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

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.

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.