Shower pump pipe sizing

31 Jan 2014
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West Midlands
United Kingdom
I am installing a shower pump. I want to use flexible coupler hoses to help minimise the vibration. There is a 22mm supply pipe from the tank in the loft, and the pump has 15mm fittings.

So I'm using a 22mm to 15mm reducer, the flexible coupler hoses (300mm long) have an internal bore of only 10mm. The pump requires minimum 0.01bar on the inlet.

On the outlet it's 15mm connection on the pump, through the flexi hose, and back to 15mm pipework. Shower head is rated for 12.5L a min. Pump is rated max working head 10m (1 bar)

Could someone more knowledgable about flow rates and such, tell me if this is a workable idea or not?

This is a Mira pump, but I notice the official Salamander flexi hoses only have a 12mm internal bore. Internal bore of 15mm copper is about 13.6mm.

So is 300mm length of hose at 10mm instead of 13.6mm going to make a massive difference?
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What MIRA pump is it? They should all come supplied with flexi pipes, use them. If you don't have them, then buy them. Normal flexi hoses will not be the same spec/materials.

Will it work, no reason why not as long as you can achieve the min flow rate at the shower head to activate the pump .... 1L/min. If it's the plastic ended pump then do remember they are not continuous rated, you only get 30mins run time then rest for 30.

BTW - You won't get any warranty from MIRA though if you don't use their parts.
Thanks, it's a Mira Platinum and Mira Mode pump. They don't come with flexi hoses, and I can't see them available for sale from Mira. Hence using standard 15mm flexi tap hoses.
Ah ok, they're digital showers. When you say a shower pump we think of stand alone impeller pumps, not a digital processor unit.

As it's a gravity fed unit (LP) they're designed to use hard pipe and be fixed down, I doubt using flexi's will change the noise output of the unit. That's more down to the location of the processor.

If it's a LP processor you really want to maximise the flow to the unit if you can, to get the best performance. Will it work though, yes it probably will, as long as you can get the min flow through the unit.
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Yeah it's an LP pumped unit. Flexi's are not going to do much for the noise. Hopefully will kill some of the vibration down the pipe though.

I've got just over 1m head to the tank, so about 0.1bar pressure. Minimum requirement is 0.01bar so it should be ok.

I just can't get my head around pressure and flow rates. You look at how narrow the pipework is and think, that's going to take forever to fill a bath (digital bath filler). And yes it would, at 0.1bar..... but add pressure and it works. Like modern microbore plumbing I suppose, that's only 10mm but gets the flow rates, so long as it's pressurised.

If it's not working very well then I'll just have to replace the flexi's with plastic pipe.
Digital shower are very low noise/vibration, especially if you fit the unit down onto a solid base, there shouldn't be very much in the way of vibration transmitted to the pipework, just have it well clipped/supported.

Think of pressure as the force behind the water pushing it through the pipe, flow is the volume (L/Min) of water that flows through that pipe every minute @ a given pressure.
Therefore a 10mm pipe @ a sustained (dynamic) pressure will flow a certain of water per min. Take the same size of pipe and double that dynamic pressure, then that same pipe will flow a higher volume of water, as the water has a higher velocity.
Don't use flexi tap hoses..the bore is too small and it is likely Mira would void your warranty should you need to claim (parts are very expensive for what they are). Perhaps consider WRAS approved full bore hoses but these pumps are designed to fit 15mm copper/plastic pipe.

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