Pump pressure switch and pump contamination

[benwatkins]

Hi,

I'm on a private water supply. I have a water pump and 60L pressure vessel with a particle filter and UV treatment system in line (before the pump obviously).

The setup was installed when I bought the house and I've always thought the pump running wasn't right. It seemed to run a long time including when there were no taps on in the house. I know the pump compresses air behind a membrane in the vessel so it will keep running to 'recharge' even when there's no water being drawn but sometimes it would run for 10-15 minutes? The pressure gauge always seemed to read either 80 or 20 psi which is way outside the 35/50 that has been written on the side of the tank so I thought the gauge was faulty.

Yesterday I filled a bucket and noticed the water coming out of the tap was hot. On checking the pump I found it to be really hot, almost too hot to touch. I ran off some more water and noticed that the gauge dropped slowly with the tap on - the first time I've noticed the gauge reading 'normally'. It got down to 20 psi then stopped dropping even though the water was still running and the pump didn't come on.

This morning I thought I'd have a go at adjusting the pump just in case a previous owner had fiddled with it without knowing what they were doing but turning the adjuster for the cut-out pressure and the difference had no effect. I watched the pressure gauge after turning on the pump and it quickly builds pressure up to about 50 then slows down and eventually gets to just over 80psi where the pressure stops rising but the pump keeps running and running.

I ran water off until it was back down to 20psi and to my horror the water I that came out was full of sediment. This is not the first time this has happened. I've had contamination in the past when my neighbour didn't fit the filter properly. I changed the filter and ran lots of water through and it has cleared a lot but there is still a small amount of sediment in there. However, I'm finding that if I run water off whilst the pump is running the water is clear but if I turn the pump off and just drain from the vessel it's contaminated.

Here's what I think has happened. The pressure switch has failed. The pump doesn't cut out when it should so just keeps running until it overheats. Sediment may have got in to the switch which is the reason for the failure. There is still some sediment stuck in the vessel which is why I'm only getting contamination when the pump isn't running.

Does that sound right? If so, any tips on flushing out the vessel? I suppose I'm going to have to drain the entire thing? There is a drain tap on the outlet of the vessel but oddly nothing comes out when I turn it on.

Any other thoughts welcome! This would happen on a bank holiday in the middle of an International crisis wouldn't it?!

 

[picasso]

Sounds like the expansion vessel has failed or is over pressurised on the air side.

 

[Madrab]

Have you checked the pressure vessel (accumulator)? On what side is the pressure gauge? A couple of pics would really help here.

If the pump is running until it's too hot to touch then that isn't right and as you suggest it's probably the pumps thermal cutout that's shutting it down.

 

[benwatkins]

Quick update...

Managed to find a replacement pressure switch and got it delivered next day (thank you RS components!). Drained the tank. Checked the pressure on the air side - next to nothing. Suspected bladder failure (which is a surprise because I haven't had any symptoms like surging or air bubbles and no water came out of the air valve). Thought it was worth pumping back up just to test it. Put exactly 1 Bar in (1.01 actually!), waited 2 hours, came back still exactly 1 Bar. Changed pressure switch which also necessitated removal of the pressure gauge because it was in the way. Both soiled by sediment. Fit new pressure switch and gauge, primed pump and switched on. Pressure built all the way up to 80 and stopped rising but pump still running (so exactly what it was doing before). Tried adjusting the cut-out pressure screw, got as far as four whole turns anti-clockwise but made no difference. Gave up!

Answering your question Rob, the pressure gauge and switch are both on the pump. There is no gauge on the vessel itself.

I haven't ruled out the possibility the pressure vessel has failed but if it has it is a very small failure because it held air when I pump it up. The valve was incredibly sensitive - the slightest touch of the needle in the middle and air came out. I suspect it might leak intermittently. But even if it has failed I can't see how this would lead to the pressure switch not cutting out.

My new theory is that the cavity in the pump housing that the pressure switch screws in to is clogged with sediment. So the pressure switch isn't getting pressurised water. Interestingly when I removed the pressure switch very little water came out of the hole whereas when I removed the gauge water came out.

 

[benwatkins]

Not the greatest pic but you can just about see the pressure switch (black box attached to the pump) and just behind it the gauge.

 

[benwatkins]

This is the pump https://www.pumpsukltd.com/dab-jet-102-m-centrifugal-pump.html

 

[benwatkins]

For the sake of anyone else reading this with the same problem I'd better finish it off...

As I suspected there was sediment clogging the pressure switch. I realised that what I thought was a threaded spigot on the pump housing was actually union and when I removed it I found the hole in it was completely clogged. So the pressure switch won't have been getting any reading at all. I replaced the union with a new one and the pump is now cutting in and out normally. The switch seems to have been pre-set to cut in at 4 Bar and out at 5. I think that's a bit high so I intend to bring it down a bit. I charged the air in the vessel up to 2 bar (which is the rating printed on the manufacturers label) so I ought to adjust the pump to cut in at just over 2. Incidentally, I checked the air pressure in the vessel again this morning and it read 1.98 so down 0.02 bar in three days. More than likely to a change in atmospheric pressure/temperature than a leak?

 

[OvertonPlumber]

Why is the expansion vessel red? Its not designed for potable water it should be grey or white or blue. A red vessel will perforate in 12_18 months as its not designed for regular water changes.

 

[benwatkins]

This is the tank: http://www.varem.com/pressure-tanks-for-potable-water-booster Their entire range of potable water tanks is red. What's the colour got to do with it?