Pump Back Pressure Problem.

[AllanB]

A friend of mine has an 8 year old fiberglass pool and couldn't get the pump to work.

We traced and fixed a biggish leak in the suction pipe from skimmer to pump and patted ourselves on the back. With the pump mounted above the waterline, we tried filling the pump bowl to bleed the system, which didn't work, so we stuffed a submersible pipe up the skimmer pipe until it flowed out of the pump bowl, shut the bowl cover and got the system running.

However when we stopped the pump it would not restart as the pump bowl was empty, the only way to stop it emptying was to shut the suction pipe isolation valve after the pump had stopped and then open it to restart,

So...we replaced the isolation valve with a check valve to make the system automatic, however, the back pressure in the system over-road the check valve leaving the bowl empty. Bugga! So again we couldn't restart the pump, as the prime had been lost.

This pump is a Leroy Somer LS60p 1.1kW and think it is a spa pump, I am told that the spa has an air feed but don't know how the air is injected. I assume the only way there can be a back pressure when the pump is switched off, is if there is air in the system upstream of the pump, since water alone cannot do this.

Does anyone know how a spa system works, where the air comes from and/or a solution to this problem.

[fdimike]

I'm not an engineer by any stretch but I would say you are going to have to get that pump below the waterline if you want it to work correctly.

Air is injected into a spa via the return lines to the spa from the pump. In other words on the high pressure side of the pump and not the suction side.

[jbrain]

If you have a check valve at the suction side then how you bowl can get empty. Check valve works only one way.Did you put the checkj valve above waterlevel?

[AllanB]

The check valve is working, but they are obviously not designed to take the high back pressure created when the pump is stopped. This back pressure can only be generated by air in the pressure side. I am trying to find out how that air is getting into the system and think it has something to do with the Leroy Somer spa pump.

Is it possible to get air into the system on the pressure side of the pump, since the metal casing of the old cartridge filter leaks quite badly?

It is desirable to have the pump below the pool waterline but not essential and digging a hole for the pump is not an easy option.

If I can't find a solution we will have to go back to shutting the manual valve after stopping the pump and opening it on start up, but air is getting into the cartridge filter, which may cause problems

[jbrain]

I still don't understand how the back pressure can override the check valve.

Do you use a ball check valve rather than a spring check valve ?

Edited May 20, 2013 by jbrain

[AllanB]

I still don't understand how the back pressure can override the check valve.

Do you use a ball check valve rather than a spring check valve ?

It has a spring, but a plastic body and valve plug, I guess it is possible it is faulty, but the back pressure is pretty violent, assumed water going forward opening the valve and air going back through an open valve.???

[XINLOI]

Could it be something in the valve itself that is not allowing it to close properly ? Dirt/rocks ect. Plastic valves are a no no. Any grit in system and it is destroyed.

[sharex]

Spring check valve is never works as i expected. The valve is always still in open position. Ball check valve is better.(At least I never had a problem with that before)

[AllanB]

We just put the check valve in and it does work under atmospheric pressure, as the bowl can be filled, I have done a few checks this morning and would list the issues as follows.

1. There appears to be another leak in the suction pipe.

2. The cover glass (perspex) is no longer transparent and has bubbles in the plastic though isn't leaking.

3. The retaining ring is not in good condition either and require a good whack to get it tight.

4. The big cartridge filter is leaking around the o-ring seal which is difficult to get tight.

I can fix a couple of the problems with some silicone grease, so any idea where to get it?

But the first thing to do is dig up some slabs and effect a repair on that 2nd leak in the suction pipe.

If this posting sounds a bit arse-about-face, it is the heat and humidly up here...and getting lumbered with a decrepit system...still it's a challenge...to stay alive in the heat.

[fdimike]

Silicone grease is not easy to find in Thailand. I bought mine from Ebay. Inexpensive and arrived in about 10 days duty free. However, the grease is used by dive shops for the "O" rings in the breather/tank. I would try a dive shop to see if they will part with or order you some or direct you a source. Please post the source if you manage to find some here in LOS.

Bubbles in the cover glass normally indicates leaks in the suction end of things.

[AllanB]

Silicone grease is not easy to find in Thailand. I bought mine from Ebay. Inexpensive and arrived in about 10 days duty free. However, the grease is used by dive shops for the "O" rings in the breather/tank. I would try a dive shop to see if they will part with or order you some or direct you a source. Please post the source if you manage to find some here in LOS.

Bubbles in the cover glass normally indicates leaks in the suction end of things.

The bubbles are in the plastic itself, the once transparent cover is now almost 100% opaque and the pump is quite obscure.

Not much chance of dive shop in Khon Kaen, I am off to the UK next month, have a long list of bits and pieces to bring back, including o-ring material.

[AllanB]

After spending the hot morning riding around Khon Kaen, I gave up and took the missus shopping at Tescos, while she was looking around, I went to the hardware section and what did I find ....Hardex multipurpose silicone spray...B169. Bugga me, so I can get things tightened up now, sort a couple fo the leaks out.

[fdimike]

Good luck with the silicone spray. It's not the same as silicone grease but may do the job. BTW: silicone grease is also available in Home Pro and a host of other shops. Silicone grease is an unknown to the locals and if you ask for it I guarantee you'll get silicone caulk.

[AllanB]

Good luck with the silicone spray. It's not the same as silicone grease but may do the job. BTW: silicone grease is also available in Home Pro and a host of other shops. Silicone grease is an unknown to the locals and if you ask for it I guarantee you'll get silicone caulk.

I managed to get the pump lid tight enough with the silicon spray, bit worried about breaking it to go any more. The filter still leaks as the o-ring is really shagged and cant find o ring material 12mm / 1/2 inch, plus the unions both leak.

We dug up another couple of slabs, couldn't find the remaining leak in the suction pipe, but can start and run the pump with a bit of fiddling and that will do until the winter.

If I can source some o-ring material for the big cartridge filter and a new top for the pump, we will fix them both, if not get a new set. At the same time we will find the leak, which I recon is at the distorted skimmer box end and fix it or fit a new skimmer.

The problem with the skimmer is this, the pool is sagging under load, so the middle is down 30mm and the ends are up 40mm, with the skimmer attached to the patio, the skimmer now sits at 25 degrees. This means the connecting pipework has become distorted and under load and my guess has split. Looks bloody awkward with lots of hard concrete everywhere, that's why we left it until last.

I have learned a few lessons from this, 10 metres is too long for a fiberglass pool in Thailand, the bending moment created by 60 tonnes of water is too much for a thin walled pool, set in soft ground. Leave the skimmer free to move with the pool. Set pipework in sand, so it is also free to move with the pool. With no hydrostatic valve emptying this pool would be very dangerous.and even with one not that reliable.

My conclusion...anything bigger than 6x4m forget plastic, go concrete

[fdimike]

Allan

I meant to say that silicone SPRAY is widely available but the grease is an unknown.

Depending on the size of the "O" ring a shop up here in Udon has tons to choose from. If you can give me the dimensions I can check to see if he has anything like that in stock or maybe it can be ordered. Do you know the name of the manufacturer for the cartridge filter? Chances are a pool shop here in LOS may still carry the brand and have the spares like the "O" ring seal available.

Where are the unions leaking from? If this is a grey colored union then there is an "O" ring inside which may need to be replaced. I've bought "O" rings from the shop up here for my unions.

Suction Leak: Look for a broken/cracked 90deg pvc fitting under the skimmer box.

You may be able to salvage the pool if you can empty it and then get someone to pump concrete under it to bring up the center and stabilize it. My builder refused to put our concrete pool in without first setting concrete pilings for it rest on. He told us the ground was too unstable to install without the pilings. I'm certainly glad we listened to him as we've had no problems with the integrity of the pool which is a free form 17m x 4m x 2m