Mains water pressure

[Penners]

This question relates to my other post, today, on the subject of a shower pump electrical supply. The background to these matters is that I'm fitting an electric shower, but I'm concerned whether I have sufficient mains water pressure for it to operate satisfactorily, without the low pressure cutout constantly interrupting the flow. The minimum specified operating pressure for the the shower is 0.75 bar.

On the mains cold water system in the house, I can get 3 bar static pressure. But if I open up a tap fully on the system, that pressure drops virtually to zero. If I open the tap about halfway, I get 1.5 bar.

Two questions:

1. Do you think the shower will operate reasonably satisfactorily, without my fitting a Salamander pump and supplying it from the header tank?

2. What sort of pressure should one normally expect in a domestic mains system? Do you think I have grounds to contact my water supplier and demand an improvement?

Anyone got any thoughts on this, please?

 

[Feltwell]

Not much help, but I would also be interested in any answers. We've 2 electric showers and they work fine until someone flushes a loo or runs a tap - then the pressure drops, the cutout operates and the shower goes freezing cold.

You can also only operate 1 shower at a time. The showers are different brands to each other, so it's not a quirk of a particular model. I suspect it's our plumbing setup - a single 15mm pipe carries the water upstairs to feed the sinks, toilets and showers. But - even if I ran a seperate pipe upstairs for the showers, it would still all feed out of the water softener we have downstairs, which in turn feeds out of the 15mm pipe directly attached to the incoming lead water pipe. We had the problem before we fitted the water softener, although it does appear to have got a little bit worse since we fitted it.

I'd be interested to hear if anyone else has had this problem and managed to resolve it. Penners, I rather expect that you'd get this problem if you went ahead and fitted your shower.

 

[Penners]

Yes, Feltwell, you have exactly the situation that I'm concerned about.

Electric showers have a low pressure cutout on the heating element, to avoid burning it out. So your system obviously has sufficient pressure to satisfy this cutout while no other taps are open, but as soon as someone flushes a loo (or whatever) the pressure drops below the shower's minimum - this is usually rated at 3/4 to 1 bar (ie: a little under 15 lb/in^2), depending on the make/model of your shower.

On thinking about it, I suppose my question 1. above was a vain hope that someone would have a magic wand that would give me a solution with my having the hassle (and cost) of fitting a pump. I suspect I just have to bite that particular bullet.

But my question 2. was also relevant. I wonder whether there is a minimum specified water pressure that your water supplier is contractually obliged to give you. If so, and if mine fell below this standard, then the hassle and cost would be supplier's and not mine!

If you want to test the water pressure in your mains system, you can pick up a plumber's mains water pressure gauge for not much money - mine cost £6.90. It has a 3/4" BSP connector, so you just hook it up to your washing machine or dishwasher's supply connector (assuming that's at mains pressure) and open the valve.

Remember, though, that static pressure (ie: with all taps on the system closed) is a snare and a delusion. It's the pressure under a flow situation that matters - as your problem with flushing loos, etc. demonstrates.

 

[FamilyWiggs]

Feltwell - your problem seems to be that the whole system is fed through the water softener and then via a single 15mm supply pipe. These constraints are difficult to overcome - remembering that you need both flow (volume) and pressure (force) for a satisfactory system. Does no one use 22mm pipe any more? I've even got 28mm in some places - but then thankfully my problem is too much mains pressure!

Header tank and pump to shower may be the only way to go for both of you for a reliable, interruption free shower.

 

[MdB]

As per FW, it is the flow rate that is the most critical part. Find a bucket of a know size and time how long it takes to fill in the room with the shower and then compare this to the showers minimum rating. (google will convert you favourite units into litres / minute)

 

[Penners]

Does no one use 22mm pipe any more?

My lament exactly, FW. The whole of this house is plumbed in 15mm, including the rising main! No wonder I can't get a satisfactory pressure.

 

[Nigel Watts]

We ended up having to replumb right back to the main in the road to get the pressure up. It seemed a ridiculous extravagence at the time but I dont regret it now. It also enabled us to dispense with the cold water tank in the roof.

 

[chuckey]

Unless you have some special industrial supply, running two electric showers really is pushing the domestic mains. I asked for a 100A supply so a guy turned up and changed the 80A fuse to a 100A fuse! So basically the incoming (supply) wiring is only rated at 80A, when I turn on my 9kW shower heater the incoming mains falls from 240(!) to 205V. I use one tank fed pumped shower and one electric shower.
I find that in summer I set my "sportsman shower" to a "temperature" of 5.5 (actually increases the flow) and in winter the dial ends up at 9.5 - right against the end stop for minimum flow. So any low pressure problems would show in summer, where you need a lot of flow which would end up as low pressure in Penners case.
The other problem I have with the pumped shower is that the minimum flow switch on the pump is set far too high - 8L/min. I am trying to put in my own which should operate at about .5L/min.
FWIW In Askrigg the mains pressure runs at about 10 Bar all the time, I know of two showers and a plastic fitting that have ruptured due to the pressure. A local plumber claims he has seen it as high as 16 Bar!!!!! Thankfully I am further up the hill so my pressure is about 3 bar less.
Frank

 

[Penners]

my "sportsman shower"

I considered the possibility of installing a "sportsman" shower, but I was afraid it might refuse to operate for me.

So I settled for a "lazy sod" model.

 

[MattW]

I wonder whether there is a minimum specified water pressure that your water supplier is contractually obliged to give you.

Yes, it is 1.0 bar. In many parts of London, Thames water is reducing the pressure down to reduce leakage in victorian pipes. 1 bar is sufficient pressure to push water up 10 meters of pipe... so no flow at all at the top of a 3 story house.

On the mains cold water system in the house, I can get 3 bar static pressure. But if I open up a tap fully on the system, that pressure drops virtually to zero. If I open the tap about halfway, I get 1.5 bar.

As MdB states, this is a flow problem. 3 bar is sufficient to run a good shower at top floor of 3 story georgian house (i.e. average 10 foot ceilings). You should measure the number of liters per minute of what that you get out of your mains - you may need to simultaneously run two taps with large buckets for this. Measure it again on the hot water taps. A material difference would suggest that your boiler is restricting the flow. The other thing to consider is, assuming you are in a hard water area, is are your pipes furred up inside?

There is a huge amount on shower pressure on DIYorNOT.com

 

[Penners]

Thanks for that, MattW. I note your comments about a flow problem, and I suppose that's down to the fact that the whole house is piped in 15mm. I did consider the possibility of limescale being a factor, but I haven't found any at all in the pipework, all of which was renewed only a few years ago.

Given the potential cost and aggravation of having to replumb the whole place, I think I'll just go for a pumped supply from the header tank.

 

[MdB]

Just for the record, those with stupidly high water pressures (6 bar here), this is very easily solved using a pressure regulating valve costing around £25 + fitting. Instant cure for water hammer.

Another thing worth noting if you have low flow rates are the typical isolation valves that now get fitted to everything. Their internal cross section is roughly half (??) the pipe size so can't do anything for the flow rate. You can get larger versions which don't look quite as good but do keep the internal bore the same as the pipe.

 

[Andrew Bodenham]

MdB: I'm interested in your experience with pressure regulating valves. I'm considering fitting one to reduce noise from valves upstream (e.g. toilet fill) operating at high pressure - water system noises are a pet hate of mine. But do you find the the PRV introduces its own noise into the incoming flow, or does it operate silently?
Andrew

 

[MdB]

MdB: I'm interested in your experience with pressure regulating valves. I'm considering fitting one to reduce noise from valves upstream (e.g. toilet fill) operating at high pressure - water system noises are a pet hate of mine. But do you find the the PRV introduces its own noise into the incoming flow, or does it operate silently?
Andrew

The 15mm version we used to have was quieter than the 22mm version we now have but they both make some noise. We have ours in the utility room and it will eventually be at the bottom of a cupboard (once I get around to building it) so the noise it does make isn't an issue. My feeling is that they make less noise as they bed in though this is a bit subjective. Having just done a quick check, it doesn't make any noise I could hear when the kitchen sink tap was turned all the way on and then all the way off. Flushing the loo however caused it to make a thurdunk noise as we have a fast fill cistern which switches off suddenly. This causes the PRV to switch off suddenly too which makes the noise.

 

[Pford75]

Bit of a latecomer to this thread....but I honestly believe that the best solution is to install a pressurised system (something similar to Dualstream). This removes the need for individual shower pumps, provides much better pressure and is not that expensive really.

 

[MdB]

Bit of a latecomer to this thread....but I honestly believe that the best solution is to install a pressurised system (something similar to Dualstream). This removes the need for individual shower pumps, provides much better pressure and is not that expensive really.

It is a good idea and it is what I have installed here (I would say it was about the same cost as a pressurised system) however, they will only work if you have a good enough flow rate which seems to be the issue here.