Expansion vessel hose

[Matt0029]

Do many merchants sell 1 meter long 3/4 male to 3/4 female. The 3/4 male screws in to the composite valve and the other end the expansion vessel. I presume came supplied with the composite valve. The flexi is leaking.

 

[Deleted member 120897]

Is this for a boiler? Usually they’re available as a spare.

 

[ShaunCorbs]

I hard pipe them

Might be easier to use a male iron and a short bit of copper and a stnd 3/4 22mm flexi ?

 

[Matt0029]

I hard pipe them

Might be easier to use a male iron and a short bit of copper and a stnd 3/4 22mm flexi ?

Screw that out and hard pipe it?

 

[ShaunCorbs]

You can do as it’s best but if you want you can use a flex

 

[Matt0029]

You can do as it’s best but if you want you can use a flex

Thanks it maybe hard to get the correct flexi. May solid pipe

 

[Matt0029]

It's a 250litre cylinder. The expansion vessel is only only 18 litres. I'm correct in saying that is under sized and should be a 25 litre expansion? I have fit 18 litre ones on 150 litre cylinders.

 

[ShaunCorbs]

Depends on mi spec but yes normally 24l /25l on 210 up

 

[Matt0029]

Thanks the pressure relief is dripping I'm wondering if the vessel possibly being under sized is the course.

 

[John.g]

If the precharge & filling pressures are correctly set then a 18L EV will have no problem in taking up the expansion from a 250L cylinder heated to 65C.
Precharge/filling/Final (24L EV final pressure in brackets)
1.8/2.0/3.12bar (2.77bar)
2.3/2.5/3.79bar (3.39bar)
2.8/3.0/4.46bar (4.0bar)

Check air end pressure, this (precharge) would have to fall to ~ 0.7bar to cause the expansion valve to lift at 6bar. If the expansion valve is only dripping in the morning then the PRV may be passing overnight, a (filling) pressure of ~ 3.5bar will result in a final pressure of 6bar when the full 250L is heated to 65C.

 

[Matt0029]

Thank you it was just this that made me wonder.

 

[John.g]

Can't post spreadsheet files but if you build your own and follow the simple displayed calculations, then you can see the effect of the different inputs, just use the same cell locations that I use.

 

[ShaunCorbs]

Pre charge is wrong jon normally 3-3.5 bar

 

[John.g]

I would have thought that it should be set at or 0.2bar below the cold water pressure after the PRV, if the pre charge is set to 3.0bar then the final pressure will be 4.36bar no matter what the cold water pressure is from = or < 3.0bar, and 5.03bar if precharge set to 3.5 bar from a cold water pressure of = or < 3.5bar.
If unregulated cold water pressure then maybe set precharge to 3.5bar?.

 

[ShaunCorbs]

That’s what it states normally see below for full spec

 

[Matt0029]

Is there anywhere on that picture where it states what size expansion is needed?

 

[ShaunCorbs]

Is there anywhere on that picture where it states what size expansion is needed?

No but mi do 2 mins

 

[ShaunCorbs]

As below

 

[Matt0029]

So that's saying 25litre expansion vessel for 250 litres

 

[John.g]

A 287L Cyl & 25L EV with precharge/filling pressures of 3.0bar/3.0bar will give a final pressure of 4.06bar
A 250L Cyl & 25L EV with precharge/filling pressures of 3.0bar/3.0bar will give a final pressure of 3.90bar

 

[Matt0029]

The cylinder is an rmc group cylinder if anyone has heard of these. I tested the pressure after the pressure reducing valve to be around 3.5 bar but the system was ok. Well the cylinder was warm.

 

[Matt0029]

So the pressure relief shouldnt really be operating.

 

[ShaunCorbs]

Eg

https://www.advancedwater.co.uk/product/caleffi-push-fit-o-ring-pressure-relief-valve-6-bar-15mm-312007cst

 

[John.g]

Having read lots of posts regarding unvented cylinder problems I have never heard of one that has a installed pressure gauge, seems a bit strange?.

 

[Chuck]

Having read lots of posts regarding unvented cylinder problems I have never heard of one that has a installed pressure gauge, seems a bit strange?.

It's a DHW system, not a nuclear reactor! If a pressure measurement is needed for some reason it's easy to attach a temporary test gauge to a HW outlet. Also, you need to be careful adding permanent pressure gauges as it's easy to create blinds (dead legs) in the process.