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Selasa, 21 September 2010

A tragic story and a stark hydraulics lesson

/ On : 06.06/ Thank you for visiting my small blog here. If you wanted to discuss or have the question around this article, please contact me e-mail at mozabani@yahoo.com

Large hydraulic cylinders are real pigs to repair.

They're not complicated. Like any other cylinder,
you've got a rod, a tube, a gland, a set of seals
and some wear bands.

So long as all tolerances are correct,
there's no rocket science involved in carrying out
an effective repair.

But as anyone who has carried out repairs on long,
large diameter hydraulic cylinders knows,
they're pigs to get apart and back together again,
even when you've got all the right equipment
at your disposal.

Give me the choice of overhauling a large piston pump
or a large cylinder and I'll take the piston pump
any day of the week.

But for most mechanical types, the complexity
of a piston pump would scare them off.

Which means it must be the apparent simplicity
of large hydraulic cylinders that lures people
into attempting repairs on them - when they
don't have the necessary equipment to get them apart
and back together again - safely.

This can be real dangerous.

And a recipe for disaster, as this tragic story
sent to me by one of our members from Venezuela

"A maintenance supervisor and mechanic were trying
to extract the rod/gland assembly from a
large hydraulic cylinder.

In their attempt to do so, they pressurized the cylinder
with approximately 100 PSI (6.9 bar) of compressed air
with the objective of pushing the gland out.

This attempt failed. So they figured that, in addition
to applying force with compressed air, they could
apply heat around the circumference of the cylinder tube,
in the vicinity of the gland.

They thought that this would expand the tube and
release its grip on the gland assembly.
So they used an oxy-acetylene torch to apply heat
to the surface of the tube.

Within minutes, the gland assembly blew out
with a deafening explosion.

The air collected the residual oil in the cylinder
as it rapidly de-compressed. And the air/oil mixture
ignited into a fiery inferno when it contacted
the torch's open flame.

Both men were knocked to the ground by the force
of the explosion.

They were both covered in hydraulic oil
as it sprayed out of the open end of the cylinder tube
and they were both engulfed in fire.

A passer-by grabbed a fire extinguisher
and doused the flames. However, the force
of the heavy gland assembly ripped
the maintenance supervisor's leg off
as the explosion blasted it out of the cylinder.
He also suffered extensive burns.

The maintenance mechanic suffered extensive burns
and a broken leg."

The obvious lesson here is:
never use compressed air and/or heat
to extract the piston rod from a cylinder tube.


But the wider lesson is:
pick your battles wisely.

KNOW what you can and can NOT accomplish (safely)
with the knowledge, tools and equipment
available to you.

I always work on the assumption
that if you're reading my stuff,
you're over 18 years of age.

So as a grown-up, far be it for me
to tell you what you can and can not do.

Just don't get killed or maimed by ignorance.

Yours for better hydraulics knowledge,

Brendan Casey

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