Hydraulic Safety

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Hydraulic Safety

• Colorado Mine Safety Training Program
• John Barton CMSP

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Our Demonstration Consists of 1 DA ram and 1
porta power
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Notice each end has a pressure gauge and the rod
end of the cylinder only has a gauge.
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Watch as we apply pressure to the closed end of
the cylinder
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400
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775
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1000
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1500
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2000
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2400
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What Happened?Why did the 2 pressure gauges read
different?
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Hydraulic Pressure Intensification
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A typical single rod single acting hydraulic
cylinder
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Fluid under pressure enters the closed end...
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Forcing the piston and rod out of the rod end
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A typical single rod double acting hydraulic
cylinder
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Fluid under pressure can enter either side of the
cylinder thus moving the piston and rod in either
direction
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Extending the rod...
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Or retracting the rod
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The problem occurs, when the rod end port or line
of a single rod double acting cylinder is
restricted and system pressure is applied to the
closed end.
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A Few Fundamentals
Force Area Pressure
Force is expressed in lbs. Area is expressed in
in² Pressure is expressed in PSI
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The FORCE of the cylinder in lbs. Is the system
pressure multiplied by piston arearemember this
area is round
The area of a circle is A p r²
Lets assume this cylinder is 4 in diameter
The area of this PISTON is 3.14 x 4 or 12.5 sq. in
Lets assume the system pressure is 1000 psi
This cylinder WILL produce 1000 x 12.5 or 12500
lbs of FORCE!
This area is known as the major area
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If Force Pressure x Area then Pressure
Force Area
With this 4 diameter cylinder, the rod diameter
is 2
We must subtract the rod Area from the Piston Area
To obtain the MINOR Area!
12.5 - 3 9.5 in²
Minor Area
Major Area is 12.5 in²
Rod Area is 3 in²
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When system pressure is applied to the closed end
and the rod end is restricted, pressure
intensification occurs
Area 9.5 in²
Pressure 1000 PSI
Pressure Force Area
12500 9.5 ??
12500 lbs of Force
X
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1325 PSI is within the rod end of this cylinder
when the rod end port is restricted and system
pressure is applied to the closed end of the
cylinder!
1000 PSI
1325 PSI
1325 PSI
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Another Scenario
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5 cylinder 4 rod working under 2200 PSI
Major Area 19.6 Rod Area 12.5 Minor
Area 7.1 Force 19.6 x 2200 or 43120
lbs Intensified Pressure 43120 7.1 or ??
X
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6073 PSI
2200 PSI
Would you like to be working near this cylinder
if this condition existed?
Where might you find this type of cylinder?
What could cause a rod end port to be restricted?
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Types of restrictions include Hose
restriction\complete blockage Hard pipe
damage Ball valve or gate valve
INSTALLATION Foreign objects/contamination
What can WE do to minimize exposure to this
HAZARD?
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Be thorough when making Equipment Examinations
Repair or replace damaged components
immediately Dont wait until the maintenance shift
NEVER use a ball valve for controlling a
hydraulic cylinder circuit
Dont adjust any circuits pressure relief valve
you may be setting yourself up for disaster
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The Accident
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A mechanic with no formal training in hydraulics
was attempting to test a hydraulic boom lifting
cylinder for leaks while attached to a large
front end loader. He used a uni-directional (one
way) inline flow meter. He installed the flow
meter in series with the cylinder between the
cylinder and the directional control valve in the
rod end hose. Asking the operator for assistance,
the mechanic instructed the operator to retract
the cylinder until it stalled against the base of
the cylinder and to hold full pressure. The
mechanic observed the flow meter and saw no
indication of leakage. He signaled to the
operator to extend the cylinder a short distance
to repeat the test.
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Uni-directional Flow meter
To directional control valve (valve bank)
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As the cylinder began to extend there was a loud
explosion. At the same instance the flow meter
assembly, still attached to one end of the hose,
came flying across the machine and skimmed across
the top of the mechanics head. The hose end had
ruptured at the crimp connection near the flow
meter. Hot oil escaping from the severed hose
sprayed his face and neck. He was treated for
minor burns.
He narrowly escaped Disaster
He did not understand that a uni-directional flow
meter contains an internal check valve
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Hydraulic accidents frequently occur and for the
most part are not understood.
Treat hydraulic systems with the same respect you
would electrical systems.
They ARE as potentially hazardous.
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Colorado Division of Minerals And Geology
Mine Safety Training Program