Pump at bottom of header tank in attic

[oldbutnotdead]

You can calculate the maximum input pressure to the shower. Vertical height from water level in cold tank to top of shower unit on the wall in metres/10 gives your maximum bar (your supply pressure will inevitably be less than that due to pressure drop in the pipework.
For the flow rate I'd just run the shower into a bucket to start with on cold (to get a litres/min reading), if you want to get a unboosted supply flow rate as well then yes do that. Or try running the shower with the power turned off (that may not work though).
Just checked Mira's site- looks as though all of them will deal with low supply pressure (0.1 bar and less with the pumped showers).

 

[andyr123]

how about this idea, and I know it is not the ideal way it should be and that the shower units should have their dedicated pipes coming from the bottom of the header tank (is this so someone in the shower wont get scalded if someone turns on the cold tap on the basin or flush the toilet?) but how about I take the cold pipe exiting from the bottom of the tank and just put a single pump on it then link up all the pipes (cold pipes to the showers, basin/sinks, toilet cisterns) to the outlet of the pump and then put another pump for the Hot pipe coming out of the immersion heater cylinder for the hot water circuit of the house ... would that be doable?

 

[andyr123]

What size pipe feeds the showers? Pressure and flow rate are two different things.

If you don't have much head pressure (ie not much fall between the tank and the outlet) you can compensate by having a larger bore pipe so that you have better flow for the same head pressure.

I think from memory when I had the covers off the shower they are 15mm - was thinking larger bore pipes but again a load of work needed taking out all the 15mm and putting in 22mm - there might not even be the space to , and in any case it will still have to be reduced down to 15mm at the shower connection

 

[andyr123]

You can calculate the maximum input pressure to the shower. Vertical height from water level in cold tank to top of shower unit on the wall in metres/10 gives your maximum bar (your supply pressure will inevitably be less than that due to pressure drop in the pipework.
For the flow rate I'd just run the shower into a bucket to start with on cold (to get a litres/min reading), if you want to get a unboosted supply flow rate as well then yes do that. Or try running the shower with the power turned off (that may not work though).
Just checked Mira's site- looks as though all of them will deal with low supply pressure (0.1 bar and less with the pumped showers).

I suppose if I wanted to check liters per minute un-pumped I could just maybe take the cover off the shower , then remove one of the spade terminals off the pump motor inside the shower (and heater?) and then just let flow into bucket for a minute.
To check that would I be better off leaving shower head on or unscrew it and measure it in bucket with the shower head off to do its test?

 

[Johntheo5]

This is the recommended installation.

Have you done the "normal" test??. these showers are notorious for pump problems, at least this test will tell alot IMO.

 

[andyr123]

looks like these mira low pressure showers will take a maximum of 1.0BAR so if i did get a 1.5Bar pump (off screwfix wherever) would they have any way to adjust/limit down to 1.0bar or under by means of switch/variable control knob?)

 

[andyr123]

Have you done the "normal" test??. these showers are notorious for pump problems, at least this test will tell alot IMO.

I dont live near them, so I will have to pop down one weekend and do the litre per minute test

 

[Johntheo5]

You could suggest running on Eco setting, 1/2 power which should at least give a steady flow temperature with a reduced flowrate of ~ 3.9LPM, the same as a 9kw shower gives in in winter at full power.

 

[andyr123]

these showers are notorious for pump problems, at least this test will tell alot IMO.

ah really , that I could look into. from memory the carbon brushes looked OK and the motor sounded fine but yes I can check that again when I am down there next.
The cold water coming out the basin taps and bath tap and very slow filling of cistern (even with a brand new float) had sort of led me to the fact that they need to up the pressure somehow and i was just thinking a pump would help a lot.

 

[Johntheo5]

You shouldn't need another pump under any circumstances as long as the shower is 0.5M or so below the bottom of the CWST even if using 15mm piping.

 

[andyr123]

You shouldn't need another pump under any circumstances as long as the shower is 0.5M or so below the bottom of the CWST even if using 15mm piping.

aside from the showers, the cold tap on the bathroom basins, the bath tap , the slow filling toilet cisterns then wouldnt it help anyway putting in a pump where I was thinking of putting it?

 

[Johntheo5]

Basically, yes, but I wouldn't have it pumping into the shower inlet even with a pressure reducing valve, you will then have to consider pumping the hot as well?, you are then looking at a twin impeller pump which don't come cheap, if the shower's flow problem isn't its own pump then it points to a restriction/blockage from the CWST which is the first thing to address as the proposed pump will not perform either, sort that out first and then make your decision.

 

[oldbutnotdead]

aside from the showers, the cold tap on the bathroom basins, the bath tap , the slow filling toilet cisterns then wouldnt it help anyway putting in a pump where I was thinking of putting it?

A pump is one option.
Another option is to investigate the pipework.
For instance, is every cold appliance in each bathroom fed from that one 15mm feed? Do that headloss calculation - a well designed run (with swept or formed bends rather than elbows) will give better performance without the noise and expense of a pump.
With the cold there are benefits (especially with a low head) to going larger on the tube size (hot is different, you can end up wasting a lot of water with oversize hot feed).

 

[andyr123]

thank you everyone for your help and helpful advice its been really useful and has given me more options and avenues and things to check.
Thanks again.

 

[andyr123]

i am going to try the suggestions first - but if I went down the road of deciding to fit a pump to improve the pressure on the cold from the storage tank I am presuming if I put the pump up in the attic for them and place it at the bottom of the header tank that I would have to go for a Negative Head pump?? - a Positive one will only work if I placed the pump in the airing cupboard instead where it has some gravity coming from the header tank yes? -

putting it at the bottom of the cold water storage tank means no gravity and so a negative head shower pump needed yes?

shame if i do as the negative head pumps seem a lot more expensive say from a place like screwfix.

Negative head pump around 500euro
Positive head pumps around 150euro