Pump not detecting flow change

[binman41]

Firstly sorry if this is a repeat post, have looked in the forum but cant find one.

I have recently installed two power showers into my bathroom and adjacent en suite. The installation is an unusual one and doesnt follow the normal orthodox ways.

Basically because of restrictions to pipes and working areas and after talking to local plumbers I decided to adopt the following installation:

The showers have a direct cold feed of the mains cold water (this is not pumped) and a feed of the hot water tank, which passes directly from the tank straight into a pump and out out again. The tank is on the same level floor as the showers meaning that the second level of the house has a pressurised hot watersystem, so even the hot sink taps have pressure.

Because of changes in cold mains pressure, and incase someone runs taps etc etc both mains cold feed, and pressurized hot feed are run through a pressure equalizer, after exiting the equalizer the pipes are split into two (by t-joint) where they each run to their respective showers and mixer units, at equal pressures. The pump is 'man' enough to cope with the length of pipes and two showers (although it is very unlikely that both will be used at the same time)

The pressurized hot water system works fine, you turn on bath taps, or sink taps, the pump sense a drop in flow rate so kicks in correctly.

The showers will work fine when the thermostatic mixer is set to cold, with good pressure. However when set to hot the showers will not run properly and the pump will not kick in.

After investigating if you run the hot water sink tap then the shower will kick in fine and the pump react giving a good pressured shower. I have checked the displacement head height and the pump reccommends a minimum of 100mm, when in fact there is over a foot of head height.

After further investigating I found that if you branch the equalizer (remove the qualizer and directly branch the gaps with pipe) then the showers also work fine, with the pump kicking in.

I thought it may be that the water in the tank is not hot enough, so adjusted the settigs and set the tank to its maximum temperature settings (which is hot!!) but still the same.

I cannot figure out why, when the hot taps on the sink are run, that the pump should then sense a drop in pressure when the shower is turned on, and not before. It must be something to do with the equalizer, perhaps the fact that, there is mains cold in and only normal hot in (although this should be pressurised and remain pressured until someone releases it, when the pump should then kick in??) that perhaps the equalization unit is restricting flow to the shower, and then when released the pipe from the equalizer is being emptied and then some kind of delay in the equalizer sorting out pressures again??

Perhaps it is also important to say that there is a very short delay with the pump kicking in anyway. when you run a hot tap in the sink or bath, the pump wont ick in for maybe 2/3 seconds.

Any thoughts at all would be very grateful!! I know that this is a strange combination and installation before people point out to me.

Cheers

A very confused! Chris

 

[ChrisR]

Fairly clear what you're doing!

Could you clarify:

I have checked the displacement head height and the pump reccommends a minimum of 100mm, when in fact there is over a foot of head height.

A foot isn't much, if that's the head on the inlet side of the pump??

ANd what pump is it? A Negative head one wouldn't have the problem, I suspect.

But what I think may be happening is that the mains CW pressure is preventing flow through the pump which would otherwise turn it on.
I would try a non-return (check) valve on the output of the pump. Hopefully then , when you open a tap the pressure would drop enough to allow flow.
What I'm saying is that the CW pressure getting back to the pump might make it lock up.

 

[binman41]

The head displacement i meant was the height of the hot water system feed tank (on the third floor) and the height of the shower head. Which is about a foot (reccommended on pump as being a minimum of 100mm). So basically the flow should be detected from the height of the shower head.....If this makes sence??

With regards to your answer about the CW pressure locking the pump, am I getting confused of how a pressure equalization unit works? The pump is only pumping hot water, as the cold is taken directly from the mains. Why should the pump be getting locked up with CW??

Cheers Chris

 

[ChrisR]

A foot is pretty minimal, I would have used a negative head pump, which would have maintained a pressure on its output even when not operating.

Why should the pump be getting locked up with CW??

It only has to present a tiny pressure at the hot input to stop the pump switching on. (0.03 bar isn't much!) EQ valves are not "perfect". Try the check valve, only a couple of pounds.

 

[binman41]

Cheers, will try check valve and let you know.....fingers crossed!

 

[binman41]

tried the check valve, still no joy. The pump is only activating when the hot water tap is being run aswell. Running the shower itself on hot, is not setting the pump off.

If i were to run the showers without the equalization unit, how would that work?? both showers have thermostatic mixers.