I’m Under Pressure

[FulmenParticipant @fulmen]

How about a balloon in a cylinder and a sliding fit piston?

[Michael GilliganParticipant @michaelgilligan61133]

Not sure that  this gets us any further, but it’s worth a look:

https://calibrationselect.co.uk/calibration/pressure

MichaelG.

[howardbParticipant @howardb]

“How do dead weight testers seal their cylinders?”

With a very thin oil.

The cylinder and piston are finely ground and lapped together, like the finish and clearance in a diesel injection pump element. The fluid used to transfer the pressure to the item being tested is the oil, like this:-

https://www.testing-instruments.com/blog/dead-weight-testers-a-step-by-step-guide-to-diagram-operation-and-applications/

I vaguely remember seeing one being demonstrated in metrology at college a long time ago, and that the “pan” which supported the weights slowly rotated on it’s own.

Another way to generate a known test pressure is with a water column, fill a hose with distilled water and hoist it up the side of your house or a tall tree.

Pressure to Head Calculator

[duncan webster 1Participant @duncanwebster1]

A gauge for testing boilers needs to go up to 250 psi. You’d need a very tall building to do it with a column of water, getting on for 600 ft.

[NealebParticipant @nealeb]

Our club’s master gauges as used by boiler inspectors are calibrated using a dead-weight tester built around a matched pair of ejector pin and sleeve, as used in injection moulding. Easily available and not that expensive. Given that the piston diameter is known to a fairly high degree of accuracy, it just comes down to measuring the weights used. If all else fails you can always take these down to the local Post Office and use their scales! I think that if the weight carrier and pin rotate easily you can assume no significant friction in the piston and cylinder at the heart of things. Maybe not to NPL standards but given that we end up checking the calibration of a pressure gauge that’s only about 3/4″ diameter, I’m not sure that NPL standards are quite necessary.

Don’t have a CE mark on it, though, so I’m sure that it will not be approved in some quarters…

[Author]

Posts