Fixed Head Shower Plumbing

[Dee Mented]

I have a low pressure system with 2 x 22mm pipes going from the loft tank and HWC to the full flow bath mixer/shower taps. The bath taps head is 0.25 bar. The flow rate at the bath with both taps on is 32l/min.
The bath mixer/shower tap has 2 x 5mm diameter holes within the diverter that feeds a 7mm diameter flexible hose feeding a standard hand held shower head which has a head of 0.1 bar. The shower head output at the correct temperature is 4l/min - which I consider suitable output.

I am intending to replace the bath/shower tap with a number of full flow Pegler 3/4" globe valves that will mix the hot and cold to feed the bath and a new fixed head shower (Bristan VR3000E type).

Can anyone advise whether there is any advantage with feeding the fixed head shower from the globe valves mixing point with either a 15mm or 22mm feed pipe (with 22mm pipe reduced to 15mm close to the shower head as I can't find a 22mm version)?

Thanks in anticipation

 

[bashmaystor]

You will achieve a bit more flow-rate if you use 22mm as far as you can.
Since its a gravity fed system, 22mm will be better suited than 15mm.
Also the head pressure at the shower head will be lower, than down at the bath taps, so again 22mm will give you an advantage.

 

[Dee Mented]

You will achieve a bit more flow-rate if you use 22mm as far as you can.
Since its a gravity fed system, 22mm will be better suited than 15mm.
Also the head pressure at the shower head will be lower, than down at the bath taps, so again 22mm will give you an advantage.

Bashmaystor - Thanks for your reply, I wasn't sure whether reducing the pipe size (22 to 15) would increase the pressure but decrease the flow rate. The present bath taps per feed reduce the 22mm cross sectional area from to 323mm2 to 310mm2 in the tap casting and then the diverter further reduces the csa to 16.62mm2. So the pressure is significantly increased (don't know the math behind all this) a bit like a hose pipe nozzel. What do I need at the shower head to give a good spray, is it flow or pressure or some of both? Anyone know the formulas?

 

[Chalked]

Flow and pressure is needed
On your system pressure is created by the head ( height) of your tanks in the roof, above the height of your shower outlet.
To create one bar (14psi) your header tank would need to be 3m above the outlet ( not the valve).
Volume of water is a bit more complicated. You can get a good volume down a large pipe at low pressure. Increasing the pipe size, has no effect on pressure. But you can get a good volume down a small pipe, if you can increase the pressure ( force).
No point going into more detail as your only fitting a shower.
Because fittings and the shower valve create resistance. Upgrading your pipework to 22mm, will have very little benefit.
To sum up . It's all about expectations, if you are happy with a low pressure low volume shower, then fine. If you want a good Gliw and pressure, you are going to have to either, lift the tanks, fit a shower pump or go for an invented hot water cylinder.

 

[NickH]

"To create one bar (14psi) your header tank would need to be 3m above the outlet ( not the valve). "

Are you sure Chalked ?
I reckon you need 10m for 1 bar.

 

[Chalked]

"To create one bar (14psi) your header tank would need to be 3m above the outlet ( not the valve). "

Are you sure Chalked ?
I reckon you need 10m for 1 bar.

Sorry , typo . It's 10 m per bar.

 

[justlead1]

Hi Dee
Are you sure that 4ltr minuet is sufficient ?
Divide 4 x 60 =seconds (0.06666 ltr)
You may have to try 4 divided by 60 plus a flannel.
When reducing pipe size as described. It is only a short length being reduced, as when calculating discharge the pipe length has an effect but very little on such a short length.
Search out Box's formula it will allow you to play with the numbers.