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…

[Howard LewisParticipant @howardlewis46836]

Once, I saw an eight wheeler have a front tyre burst, (the spring ring stayed in place) on the M25. Don’t what it was like for the vehicle overtaking at the time, but it was unnerving seen from just behind!

At least he had another wheel to support the front end, and to steer onto the hard shoulder.

Any rapid deflation is frightening, and can lead to loss of control.

As Diogenes says, until all the facts are known, a conclusion cannot be reached.

Howard

[howardbParticipant @howardb]

Wrapping this thread up, going back to the original subject.

We went on our usual shopping run last Saturday, very hot here around lunch time 30 – 32 C. Parked under cover so went back to the car around 2-15- 2.30 – tpms pressures all over the place 37 39 36 38 etc, so after loading shopping, a gentle bimble back home on straight roads at 40-50 mph, checked tpms – all tyres reading 41 psi – they were originally set at 34 psi.

They are picking up heat from the hot tarmac road it seems.

 

[howardb]

On howardb Said:

 

They are picking up heat from the hot tarmac road it seems.

 

Tyres, even in sub-zero C weather, heat up as you drive, due to the deformation and flexing of the tread and sidewalls. Situation normal. Nothing to worry about. In fact it’s a good thing. Warmed up tyres grip better than cold tyres.

In racing, tyre pressures can be measured hot after a few laps and set to a desired percentage above the cold pressure. With track temperatures exceeding 50C at places like the Malaysian GP, it can be a bit of a dark art.

[DiogenesParticipant @diogenes]

Tyres can rise to that kind of pressure even on cold days just from flexing & friction, they operate within a range which will vary within any particular trip dependent on driving conditions, road surface, and whether one is ‘working’ them or not – the pressures may not even be same in all four tyres at any given point – vehicle loading, camber, style of driving etc. being but three of many variables that contribute to this.

Tyres are set cold because only then are the tyres stable and in ‘steady state’ suitable for a ‘benchmark’ pressure level set in the expectation that it will rise to be within what the manufacturer considers to be a safe working range once warmed up.

The 41psi sounds a perfectly reasonable working pressure under the conditions you describe.

*the TPMS readings (lowest 36, highest 39) were all within 1.5psi of mean and would have been safe to drive as normal.

[Michael GilliganParticipant @michaelgilligan61133]

The darksidedevelopments video that I linked previously is quite informative.

MichaelG.

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