Pressurizing a vented cylinder

[seanEE]

Hi guys, I have a question regarding converting an open vent system (copper cylinder) to pressurized, reason being not enough drop from the loft to power a shower, while i know the common advice is to buy a special unvented cylinder I can see no reason why an unvented copper cylinder cannot be pressurized (To a reasonable degree) no more than it would be if it were fed by a cistern placed sufficiently high, if i take the (cold in) that comes from my loft cistern and plumb a low pressure pumped supply in there, I could tune the shallow well pump down to the lowest pressure required to power a shower and with various over pressure relief valves along the system this seems a safe and much cheaper option? i would leave the coil fed by an open cistern, only direct feed the cold in. any input would be appreciated and of course will not be taken as advise merely throwing ideas around..

 

[PETE 123]

The cylinder will be thin walled so if pressure goes above design pressure will contract and expand and will split.

 

[SimonG]

Or you could just get it done properly!

 

[gmartine]

Tbf in theory you could pressurise a grade 1 OV cylinder to 2.5 bar as they are designed with thicker walls, just don't tell your home insurance.

 

[seanEE]

Tbf in theory you could pressurise a grade 1 OV cylinder to 2.5 bar as they are designed with thicker walls, just don't tell your home insurance.

That's what i was thinking, I couldn't find anything online so thought id ask to see if i was missing something, ''of course its a good idea to get a porpuse built unit and i would never install a system like that'' but thanks for the input!

 

[seanEE]

The cylinder will be thin walled so if pressure goes above design pressure will contract and expand and will split.

yeah i would never push it above rated pressure, just bellow rated pressure would be grand..

 

[gmartine]

An unvented cylinder is usually max rated at 8+ bar for good reason even though the working pressure is 3 bar. Any fluctuation of incoming pressure for whatever reason into an vented cylinder and you're fcuked, install a pump.

 

[seanEE]

An unvented cylinder is usually max rated at 8+ bar for good reason even though the working pressure is 3 bar. Any fluctuation of incoming pressure for whatever reason into an vented cylinder and you're fcuked, install a pump.

Ok well just viewing this as a thought experiment, what could cause a pressure fluctuation? presuming that two over presure relife valves are used having one for redundancy? im thinking perhaps when shuting off a tap there could be a momentary increase in pressure? i wonder how much?

 

[fowlerboi]

It's a bit late for April fools


That is why you have to have a ticket to install them. It prevents idiots from blowing up theirs and the neighbours house

 

[PETE 123]

What about a neg pressure pump.

 

[Chuck]

When a hot water system is changed from vented to unvented the local authority have to be notified. No G3-qualified person is going to do this work so that puts the responsibility on the householder to notify the LA and pay for them to inspect and approve the work. Failing to notify is a criminal offence.

IMO, the chance of an LA inspector approving your proposed installation is zero. My guess is they'll take one look declare the building dangerous, so it can't be occupied, until the work is remedied by a qualified plumber using the proper components.

 

[seanEE]

It's a bit late for April fools


That is why you have to have a ticket to install them. It prevents idiots from blowing up theirs and the neighbours house

pretty sure that's a bit more than 2bar

 

[fowlerboi]

When water turns to steam it expands 1600 times its volume. Your cylinder could be 0.1 bar and still do this without a vent and proper controls, which you wont have because your cylinder isn’t designed for it.

Quit being a moron

 

[Timmy D]

That's what i was thinking, I couldn't find anything online so thought id ask to see if i was missing something, ''of course its a good idea to get a porpuse built unit and i would never install a system like that'' but thanks for the input!

It’s cheaper to buy an unvented cylinder (8 bar) than a grade 1 copper vented (2.5 bar).

yeah i would never push it above rated pressure, just bellow rated pressure would be grand..

95% of cylinders out there are grade 3 (1 bar). Just pump the hot outlet