Atmospheric pressure - can affect relief valves?

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geekIT

2421 posts

Uber Geek

#230558 1-Mar-2018 15:34

I'm talking about the valve on the cylinder's outlet. It was dripping so I backed off the PRV, but it got me wondering if air pressure could affect output valves.

'Those who can make you believe absurdities can make you commit atrocities.' Voltaire

'A patriot must always be ready to defend his country against his government.' Edward Abbey

wellygary

8328 posts

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#1966587 1-Mar-2018 16:07

Mains pressure?

Not really, this one is spec'd at 850Kpa or 8.5 Bar, a Tropical cyclone drops pressure 50-80 mb, or .05 - .08 bar,

http://www.aquafire.co.nz/Portals/1120/HJ%20Cooper%20Mains%20Pressure%20Duplex%202304%20Stainless%20Steel%20Cylinders.pdf

geekIT

2421 posts

Uber Geek

#1967161 2-Mar-2018 16:42

I don't think I worded my question properly.

My HWC originally had an overhead pipe to provide pressure for my new 135l 76KPa cylinder.

I shortened the overhead pipe, bent it 180 and added a 3.7m PRV.

Effectively, the pressure requirements are well under the limit for the cylinder.

All is good now, excellent pressure from the shower and basins.

Except the valve occasionally drips. But not always.

Which made me wonder if these valves could be affected by atmospheric pressure differences.

'Those who can make you believe absurdities can make you commit atrocities.' Voltaire

'A patriot must always be ready to defend his country against his government.' Edward Abbey

Aredwood

3885 posts

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#1967317 2-Mar-2018 22:38

Short answer - no. As the reducing valve has a vent open to atmosphere. So the reducing valve outlet pressure will also change slightly as well with atmospheric pressure changes.

Dripping sometimes is most commonly caused by thermal expansion as the cylinder reheats. Next time the valve is dripping, switch off the power to the cylinder. And see if the dripping stops.

Normal amount of water discharged is around 1% of your hot water usage. Note that if your roof is coloursteel, that dripping will damage the roof.

geekIT

2421 posts

Uber Geek

#1967514 3-Mar-2018 13:56

Aredwood, thanks for the explanation :-)

Sounds like it'll drip the most after a heating cycle, then.

Down here in deepest, darkest Southland the ripple control only seems to be on from 11pm to 7am and 1pm to 4pm.

I'll keep an eye on it.

'Those who can make you believe absurdities can make you commit atrocities.' Voltaire

'A patriot must always be ready to defend his country against his government.' Edward Abbey