Pressures in Hydraulic Machinery 1

[dsg1985]

Not sure if this is the right forum, but...

We have a mechanical specification for hydraulic machinery that lists all rock breakers must operate at pressures below 180 bar.

I've had a look at a number of rock breakers on the market and pressures far above this (over 300 bar) are common. My question - why would this pressure limit be required? Possibly it's from an old specification when systems operating within these ranges were dangerous (and are not anymore)?

Any hydraulic experts? Is it a safety issue or maintenance/cost/other?

 

[MikeHalloran]

Somewhere above 180 bar or so, o-rings require backup rings _and_ reduced clearance glands with extra tight tolerances, which makes manufacture and maintenance more expensive than units rated for lower pressures.

Additionally, rock breakers are no doubt subject to continuous impact events that produce large, destructive hydraulic transients.

Additionally, the parenthetical assertion that hydraulics operating at pressures below 180 bar are no longer dangerous, is fallacious.



Mike Halloran
Pembroke Pines, FL, USA

 

[micalbrch]

I guess the reasons are wear and noise.

 

[hydromech]

Is it just rock breakers that are subject to the 180 BAR limit?

Who issued the specification?

There could be any number of reason for the 180 BAR limit.

It seems counter productive to put such limits on the hardware. Such low pressures will necessitate larger diameter actuators to achieve the desired forces. The machines just become bigger and slower.

If is to preserve the hardware, it does make sense as the higher pressure will reduce the fatigue limits of the materials.

Adrian

 

[MiketheEngineer]

Call the mfg or specifier and ASK why??

 

[hydtools]

Many breakers operate at 1500-2500psi(100-170bar) when fed with recommended flow rates. Designs from when carrier systems were capable of 3000psi(200bar). Breakers should be operated with recommended flow rates. Breaker operating pressures are stated so that the end user will understand that the carrier must be capable of delivering that pressure at recommended flow in order for the breaker to deliver stated performance. Do not adjust pressure valves to match breaker operating pressures, adjust flow to that recommended for the breaker. If you adjust system pressure, you will generate excess heat and limit breaker performance. The breaker will demand only that pressure required at recommended flows.

Many carriers today can deliver, have the capacity to deliver, 5000psi(345bar) or higher and that is generally not an issue when running breakers.

Ted