troubleshooting and preventive maintenance of hydraulic ... · hydraulic pumps fixed displacement...
TRANSCRIPT
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Troubleshooting and Preventive Maintenance
of Hydraulic Systems Learning to Read the Signs of Future
System FailuresInstructed by:
Al Smiley & Alan Dellinger
Copyright, 2005 © GPM Hydraulic Consulting, Inc.
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Hydraulic PumpsFixed Displacement Pumps
The GPM of the fixed displacement pump can not be varied.
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Gear Pump
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Relief Valves and Fixed Displacement Pumps
• Provides a flow path for the pump volume back to tank
• Limits the maximum system pressure
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Relief Valve
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Setting the Relief Valve in a Fixed Displacement Pump Circuit
• Observe the pressure while operating.
• Open all flow controls and isolate any accumulators.
• Set the relief valve 200 PSI above the maximum operating pressure
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• Close the Hand Valve.
• Adjust the relief to1200 PSI. (For this example)
• Turn the system off, open the hand valve and remove the gauge.
Setting the Relief Valve in a Fixed Displacement Pump Circuit
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Troubleshooting Fixed Displacement Pump Circuits
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Sound Checks
Cavitation is the formation and collapse of air cavities in the liquid.
A pump that is cavitating will put out areduced flow until it destroys itself.
Cavitation is caused by:• Oil viscosity too high• Plugged suction filter• Electric motor RPM too high
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AerationAeration occurs when outside air enters the suction
side of the pump. Aeration is caused by:
•Air leak in the suction line•Bad shaft seal on a fixed displacement pump•Fluid level too low•Improper Installation:
•Coupling is not properly aligned•Wrong shaft rotation
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Checking the Fixed Displacement Pump
• Check the pump housing for heat
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• Check the current draw on the electric drive motor
HP = GPM X PSI X .000583
If the pump is bypassing and the GPM output is lower, then the drive motor’s current drawwill also be lower
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Checking the Fixed Displacement Pump Through the Relief Valve
• Turn the relief valve CCW and observe the flow• Gradually turn the relief CW and observe the flow
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Variable Displacement Pumps• Variable Displacement Pumps are used
when the volume requirements change in the system
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Pressure Compensating Piston Pump
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Pressure Compensating Piston Pump
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Compensator
Case Drain
Pressure Compensating Piston Pump
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Pump Compensator
Spool
Spring
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Case Drain
Normal bypassing is 1-3% of the total pump volume.
• Most Variable Displacement Pumps have an external case drain piped directly back to tank.
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Pressure Compensating Piston Pump
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Case Drain Flow Method #1There are two methods of checking case
drain flow:Run the case drain flow into a container of known size and time it
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Case Drain Flow Method #2• A flow meter may be permanently
installed in the case drain line.
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Case Drain Line Cooler
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Pressure Compensating Piston Pump
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Pressure Compensating Pump Example
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Pressure Compensating Pump Example
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Pressure Compensating Pump Example
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Systems With Relief ValvesThe purposes of a relief valve in a
pressure compensating pump system are:
• Absorb pressure spikes• Operate as an extreme safety device
The only time the relief valve should open is when the pressure rises above the compensator setting.
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Adjustment Procedure
• Observe the system to find the maximum operating pressure
• Establish a deadhead condition• Turn the relief valve fully CCW• Turn the compensator fully CW
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• Turn the relief valve CW to 1450 PSI• Turn the compensator to 1200 PSI
Adjustment Procedure
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Relief Set Below Compensator
• If the relief valve is set below the compensator, the pump will act as a fixed displacement pump.
Heat will be generated!
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Calculating Heat & Electrical Power
• HP = GPM X PSI X .000583= 30 X 1450 X .000583= 25 HP
• 746 Watts = 1 Horsepower
Electrical Power = 746 X 25= 18,650 Watts
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AccumulatorsHydraulic accumulators are used
to store pressurized fluid
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Bladder Accumulator
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Piston AccumulatorPiston Accumulator
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Accumulators
• Supply additional oil flow to the system at a very fast rate
• Absorb shock
Accumulators are used for ONE of two purposes depending upon the PRECHARGE
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AccumulatorsDry Nitrogen is used to precharge the top portion of an
accumulator
1% Argon and other
gases 21% Oxygen
78% Nitrogen
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Accumulators
NEVER use Oxygen orCompressed Air to
precharge an accumulator!
Rule of Thumb - Precharge to one-half of the maximum system
pressure
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1000
PSI
Precharge
2000
PSI
Compensator Setting
0
PSI
System Pressure
1
2
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Using the Charging RigGauge
Gas Chuck Handle
Bleeder Valve
Nitrogen Bottle
Connection
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Checking the Precharge Hydraulically
Pump turned off
Dump Valve
Closed
2000
PSI
2000
PSI
Pressure Locked in System
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Checking the Precharge Hydraulically
Dump Valve Open
Pressure slowly drops to precharge, then
immediately to 0 PSI
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Types of Accumulators
Piston Accumulators
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Example Circuit
1000 PSI
1/4” Dump Valve (Open when the power is turned
off)2000 PSI
Isolation Valve
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Example Circuit
2000 PSI
1/4” Dump Valve (Closed) 2000
PSI
Isolation Valve
2000 PSI
Power On
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Example Circuit
1/4” Dump Valve (Closed)
2000 PSI
Isolation Valve
1800 PSI
Extend Cylinder
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Checking the Piston Accumulator
2000 PSI
2000 PSI
System pressure should build to the
compensator setting whenever actuators
are not cycling
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1800 PSI
Checking the Piston Accumulator
System pressure should not drop more
than 100-200 PSI when the directional
valve opens
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Checking the Piston Accumulator
Piston Travel
Heat should be felt from here
to here:
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Checking the Piston Accumulator
1000 PSI
100 PSI
Dropping to a very LOW pressure usually
indicates an accumulator problem
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Overcharged
HeatPiston
Movement
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Overcharged
Oil Bypasses Around Piston
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Piston Removal
3
2
1
•With the pump on, open the #3 bleeder valve on the charging rig
•Close the #1 isolation valve
•Open the #2 manual dump valve
•Remove the charging rig and the top of the accumulator
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Undercharged
Leak Paths for Nitrogen
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Undercharged
HeatHydraulic pressure drives piston near the
top
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Poppet Valve
Bladder Accumulator
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Bladder Accumulator
Poppet Valve
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Poppet Valve
Bladder Accumulator
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Bladder Accumulator
Poppet Valve
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Heat should be felt between
these two points
Checking The Bladder Accumulator
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If no heat is felt on the bladder accumulator, then one of two things has happened:
•The precharge is above the maximum system pressure
•The bladder is ruptured
•The nitrogen has leaked out of the bladder
Checking The Bladder Accumulator
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ANY circuit using an accumulator MUST have some method of bleeding the pressure down when the
system is turned off
Prior to working on the system, you should VERIFY that the pressure is bled down by observing the gauge
Accumulator Dump Valves
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Manual Dump Valve
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Solenoid Operated Dump Valve
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Tolerances In Components
• Tolerances in hydraulic pumps and valves: 5 - 8 microns (.0002 - .0003”)
• Tolerances inside servo valves: 3 microns (.0001”)
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Sources of Contamination
New oil leaving the refinery is relatively clean
By the time it reaches your mill it meets a 50 -200 micron standard
Oil should always be filtered prior to entering the reservoir
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Built In Contamination
• Metal Chips• Dirt• Sand• Pipe Sealant
• Burrs• Dust• Weld Splatter• Paint
When a system is first built and installed, contamination may be in the form of:
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Ingressed Contamination
• Breather Cap• Access Plates• Hose and Component Replacement• Cylinder Seals
There are four ways contamination can enter the system from the outside:
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Fluid SamplingThe biggest problem in hydraulic systems is
CONTAMINATION
The key to controlling it is through an effective fluid sampling and filter maintenance program
Sample Bottle
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Oil Analysis
The size and number of particles taken from 1ml of the sample are measured by a particle counter
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ISO Cleanliness Code
Recommended Servo Level is 14/11
System 1 passes with a level of 13/11
System 2 failswith a level of 16/14
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Filter Selection
Filters are selected by a Beta rating - the ratio of the number of particles upstream of the filter versus the number of particles downstream of a specific size
Fluid entering and fluid leaving the filter is measured with a particle counter
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Beta Rating
2 3m particles in
1 3m particle out
β3 = 2
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Beta Rating
75 10m particles in
1 10m particle out
β10 = 75
Hydraulic systems require a beta rating of 75 to 100
98.7% Efficient
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Filter Placement
There are primarily three locations for filters in the system (other than the suction strainer):
•Pressure Line
•Separate Recirculating System
•Return Line
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Pressure Line FilterUpstream of ANY Servo Valve
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Pressure Line FilterDownstream of a Fixed Displacement Pump operating at
pressures exceeding 2250 PSI
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Pressure Line FilterDownstream of a Variable Displacement Pump operating
at pressures exceeding 1500 PSI
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Return Line Filter
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Separate Recirculating System
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Leakage ControlProblems with leaks:
• Expensive - at $3.00 a gallon, one leak that drips one drop per second will cost:– $3.38 a day– $102 a month– $1225 a year
• Unsafe - dangerous conditions• Environmentally Hazardous - EPA
setting stricter standards and penalties
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Causes of Leaks
• Use the proper schedule of pipe– Schedule 40 for suction and return lines– Schedule 80 or 160 for pressure lines
• Apply sealant properly
The main reason hydraulic systems leak is because of a bad installation
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Proper Clamping
5’ 5’ 6”
Hose
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Socket Weld Flanges
PIPE
Weld
O-Ring
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Hose Installation
• Proper Crimping
• Proper Length
• Protective Sleeves
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Drain LinesCase drain lines should be piped directly back to tank
Below Fluid Level
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Other Causes of Leaks
•Pressure settings and shock - pressures set too high result in excess force. Absorbed by the system, excess force shows up as leaks
•Contamination - Cylinder rod seals are not 100% efficient. In unfriendly environments, a protective cover or boot should be used
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Thank You For Attending!
Copyright, 2005 © GPM Hydraulic Consulting, Inc.