How to find a suction leak

[BeezFun]

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.

It's hard mounted to the cylinder, I've attached two pages out of parts manual that shows it.

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.

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.

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.

I don't see it called out in parts manual, only appears on schematic. I'll look for that also tomorrow.

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?

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?

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.

No movement, I've grabbed it and tried to wiggle it. No matter what position the lift is in it's tight.

Sorry for all the questions but hopefully they will help guide us to the root cause of this problem.

Appreciate your time and help, the more questions the better.

 

[rScotty]

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

 

[repete]

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.

 

[rScotty]

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.
We had to take a sledge hammer to the pins to get them out. They were disgustedly rusted solid.
It does not stay outside anymore.

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

 

[BeezFun]

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.

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.

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 aboe is true then it does make some sense that the rod could extends in both compression and extension. One direction compresses an air pocket, and the other direction lowers 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 off with those specs.
rScotty

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.

 

[BeezFun]

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.

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]

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.

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

 

[BeezFun]

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]

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.

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]

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.

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.