Unvented cylinder - vibrating noise after h/w is drawn off.

[Servotech]

Got called to this today.
It sounds just like the water hammer that we used to get from the from the ballvalve on a vented system and yes opening the cold tap does stop the noise.
The pipework seems secure and well clipped.
I think it could be the pressure reducing valve that's at fault
Any different ideas?

 

[dcawkwell]

I have that on my own unvented cylinder.
If the water is being drawn off too quickly and the expansion vessel is dissipated of all the stored water you get a hammer at the pressure reducing valve.

Perhaps a flow restrictor to restrict the flow to the speed that the mains
can handle or additional expansion/accumulator tank.

 

[HERTS P&D]

What should the PRV be set to, if fitted on the incoming mains?


Andy

 

[Servotech]

I have that on my own unvented cylinder.
If the water is being drawn off too quickly and the expansion vessel is dissipated of all the stored water you get a hammer at the pressure reducing valve.

Perhaps a flow restrictor to restrict the flow to the speed that the mains
can handle or additional expansion/accumulator tank.

A larger expansion vessel; I'd never thought of that;did it cure your water hammer?
Customer says it was all fine until the water board did some work outside and ever since they've had this awful water hammer.
I've already fitted a isolation valve to adjust the pressure with no effect until I switch it completely off (which instantly stops the noise).
The instalation itself is only about 6 months old!

 

[Servotech]

What should the PRV be set to, if fitted on the incoming mains?


Andy

They are all pre-set to 2bar on this type of installation.

 

[picasso]

Had this a few times on megaflos, changing the prv cures the problem.

 

[mickyg]

Its because the charge pressure in the EV is higher than the dynamic pressure. You need to measure the dynamic/working pressure then set the EV pressure the same.

 

[Agile]

It also often helps to have a bit of resistance in the pipe to the EXV.

 

[Servotech]

Had this a few times on megaflos, changing the prv cures the problem.

Thanks, I think that's what I'll do.

Plumbers are having to learn/adapt to this new technology whilst at the same time are expected to know everything and fix problems they've never come across before!

 

[Servotech]

Its because the charge pressure in the EV is higher than the dynamic pressure. You need to measure the dynamic/working pressure then set the EV pressure the same.

Not sure what you mean by this.
The expansion vessel is set at 3.1bar
The Pressure reducing valve is pre-set at 2bar
The incoming mains - well it fluctuates according to demand (time of day). I wouldn't have thought it rarely gets above 2bar during day usage, but it may during the night when less people are drawing off the water supply.

However, I can't relate any of this to the problem my customer is having, can you simplify please?

 

[steve32]

Its because the charge pressure in the EV is higher than the dynamic pressure. You need to measure the dynamic/working pressure then set the EV pressure the same.

Not sure what you mean by this.
The expansion vessel is set at 3.1bar
The Pressure reducing valve is pre-set at 2bar
The incoming mains - well it fluctuates according to demand (time of day). I wouldn't have thought it rarely gets above 2bar during day usage, but it may during the night when less people are drawing off the water supply.



However, I can't relate any of this to the problem my customer is having, can you simplify please?

If you are G3 registered to work on unvented you will know that units are pre charged to 3bar and you adjust them on site to suit water pressure

 

[mickyg]

Its because the charge pressure in the EV is higher than the dynamic pressure. You need to measure the dynamic/working pressure then set the EV pressure the same.

Not sure what you mean by this.
The expansion vessel is set at 3.1bar
The Pressure reducing valve is pre-set at 2bar
The incoming mains - well it fluctuates according to demand (time of day). I wouldn't have thought it rarely gets above 2bar during day usage, but it may during the night when less people are drawing off the water supply.

However, I can't relate any of this to the problem my customer is having, can you simplify please?

i thought it was fairly simple. if your dynamic pressure is 2 bar then set the EV to 2bar. done.

 

[Servotech]

Its because the charge pressure in the EV is higher than the dynamic pressure. You need to measure the dynamic/working pressure then set the EV pressure the same.

Not sure what you mean by this.
The expansion vessel is set at 3.1bar
The Pressure reducing valve is pre-set at 2bar
The incoming mains - well it fluctuates according to demand (time of day). I wouldn't have thought it rarely gets above 2bar during day usage, but it may during the night when less people are drawing off the water supply.



However, I can't relate any of this to the problem my customer is having, can you simplify please?

If you are G3 registered to work on unvented you will know that units are pre charged to 3bar and you adjust them on site to suit water pressure

OK I think I'm with you now.
Although my company is G3 reg we've not yet got round to getting all employees G3 reg (just yet).
I still get sent to some of these jobs though, and when I do the boss still expects me to move the job forwards!
Even though I wouldn't get the job of actual fitting the new pressure regulating valve or adjusting the pressure even.

 

[Servotech]

Its because the charge pressure in the EV is higher than the dynamic pressure. You need to measure the dynamic/working pressure then set the EV pressure the same.

Not sure what you mean by this.
The expansion vessel is set at 3.1bar
The Pressure reducing valve is pre-set at 2bar
The incoming mains - well it fluctuates according to demand (time of day). I wouldn't have thought it rarely gets above 2bar during day usage, but it may during the night when less people are drawing off the water supply.

However, I can't relate any of this to the problem my customer is having, can you simplify please?

i thought it was fairly simple. if your dynamic pressure is 2 bar then set the EV to 2bar. done.

Many thanks for this information - the gaffer will wonder how I've become such an expert on unvented

 

[sooey]

I thought you worked for yourself Roger....when you're not working for the BBC making the rest of us look like a gang of cnts.