shower pump pulsing

[fraggle]

Hi, looking for a bit of advice....

we had our bathroom done a few months ago, part of which required a pump to be fitted for sufficient pressure for the shower.

the pump is fitted right next to the cylinder so all hot water for the house gets pumped.
For the last few weeks when a tap is run or the shower used, the pump kicks in as normal but when tap is turned off the pump continues to 'pulse' on and off, ie 2 secs on, 2 secs off for anywhere up to 2 minutes.

This obviously shouldn't happen and I was worried about damage to the pump with it running dry. I contacted CS and was told it wasn't damaging the pump, the issue was caused by air getting into the pump somehow. I was told short term to 'purge the system' which I do not know how to do, long term fit a low pressure non return valve to the outlet side of the pump to stop air getting into it.

Does this sound right? I bought the valve today but am a bit wary of fitting it as it might well reduce the pressure.

Anyone experienced similar or have any thoughts on this?

Thanks

 

[Gray0689]

Yes non return valves should sort it out

 

[Best]

Who fitted the pump?
If it was a tradesman, then get him back to sort it, as he should have done it to MIs.

 

[Plumb Ugly]

shower pumps often require a boss into the side of the cylinder for the hot connection or they can drag air off the top of the cylinder not sure why it would have just started happening though

 

[Paulus]

As Best says, non-return valves aon the outlet pipes from the pump should solve the problem. Get whoever installed the pump back in to sort it, that's what I would expect my customers to do.

 

[plumber0808]

Its not a requirement to fit non return valves on shower pumps, I've never seen that on any I've fitted. Just to be piped correctly so this doesn't happen.

 

[Whn1]

Not saying its right or wrong but I've never seen NRVs on shower pumps unless some come built in, which I don't think they do.

 

[BLOD]

Pulsing when the outlet is turned off is quite a common problem, it's usually the water bouncing between the outlet and the tank - putting in a non return (flap type) valve on the hot outlet can cure it.

 

[BLOD]

Not saying its right or wrong but I've never seen NRVs on shower pumps unless some come built in, which I don't think they do.

If you had this problem Salamander used to send you a nrv that screwed between the flexi and the pump for free.

 

[Whn1]

Surely on a neg head pump, bouncing water wouldn't activate the pressure switch, I can see why it would with a pos head.

 

[BLOD]

Surely on a neg head pump, bouncing water wouldn't activate the pressure switch, I can see why it would with a pos head.

Didn't think the op said it was a neg pump ?

 

[fraggle]

thanks for all replies, looks like I might have to try and fit the NRV. Can anyone tell me the difference in pressure that fitting it will cause? ie is it noticable?

thanks

 

[Dannypipe]

With a low pressure NRV you won't notice the difference. Some reduce the flow rate a bit, but not the pressure.

 

[fraggle]

With a low pressure NRV you won't notice the difference. Some reduce the flow rate a bit, but not the pressure.

what's the difference???

 

[Dannypipe]

The difference between pressure and flow?

An easy way to show you is this. Put the kitchen cold tap on just a very small amount, so it's just dribbling. Then jam your thumb over the outlet. Within a couple of minutes the water will be getting past your thumb, the pressure of the cold main is high. However the flow rate is low as you have restricted the passage of water. If you slightly move your thumb the water will most likely spurt a fair distance.

If you did the same with the hot tap (providing your system is gravity fed) the chances are you would be able to stop the water with your thumb, and it wouldn't spurt as far, as the pressure is low. In fact you could have the water flowing at a higher rate, and still stop it with your thumb as the pressure is as I said lower.

Does that make sense?

 

[Dannypipe]

 

[dancinplumba]

View attachment 10440

picasso at his best

 

[Dannypipe]

Here I did a quick drawing. Please don't laugh!!

The top tank has greater pressure, the tank is higher...however the pipe is smaller and therefore this reduces the amount of water able to flow through it (we know what flow rates we can achieve at certain pressures, with various common pipe sizes).

The lower tank, has lower pressure. It doesn't matter that the holding tank is much larger, the pressure is less. However I've drawn the outlet pipe in much than the other tank. Therefore the flow rate in litres per minute will be greater.

 

[dancinplumba]

not laughing danny, i dont know how to draw summat and post it, no offence

 

[Dannypipe]

LOL!! I know awful.

 

[Dannypipe]

not laughing danny, i dont know how to draw summat and post it, no offence

Mate, not offended at all!

Believe me, most people would be hard pushed to offend me!!