Brake Release Pressure Leak Testing

[zenovy]

Hi there,

I work in heavy machinery rebuilding and we were reviewing a leak test procedure to make it standardized. Essentially, the brake piston squeezes together the clutch plates (stationary) and the friction disks (which move with the shaft). The piston is pushed by compressed springs between the piston and the housing. Brake fluid pushes from the other side in a sealed chamber at about 600 psi to disengage the brakes, and it is depressurized when the brakes need to be used.
The status quo for testing is to fill the brake fluid chamber to the standard operating pressure (about 600 psi) and attach a dial pressure gauge on one end while closing a valve on the other side. The gauge is observed for a minute or two and if there is any drop in pressure larger than about 15 psi it is determined to be a problem. I feel like there needs to be a safety factor in the test, but the technicians think that it will damage the seals. They've observed that after a certain pressure (around 800psi) the seals just blow out of the chamber.
Does anybody have any ideas/insight they could bring? The procedure has been an on-again off-again job among the engineers here for years. Also, if you could bring some solid evidence to the table, that would be preferred to industry anecdotes (although anecdotes are helpful too!)

Thanks!

 

[AlephZero]

Just thinking this through:

Presumably the brake system is fairly critical to safe operation of the machinery. If it is meant to operate at 600 psi and it "blows the seals out" at 800 psi, then there should be some design feature that stops it ever reaching 800 psi (e.g. a pressure relief value).

In that case, it seems to me you have two different things to demonstrate.
1. The system will hold pressure at its design condition (600 psi)
2. The system can't fail through overpressure.

IMO your test is about case 1. What you do about case 2 is a separate issue (but just ignoring it probably isn't very sensible!).

 

[zenovy]

Just thinking this through:

Presumably the brake system is fairly critical to safe operation of the machinery. If it is meant to operate at 600 psi and it "blows the seals out" at 800 psi, then there should be some design feature that stops it ever reaching 800 psi (e.g. a pressure relief value).

In that case, it seems to me you have two different things to demonstrate.
1. The system will hold pressure at its design condition (600 psi)
2. The system can't fail through overpressure.

IMO your test is about case 1. What you do about case 2 is a separate issue (but just ignoring it probably isn't very sensible!).

Thanks for the reply!

I think worrying about overpressurization is way out of my scope as my company doesn't have access to much of the design data; it's provided on a need-to-know basis. I think I'm going to see if the place it leaks into contains the same fluid. If so, then leaking isn't that big of a deal, since the oil ends up in the same reservoir.