Go Back  DoItYourself.com Community Forums > Garden and Outdoor Center > Pools, Spas and Hot Tubs
Reload this Page >

When the pump is turned off, the water drains back into the pool from the pump/filter

When the pump is turned off, the water drains back into the pool from the pump/filter

Old 08-01-05, 12:35 PM
Visiting Guest
Posts: n/a
When the pump is turned off, the water drains back into the pool from the pump/filter

What a weekend! I awoke on Saturday morning to discover that a hose leading from the pool filter out to the pool had broken resulting in ~10,000 gallons of water to be pumped out into the yard. The pump had also run dry (as the water was now below the inlets) and I feared the worst - buying another new pump this year! (I just bought it last summer). But after fixing the hose problem, the pump started up and runs great. But all is not well after-all - when I shut it off, the water runs back from the filter to the pool resulting in an unprimed pump (and a large gush of water out of the skimmer onto the deck / into the pool).

I fear I have created a situation where pressure is pushing the water back - I'll give some background:

On the oulet side of the filter head, the previous owner had connected a 4' length 1.75" Flexible hose to a 35' piece of 1" Irrigation pipe (ABS) using another piece of flex-hose (in-between the sizes) using a few hose clamps. (I knew I needed to fix that up but I just never got around to it.) Needless to say the 'system' came apart. I spent the day running around and getting various plumbing fittings to connect the 1" Irrigation pipe directly to the filter outlet (with a union so I can unscrew the filter if required).

To connect all this up, I ended up having to use a short 3/4" section of pipe to act as a 'nipple' to connect the outlet pipe to the series of fittings I had just used to get all this connected together... As I expected, the water pressure at the pool outlet had increased somewhat but nothing too dramatic. The pump wasn't straining while it was running nor did there seem to be any particular problems (and the pump appears to have survived the period when it ran dry - whew).

Now for the problem - when I shut the pump off for the night, the water pushed backwards down the inlet pipe and 'blew' the lid right off the skimmer. It drained all the water from the pump basket and inlet side of the filter out into the pool. I reprimed the pump, turned it on and everything ran fine; however, when I turned it back off, the same thing happened.

What have I created? Is this a case of there being too much pressure 'upstream' from the pump caused by the small diameter connectors? Just to clarify, I have 1.75" coming 10' from the pool to the pump (hard ABS), then 1.75" flexible tubing running from the pump to the filter (as it was before). On the outlet side of the filter, I reduce down to a 1" pipe which involves a very short piece (about 4 or 5 inches or so) of 3/4" pipe acting as a male connector. The run of 1" irrigation pipe runs about 35' to the other end of the pool where the outlet is.

The pool is an inground one with the pump/filter located about 10' away at ground level. I don't remember the HP of the pump off hand but it is a fairly big (and expensive) one.

Can anyone:

1) Confirm or further enlighten me on why this is happening?
2) Make an suggestion on how to fix this?

Thanks in advance!

Old 08-01-05, 03:02 PM
Join Date: Jul 2005
Location: SE Wisconsin
Posts: 30
Likes: 0
Received 0 Likes on 0 Posts
Two things. First and most important - the makeshift piping is way too small. Not knowing how many HP your pump is, I can't tell you what size it should be, however since there is 1.75" coming from skimmer to pump, that is what should be used everywhere. (or at the very least 1.5") I have a 3/4 HP pump for my above ground pool and it uses 1.5" hose. Having that small 3/4" pipe is creating alot of backpressure in the filter - what's your pressure guage reading? When the pump is turned off, all that pressure rushes out of the filter and back into the pool.

Now with the pump loosing prime. I have a feeling that there is a leak somewhere in the piping or filter that is letting air in. Does anything drip water when it is running? With having such high water pressure in the filter, a seal could have been damaged.

Hope this doesn't scare you too much, but you need to get bigger piping on as soon as possible. I wouldn't run the pump until you have done this.

Old 08-02-05, 07:16 AM
Visiting Guest
Posts: n/a
That is what I am suspecting... I should point out that while researching this yesterday I came across more than one website operated by pool companies that actually recommend restricting from 2" or 1.5" down to a 3/4" or even 1/2" pipe on the outlet side to increase circulation speed and pressure for more even distribution of chemicals in large pools. I can't believe that is good advice but there are indeed some professionals out there that indicate this is acceptable (I agree that it is likely way too small diameter).

The pressure gauage is reading around 20 lbs which is around where it was before - so that is nothing too extreme. Replacing the 1" pipe is not an option at this time. It would require major excavation of the yard and removal of a deck - it would likely be cheaper to replace a pump ot two that burn out from the back-pressure. My neighbor, a plumber, indicated that he would help me figure out a way of connecting the piping to the filter using various connectors but he actually ended up with the same set of connectors that I did.

There are no leaks (at least above ground) and the pool does not appear to be losing water. I should mention that yesterday the pump acted normally and did not push anything backwards when I turned it off. I plan to replace the above ground portion of the piping with hard ABS piping and use normal plumbing fittings instead of a mix of irrigation fittings (barbed) and regular ones. The previous owner of the house took every shortcut he could with everything. I spend all my time undoing his handywork and correcting it! This is just the latest in a long string of head-shaking events...

I appreciate the quick feedback and confirmation of my suspicions about too much pressure involved. Actually, it is obvious that is what is must be.


Old 08-02-05, 09:06 PM
Join Date: Dec 2004
Location: So. Calif.
Posts: 540
Likes: 0
Received 0 Likes on 0 Posts
to re state what has allready been said, if you have 1 1/2 " on the suction side [ we go by the I D of pipe not O D ] by all means keep the rest of your piping the same 1 1/2 " as you stated the 1 " is in place and would be a bear to replace , simply T off after the filter [ before the 1 " and run a secondary line T them back togeather as close to the pool as possible.

and unless your pump is below the water level of your pool , install a check valve , preferably on the suction side of your pump.


Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: