge end that doesn't have any water in it, yet. Hope this helps. I prime from the main drain or the skimmer with equally good results (pump is below water line) but I keep the "Main Return" closed until it is called for. (Sylvan calls it "Pool Drain Return".)