Shower pump on/off issue

[SteUK]

Hi all!

Had a shower issue for years and years. I put it down to the old shower mixer being, well, old...and lived with the problem knowing I was going to renovate the bathroom at some point. That time has now come and gone, and the new shower mixer/pipework is giving me the same headache. Here is a video that shows the issue I see at the pump end when I turn the shower head off after use...

The pipework is pretty simple. Cold feed to the pump is down from the tank in the loft above. Hot feed to the pump is out the top of cylinder (behind pump) via a flange. Out of the pump to the shower is up into the loft, dropping down into the bathroom. With bottle vents at the top of the drop (raised above the cold tank level
I believe).

Can anyone offer any help to my conundrum?

 

[SteUK]

Some more pics...

 

[Madrab]

When the water is turned off, the valve on the shower will be sending a pulse back down the pipe, the water movement is being picked up by the pump flow switches and activates the pump, that then turns into a vicious circle as the pump pulses it sends that down the pipe, and then it returns, so on and so forth.

It could also be some air trapped in the pipework and that would have the same effect. Auto air vents are not the best things to use with a shower pump as they have a float that can create water movement when the pumps pulse .

1st place I'd look at would be to change to manual bleed valves with as short a stub of pipe as possible.

 

[SteUK]

Roger that! Something like this maybe? http://www.screwfix.com/p/end-feed-air-vent-cap-15mm-x/52451

Chop off the pipe to the bottle vents and jam them on the end as low as I dare go?

 

[Madrab]

As long as they are installed higher than the highest point of the pipe it is meant to vent then it'll do the job. Jamming them on won't work, they need to be soldered on.