Yes, I can put a jack under the edge of the cage and raise it slowly. I think I can tell when the cage weight is neutralized so I can see if the cylinder is compressing air.
How to find a suction leak
- Thread starter BeezFun
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The loop is goofy, I bought this from a rental place. I'm guessing that's their handy work.
rScotty
Super Member
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I wonder about that loop and the upsidedown filter. Did the rental place change the plumbing around so that they could use cheaper filters?
Do you have any picture of how it was plumbed originally.
How old are the hoses? Can a work drive clamp even tighten enough to seal that heavy of a hydraulic hose like they are using for the suction line?? The classic problem with worm drive hose clamps is they rely on the elasticity of the rubber to make the seal. They can't tighten up to compensate as the hose gets old and hard.
Most old hoses that cause suction leaks are longitudinal splits along the inner surface of the hose, and they tend to run parallel to the hose direction. So you rarely see cracks by inspecting the ends of the hose.
The reason you may not be seeing air in the oil might simply be that vertical distance and low flow between the sump and the cage the air may give the air time to exit the oil and form a bubble at the highest point.
I love reading oldnslo's pressure analysis; what a good analytic mind he has! .....but I think your best clues are simpler: 1. it's happening at the cage, and 2. it is getting worse. I'd like to explore your original idea of isolating & pressurizing the suction circuit to look for leaks. And also compare the suction circuit with OEM.
rScotty
Do you have any picture of how it was plumbed originally.
How old are the hoses? Can a work drive clamp even tighten enough to seal that heavy of a hydraulic hose like they are using for the suction line?? The classic problem with worm drive hose clamps is they rely on the elasticity of the rubber to make the seal. They can't tighten up to compensate as the hose gets old and hard.
Most old hoses that cause suction leaks are longitudinal splits along the inner surface of the hose, and they tend to run parallel to the hose direction. So you rarely see cracks by inspecting the ends of the hose.
The reason you may not be seeing air in the oil might simply be that vertical distance and low flow between the sump and the cage the air may give the air time to exit the oil and form a bubble at the highest point.
I love reading oldnslo's pressure analysis; what a good analytic mind he has! .....but I think your best clues are simpler: 1. it's happening at the cage, and 2. it is getting worse. I'd like to explore your original idea of isolating & pressurizing the suction circuit to look for leaks. And also compare the suction circuit with OEM.
rScotty
oldnslo
Super Member
My thoughts on pump suction or inlet leak as that it would show up in the lift functions being spongy long before showing in leveling circuit. Leveling circuit in normal use it not even connected to the pump it is a self contained system.
example: operator gets in bucket at ground level and adjusts level if required. Then raises the mast. While raising the knuckle cylinder is being mechanically retracted forcing oil from knuckle cylinder into the cage cylinder. Bucket levels with no connection to pump pressure. While lowering the knuckle cylinder is mechanically extended forcing oil from rod end to rod end. Again totally self contained with no connection to pressure line.
the big unknown is what pressure is required in leveling system and is there enough pressure that some oil is being bled off in the rod ends of the leveling circuit effectively creating an air pocket.
leak paths are:
1) across the 145 bar relief to tank
2) across the directional control valve
3) not knowing how cross over and P.O. check are could they have leak from pilot to system??
4) external which I suspect Beez would have seen by now
5) others: if seal is bad in one of the cylinders not sure what type of failure they would have.
I am in no way saying there is not a pump suction leak just be surprised if this was the only function being affected.
example: operator gets in bucket at ground level and adjusts level if required. Then raises the mast. While raising the knuckle cylinder is being mechanically retracted forcing oil from knuckle cylinder into the cage cylinder. Bucket levels with no connection to pump pressure. While lowering the knuckle cylinder is mechanically extended forcing oil from rod end to rod end. Again totally self contained with no connection to pressure line.
the big unknown is what pressure is required in leveling system and is there enough pressure that some oil is being bled off in the rod ends of the leveling circuit effectively creating an air pocket.
leak paths are:
1) across the 145 bar relief to tank
2) across the directional control valve
3) not knowing how cross over and P.O. check are could they have leak from pilot to system??
4) external which I suspect Beez would have seen by now
5) others: if seal is bad in one of the cylinders not sure what type of failure they would have.
I am in no way saying there is not a pump suction leak just be surprised if this was the only function being affected.
Did some testing, to force the cage leveling cylinder to extend I used a ratchet strap attached to my tractor bucket to pull on the top of the cage:
I attached a strap to the lift to force the cylinder to retract:
I put a piece of painters tape on the rod so I could see what was happening:
When I force extension, the rod extends about 1/4". I released the strap and waited, the rod extended another 1/2" and then didn't move any more.
When I force retraction, the rod retracts about 1/8". I release the strap and waited, the rod EXTENDED about 1/2" and then didn't move any more.
So in both cases after pulling on the cylinder to extend and retract, it drifts in the extended direction after I release it. The weight of the cage is trying to make the rod retract. So the fact that it drifts in the extend direction means there has to be a force on rod end of the cylinder.
I attached a strap to the lift to force the cylinder to retract:
I put a piece of painters tape on the rod so I could see what was happening:
When I force extension, the rod extends about 1/4". I released the strap and waited, the rod extended another 1/2" and then didn't move any more.
When I force retraction, the rod retracts about 1/8". I release the strap and waited, the rod EXTENDED about 1/2" and then didn't move any more.
So in both cases after pulling on the cylinder to extend and retract, it drifts in the extended direction after I release it. The weight of the cage is trying to make the rod retract. So the fact that it drifts in the extend direction means there has to be a force on rod end of the cylinder.
I've seen this model lift when it's new (they still make it), the suction plumbing is all original except that piece of hose that has the loop in it. The filter and housing are OEM. I believe all hoses are original except the goofy loop hose.
Smokeydog
Elite Member
Any rubber lines on the suction side are suspect. May not see external damage. Remove to inspect internally and sealing surfaces the only way.
How many times have you changed the filter? Hydraulic filters come in lots of micron filtering sizes. Using the right one?
Filter tight? sealing? Only one gasket?
People lifting equipment have a much more hydraulic component replacement schedule than tractors.
How many times have you changed the filter? Hydraulic filters come in lots of micron filtering sizes. Using the right one?
Filter tight? sealing? Only one gasket?
People lifting equipment have a much more hydraulic component replacement schedule than tractors.
Smokeydog
Elite Member
My Dad bought a 1ton bucket truck from TVA. Came with maintenance records. Inspected before each use. Load tested yearly and all fluid, filter (3x bigger than normal) and all rubber hoses replaced every two years. We didn’t.
You mentioned British built. Most likely British threads on hydraulic fittings that are slightly different from SAE. Could also be leak point.
You mentioned British built. Most likely British threads on hydraulic fittings that are slightly different from SAE. Could also be leak point.
KWentling
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I looked up a Carquest 85546 filter. Looks to be a 16 micron with no bypass. Way too fine for a suction filter I would think.
oldnslo
Super Member
Beez,
From the amount of cylinder movement it does not sound like there is a excessive amount of air trapped in the cage cylinder. But the really puzzling thing and potentially a big clue is the extension after releasing the external load in both directions. I am just trying to visualize what could cause this extension to occur.
Couple of more questions:
1) The pictures looks like a hard line on the rod end going back towards the cap end of the cage cylinder. Does this connect to a block on the cap end or to the cap that have a valve in it? Trying rod determine if the PO check is hard mounted to the cage cylinder.
2) Any idea where the over center valve is mounted? should be in the rod end line with a hose or line connected to cap end. Possible in one body at cap end of cage cylinder.
3 ) same with two relief valves set at 145 Bar. Are they separate line bodies or in a common valve body. Not sure if these are in play but trying to gain a fuller picture of how this is plumbed.
Reason for questions above is trying to estimate trapped oil volume while doing the manual tilt test. The PO check should stop all flow out of the cap end and it appears the check did stop movement.
The over center valve could allow flow if you applied enough force to over come the preset pressure setting. At least the schematic shows having this pressure to open feature. Now the $64 question is where could any oil getting past the over center valve go?
Another off the wall question: Do you see any free play in the knuckle cylinder mounts? I.e. can it extend and retract without the main mast moving? Again doubt there is but trying to eliminate potential sources of unknown movement.
Sorry for all the questions but hopefully they will help guide us to the root cause of this problem.
From the amount of cylinder movement it does not sound like there is a excessive amount of air trapped in the cage cylinder. But the really puzzling thing and potentially a big clue is the extension after releasing the external load in both directions. I am just trying to visualize what could cause this extension to occur.
Couple of more questions:
1) The pictures looks like a hard line on the rod end going back towards the cap end of the cage cylinder. Does this connect to a block on the cap end or to the cap that have a valve in it? Trying rod determine if the PO check is hard mounted to the cage cylinder.
2) Any idea where the over center valve is mounted? should be in the rod end line with a hose or line connected to cap end. Possible in one body at cap end of cage cylinder.
3 ) same with two relief valves set at 145 Bar. Are they separate line bodies or in a common valve body. Not sure if these are in play but trying to gain a fuller picture of how this is plumbed.
Reason for questions above is trying to estimate trapped oil volume while doing the manual tilt test. The PO check should stop all flow out of the cap end and it appears the check did stop movement.
The over center valve could allow flow if you applied enough force to over come the preset pressure setting. At least the schematic shows having this pressure to open feature. Now the $64 question is where could any oil getting past the over center valve go?
Another off the wall question: Do you see any free play in the knuckle cylinder mounts? I.e. can it extend and retract without the main mast moving? Again doubt there is but trying to eliminate potential sources of unknown movement.
Sorry for all the questions but hopefully they will help guide us to the root cause of this problem.
