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
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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.
It's hard mounted to the cylinder, I've attached two pages out of parts manual that shows it.
I think it's in the block that's mounted right to the cylinder. I've looked through the parts manual, can't find it called out anywhere specific so must be part of the same block shown on attached parts diagram. I'll check tomorrow and follow the lines to confirm that.
I don't see it called out in parts manual, only appears on schematic. I'll look for that also tomorrow.
Looking at schematic it can only go through the 145 bar relief or back through the valve that controls the cage. Could the spool be leaking back to tank?
No movement, I've grabbed it and tried to wiggle it. No matter what position the lift is in it's tight.
Appreciate your time and help, the more questions the better.
rScotty
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You say, "My thoughts on pump suction or inlet leak is 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."
I'm confused. If not connected, how does the bleeding procedure work? And during the bleeding procedure, where does the bled off air go? Can you come up with anything other than air which would be cured by the bleeding procedure? Apparently it does cure the problem for awhile.
Also, I'm not at all sure that entrained micro bubbles would show up as spongy fluid. I'm not sure just how the compressibility of oil with entrained tiny bubbles in it differs from what we know about a larger discrete air pocket in a cylinder. There may be surface tension effects in tiny bubbles that make oil+micro bubbles act more like a single incompressible fluid.
To me, if any of the above is true then it does make some sense that the rod could extend in both compression and extension after a load is removed. Forcing the rod in one direction compresses an air pocket, and forcing it the other way could lower the fluid pressure in the cylinder - perhaps allowing entrained air to exit the fluid and form a larger air pocket.
I'm not sure about the carquest filter specs. In my experience a 16 or 20 micron filter in a can that size does not go along with 22 gallon per minute flow rate. Something is seeming off with those specs.
rScotty
I'm confused. If not connected, how does the bleeding procedure work? And during the bleeding procedure, where does the bled off air go? Can you come up with anything other than air which would be cured by the bleeding procedure? Apparently it does cure the problem for awhile.
Also, I'm not at all sure that entrained micro bubbles would show up as spongy fluid. I'm not sure just how the compressibility of oil with entrained tiny bubbles in it differs from what we know about a larger discrete air pocket in a cylinder. There may be surface tension effects in tiny bubbles that make oil+micro bubbles act more like a single incompressible fluid.
To me, if any of the above is true then it does make some sense that the rod could extend in both compression and extension after a load is removed. Forcing the rod in one direction compresses an air pocket, and forcing it the other way could lower the fluid pressure in the cylinder - perhaps allowing entrained air to exit the fluid and form a larger air pocket.
I'm not sure about the carquest filter specs. In my experience a 16 or 20 micron filter in a can that size does not go along with 22 gallon per minute flow rate. Something is seeming off with those specs.
rScotty
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repete
Veteran Member
My brother has one of these lifts and it creaked and jerked when it moved and we had to remove every pin from the assembly and grease every joint. I cannot believe it did not come with grease fittings from the factory. Only grease fitting was on the turntable.
Edit: He bought it (well) used from a rental place that stored it outdoors.
We had to take a sledge hammer to the pins to get them out. They were disgustedly rusted solid. We polished the pins with emery cloth on the lathe and used a wire wheel brush to polish the inside of the cylinder and structure. Greased all the pins and reinstalled. Afterward we had smooth operation, no "jerkyness" and no noise.
Not saying it relates to the issue you are having but it sure made a difference to this 35' Bil-Jax unit.
It does not stay outside anymore.
Edit: He bought it (well) used from a rental place that stored it outdoors.
We had to take a sledge hammer to the pins to get them out. They were disgustedly rusted solid. We polished the pins with emery cloth on the lathe and used a wire wheel brush to polish the inside of the cylinder and structure. Greased all the pins and reinstalled. Afterward we had smooth operation, no "jerkyness" and no noise.
Not saying it relates to the issue you are having but it sure made a difference to this 35' Bil-Jax unit.
It does not stay outside anymore.
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rScotty
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It didn't take too long when I started working with machinery to realize that mechanics could often tell where something originated by looking at the design. British mechanical design is famous for being innovative and at the same time astonishingly blind to basics: i.e. unlubricated sliding joints, non-syncro racing gear boxes, positive ground electrics, insideout magnetos....the list is endless. Design can be like a mechanical signature.
rScotty
The only time the leveling circuit is connected to the pump is when I manually actuate the leveling valve. If you look at the hydraulic schematic, the way that valve works is it connects the knuckle cylinder to the cage cylinder when it's in the neutral position. It's isolated from the pump in that position. It's not until the valve is actuated by hand that the pump is connected to the cage cylinder. I think what happens to the air is it gets forced through that 145 bar relief valve and back to tank. Notice that all the relief valves in the system are set at 200bar except the cage system, which is at 145. That ensures the fluid/air from the cage can't end up going anywhere in the system because that relief valve is set so much lower than the other reliefs.
The original filter is a Parker Hannifan, it's spec is 10 micron. The oil used is ISO 22, which is SAE 10W, so that's much thinner than most tractor fluids which are generally ISO 32 or somewhere around 20W oil.
I agree it's crazy there aren't more grease fittings. Some of my cylinders do have some kind of non metallic bushing around the pins that were probably intended to eliminate the need for lubrication. I've oiled all my pins and pivots with oil on a regular basis. I think my lift must have had a lot of use and maybe was stored indoors because it had no rust on it anywhere and the pins all look like they're brand new, even now that it's 15 years old.
rScotty
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Yes, I did notice those things. So does this put us back to the problem being air in the leveling system? Where would that air come from if it didn't come in with fluid? Is there any air source other than from the suction side of the pump?
The OP's original question was whether it made sense to put some small pressure on the suction side to see if a leak would declare itself. What do you all think of that option now?
rScotty
I'd like to continue to pursue oldnslo idea that the problem is related to one of the control components in the leveling circuit not working properly, or leaking. Even if it eventually ends up being air, at least I'll understand how this thing works.
As far as the suction system, I've had a thought. The suction lines for the gas driven pump and the electric driven pump are completely separate. The electric system pump lives inside the reservoir tank, including the filter. So if I only use the electric driven pump and I observe that the problem goes away, that would tell me there is an air leak in the suction lines that serve the gas driven pump. The gas driven suction lines include that upside down filter and the two large black hoses that are about 2" diameter. If the problem doesn't go away when I only use the electric pump, then I am inclined to conclude the problem can't be due to air. Why the bleeding process seems to make the problem better is a separate question and I can't answer it right now.
rScotty
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I think it's a fine idea to work on the possibility of a control component not working properly or leaking. I'm on board with that. The physics of failure is probably going to be more familiar, and that's always nice. The problem I have with that is I have not figured out how a failed component would work with what you found bleeding the system.
Your idea of using the electric pump makes sense, and alternating between it and the gas driven pump might just be enough to put the air theory to rest....or not.
Completely as an aside, at the back of my mind I recall years ago hearing about an entrained air problem where a tank farm was trying to measure how much air entrained crude oil was flowing - and having problems which somehow involved the the bends in the pipe & hoses. But don't remember anything more about the solution other than the fluid mass measurement being non-linear & velocity sensitive. So it might have had to do with air coming out of solution.
rScotty
Smokeydog
Elite Member
Wonder if the OEM filter had cold oil bypass? Type of filter media also determines flow resistance as well as micron rating. Important issue of proper weight oil used. Both could cause pump cavitation. Makes bubbles from extreme micro localized heat and pressure explosions breaking down the hydraulic fluid.
Replacing filter to OEM spec and making sure running the correct weight fluid for the design would be my first step in troubleshooting.
Many HST tractor owners have experienced poor performance from non manufacturer filters and fluids.
