Positive /negative head shower pump

Groovygirl

Many years ago we had a pre formed shower cubicle installed and a pump because both hot/cold are gravity fed from tanks, the pump (2 bar) never worked properly as we always had to lower the adjustable shower head (nearly to the floor) before the pump would start. Now we’ve got rid of the old shower and installed a dual valve riser shower with a rainfall head and adjustable shower head/wand (max 3 bar) and we still have to lower the adjustable head before the pump would work. After a bit of research I believe that we need a negative/universal pump for it to work as it should as the rainfall head is inline with the bottom of the cold water tank, the original pump is a positive pump. We were looking at installing a 3 bar pump but as all the plumbing is on 15mm pipe work it’s not possible. All the tanks are in an airing cupboard in the bathroom and the tanks are big enough to cope with the flow of water to the shower.

So my questions are ....
Do we need a negative/universal pump?
Which manufacturer would you recommend? Been looking at Stuart Turner.
And would you install a 2 bar or 2.6? As I believe that’s the maximum we can go with due to pipework.
Many thanks for reading.

Grenage

Stuart Turner pumps are decent; you'll certainly want a negative pump if the outlet is higher than the tank.  We have a 2 bar for our 5cm shower head and it's fine.  I'd probably go larger with a large shower head.

bob_a_builder

I have almost exactly the same issue as the OP.
I would also be interested to know if a negative pump would resolve the issues
Since I believe the problem is actually down to the lack of head - or more accurately a lack of enough flow to allow the pump to start

My setup is normal shower head @ 2' 6" below ceiling height, rain head @ 1ft below ceiling height.  Bottom of tank is  1' 6" above ceiling height with the about 3' of water in the tank  - The shower is powered by a Stuart & Turner 1.5 bar positive pump mounted at  7' below ceiling height - all pipes are 22mm to the the last drop to the shower itself

The shower will never start if set to Rain Head, the normal head will start 75%  of the time but there will be a significant variable delay between turning it on and water actually flowing - of course times expands while you are waiting for something - if I get bored waiting or its one of the 25% when doesn't seem to start - I will turn on the sink tap on/off ( on same pump)  to start the shower flowing.

So as I said at the beginning I think this is due to a lack of head which is not able to force enough flow to start the pump which the spec says is 0.8 l/ min  ?

Could a negative pump resolve this ?

BUFF

Stuart Turner/Salamander/Grundfos
Salamander have an advisory service https://www.salamanderpumps.co.uk

bob_a_builder

Found this on the Salamander install instructions on their web site, which seems to address my point about the lack of flow to start the pump 

"Negative head systems exist where insufficient natural flow of water goes to the outlet because either the outlet or the pipework to the outlet are above the height of the base of the cold water cistern. Most instances of negative head systems occur in loft conversions or where the cold water cistern sits on the joists in the loft. If the distance between the bottom of the cold water cistern and the highest point in the system after the pump is 2 feet (610mm) or less, it is also possible that a universal pump will be required.
Salamander’s universal range of pumps activate the pump automatically even where insufficient natural flow exists."

knightstyle

I fitted this to my DDs shower in her flat to make the shower pump come on without having to lower the shower head, added a chrome hose adaptor to the outlet and it worked fine till the boiler failed and she got a combi.   Cheap effective fix.