What is the point of the low pressure cut-out in an electric shower?

phil63 · 22 Sep 2020

After my recent travails with a new Triton T80, I am intrigued as to what purpose the pressure switch plays in these showers: In an installation like mine, that appears to be at the limits of the required flow rate/pressure (and it varies throughout the day) to cool the shower (by increasing the flow rate control), causes a reduction in pressure, enough to occasionally cut-out on the pressure switch.
So the pressure cut-out is not a 'safety' feature as such: if you reduce the flow, the pressure rises, power cuts back in, and the shower can run as hot as you like. It still has the thermal cut-out and the overall safety fuse, aswell as PRD. And my previous shower never had any pressure switch.
Is there a standard or requirement for pressure switch control that has been introduced since my old Aqualisa? It just seems like an extra thing to go wrong and cause a nuisance of itself!

AdrianUK · 22 Sep 2020

Is it a "low pressure cut-out".... or it is really a "pressure above minimum so cut in ie. power the heater since we have water flow" ????

phil63 · 22 Sep 2020

I guess what I'm arguing is that the 'pressure cut-in' is a a very crude mechanism that works against the the actual shower mechanism in practise: Which is, that with a gentle but perfectly useable maximum flow through the shower, the pressure switch cuts out randomly. If you turn the flow down, it will stay on, but is scalding hot! Some kind of flow sensor would of course work and do the job.You get what you pay for I suppose.
I can't see a massive safety benefit in having the pressure switch, beyond that of the temperature cut-out and thermal fuse. I may have to convert this Triton to the, ahem, Aqualisa spec.

.

ianmcd · 22 Sep 2020

not a good idea to multi -post the same problem, stick with your origional post

phil63 · 22 Sep 2020

Sorry Ian, I was interested in discussing this as a general product design question, independent of my specific shower problems: Low pressure cut-outs on showers; retrograde design decision with few safety benefits? Discuss.

JohnD · 23 Sep 2020

phil63 said:
Discuss.

What is the purpose of that word?

martin hill · 23 Sep 2020

Pressure switch... So the shower is basically a kettle.

If the flow/pressure is too low the water will nearly boil in the shower heater as not enough cold water is constantly coming thru and the steams escape route is only the hose. Kettle boils it comes thru the spout.

bernardgreen · 23 Sep 2020

phil63 said:
Low pressure cut-outs on showers; retrograde design decision with few safety benefits?

The pressure at the inlet has to be high enough to force enough water through the heating chamber. If the pressure is too low then the flow through the chamber will be insufficient to safely remove the heat generated. Safely in that the water temperature is low enough so as not to scald a person in the shower

phil63 · 23 Sep 2020

"If the pressure is too low then the flow through the chamber will be insufficient to safely remove the heat generated".. that is precisely the opposite of what is happening in practise, which is my point: as you increase the flow on the control, cooling the shower, naturally the dynamic pressure will reduce.. only then does the low-pressure activate! So you get the counter-intuitive result of increasing the flow to cool the shower and take more heat from the elements, running them cooler and safer: but the increased flow is causing enough drop in the dynamic pressure to cut out the elements completely! Even though you were taking the maximum amount of heat from the elements that the pressure/flow of the system allows!
I should emphasise, this problem is obviously because the specification of my system is at the limit of acceptability: sometimes it's fine, but any general drop, or activity downstairs, knocks the pressure down just enough to cause these occasional annoying problems.

durhamplumber · 24 Sep 2020

The clue is in the name.

ianmcd · 24 Sep 2020

durhamplumber said:
The clue is in the name.

But why would you just accept that , when you can make it so complicated to pretend it is something else

phil63 · 24 Sep 2020

OK, maybe I should've worded the post differently. Or maybe just not bothered. My point is that using a pressure switch as a 'safety feature' (rather than, say a flow sensor, or quick-acting thermostat or thermal trip) is crude and prone to nuisance tripping; it trips when the flow is at it's maximum through the shower as the dynamic pressure drops, on any installation that is prone to variable pressure and marginal flow, which it seems to me is a significant number.
Anyway, I've vented my spleen, to a significantly unimpressed audience, and I'll shut up now. Wrong forum for this I guess; it's really a fundamental product design issue.

ianmcd · 24 Sep 2020

sorry but you are talking about an electric shower, a cheap throw away unit that is manufactured for under£10 but you expect space station control, never gonna happen, all safety devices have to conform to CE standards to change that is expensive

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What is the point of the low pressure cut-out in an electric shower?

durhamplumber

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