Unvented pressure problems

[Benjibalz]

I have just looked at a unvented cylinder with pressure problems. The customer called me in asking me to fit a pump on the mains but the mains pressure is 2.5bar and flow rate over 22l/min which should be fine for an unvented cylinder.

The problem is that when the two showers in the house are used there is a slight drop in pressure. However, in the coach house if the shower is run the supply to the showers in the main house stops completely. This has been a problem since day 1 of the installation(installer refused to return once he had his cheque!), has anyone ran 3 showers off of UV at this kind of pressure?

As this has always been a prob I thought the expansion vessel or blocked line strainer shouldnt be an issue although should have checked them on 1st visit I know! Also, pressure on hot outlet is fine so I think blockage would not be the prob.

So...2.5bar enough for 3 showers?.....ex vessel?.....pump it?

Any thoughts appreciated. Cheers.

 

[Fluffster]

I take it you are G3 certified.
The pressure is not the main issue the flow at 22lm is not going to go far with 2 outlets open.

Is there a second tapping for a hot water draw off which you could use as a dedicated feed to the coach house shower?

Pete

 

[Tipper]

What are the relative pipe sizes. It's all down to pipe size and pressure drop for a given size(s) of pipe. Small bore and high flow = big pressure drop, etc.

 

[Benjibalz]

I am G3 certified pete. There is no other tapping available, I was suprised that the flow to the bathroom shower stopped completely when the shower in the coach house was running although the two bathrooms in the house are upstairs but the coach house is on the ground floor which is the same level as the cylinder. Obviously the water is just taking the easiest route.

The cylinder is supplied in 22mm and as far as I can see the hot and balanced cold are both in 22mm.

It seems the flow is the problem so I guess a break tank and pumping the incoming supply is the way to resolve it, unless anyone has any other ideas?

Thanks guys. Ben

 

[Benjibalz]

Have just been on www.gasapplianceguide.co.uk coz my life is so exciting. They actually say that pumping unvented directly is not allowed under water bye-laws.

I thought bye-laws were now water regs but hey-ho...I think a chat with the supplier is needed, maybe a larger supply pipe to the property if it is undersized as the customer suspects.

 

[cider]

Have just been on www.gasapplianceguide.co.uk coz my life is so exciting. They actually say that pumping unvented directly is not allowed under water bye-laws.

you learn something every day

 

[ajstoneservices]

We had a similar problem where the dynamic pressure dropped at certain times of the day(never when we tested it) in the end we used a couple of 50gallon CWS's and one of these http://www.heatandplumb.com/acatalog/Grundfos_Whole_House_Single_Booster_Pumps.html


works a treat.

 

[simond]

You need to fit an accumulator to the water main. 500litre nominal, 260 litre actual water capacity.

www.gah.co.uk

Other products are available.

 

[holty]

iv known a few problems when fitting unvented in winter when theres not many tourist about. then come summer, water pressure is a nightmare. so i now have to assess if theres camping sites nearby etc. i think ajstoneservices is a good way to get by this problem.

 

[simond]

Only if you want unnecessary noise, and no water in a power cut.

Clearly you haven't fitted any accumulators; because if you had, you wouldn't be recommending a pumpset.

Sorry, that sounds a bit patronising like Big Burner. He must be getting to me. Fit a Broag, must fit a Broag.

 

[Fluffster]

No you must fit 2 Broags apparently on every single property!!

Pete

 

[ajstoneservices]

Only if you want unnecessary noise, and no water in a power cut.

Clearly you haven't fitted any accumulators; because if you had, you wouldn't be recommending a pumpset.

Sorry, that sounds a bit patronising like Big Burner. He must be getting to me. Fit a Broag, must fit a Broag.

Are you saying that in every circumstance with intermittent flow/pressure to an unvented cylinder an accumulator is the only way to go. What if the the flow/pressure drops to such an extent that it cant recharge the accumulator (add a bigger/another) what if the building cant take the additional load or have room for another vessel. they do work but are IMHO not right for every installation and neither is a pump.

Oh and pump isn't noisy, its barely audible.

 

[simond]

Clearly an accumulator - or for that matter any other solution - will not be the answer to every problem.

From the figures the OP supplied, a pump would be a pointless complication when you already have 2.5bar.

There is no mention from the OP about a 'fluctuating static pressure', just like there was no mention from me about 'every circumstance'.

Therefore I'm struggling to see the relevence of your last post, other than to say that it is best to specify the right product for the task. I am in agreement with that sentiment.

 

[ajstoneservices]

Clearly you haven't fitted any accumulators; because if you had, you wouldn't be recommending a pumpset.

Sorry, that sounds a bit patronising like Big Burner. He must be getting to me. Fit a Broag, must fit a Broag.

You may have apologised for it, but you came across like BB, read what you've typed.

 

[simond]

Another bathroom changer.

Read it again. Read and learn.