Non return valve

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RonPace
Swimming Pool Wizard
Swimming Pool Wizard
Posts: 61
Joined: Thu 26 Aug, 2021 09:45
My Pool: Uncovered inground 12x6M, Cl and Ph solenoid doser. Glass media filter. South France

Non return valve

Postby RonPace » Tue 05 Oct, 2021 08:35

I am tidying up my pump room following fitting a Zodiac salt water generator, and one job is - yet again - the non return valve on the suction side of the pump.

What a palava! I have two old ones sitting on the shelf both useless, one a chinese ebay thing cost 10€ - say no more. Another unmarked one - unmarked but looks cheap. Currently fitted is a 'Plasson' so called professional with a flap valve onto a rubber sealing ring - the water drains back overnight, so pretty useless. The other day I purchased a heavier one from my local Apic'o pool shop - good and sturdy with a proper spring holding a solid looking ball into a rubber sealing ring - useless as the pump cannot suck the spring open! I see on another supplier website the same item but showing it as 'for industrial use', so another waste of 30€ :D

So the first question to a pool installer - is there a NRV, 63mm, that does what it is meant to do? If so, can you recommend please?

My second question - when is a NRV actually of any use?

And my third question - for how long can a modern pump run dry?

OK, detail. I have a nominal 90/100 M3 pool (i seem to remember an installation paper saying 88M3). It originally had a large pump but cannot remember the size. Currently, as suggested by Irrijardin (a French pool shop) I am running a much smaller pump that with the resistance of head of the filter, a good handful of 90 degree bends, a few probes and now the SWG, my flow meter is showing slightly under 300Lph (this device is only a simple perspex tower with a tube running up the centre where a little ball sits on the surface of the water in the tube, so may not be dead accurate). It works well. This is only for info and not relevant to a NRV.

Now, the pump 63mm intake is maybe 300mm above the actual water level of the pool, max of 500mm, so let's say 500mm. The pump is 1.5M from the water - ie there is only 1.5M empty pipe between the water level and the pump impetter.

With the last NRV, the pump priming chamber was emptied over night. The pump primes itself though in a couple of minutes without any apparent fuss and happily continues all day long .

Will an installer confirm if a 'suck' head of 500mm and a dry distance of 1.5M of 63mm pipe is damaging my pump on start up please? Do I really need an NRV? And if so, back to my first question, is there on that works?


Teapot1
Pool Industry Leader
Pool Industry Leader
Posts: 1175
Joined: Thu 29 Apr, 2021 00:43
My Pool: 12000 gallons vinyl liner,

Re: Non return valve

Postby Teapot1 » Wed 06 Oct, 2021 02:24

Ron, although you say it takes 1min? To prime the pump the important issue is does the pump prefilter have water in it? If it does retain the water how long after starting and before priming does the water stay around? The important part is the bearing and seals should never run dry with an industry std (check pump instructions) for no more than 30 seconds.
I use Valterra NRV's when required and position them vertically, usually the un sprung version.
I much prefer to mount the pump below the water line to flood the pump and do away with the issue.
I may not give you the answer you want to hear, but I will give an honest opinion of your situation as you decribe it.
RonPace
Swimming Pool Wizard
Swimming Pool Wizard
Posts: 61
Joined: Thu 26 Aug, 2021 09:45
My Pool: Uncovered inground 12x6M, Cl and Ph solenoid doser. Glass media filter. South France

Re: Non return valve

Postby RonPace » Thu 07 Oct, 2021 02:44

As I say, the NRV lets all the water drain back - ie, yes, the pre filter, is dry.

I will check out this Valterra range.

Yes, I thought of cutting in a sump in the pool room floor to lower the pump to water level, but the thought and slight bother has put me off. Anyway, the last pump lasted six years and this is in its third I think, and with the cost of pumps - that are going to fail anyway - maybe just as cheap to carry on than drag in builders...
Teapot1
Pool Industry Leader
Pool Industry Leader
Posts: 1175
Joined: Thu 29 Apr, 2021 00:43
My Pool: 12000 gallons vinyl liner,

Re: Non return valve

Postby Teapot1 » Thu 07 Oct, 2021 03:54

Understand Ron, just as a question which pump are you using? With a speed controller you put a lot less strain on the pump so should last longer. Admittedly I did blow the budget 12 years ago when variable flow pumps were in their infancy to the pool market but the pump has saved around £2700 in electricity in that time over a standard setup which is also a huge amount of CO2 and produced far better water quality when coupled to the AFM filter media. Everything working together to produce a better result.
I may not give you the answer you want to hear, but I will give an honest opinion of your situation as you decribe it.

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