much higher cold pressure than hot - shower question

nickdesign · 28 Jul 2008

Hi guys,

am doing the bathroom and getting a plumber in shortly to install various bits. I live in a flat that has a communal and v large hot water tank along with a much higher pressure cold supply.

I am looking at purchasing a digital pumped grohe shower as we want a specific model - the max pressure for the shower is 1bar through each feed.

The hot is easily below this, whilst the cold is far above this.

The advice I have had from the shower company is to put a pressure reducer on the cold supply, therefore taking it beneath 1 bar, and they say as long as the pressure ratio is less than 5:1 things should be fine. then take both the hot and cold feeds through the digital pump.

I am looking at installing a caleffi pressure reducing valve - are these good enough quality ones?

does this method of doing this seem to sound okay as i'm intending to purchase the shower in the next couple of days

thanks very much

Newboy · 28 Jul 2008

It sounds like mains cold & tank fed hot.

I'd avoid trying to balance them - you will have to cope with other people drawing mains cold and hence have fluctuating pressure.

If the shower manufacturer says it's OK then get them to confirm in writing that this is the case - nobody will remember telling you it's OK if it doesn't work!

With you situation I'd be more inclined to go with a venturi shower and use the higher cold pressure/flow to boost the hot flow. With suppies both "well below" 1 bar you might be disappointed with the flow rate in your new shower.

nickdesign · 29 Jul 2008

thanks for your reply -

currently we have a pressure reducer on the cold leading to a mixer attachment on the bath, and this seems to cope fine, we have consistent water flow despite number of users etc....

we really need to buy this specific shower so do not want to consider the venturi options etc, but thanks for pointing them out.

nickdesign · 29 Jul 2008

i suppose i'm also trying to verify that it is okay to have a pump on a water supply that has a pressure reducing valve on it before the pump.

would i be better using a twin pump with a pressure reducer on the cold supply before the pump or simply a single impeller pump on the hot supply with a pressure reducer on the cold supply to get them to similar pressures?

does anyone know?

Newboy · 29 Jul 2008

Short reply - you are not allowed to fit a pump that draws from the mains water feed.

seco services · 29 Jul 2008

you won't be disapointed with the grohe digital pumped.
it will work perfectly ok with gravity hot and a pressure reducing valve on the cold.
these showers don't work in the same way as having a mixer valve and a pump on the floor in the airing cupboard.

they don't need to be a certain distance below your water tank, they don't need their own supply from the cylinder etc.

nickdesign · 29 Jul 2008

thanks for the reply seco - however, talking to grohe today...

they advised that they think i will get a better result by boosting the hot supply with a pump and reducing the cold pressure with a PRV so they are fairly close and then taking them through the unpumped grohe digital shower - their logic is that I won't be trying to take the pressure right down under 1 bar (the requirement for the pumped version) and will therefore be keeping a higher pressure which will result in a better shower

do you guys think they're right?

either i get the pumped version and take the cold pressure right down (under 1 bar) before taking it through the unit

OR

i purchase the unpumped version, fit a single pump to the gravity fed hot and bring the cold pressure down slightly using a PRV before taking through the unpumped unit......

Which would you choose?

nickdesign · 30 Jul 2008

well i bit the bullet and purchased the pumped version which will mean putting a pressure reducing valve on the cold supply before it enters the pump.

you think this will work okay then serco - have you fitted one in a similar setup?

seco services · 30 Jul 2008

where are you putting the grohe unit ?

nickdesign · 30 Jul 2008

not sure yet, can be pretty flexible really - I am leaning towards putting it under the bath (it will be an over bath shower) - do you recommend positioning in a certain place?

seco services · 30 Jul 2008

nickdesign said:
their logic is that I won't be trying to take the pressure right down under 1 bar (the requirement for the pumped version) and will therefore be keeping a higher pressure which will result in a better shower

you have the pumped version. which if you read the tech data states.
page 5 i think.
max 1 bar pressure min 0.1 bar.
so if you take the mains feeding the unit down to 0.3 bar say you will still get a blinding shower.

as they say you can fit these in the loft which i have done 9/10 times next to the cws tank which has made the pressure 0.1 bar and the shower has been 100 %.
if the pressure is low to the unit it can show a code when you first prime the shower.
but thats not a problem, they take 2 mins to prime.

nickdesign · 30 Jul 2008

so the fact that i'm using a pressure reducer right before the cold enters the unit shouldn't throw up any issues with it? I was worried that the draw from the pump might have an adverse effect on the pressure reducing valve.

seco services · 30 Jul 2008

no will be sound. let us know how it is when done.

and don't forget the flow restrictor on the cold inlet it is supplied.
make sure you read the instructions.

if you get any codes come up let us know
their is only about 5 codes.

nickdesign · 30 Jul 2008

do they supply a flow restrictor then? what does that do - sorry really stupid question i know

the other issue is I have a calleffi pressure reducing valve, which according to the specs will only take the water down to a minimum of 1 bar - will this be cutting it too close the the max input of the unit? do you recommend any PRVs that will take it below 1 bar and not fall apart after 5min?

thanks very much for all your help!

seco services · 30 Jul 2008

i think most are about 1 bar min.

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much higher cold pressure than hot - shower question

Newboy

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