Unvented Water Systems

[John84]

Evening all.

A quick question on unvented hot water cylinders.

Is it possible to have a vented cold water cistern to serve cold water to an unvented hot water cylinder?

I am assuming no because this could cause backflow of water due to the pressure differential between gravity and the pressure in hot water cylinder.

In the case of mains cold water serving an unvented hot water cylinder, wouldnt the pressure be high in the hot water cylinder aswell creating a potential backflow?

Can any one shed any light on this?

Any suggestions appreciated

 

[migoplumber]

youve answered your own question!

shaun

 

[John84]

but how would mains cold water overcome the pressure difference because the pressure in the hot water cylinder could be greater than mains cold pressure?

basically even mains cold water would be under pressure wouldnt it?

 

[Puddle]

A quick question on unvented hot water cylinders.

Is it possible to have a vented cold water cistern to serve cold water to an unvented hot water cylinder?


Well in normal siduations why would you go to the expense of fitting a pressurised cylinder on a open vented cold water tank
But Yes,you could purchase a pressurised cylinder and feed it from a tank, And it is worth remembering,it is still being used as a presurised cylinder,only at what ever the head presure is of the tank attached (10m of head gives you 1 bar in pressure),up to the cylinder allowed pressure, a pump may be fitted to increase presure in cylinder,this can be done in low pressure areas

I am assuming no because this could cause backflow of water due to the pressure differential between gravity and the pressure in hot water cylinder.

Well there would not be any back flow any more than a normal cylinder because there would not be any abnormal pressure differential
For there to be a pressure increase,the water would have to be heated in a restricted area,thus restricting water expansion. leading to pressure build up and in the case of a pressurised cylinder the open vent is replaced by an expansion vessel or a built in expansion air pocket to take care of any pressure build up


In the case of mains cold water serving an unvented hot water cylinder, wouldnt the pressure be high in the hot water cylinder aswell creating a potential backflow?

Again you are not taking in to account the expansion vessel fitted in the cylinder to provent pressure build up when water heated however a non return valve is fitted on inlet to provent any slight back feed and contamination
Also if expansion was not taken care off by expansion vessel you would not be able to mix at a shower as hot would over power the cold

 

[david williams]

what is the reason for wanting to do this,and pressure in cylinder when heated if becomes over presuriesd will be let out of temp and presure relief valve