Air pressure in a pressure vessel

[pryder747]

I have a house in France with no mains whatsoever. Water comes from a 10 metres deep borehole, pump at the bottom, pressure vessel at the top, all installed new a year ago but I haven't been able to contact the installer because my agent in France is on holiday and I don't have the details (stupid, I know).

The check valve in the pump recently failed and I am left wondering if the pressure vessel might be at fault. It has a membrane with air on one side and water on the other. Some visitors in January messed about with it and I think they probably let some air out. My understanding is that the function of the air is take the compression which the water resists. making it easier to cpressurise the whole system. Water alone is much harder to compress. If there is insufficient air might this have placed too much pressure on the pump?

I know I am clutching at straws because my first suspect for the failure is the small amount of sand in the well water which has a scouring effect and which may have abraded the check valve in the pump down so it no longer functions but I still need to be sure the pressure vessel air is OK so my question is, what air pressure should I have in the pressure vessel. It is set to switch the pump on at 2 bar and off at 3,5 bar.

Thanks

Peter




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[Plouasne]

Where about's in France are you ??

When you are at your place in France

Use a tyre pressure gauge to check that the Nitrogen (Azote in French) is at the correct pressure, if not use a foot pump to re-pressurise it to the correct pressure, the pressure should be on the manufacturers plate on the pump set

Firms like Brossett, (part of the Wollesley group) Frans-Bonhomme, P U M plastics, should be able to supply a new foot valve/strainer
Otherwise try the sheds like Castorama (part of the Kingfisher group, like B&Q but better and cheaper) Leroy-Merlin

Reading your question again, the principle of a pressure set is to give you a pressurised supply of water before the pump cuts in, (in this case 2 bar) and after the appliance used stops needing water, the pump will run on until the set pressure is reached (3.5 bar)

The pressure switch should cut the pump in when the pressure falls below 2 bar, and cut it off when the pressure reaches 3.5 bar, if the foot valve was faulty and is letting by, the pump should be continually running, because the pressure would drop, so I think that rules out the foot valve, unless the pump has burnt out by continually running

I would check the electrics, it has been a bad winter in France and there have been power cuts, with lines down, if the disjoncteur principale (companies main fuse) or a disjoncteur (fuse) has tripped that could be your answer, it could be that the pressure switch has been damaged, if the disjoncteur principale is faulty get EDF or your electric supplier to change it

Another possible cause, could be a lightning strike that has fried the electrics, in some parts of France a surge arrestor (para faudra) is mandatory because of this problem

Again you do not say if the electrical supply is mono phase or three phase, if one of the phases (if the pump is 3 phase) is out, that could be your problem, or if the installation is 3 phase and the set up is unbalanced across the phases this could cause the problem

 

[pryder747]

Thanks - sorry I've not got back to you but my computer caught a virus and nothing has been working properly for quite some time. I've just bought a new hard drive and reinstalled windows so it is clean again. What a hassle.

The pump is at the bottom of teh well so I can't inspect the plate to see the air pressure setting. I've got the chap coming out to see it next week so it should get sorted then.

The electrics are all Ok and everything else was working fine once I had installed the extra non-return valve. I shall make sure I get told the pressure needed so I can check it in future. I've got a pump with a pressure guage.