Bypass Valve question

[Gunslinger]

for a pumped shower system, details are not important.

what i need is preferably an inline bypass valve which will open on a selectable pressure, to replace a manual valve

does anyone know of an inline version ? i know sunvic make one of the right angle variety

i'm looking for it to open at about 2.5 bar basically so i dont damage the pump

 

[puzzlebobble]

Hi,
I'n not a pro and from what you've said I don't understand why you want an auto by-pass but i've fitted an in line one (honeywell straight auto-bypass) in my system and it works fine:

http://www.screwfix.com/prods/34127...ols/Honeywell-Straight-Auto-Bypass-Valve-22mm

2.5 bar is within the range you can set it to. It's 22mm though, what diameter are the pipes where you want to fit the bypass?

PB

 

[Gunslinger]

22mm is fine that is the size of the pipework.

i need an auto valve because the pump is supplying an electric shower running in full auto mode ... i know, i know, if you ask the experts they'll all tell you that that wont work, but if you use a decent pump and flow sensor, it will - however, unless the pump is of the negative head type, you have to be careful of over pressuring the line to the shower, hence the bypass loop, but to be on the safe side i probably have it open a little more than ideal, this reduces the pressure behind the shower, lower than ideal, but better than over pressuring it or causing a problem for the pump.

That one looks ideal, if it will blow open when the pressure reaches 2.5 bar.

the pump is rated at 2.3 bar at some monstrous flow rate !

cheers

 

[andytheplumber]

I think you need to do some serious reading and thinking before you go down this route. What you are coming up with does not make sense

 

[Gunslinger]

it's not ideal, agreed, but as a temporary fix for the low pressure problem (the electric shower wont run off the mains cold, it shuts down) it will have to surfice, until i can get the whole system swapped out for a pumped system. running the mains through a non-return valve and the hot also into a mixer valve makes the shower almost pointless because of the terrible pressure and flow rate.

it's been running with the manual bypass in there for a few months with no issues

 

[puzzlebobble]

just for my interest Gunslinger; where does the water go to if it runs through the bypass?

 

[Gunslinger]

back into the feed pipe for the pump, close to the pump inlet, the feed pipe comes from the cold storage tank in the loft, so the return must be close to the pump to avoid back feeding the supply, this way i can effectively recycle the unused pumped water back into the feed and minimise the draw on the storage tank

Like i said this is not an ideal way of doing things, and you can see that some have raised eyebrows over the idea of it, but for my circumstances it was the only logical option cost wise to have a working shower straight away, without major reworking of stuff, as i already had a good quality shower fitted that could accept a high pressure and flow rate (relative) but not working sufficiently well, and i had a 2.3 bar pump spare along with the relevant circuit protection parts, plus the wall in the bathroom that the shower is mounted on, backs onto the airing cupboard, so it was actually not that difficult to do, i'd just like to make the bypass a little more efficient to keep the optimum pressure behind the shower unit, and as stable a pressure as possible, bearing in mind the back pressure will vary as the shower unit throttles the supply to produce the set temperature vs flow requested


looking again at that honeywell valve, and i am not so sure it will actually hold closed upto the pressure i am looking for, i do need one of those later for part of my replacement heating system, so i might grab one and if it's not suitable i havent lost anything as i will need it later

 

[puzzlebobble]

Interesting use of the bits you had spare! I hope it works. How have you got the pump to be triggered by someone using the shower? I guess you don't have it running all the time or the water running round and round in a circle would cause a bit of a racket.

I've just had a look upstairs and the valve I mentioned goes up to 6 bar.

 

[Gunslinger]

6 bar, or .6bar ?

the pump is triggered from a flow sensor on the output line, the pump is badged Rada or something like that, but it is a Stuart Turner 2.3 bar Monsoon Extra, so is not one of your cheap and cheerful B&Q specials !
i don't have a pressure vessel in the output line, so the bypass is also utilised to take up any shock wave caused by the shower shutting off (if i had a spare pressure vessel at the time, i would have fitted one)

The shower is a mira advance, older version now, cant remember the kw rating now off the top of my head, but i think it was over 9kw

it works ok, i wont say it's stunning performance, but for an electric shower it is not bad at all, being able to maintain a constant pressure behind it will i think improve it though. pump is somewhat under utilised, but as i already had it, i didn't have to spend a penny to get it all working, and after i've finished with it, the pump will still be perfectly usable and fine and will surfice as a backup for the others in the replacement system

Edit: forget to say, the pump is bearly audible inside the shower above the sound of the water and bathrrom fan, and from the hall way outside the airing cupboard it's not too bad either

 

[puzzlebobble]

You are right, sorry. it is 0.6 bar. It's installed with the letters upside down and I read it as 6.0 because I forgot to swap the numbers around.

But having looked up the conversion of 1 bar to hight of a water column. Will your pump not be equivalent to (10.2x2.3)= 23.5 metres high of water.

Aren't you worried about being hosed out of the bathroom?

 

[Gunslinger]

thanks for the reply, i've been doing a little research on the type of auto valve i would need, and i think i made a booboo when i called it a bypass valve, because that is what i want to use it as, however, looking at the bypass valves available, and how they work, it is unlikely i will find a suitable one, because they work on a differential pressure basis, and i doubt anyone would expect a differential of 2.5 to 3 bar across the valve

.. what i actually need is a self resetting pressure relief valve

so, sorry, by bad on using the wrong phraseology


23.5 metres, could well be about right, it sounds about right ... to be honest, i've not actually worked it out

and yes, initial tests on the pump and pipework during the flushing stage, with the supply disconnected from the shower, and the flow triggered via a makeshift pipe pointed into the bath with a full bore valve to open and close the end resulted in the bath filling faster than it could drain
But, this was with the bypass closed completely, and i knew that would never be the case when the shower was fitted because of it's method of restricting the flow to allow time to heat the water (and also supply pipe size at the shower inlet) the only reason i am thinking of an auto system rather than the manual valve is that like electricity, water will take the path of least resistance, so if i have the manual bypass open too far, the pressure behind the shower unit is somewhat low and not exactly optimum, however, if i close it off too much and someone turns up the temp fairly high, with the shower set to low flow via the selectable buttons, then i would create too much back pressure at the pump !

the pump btw, is rated at 45 litres per minute, so i have to feed the excess back into it's supply line, or the storage tank would be gone before i had time to finish washing my hair

 

[ChrisR]

WHy do you think your pump will provide too much pressure for a shower which is designed to work on mains which could be 10 bar??

No valve needed.

i need an auto valve because the pump is supplying an electric shower running in full auto mode ... i know, i know, if you ask the experts they'll all tell you that that wont work,

No, it's a perfectly ordinary thing to do.

 

[Gunslinger]

yes the shower is rated fairly high, and can certainly handle the pressure provided from the pump.

It was damage to the pump i wanted to ensure i avoid. The shower is an electric solenoid shut off, which closes and opens rather abruptly, so i was concerned about any shockwaves that may result from this action.

Also, as the pump is only supplying the one shower, with a 15mm inlet, it is somewhat under utilised, and the flow rate through the shower is tiny compared to the pumps capabilities, and all the info i found indicated that a bypass loop was advised to decrease the back pressure produced as the shower shuts off or restricts the inlet if an expansion vessel was not used.

The part you quoted, is interesting, as a lot of advice i got at the time was that the flow sensor probably wouldnt work properly, maybe even causing the pump to over run or not switch on, and a negative head setup was advised, even though it was not going to be in a negative head scenario.
If i remember correctly it was even suggested that i use a separate pull cord ceiling switch to control the pump.


When you say "No valve needed" are you suggesting that it will probably actually be ok if i close off the manual bypass loop fully ?

thanks for the replies btw