- GPM Hydraulic Consulting, Inc.

CONSULTING REPORT
TO:
FROM:
Al Smiley
GPM Hydraulic Consulting Inc.
RE:
In-Plant Hydraulic Systems
DATE:
July 7 – 8, 2005
Reason for Consult
I was called in to analyze each hydraulic system and to make specific recommendations
and adjustments for improving the machine operations. A detailed report follows on each
system, which includes the information gathered during the consult.
North Side Debarker
Pump
PVQ 10 Vickers, 4.6 GPM pressure compensating, externally drained, piston pump. The
pump volume is used to direct oil to the cylinders when raising the conveyor. Normal
bypassing out of the case drain line should be .05-.15 GPM.
Pressure Adjustments
The setting of the compensator determines the maximum pressure at the pump outlet port.
A relief valve is used as a safety back up in the event the compensator were to fail. The
relief valve will also absorb pressure spikes. The compensator was set to 1100 PSI and
the relief valve to 1400 PSI.
One of the adjustments on the manifold below the accumulator is a pressure-reducing
valve. The setting of this valve determines the pressure to the cylinders when raising.
The valve should only be set high enough to hold the conveyor in the raised position. On
other conveyors of this design, the valve is normally set to 600 - 700 PSI.
Speed Adjustments
One of the cartridge valves on the manifold will determine the flow from the pump when
raising the conveyor. Another valve is used to determine the flow rate from the
accumulator to the cylinders when raising.
Oil Temperature – 226° F
Filters, Breathers and Gauges
The gauge at the return filter read 50 PSI. This means that the pressure has built up to the
internal check valve’s spring setting. The return oil is flowing through the internal check
valve and back to tank. This filter should be changed as soon as possible.
The breather cap is extremely dirty and oily. This should be replaced. The gauge located
on the accumulator manifold is bad. This gauge will indicate the setting of the pressure
in the accumulator. Once replaced, this gauge should read 0 PSI prior to working on or
around the infeed conveyor. The manifold contains an automatic, hydraulic accumulator
dump valve. This valve should open when the pump is turned off. This allows the
pressurized oil in the accumulator to bleed down to 0 PSI.
Accumulator
The nitrogen pre-charge in this accumulator was checked and found to be 450 PSI. The
precharge is normally approximately 100 PSI below the pressure required to hold the
conveyor in the raised position.
Additional Actions and Recommendations
The high oil temperature, 226 ° F, was caused by the relief valve being set below the
pump compensator setting. Dennis and I properly set the compensator to 1100 PSI and
the relief valve to 1400 PSI.
Due to the extreme high oil temperature, the oil has broken down and should be changed.
Prior to changing the oil, the reservoir should be cleaned to remove this sludge and
contamination. This high temperature has also caused varnish to develop in the pump,
valves and cylinders. I recommend using an additive by Mobil, called Mobil Sol A. You
can contact your local Mobil supplier or call 1-800-662-4525 for this product.
The seals on the cylinders are leaking, most probably due to the high oil temperature.
Log Turner, Bed Lift and Shift Infeed Spike Rolls
Pump
The pump is a 37 GPM, variable displacement, externally drained pump with a maximum
pressure of 3000 PSI. At the time of the consult a new pump had just been installed.
Normal flow rate out of the case drain line should be 1/3 – 1 ¾ GPM.
Pressure Adjustments
The setting of the pump compensator determines the maximum system pressure. Upon
initially inspecting the unit the compensator was set at 2950 PSI. After the system
accumulators were properly pre-charged, the setting was lowered to 2600 PSI.
There is no relief valve in this system. If the compensator were to fail then the pump
would deliver maximum volume until the weak point ruptures. A relief valve should be
installed as a safety back up.
Oil Temperature
The temperature gauge on the unit is defective and should be replaced. When shooting
the reservoir with a heat gun 135° F was indicated.
Accumulators
There are two accumulators located upstairs near the machine. One accumulator supplies
the Log Turner cylinders. A block located at the accumulator base contains a check valve
and automatic dump valve. The check valve will prevent the accumulator from
discharging oil to the Lift, Shift and Infeed Spike Rolls positioners. The precharge on
this accumulator was found to be 900 PSI. Accumulators should be pre-charged to ½ 2/3rds the pump compensator setting (2600 PSI). An attempt was made to increase the
pre-charge to 1300 PSI. Only 1200 PSI could be reached due to the pressure in the
nitrogen bottle.
The other accumulator supplies oil to the Bed Lift and Shift as well as the Infeed Spike
Rolls. The pre-charge on this accumulator was found to be 400 PSI. The precharge was
increased to 1200 PSI, which is all that was available in the nitrogen bottle. This
accumulator also contains a check and dump valve block. This allows the accumulator to
only supply the above-mentioned circuits.
Additional Actions and Recommendations
The original problem on this unit that the Bed was lifting too slow. Once the
accumulator was properly charged, the operator indicated that he no longer received any
alarms on the bed position.
The flow meter in the case drain line is a 0 – 30 GPM meter. A smaller meter, 0 – 10
GPM, should be installed. The case drain flow was reading well below the lowest
reading on the meter, 3 GPM.
The hose out of the pressure filter is too long and rubbing. The hose should be replaced
with a shorter hose or a “sleeve” installed at the contact point.
Saw Box
Pump
The system is supplied with an Oilgear, 34 GPM piston type pump. The flow meter in
the case drain line indicated a flow rate of 1 ½ GPM. This check was made when the oil
temperature was at 166° F. Less bypassing will occur when the oil temperature drops.
Normal flow for this pump should be 1/3 – 1 GPM.
Pressure and Flow Adjustments
The block on top of the pump has two adjustments; the pressure compensator and
maximum volume stop. The compensator setting determines the maximum system
pressure. A relief valve is used as a safety back up in the event the compensator fails
closed. This would allow the pump volume to dump to tank preventing damage to the
system.
The volume stop on the Oilgear pump should be turned in 1½ turns to prevent the internal
swash plate pin from shearing off. This adjustment was properly set on the pump.
When initially surveying this unit, the oil temperature was 166° F. The tank line of the
relief valve was found to be 179° F. This indicated that oil was flowing through the
valve. Dennis and I set the compensator to 1550 PSI and the relief valve to 1850 PSI.
The temperature of the unit was checked the next day and found to be 108° F. This heat
problem was caused by improper pressure settings.
Filters
The filter dirt alarm in the filtering and cooling circuit indicated that the element was
dirty. The element should be changed as soon as possible.
Accumulator
An Accumulator has been added to this system to increase the positioner speed. No
accumulator dump valve is present in the system. An electrical solenoid or hydraulic
dump valve should be installed to bleed the pressure down to 0 PSI prior to working on
the system. THIS NEEDS TO BE DONE IMMEDIATELY. I also recommend that a
manual valve be installed as a safety in the event the dump valve fails.
Additional Actions and Recommendations
Since this system has been operating at elevated temperatures the oil has been degraded.
Varnish may have developed in the lines and proportional valve spool. A flushing
compound, Mobil Sol A, may be required to remove the varnish. Install flushing valves
or blocks to allow the oil to move through the lines. Once flushed, the oil should be
drained and the reservoir cleaned.
Chip – N – Saw Heads
Pump
The system is supplied with a 30 GPM, vane type, pressure compensating, externally
drained vane pump. The case drain line is ported through a cooler prior to returning back
to tank. This is an effective method of removing heat in this system.
Pressures
The compensator setting on the pump determines the maximum system pressure. The
setting of the compensator is 1950 PSI. There was no schematic available to reference
the recommended setting of the compensator.
Oil Temperature - 125° F
Accumulators
There are two bladder accumulators in this system that supply oil at a high flow rate to
the positioners. The precharge on one accumulator is 1000 PSI, on the other, 950 PSI.
This is considered an adequate precharge with a compensator setting of 1950 PSI.
Recommendations
The block on top of the reservoir contains the pump isolation check valve, the pressure
gauge and the accumulator dump valve. The dump valve will open when the pump is
turned off directing the pressurized fluid in the accumulators back to the tank. Always
check the pressure gauge to verify that the pressure has bled down to 0 PSI prior to
working on or around the system. If the gauge does not read 0 PSI, then the accumulator
is pressurized and the dump valve is stuck closed.
Edger
Pump
The PVG 130C Oilgear pump has a maximum volume of 60 GPM and has a pressure
compensator and a volume stop. The pump will deliver maximum volume, 60 GPM,
until the compensator setting is reached. The compensator spool will then shift reducing
the volume to only what is required to maintain the compensator setting.
The setting of the volume stop determines the maximum flow rate out of the pump.
Turning the adjustment clockwise reduces the maximum volume.
Case Drain Flow
The normal flow rate out of the case drain line for this pump at 2000 PSI is 2.59 GPM.
Dennis and I removed the case drain line and timed the flow into a 5-gallon container.
The flow rate was approximately 5.5 GPM. This indicates a badly worn pump. This
high flow rate is also generating heat.
Pressures
The compensator in this system is set at 1800 PSI. The recommended setting on the
manufacturer’s print is 1500 PSI. This was not adjusted due to the slow raise speed of
the top head. No relief valve is installed in the system.
Oil Temperature
The tank was shot in various locations with a heat gun and found to be 142° - 150°.
Filters and Breathers
John said that the breather cap had been left off the unit for an extended period of time.
This obviously allowed contamination to enter the reservoir. There is a pressure filter
located upstairs near the accumulator. Due to the problem with the Top Head raise speed
this filter should be changed, as the Top Head Bosch valve may be defective.
Speed Problems
The Top Head is raising too slow. All other positioners are operating at normal speed.
The voltage to the Top Head proportional valve was checked and found to be slightly
above 9 volts when raising. The LVDT indicator on the amplifier card illuminated to the
near full stroke position when the head raised. This indicates that the Bosch valve is
shifting properly. The valve spool however, may be badly worn allowing bypassing back
to the tank.
The cylinder seals bypassing may also cause the slow speed. This is difficult to check
because the Bosch valve is mounted directly to the cylinder.
The original print shows a counter balance valve and cylinder. This valve is not on the
positioner assembly. The purpose of this valve is to hold the head in the raised position
when the power is turned off. The valve will also maintain a back pressure in the rod
side of the cylinder when lowering. Without this valve in the system, the head can free
fall faster than oil is delivered by the system. This can cause cavitation and damage to
the cylinder. It is recommended that the valve be installed in the system.
Hoses
The pressure line hose from the pump is too long and rubbing. A sleeve or protective
guard should be installed to prevent premature failure.
Accumulator
The recommended nitrogen pre-charge for the accumulator is 900 PSI. The temperature
of the accumulator was hotter in the lower half that the top half. This indicated that the
accumulator is operating normally. This accumulator supplies oil to all the linear
positioner circuits.
Additional Actions and Recommendations
The high oil temperature (142° - 150°) is caused by the excessive pump bypassing. The
reservoir should be cleaned out and the return filter replaced. A new pump should then
be installed.
A relief valve should be added in this system as a safety back up for the pump
compensator and as a shock absorber. The valve should be set 250 – 300 PSI above the
compensator setting.
Once the top head speed problem is corrected the compensator should be turned down to
1500 PSI.
A gauge should be installed on the valve block located just below the accumulator. This
gauge should be checked prior to working on the machine to verify that pressure in the
accumulator has dropped to 0 PSI.
Trimmer
Pumps
The trimmer power unit contains two pumps; one is used as a back up pump. The online
pump at the time of the unit survey was the Continental PVR50 vane, pressurecompensating pump. The standby pump is an Oilgear piston, pressure compensating
design. The pump also has a maximum volume stop. The exact volumes that the pumps
deliver are not known due to incomplete part numbers.
Pressures
The setting of the PVR50 pump compensator is 1300 PSI. No schematic was available to
indicate the desired compensator setting. The compensator should, however be set 200
PSI above the pressure required to move the maximum load.
Oil Temperature - 106° F
Hoses
The pressure hose connected to the Continental pump is rubbing on the return line hose.
The piston pump pressure line hose is rubbing on the drip pan. Maximum hose length
should be 4 – 5’. The hoses should be shortened, if possible or protective sleeves
installed to prevent premature failure.
Additional Actions and Recommendations
There is no relief valve installed as a safety back up. A relief valve should be connected
downstream of the pump isolation hand valves. The valve should be set 250 – 300 PSI
above the setting of the pump compensator.
Green End Sorter
Pumps
The sorter unit has two pressure compensating pumps. One is used as a back up or spare
pump. One pump is a vane and the other is a piston type. No part numbers could be seen
to determine the pumps’ volumes. The vane pump should normally bypass 3 – 5% of its
maximum volume through the case drain line. The piston pump should bypass slightly
less, 1 – 3%.
Pressures
The setting of the online pump compensator determines the maximum system pressure.
At the time of the survey the piston pump was used to operate the bays. The compensator
setting on the piston pump is 1500 PSI.
Filters
There is a leak at the return filter that is dripping at approximately 1 drop per second.
This will result in a loss of 405 gallons per year. The filter indicator is damaged and
should be replaced.
Additional Actions and Recommendations
There is no relief valve in this system as a safety back up in the event the compensator
was to stick. This could cause the pressure to build extremely high until the weak point
in the system ruptures. A relief should be installed and set 250 – 300 PSI above the
compensator setting.
The system was designed with a single solenoid directional valve was to allow the pump
to compensate at a lower pressure (500 PSI) when not operating the bays. This decreases
the heat and electric motor amp draw when in the idle mode. Consideration should be
given to re-connecting the valve to operate the system more efficiently with the piston
pump.
Green Lumber Stacker - Unscrambler and Even Ending Rolls
Pumps
Two pressure-compensating pumps are used on this unit. One pump supplies the
Unscrambler conveyor, the other pump the Even Ending Rolls. No part number is visible
on either pump, however the pumps appeared to be in the 37 – 57 GPM range. Case
drain flow should be 1 – 3% of the maximum pump volume. At this time the even
ending rolls pump is bypassing 9 GPM. This indicates that the pump is badly worn and
should be changed if this unit is not converted to an electric drive within the next month.
Pressures
The setting of the pump compensators determines the maximum system pressures. These
pressures could not be recorded, as there were no gauges located at the pumps.
There is a relief valve located near the Unscrambler hydraulic motor. This valve is used
to absorb shock when starting and stopping the conveyor. The valve should be set 200
PSI above the pressure required to drive the conveyor fully loaded.
There is a relief valve located in a block underneath the even ending rolls valves. Dennis
and I attempted to set this valve, however the pressure never changed. This valve should
be changed and set 250 – 300 PSI above the pump compensator setting.
Speed Controls
There are inline flow controls that are used to set the unscrambler and even ending rolls’
speeds. The valves are located near the unscrambler hydraulic motor.
Oil Temperature - 186° F
Filters
The return filter element on the unit needs to be replaced.
Additional Actions and Recommendations
The unit is running excessively hot. This is caused by the high bypassing of the Even
Ending Rolls pump. Since the relief valve in the Even Ending Rolls circuit could not be
adjusted it may be bypassing some oil as well as generating heat.
If this unit is to be kept in service the oil needs to be drained and the reservoir cleaned.
The return filter element should be replaced and the Even Ending Rolls pump replaced.
A relief valve needs to be installed as a safety back up in the Unscrambler circuit. This
valve can be of the “sandwich” design and mounted underneath the directional valve.
Stacker – Forks Drive
Pumps
The pump on the right side is a hydrostatic pump that supplies oil to drive the forks in
and out. This circuit is known as a closed loop drive. The ports of the pump are
connected to the ports on the hydraulic motor. Some oil will be lost to leakage over the
pump case drain line. A charge pump is necessary to supply oil to the charge pump to
make up for the leakage. This charge pump is located inside the main pump assembly.
When in the idle mode the charge pump volume will be ported through the charge pump
relief at 320 PSI.
The flow meter in the case drain line will indicate the charge pump flow when in idle.
The meter read 5.5 GPM during the survey.
A DC voltage is applied to the servo valve on the pump to drive the forks. A positive DC
signal will stroke the pump swash plate on one side of the center to drive the motor in one
direction. A negative DC voltage strokes the pump in the opposite direction for reversing
the motor. There is a “tear drop” manual actuator on top of the servo valve housing. If
the motor will not drive properly the actuator can be moved to stroke the pump. If the
motor operates normally then the servo coil may be bad or there may be a faulty electric
supply signal.
Pressures
As previously mentioned the charge pump relief is set at 320 PSI. This pressure will be
read on both gauges when in the idle mode.
The system has a shuttle valve and shuttle relief mounted in one block. The shuttle valve
spool will shift when driving the motor directing oil in the suction side of the loop back
to tank through the shuttle relief. Since the charge pump delivers more oil than the pump
needs at it’s suction, pressure should build up. Once the shuttle relief valve setting is
reached the excess oil will return to the tank. This allows some oil in the loop to return to
tank for filtering and cooling.
The tank line of the shuttle relief should be warm or hot when operating. On this unit the
line is cool. This means that the shuttle relief is set higher than the charge pump relief or
the shuttle valve spool is stuck closed. The pump manufacturer’s original specifications
should be checked as to the shuttle relief setting. Normally the valve is 50 – 100 PSI
below the charge pumps relief setting.
To set the shuttle relief, operate the forks at as slow of a speed as possible. Rotate the
shuttle relief valve setting counterclockwise until the pressure starts dropping on the lowpressure side of the loop. Adjust until the desired setting is reached.
There are crossport relief valves on the pump. These valves should be set 400 PSI above
the pressure required to drive the forks. When driving the forks the pressure initially
spiked to 2000 PSI then dropped to 1200 PSI. Considering that a higher pressure will be
required to move the forks initially a setting of 2000 PSI would be a starting point. To
set the valves, the flow to the motor must be blocked. Stroke the pump forward and set
the appropriate valve. Reverse the pump and set the opposite valve.
Filters
The charge pump pressure filter has a connection for oil flowing into the canister but no
outlet port. This filter is used to filter the charge pump flow to the servo valve. The
original pump manufacturer’s literature should be checked and this filter reconnected
properly.
There is a pressure filter in the main loop. This filter should be charged a minimum of
every three months.
Additional Actions and Recommendations
There is a good deal of shock as the forks operate. This is partly caused by the improper
pipe clamps installed in the system. These clamps need to be replaced with a hydraulic
clamp such as those made by Stauff.
Stacker – Hoist and Accessory Circuits
Pumps
Two pressure compensating piston type pumps are used to supply the Hoist and
Accessory circuits. There was no part numbers visible on the pumps, however they
appeared to be in the 37 – 57 GPM range.
The expected flow rate out of the pump’s case drain lines should be 1/3 – 1 ½ GPM.
Both pumps were considerably above this level. The pump on the left side of the skid is
bypassing in excess of 10 GPM. This high flow rate slows the system down and heats the
oil considerably.
The center pump’s case drain flow is 3 GPM. Normally a pump should be changed when
the case flow is 10% of the maximum pump volume. The flow rate on this pump is
borderline at this time.
Pressures
There was no gauge in the pump’s line on the left side. A gauge with a manual shut off
valve should be installed. Once installed the compensator on the pump should be set 200
PSI above the maximum pressure to move the load.
The setting of the center pump’s compensator is 1700 PSI.
Filters and Breathers
The filters need visual bypass indicators for monitoring the condition of the element. The
breather cap on this unit is dirty and needs to be changed.
Oil Temperature
The oil temperature is estimated at 170° F. The temperature gauge was not readable
however the reservoir wall was shot with a heat gun.
Additional Actions and Recommendations
The high oil temperature is caused primarily by the high flow rate of oil exhausting out of
the left side pump’s case drain line. It was mentioned that the filters on this unit have
never been changed.
To remove the varnish in the piping and valves add a 5 – 10% solution of Mobil Sol A or
a comparable product to existing oil. Run the mixture for 24 – 72 hours. Then drain the
oil and clean the reservoir. Secondly, install all new filter elements in the system. With
the dirt alarms on the filters monitor the elements conditions. Change them as necessary
or after the first 50 hours. The pump on the left side of the skid should then be changed.
The manifold block on top of the reservoir contains several cartridge valves. To
effectively troubleshoot when a problem occurs, a schematic is need for the system and
manifold block.
There are several adjustments on the back of the block. One or more of these may be
relief valves that may need to be set.
The left side pump circuit needs a relief valve installed as a safety back up in the event
the compensator fails. The center pump may need one as well depending on exactly what
the cartridge valves are in the manifold.
The clamps for the piping are not the proper type. This causes excessive shock and
leakage in the system. Clamps made by Stauff or another manufacturer should be
installed.
Planer Feed Table
Pump
The 57 GPM, bi-directional, externally drained, piston pump drives the Infeed Table in
forward and reverse. The voltage to the servo valve coil determines the direction and
amount of flow the pump delivers. A mechanical actuator on the servo valve can be
moved to determine if the problem is electrical or hydraulic.
If the system operates normally when moving the manual actuator then ether the servo
valve coil is bad or there is another electrical problem.
The servo valve also has an Allen head null adjustment located under the flat head screw
on the pilot section of the valve. If the motors are drifting then the valve may need to be
nulled. To null, disconnect the cable and slowly rotate the Allen head until the drifting
stops.
The pump assembly contains a charge pump mounted on the back end. The charge pump
supplies make up oil to the pump suction as well as oil to the servo valve for stroking the
pump.
When in idle, the charge pump pressure will build to the charge pump relief valve setting,
approximately 400 PSI. The oil will then return to tank through the case drain line of the
main pump. A flow meter in this line will indicate this flow rate.
Pressures
As mentioned in the pump section the charge pump relief setting is 400 PSI. A separate
block contains a shuttle valve, shuttle valve relief and two crossport reliefs. The shuttle
valve and relief will allow some of the oil that exhausts out of the motors to return to the
tank. The shuttle relief should be 60 – 80 PSI below the charge pump relief setting to
verify that the shuttle relief is set below the charge pump relief, feel the tank of the block.
This line should be hot or warm when driving the motors. If not, turn the shuttle relief
counterclockwise until the pressure on the suction side reads 320 – 340 PSI.
When driving the motors the pressure is 900 – 1500 PSI. The crossport relief valves are
used to limit the maximum pressure in the forward and reverse directions. These are
normally set at 2500 PSI as recommended by the manufacturer. To set the valves, the
hoses to the motors should be removed and pipe plugs inserted in the crossport block.
Stroke the pump at a low volume and set the specific valve until 2500 PSI is read on the
gauge. Then stroke the pump in the opposite direction and adjust the other crossport to
2500 PSI.
There are relief valves mounted at the outlet port of the flow divider. These valves
should be set 200 – 400 PSI above the pressure required to drive the largest size board.
To determine the load pressure, install a gauge at the inlet of the relief, if possible. Once
the load pressure is known turn the pump off and lockout the system. Remove the hoses
to the motors and install pipe plugs. Stroke the pump at slow speed in the forward
direction and adjust each valve to the appropriate setting.
Filtering, Coolers and Breathers
There are two inline filters that remove contamination from the motors to the pump.
These elements should be changed as dictated by an oil analysis or every 3 months.
The cooler fins need to be “combed” and cleaned. This is essential, as hydrostatic drives
tend to normally run hot.
The breather cap on the reservoir is very dirty and should be changed immediately.
A manual hand pump is used to refill the reservoir. At this time the pump suction pipe is
stuck down inside the 55-gallon drum. The outside air has contaminated the oil in the
drum. When not being used the drum should be sealed. The oil should also be filtered
prior to pumping it into the tank with a 10-micron filter.
There is a suction filter connected in the charge pump suction line. Eaton, the pump
manufacturer, recommends the filter have a 10-micron rating and is of the non-bypassing
type. If this filter becomes contaminated, the charge pump can cavitate causing eventual
cavitations of the main pump.
Oil Temperature - 135° F
Motor Case Drain Temperatures -
159° - 160° F
Hoses
Several hoses were too long and rubbing. Upon examining the hoses wear points exist,
and in one case, the wire of the hose is exposed.
Normal hose length should be 3 –4 feet. This system needs to be re-piped to eliminate
these potential leak points.
Planer Mill Sorter
Pump
The pump is a 45 GPM, pressure compensating, Vickers piston type pump. The setting
of the compensator determines the maximum system pressure 1500 PSI.
The flow out of the case drain line can be checked to determine pump wear. Normal
bypassing for this pump is ½ - 1 ½ GPM. When the flow rate reaches 4.5 GPM the pump
should be changed.
Oil Temperature
134° - 139° F was indicated when the reservoir was shot with a heat gun.
Leaks
Oil is leaking at the return filter gasket.
Additional Actions and Recommendations
The original design of the system was to vent the pump compensator when the bays were
not operating. This was done with a single solenoid directional valve. The valve is still
mounted on the reservoir but is not connected in the system.
The temperature of this system is approaching 140° F. Oil will start breaking down
above that temperature. By reconnecting the directional valve, the pump will compensate
at a lower pressure. This will reduce heat and electrical energy when in the idle mode.
This system does not have a relief valve as a safety back up. If the compensator spool
were to stick closed, pressure would build until the weak point ruptures. A relief valve
should be installed immediately down stream of the pump.
Planer Hold Down Rolls
Pump
A 5 – 6 GPM, pressure compensating, piston pump supplies oil to the hold down roll
cylinders. The setting of the pump compensator determines the infeed hold down
pressure. There was not a gauge at the pump outlet port to read the compensator setting.
The flow out of the case drain line for this pump should be .05 - .15 GPM. A severe
increase in this flow rate indicates a worn pump.
Pressures
The compensator on the pump should be set to the pressure required at the infeed hold
down rolls. A pressure-reducing valve on the manifold is used to limit the pressure to the
outfeed roll. The reducing valve is set to 750 PSI.
Oil Temperature - 129° F
Accumulators
Two piston accumulators are mounted on the reservoir. The larger accumulator is used to
supply additional volume for raising and lowering the rolls. The precharge on this
accumulator should be ½ - 2/3rds the pump compensator setting.
The smaller accumulator is used to absorb shock in the rolls circuit. The nitrogen
precharge should be 100 PSI below the compensator setting.
Hoses
Several hoses on this unit are too long and rubbing. Protective sleeves should be installed
or shorter hoses should be made.
Additional Actions and Recommendations
A gauge should be installed to read the pressure at the outlet port of the pump. This
gauge should be checked to make sure the pressure has bled down to 0 PSI before
working on or around the feedrolls. To make sure that the pressure has bled down from
both accumulators the manual overrides on the end of directional valve solenoids can be
actuated. All personnel should be clear of the rolls when this is done.
The breather cap-mounting base is split allowing sawdust and other contamination into
the reservoir. This needs replacing as soon as possible.
Planer Mill Stacker
Pump
The system is supplied by a 20 GPM, Oilgear piston pump. The block on top of the
pump contains the compensator. The compensator setting determines the maximum
system pressure.
Normal bypassing out of the case drain line of this pump is approximately 1 GPM. A
severe increase in this flow rate indicates a badly worn pump.
Pressures
The compensator adjustment is set to 1500 PSI. A relief valve is located in a block on
top of the reservoir. The relief valve should be set 250 – 300 PSI above the compensator
setting. To properly set the valves perform the following procedure:
1.
2.
3.
4.
Turn the relief valve fully counterclockwise.
Turn the compensator fully clockwise.
Turn the relief clockwise until 1800 PSI is read on the gauge.
Turn the compensator counterclockwise until 1500 PSI is indicated on the gauge.
Oil Temperature
132° - 134° F when shooting the reservoir with a heat gun.
Filter and Cooler
The visual dirt alarm on the filter is bad and needs replacing. The cooler fins have some
dirt build up and should be cleaned.
Strapper
Pump
A 20 GPM variable displacement, pressure compensating Rexroth pump supplies oil to
operate the strapper actuators. A “load sensing” spool is mounting on top of the
compensator valve. The “X” port of the load-sensing spool is connected to a vent
solenoid valve.
When the solenoid valve is open the load sensing spool will shift at 500 PSI allowing the
pump volume to be reduced to near 0. The pump will only deliver enough oil to maintain
the load sensing spring setting, 500 PSI.
When necessary to operate the strapper, the vent solenoid energizes. Pressure can now
build to the setting of the compensator, 1450 PSI. Once this setting is reached the pump
volume is automatically reduced to only what the system needs.
The pump has a maximum volume stop on the end of the housing. If this adjustment is
turned clockwise, the pump will deliver a lower volume of oil. On this application, this
adjustment should be all the way out allowing the pump to deliver maximum volume
when needed.
Pressures
Refer to the pump description for the setting and operation of the compensator and load
sensing springs.
Return Filter
A red button on top of the filter housing will pop up when the element is dirty. The
element momentarily pops up when the top squeeze cylinders retract. This may be
caused by the filter being sized too small or the element may be nearly contaminated.
Additional Actions and Recommendations
There is no relief valve in the system for protection in the event the pump compensator
fails closed. A relief should be installed and set 250 – 300 PSI above the pump
compensator setting.
The easiest location to install the relief may be underneath the top or side squeeze
directional valves. A longer bolt kit will be needed.
Consult Summary
Several reoccurring problems were found during the two-day survey of the units. The
first is improper pressure settings, which results in extremely high oil temperatures. This
was the case on the Saw Box and North Side Debarker. This is a common problem in
mills because pressures are randomly adjusted in an attempt to increase the speed of the
machine. In both cases the relief valve was set below the pump compensator. This
causes the entire pump volume to dump over the relief valve when not being used to
moving the load. Hydraulic systems are designed to normally operate below 140° F.
When a high oil temperature exists in a system with a compensating pump and relief
valve, the first thing that should be done is to properly set the pressures. In the case of
the Saw Box, the oil temperature dropped from 166° F to 108° F once this was done.
On other systems, high oil temperature was caused by excessive case drain flow of the
pumps. The Edger and Stacker units exhibited this problem. The first recommendation
here is to install a flow meter in the case drain line of all pump. This will allow the flow
to be to be checked quickly and easily. The bypassing of any pump will gradually
increase over time. Several factors will cause the flow to increase prematurely: poor
filter maintenance, high oil temperature and pressure settings being too high.
If a regular filter maintenance program is not in place, then one should be started. The
best method of establishing a schedule is to have the oil analyzed by a qualified company.
Based on the fluid cleanliness (or lack thereof) a filter change out schedule can be
developed.
If oil analysis is not done, then as a general rule, change the elements every 3 months.
An even better method however is to have visual dirt alarms and checking them monthly.
Many of the system filters lacked dirt alarms or if they had them they were not working.
A fluid cleanliness level of 17/13 should be maintained in non-servo systems. On
systems using servo and proportional valves a 14/11 standard should be met.
The reservoir of any hydraulic system should be cleaned out once a year. Use a lint free
cloth when wiping the reservoir down. The systems that have run above 140° F for an
extended period of time need to be cleaned immediately. Varnish and sludge will be
present in the reservoir, lines and valves. In several sections of this report I recommend
the use of a Mobil product called Mobil Sol A. This flushing solvent will remove the
varnish and gummy deposits in the system. Product and flushing procedure data sheets
are included with this report on Mobil Sol A.
Several breathers were found to be fully contaminated or not properly mounted. If the
breather plugs up then dirty air will enter through a return line gasket, mounting bolt, etc.
The breather on the unit should filter the air to a 10 – 40 micron level. Breathers should
be changed a minimum of once a year.
Many systems using pressure-compensating pumps are installed without a relief valve as
a safety backup. If there is no relief in the system and the compensator fails to shift,
pressure will build up until the weak point ruptures. The weak point may be a blown
hose, O-ring, the physical structure of the machine, or the electric motor overload. A
relief valve should be installed on all units that utilize pressure-compensating pumps.
Many units had hoses that were over 4’ in length. Most of these hoses were rubbing on
another hose, reservoir, beam, etc. This will result in premature failure of the hose and
mill downtime. Proper hydraulic plumbing is to connect a hose out of the pump to the
pipe header. A hose should be connected off the header prior to connecting to the valve
or cylinder. The exception to this rule is if the cylinder is operating a vertical load. A
valve called a velocity fuse should be connected at the cylinder before the hose is
attached. This will prevent free falling of the load in the event the hose ruptures.
Several leaks were found during the two-day visit. When a leak occurs, there is a reason
for it. This may be caused by high oil temperature, improper clamping or worn seals and
gaskets. A leak that drips once per second will cause a loss of 405 gallons in a year’s
time.
Once the problems on the units are corrected regular preventative maintenance checks
should be made. I have included our standard Hydraulic Preventative Maintenance
Checklist with this report. Although all the checks will not apply to all systems a
thorough P.M. of the unit will be done when completed. I would recommend making
these checks once a month to insure system reliability.
I would like to thank everyone who assisted me during my visit especially John Love,
Dale Dyals, Dennis Cumbee, Richard Hayes and Willie Taylor. I hope the information
contained in this report will assist you in improving your hydraulic maintenance and
increase your operating efficiency. Please do not hesitate to call if I or anyone here at
GPM can help you in any way.
Sincerely,
C.A. (Al) Smiley, Jr.
President
GPM Hydraulic Consulting, Inc.