Pulsating Shower Pump

[Alanka]

I do not believe the orientation of the mixer unit has anything to do with the pulsation problem.

The pump motor is activated by flow of water in the correct direction through a flow switch in the pump -- usually a pair of switches, one in the hot and one in the cold pipe, either of which turns on the pump.

Turning on the shower outlet valve usually allows sufficient flow to do this. If the flow falls below a certain rate the flow switch cuts out the motor. Raising the shower rose reduces the natural flow (due to reduced head of water). If your pressure is borderline anyway (cold water cistern only a bit higher than the shower rose) the flow can be so low when you turn on that the flow switch only just operates and starts the motor. But as soon as the pump starts to suck water via the pipework a slight partial vacuum occurs upstream of the pump. This causes a brief backflow of water in the wrong direction, which instantly deactivates the flow switch(es) and shuts off the pump.

The natural flow then restarts the pump which triggers the on/off cycle again, leading to pulsations.

Putting a non-return valve (single checkvalve) on the hot water outlet of the pump prevents these brief backflows, and so stops the pulsations. I'm not sure why you use the hot water outlet rather than the cold, but it may be because the hot supply usually has a lower flow/pressure due to longer pipework from cold water cistern to the pump.

Originally Posted by Alanka

I do not believe the orientation of the mixer unit has anything to do with the pulsation problem.

The pump motor is activated by flow of water in the correct direction through a flow switch in the pump -- usually a pair of switches, one in the hot and one in the cold pipe, either of which turns on the pump.

Turning on the shower outlet valve usually allows sufficient flow to do this. If the flow falls below a certain rate the flow switch cuts out the motor. Raising the shower rose reduces the natural flow (due to reduced head of water). If your pressure is borderline anyway (cold water cistern only a bit higher than the shower rose) the flow can be so low when you turn on that the flow switch only just operates and starts the motor. But as soon as the pump starts to suck water via the pipework a slight partial vacuum occurs upstream of the pump. This causes a brief backflow of water in the wrong direction, which instantly deactivates the flow switch(es) and shuts off the pump.

The natural flow then restarts the pump which triggers the on/off cycle again, leading to pulsations.

Putting a non-return valve (single checkvalve) on the hot water outlet of the pump prevents these brief backflows, and so stops the pulsations. I'm not sure why you use the hot water outlet rather than the cold, but it may be because the hot supply usually has a lower flow/pressure due to longer pipework from cold water cistern to the pump.

we have already been down that path and was chosen to be ignored.

[didydave]

Hi AJS and Alanka I have now had a reply from Salamandar pumps who say the following.

" Thank you for your e mail for what u are experiencing the non salamander pump is not producing enough pressure to shower head after a certain height which in plumbing terms is a negative head.

A non return valve would only make the matter worse and restrict the flow even more. You possibly may need a momentary pull cord switch to enable the pump to keep running when the shower head goes over a certain height.

Please call the following number for further assistance 0845 129 5010"

What pray is a momentary pull cord? I ask.
Never mind, the client has now told me that the problem appears to have solved it's self and the shower is now not pulsating so i think that it may have been a small air block in the rather complicated pipe work under the floor.
Again thanks for all the advice. What a great way to get help.

[Alanka]

Ha-ha! Who needs plumbers? The problems solve themselves if left alone!

Seriously, though, I would guess that a 'momentary pull cord switch' is a switch that you can operate safely from the shower, that bypasses the flow switch(es) and so starts the pump even when there's insufficient flow.

When you let the cord go the switch reopens, but the flow switch(es) stay closed due to the pumped water now flowing through them.

(Or maybe the switch reopens itself after a very short time period even if you haven't let go?)

Cunning, eh?