shower flow problem All aspects of plumbing questions and answers, help, tips and information

[tools1234]

Hi what is ment by neg or pos pump? I also am not sure what you mean by saying ten will give me five that the take off is from the vent pipe. What and where would the gravity loop be. The drawing down of hot water is a strong pos. thanks.

[plumbbob]

Not quite sure what all your questions mean, but a negative head is where the shower head is close to or above the water level in the header tank.

Normal pumps which require a positive head need a small natural flow of water to trigger the flow switch and start the pump. Negative head pumps get round this by pressurising the feed and the pump is activated by the fall in pressure when the shower is switched on.

See this post.

https://www.diydoctor.org.uk/forums/view ... hp?p=50186

What do you mean 10 will give 5?? Gravity loop???

[Dave From Leeds]

Hi plumbbob,

I think tools1234's post here is referring to answers he got to his other thread entitled "shower flow to ensuit". In particular to a reply from rosebery which I am reproducing here.

"Negative head pump or positive?

If it's positive which I suspect ten will get you five that the take off for the shower is off the vent pipe of your cylinder and theres no gravity loop fitted.

I'll hazard another guess that the hot supply to the bathroom is teed of the same pipe that feeds the pump.

Air is being drawn into the pipework through the vent which is preventing flow to the pump. Flow switches on pump detect no flow so pump doesn't run.

Opening the hot tap is enough to draw water through which reaches the pump and then it runs.

In other words it sounds as though it's piped incorrectly.


I think the translation of this bit

"If it's positive which I suspect ten will get you five that the take off for the shower is off the vent pipe of your cylinder and theres no gravity loop fitted."

is "....which I suspect then will bet you five quid that........".


Guess that's what the reference to ten will get you five is. I also suspect that tools1234 didn't mean to start a new thread here, but to add this to his original one.