Hello Everyone;
By comparable standards I'm really new to Hydraulic troubleshooting (although I do a lot of install work). A friend of mine brought me his bucket truck. It uses pilot operated main valves down at the lower section. The pilot controls (oil) are fed up the boom to the bucket.
The initial problems that he was facing was a slow/sluggish response from the control handle located in the bucket. During operation on one of their last jobs, a chunck of wood fell and shattered the pilot supply line comming from the valve bank at the lower section.
He reports having tried all different types of nylon and poly tubing, all having exploded within minutes of install. Checking the pressure of the pilot line revealed the control valve set to 1000 psi. From all of the research that I have done, it sounds to me like there are few, if any nylon tubing sources that supply this high a working pressure of tube.
I performed the normal maintenance of his truck, pulled the return and supply filters to change/clean. Upon disection of the return filter, I found it completely clogged with contaminents. The return housing had been operating in bypass mode for so long that the bypass spring was permently compressed. The suction filter from the tank was a 100uf (I believe) washable steel filter element. After some time in the dip tank, it came clean once again (packed with debries before it went for a little dip).
Realizing the level of contamination that was in the system, I proceeded with a complete teardown. All internal pipes were opened, tank was opened and manually cleaned, pump was tested for GPM flow and Pressure to determine state (was functioning within 90% of spec'd tolerances). Pressure bypass/relief valve was jammed open by debries. I stripped the bank valve set apart and found not only high levels of varnish and steel shavings, but the classic "gray goo" of a poorly maintained system.
Questioning my friend revealed that it had not been regularly serviced for about 15 years, but the pump had been replaced by his diesel mechanic no more than a month or two ago.
While I had the bank valves dissassembled (spring centered spool type) I tested the pilot ports and their associated chambers for leakage. Leakage rates were low, in the area of 15/20 drops per min. Spools on valves were in decent shape (I've seen worse function fine). Manual handles that operated main valves were in decent condition, as well as their connecting assemblies to the spools. I reassembled the bank assembly and tested it "on the bench" It operated correctly, shifting nicely and providing power with minimal leakage across the open spools. GPM ratings were at maximum when all valves were centered to their open position.
As we used the same type of pressure reducing relieving valves here in the shop that was used to control the pilot pressure to remote control, I cleaned and tested the valve, which function well.
Knowing the state of the system below, I removed and disassembled the remote control device that was located in the bucket of the truck. I found a filter assembly at the bottom of the device that was heavily plugged with debries. I cleaned the filter and continued to strip the remote to check the spool assemblies for damage and dirt. Inside of the supply mainifold where the main supply is divided into six individual supplies, there were pilot orifices installed. All of the orifices were plugged.
I removed and cleaned all of the orifices being careful as to their placement. Inspection revealed that two of the orifices were replaced (color difference) with a larger orifice. Aparently at some point in time this device had been previously serviced.
To finish, the remote is an open center device. I recieve full pilot pressure at the supply manifold located at the remote, as well as the same GPM readings that I receive at the lower end of the pilot line. Upon reassembly of the valve, there were only two functions out of six that would correctly function. These two functions were not on the same pilot operated valve. Upon more investigation it was revealed that the remote had been shiped out at some point to be repaired. The remote filter had been left behind - but a list of problems was sent along with the device (valve 1 A side not functing, valve 3 B side not functioning ...). This previous report corresponded to the changed orifices - the larger orifices not coinciding with the working valves.
I flushed and filled the system multiple times, used remote filtration devices - filtered down to 2micron over the course of 8 hourse - cycling cylinders and such to ensure good fluid exchange. I purged all of the air and old oil from the pilot lines.
Checking the pilot pressure on the valve side when the remote is activated shows the following:
Pilot pressure set to 500psi: Valve pressure 0
Pilot pressure 1000psi: Valve pressure 25psi (barely shifting).
I'm trying to determine:
a)could this be an orifice issue
b)Knowing that the valve is open center, and seeing that there are no o-rings or other contact wipers (so it's designed with leakage in mind given the return hose of 3/8 over the 1/4 supply pilot) what else would cause such a drastic pressure drop in the remote? (I checked output pressure from the remote directly which revealed similar results as the valve tests - all PSI readings a little higher (3 to 5 psi).
Any help in understanding orifices and their use/application would be extremely appreciated. Oh yeah - and as for sending the remote back to the same company that built it - they went out of business and no-one else that I have found is willing to touch it; they all just want to sell me new valves since the old one is 30+ years of age.
Chris
By comparable standards I'm really new to Hydraulic troubleshooting (although I do a lot of install work). A friend of mine brought me his bucket truck. It uses pilot operated main valves down at the lower section. The pilot controls (oil) are fed up the boom to the bucket.
The initial problems that he was facing was a slow/sluggish response from the control handle located in the bucket. During operation on one of their last jobs, a chunck of wood fell and shattered the pilot supply line comming from the valve bank at the lower section.
He reports having tried all different types of nylon and poly tubing, all having exploded within minutes of install. Checking the pressure of the pilot line revealed the control valve set to 1000 psi. From all of the research that I have done, it sounds to me like there are few, if any nylon tubing sources that supply this high a working pressure of tube.
I performed the normal maintenance of his truck, pulled the return and supply filters to change/clean. Upon disection of the return filter, I found it completely clogged with contaminents. The return housing had been operating in bypass mode for so long that the bypass spring was permently compressed. The suction filter from the tank was a 100uf (I believe) washable steel filter element. After some time in the dip tank, it came clean once again (packed with debries before it went for a little dip).
Realizing the level of contamination that was in the system, I proceeded with a complete teardown. All internal pipes were opened, tank was opened and manually cleaned, pump was tested for GPM flow and Pressure to determine state (was functioning within 90% of spec'd tolerances). Pressure bypass/relief valve was jammed open by debries. I stripped the bank valve set apart and found not only high levels of varnish and steel shavings, but the classic "gray goo" of a poorly maintained system.
Questioning my friend revealed that it had not been regularly serviced for about 15 years, but the pump had been replaced by his diesel mechanic no more than a month or two ago.
While I had the bank valves dissassembled (spring centered spool type) I tested the pilot ports and their associated chambers for leakage. Leakage rates were low, in the area of 15/20 drops per min. Spools on valves were in decent shape (I've seen worse function fine). Manual handles that operated main valves were in decent condition, as well as their connecting assemblies to the spools. I reassembled the bank assembly and tested it "on the bench" It operated correctly, shifting nicely and providing power with minimal leakage across the open spools. GPM ratings were at maximum when all valves were centered to their open position.
As we used the same type of pressure reducing relieving valves here in the shop that was used to control the pilot pressure to remote control, I cleaned and tested the valve, which function well.
Knowing the state of the system below, I removed and disassembled the remote control device that was located in the bucket of the truck. I found a filter assembly at the bottom of the device that was heavily plugged with debries. I cleaned the filter and continued to strip the remote to check the spool assemblies for damage and dirt. Inside of the supply mainifold where the main supply is divided into six individual supplies, there were pilot orifices installed. All of the orifices were plugged.
I removed and cleaned all of the orifices being careful as to their placement. Inspection revealed that two of the orifices were replaced (color difference) with a larger orifice. Aparently at some point in time this device had been previously serviced.
To finish, the remote is an open center device. I recieve full pilot pressure at the supply manifold located at the remote, as well as the same GPM readings that I receive at the lower end of the pilot line. Upon reassembly of the valve, there were only two functions out of six that would correctly function. These two functions were not on the same pilot operated valve. Upon more investigation it was revealed that the remote had been shiped out at some point to be repaired. The remote filter had been left behind - but a list of problems was sent along with the device (valve 1 A side not functing, valve 3 B side not functioning ...). This previous report corresponded to the changed orifices - the larger orifices not coinciding with the working valves.
I flushed and filled the system multiple times, used remote filtration devices - filtered down to 2micron over the course of 8 hourse - cycling cylinders and such to ensure good fluid exchange. I purged all of the air and old oil from the pilot lines.
Checking the pilot pressure on the valve side when the remote is activated shows the following:
Pilot pressure set to 500psi: Valve pressure 0
Pilot pressure 1000psi: Valve pressure 25psi (barely shifting).
I'm trying to determine:
a)could this be an orifice issue
b)Knowing that the valve is open center, and seeing that there are no o-rings or other contact wipers (so it's designed with leakage in mind given the return hose of 3/8 over the 1/4 supply pilot) what else would cause such a drastic pressure drop in the remote? (I checked output pressure from the remote directly which revealed similar results as the valve tests - all PSI readings a little higher (3 to 5 psi).
Any help in understanding orifices and their use/application would be extremely appreciated. Oh yeah - and as for sending the remote back to the same company that built it - they went out of business and no-one else that I have found is willing to touch it; they all just want to sell me new valves since the old one is 30+ years of age.
Chris
