Unvented cylinder needs 22mm - water meter issue?

[caravanboy]

Hi,
I'm having a new feed into my house that will have 22mm pipework to feed a new unvented cylinder. The plumber suggested that having a very short piece of 15mm pipework just inside the house (around the existing water meter, which the water company has said he can re-fit) should not be an issue. Can anyone confirm this, or is it a problem that it goes through ANY run of 15mm pipe, no matter how short.

I presume the fact that the internal water meter has 15mm pipe each side means that even if it was possible to fit 22mm directly to either side of it then the flow/capacity of the meter may be an issue?

Thanks in advance for any advice/comments!

 

[Terry lambert]

The flow can only be the maximum that the narrowest part can carry

 

[caravanboy]

The flow can only be the maximum that the narrowest part can carry

Thanks. I guess that means if the cylinder specifies it needs a 22mm feed from the mains then I'll need to get the water meter swapped for one with a larger/fatter bore. Anyone know if water companies deal with that kind of enquiry regularly or am I likely to struggle to get across my requirements?

 

[Terry lambert]

Contact them and if they can't deal with it they will be able to advise you.

Also make sure you run at least a 25 mm main from the street or even bigger.

Your water supplier should also be able to advise you of the size of the pipe from the meter to the main distribution and then upgrade that if need be.

 

[ALEC1]

a small piece of 15 wont matter, assuming the pressure is adequate..

the higher the pressure the less it matters..

as said connect back to the main in the street in at least 25mm..

 

[caravanboy]

a small piece of 15 wont matter, assuming the pressure is adequate..

the higher the pressure the less it matters..

as said connect back to the main in the street in at least 25mm..

Hmm, so I may not need a larger meter then. That would be good if I don't. The plumbers had suggested they would leave a couple of inches of 15mm on each side and reinstall it off the new 22mm inlet (off 25mm MDPE).

We're installing new 25mm MDPE from the road tomorrow so that we get rid of the partial lead pipe that it currently comes through. The water company said that they'd replace the lead on their side once ours is done.

The inlet to the house is about 25 meters from the road. Does the length of that underground pipe matter? Perhaps I should take the 25mm back and get a fatter version? I presume the water company wouldn't care if it was fatter? They'll still get paid for the same amount of water coming through the meter.

 

[Terry lambert]

They will connect on to what you lay.

See what performance you get with the meter attached and then measure with the meter temporarily removed and bridged with 22 mm ( this should be easy) then you can decide whether to change it or not.

Post back the result, as i would be very interested to know

 

[dcawkwell]

Get another plumber.

22mm all the way.

 

[Terry lambert]

That's what I would say.

When you bridge the meter to test, don't use flex connectors as they are restrictive.

Also make sure you only have full bore valves for isolation

 

[caravanboy]

When you bridge the meter to test, don't use flex connectors as they are restrictive. Also make sure you only have full bore valves for isolation

Thanks, I like that idea. Will see if I can get plumbers to do that. When you say "flex", would 22mm push-fit do the job or is that also restrictive?

We ended up laying 50m of 32mm MDPE from the road yesterday but the house is 53m away so the last 3m dropped down to 25mm. Just need to get the 'Insuduct' now to get it through the wall and then the plumbers can take over on the inside.

I'll post the results of the with/without meter test if I can get them to do that.

 

[CBF]

you also need to make sure the plumbers hold the G3 cert for installing un-vented cylinders not just any plumber can install these you need to be qualified.

 

[caravanboy]

you also need to make sure the plumbers hold the G3 cert for installing un-vented cylinders not just any plumber can install these you need to be qualified.

Will do, I didn't realise they needed a special certificate! They were recommended by the builder who's doing the main renovation works and we've seen a similar system that they installed in another house. They're from a reasonable sized plumbing firm (i.e. not just a one man outfit) and they also sent a different guy who was LPG certified since our boiler is not on mains gas. Presumably they'll know about these "G3" regs so I would hope they are using the right chap. I'll check anyway.

 

[Agile]

I was going to say fit 32mm even based on your initial statement that its 25m from the road.

How could you so much underestimate the distance?

I would say make sure you increase the 3m of 25mm but it all depends on the dynamic flow rate which your cylinder installer should have measured.

Tony

 

[Agile]

The flow can only be the maximum that the narrowest part can carry

That is of course totally true but unfortunately often gives DIYers a wrong idea of how water and gas actually flow.

Many think that a 15 mm pipe will only allow a certain flow rate BECAUSE its only 15 mm.

The reality is that when flowing through a small pipe the water needs to pass faster and then it slows down in a larger pipe. The result of this is a resistance to flow which needs a higher supply pressure to create a certain flow.

For those familiar with electricity the flow of water is exactly the same but I cannot use that to explain it except to those familiar with electrical laws.

Tony

 

[caravanboy]

I was going to say fit 32mm even based on your initial statement that its 25m from the road.
How could you so much underestimate the distance?
I would say make sure you increase the 3m of 25mm but it all depends on the dynamic flow rate which your cylinder installer should have measured

Thanks, Tony. I guess my mental measurement isn't very good!. I was at work and knew the house was 12m long and that the pipe was going to the back end. I thought the distance from the roadside was about the same again, hence the 25m estimate. Of course, when I got home and we measured the actual route it was much more. I had bought 50m of 25mm pipe but then when the digger chap installing the pipe saw the distance he suggested 32mm too so we had to go an buy that Saturday morning.

Re. your other post, I'm much more familiar with electrical stuff than plumbing. I think I've heard people say that water pipe diameter is just like resistors(?) hence my concern that the plumbers told me a short piece of 15mm wouldn't matter. In electrical terms, if you stick a resistor in a circuit then it will affect everything after it, although thinking about that, I guess you're going to say that a short piece of 15mm is just like a very low value resistor, perhaps?

I don't suppose you can help with another related query... I'm at work at the moment and the plumber hasn't been able to tell me yet what sort of connector he will need to go on the end of the 32mm pipe to connect to the road-side stop tap. The old water pipe from the house is lead and looks about 32mm ish and that connects to the road-side bit. Do the road side stop taps have any kind of standard fitting on them or are they all different? I'd guess that it is relatively modern fitting, say in the last 20-30 years (it's a plastic cylinder going down about 6" across with the tap in the bottom and has a round metal cover at the top like those that usually have water meters underneath. He said he's going to get in the hole and take a look and see if he can work it out but that was a while ago now...

Thanks