how should I flush hydraulic fluid?

[Luke'sScreenName]

So I recently bought a used Woods backhoe attachment. I do not know the service history.
Before I put it on my hydrostatic MX4800 in the spring, I was thinking I should flush out the old hydraulic fluid so as to not contaminate my UDT2.

Several people were nice enough to describe how they have done it here:

http://www.tractorbynet.com/forums/attachments/349544-how-i-mount-bh90-x.html

What they describe seems like a major PITA!.. But may just be the way it goes.

Anyone have an easier way?

I will not be able to mount the hoe to my tractor prior to flushing it.

 

[davesl708]

When I bought my BX used the service history was questionable at best. The fluid was pretty dirty. I used UDT to flush the system and replaced the filter then flushed the system again before putting SUDT2 in.

The old oil was so dirty the FEL was having problems with flow through the control valve.

 

[The Fred]

I would change the HST oil in your tractor then flush the backhoe with your old oil, killing two birds with one stone.

Good luck, Fred

 

[bigdeano]

I'd hook an air compressor to the pressure line. Pull the pins on the rod ends of the cylinders and cycle the cylinders with air. Should blow most of the oil out the return line which hopefully you've put in a container of some sort.

 

[Harry in Ky]

I use a method that works well for me when flushing dirty or water contaminated systems. First, drain and refill, drain and refill as needed, the tractor alone, without operating any external cylinders. (In your case, that part would not be necessary) Next, remove the sump return hose from loader (or in this case backhoe) valve and drop it into a bucket. Start the tractor and cycle each cylinder system one at a time. The oil returning from cylinders and related lines will go into the bucket and not back into the tractor. Cycle each system as needed until the oil coming out looks clean then move on to the next circuit. With small tractors, fresh oil needs to be added frequently, but the end result is clean oil throughout, with a minimum of mess, and a lot less effort.

 

[Luke'sScreenName]

I would change the HST oil in your tractor then flush the backhoe with your old oil, killing two birds with one stone.

Good luck, Fred

My expensive SUDT2 fluid is not due for a change so hooking up to the tractor system that's not really a good option for me.

 

[Luke'sScreenName]

I'd hook an air compressor to the pressure line. Pull the pins on the rod ends of the cylinders and cycle the cylinders with air. Should blow most of the oil out the return line which hopefully you've put in a container of some sort.

What fittings do you use to do this? Is blowing seals a problem?

 

[Luke'sScreenName]

I use a method that works well for me when flushing dirty or water contaminated systems. First, drain and refill, drain and refill as needed, the tractor alone, without operating any external cylinders. (In your case, that part would not be necessary) Next, remove the sump return hose from loader (or in this case backhoe) valve and drop it into a bucket. Start the tractor and cycle each cylinder system one at a time. The oil returning from cylinders and related lines will go into the bucket and not back into the tractor. Cycle each system as needed until the oil coming out looks clean then move on to the next circuit. With small tractors, fresh oil needs to be added frequently, but the end result is clean oil throughout, with a minimum of mess, and a lot less effort.

Ok, interesting idea. Anyone else done this?

 

[dfkrug]

What fittings do you use to do this? Is blowing
seals a problem?

Air pressure will not blow any seals, as you are using only 100 psi or so. What MAY
happen is sudden mechanical movement as the pressure builds up enough for
a cylinder to extend or retract. Be careful if you do it this way.

I have not done it this way, but I have used air pressure to disassemble cylinders,
and that can be dramatic. And dangerous.

I have only flushed implements (hoes and FELs) with external mechanical force
applied to them to articulate all the cylinders and collect the fluid via the tank
return hose. Doing this dynamically with the tractor hyd pump running would
work, but I have not tried it. I don't want to lose too much clean expensive fluid.

 

[Coyote machine]

Luke, not my son, this is your father, Darth....
Here's my idea, not sure if it would work with the pressures needed to get the fluid out/through the circuits/cylinders but here's the theory-
rent a (sump pump, ? or similar), that could push clean hydraulic fluid from a 5 gallon bucket into the inlet hose of the hoe. Cycle all the levers/valves on the hoe to allow fluid to flow in, then use the return to tank line for the 'waste' oil coming out into a separate bucket. Do this until you are seeing fresh clean hyd fluid coming out the return line.
You may have to work out what type of pump would get the job done, but there has to be something available on the cheap- you're not trying to run the hoe, merely trying to push fluid through the circuits- not sure how much pressure that would require?

 

[Soundguy]

What fittings do you use to do this? Is blowing seals a problem?

blown seal?

ag hyds usually operate around 2500 psi

Most air compressors operate between 120 and 150 psi.


Does your air compressor put out more than 2500 psi?

If so.. I'm impressed!

 

[Luke'sScreenName]

blown seal?

ag hyds usually operate around 2500 psi

Most air compressors operate between 120 and 150 psi.


Does your air compressor put out more than 2500 psi?

If so.. I'm impressed!

Well my assumption is that the packing is designed for viscous hydraulic fluid not nitrogen gas. So a PSI is not necessarily a PSI.

 

[Soundguy]

Well my assumption is that the packing is designed for viscous hydraulic fluid not nitrogen gas. So a PSI is not necessarily a PSI.

and??? what's the possible worst that will happen.. a temp air leak?

remember.. again.. the seals are designed to contain 2500 psi of essentially uncompressible fluid...

150 psi of quite compressable gas is laughable.... hard to even make a comparison really.

 

[Luke'sScreenName]

I have only flushed implements (hoes and FELs) with external mechanical force
applied to them to articulate all the cylinders and collect the fluid via the tank
return hose. Doing this dynamically with the tractor hyd pump running would
work, but I have not tried it. I don't want to lose too much clean expensive fluid.

Ya, it just occurred to me that the hoe valve bank is probably open center so I'd be loosing 12+ GPM of good fluid from the time I start the engine (and not just when I actuated a valve)!
Is my thinking correct?
If so, I'm back to manually cycling the pistons or using air.
I wonder what the large dealers do?

 

[dfkrug]

I wonder what the large dealers do?

Not a danm thing, I will bet.

You will lose some fluid if you run the tractor. Even at idle, prob 3 GPM thru the open-center
valve. Too much? That's your call.

 

[Harry in Ky]

The suggestion I offered was intended for use with an open center, power beyond type system, using a third, sump return line. In which case no oil flows through this line unless a valve is in use. If your hoe has only two hoses connected to tractor hydraulics, that's a different matter. As for the listed methods for removing existing fluids from cylinders and lines, I'm sure any/all of them would be effective. I made my comments based on your first post, in which you asked about a simpler method.

 

[Luke'sScreenName]

Harry, I really appreciate your help and did not mean to ignore it. On my Case 680s there was 2 return lines. I'll have to go out and look at the Woods hoe this weekend when I'm home while it's light. There are only two lines connected to the tractor but the return lines may Y together upstream.

I does make sence that there should be a return line from the valve assembly when all the valves are closed and another return line from the cylinders. There would only be fluid returning from this second line when one of the valves is opened.
Am I thinking about this correctly?
What are the proper names for these lines? Sump return and.. ?
Will it be obvious which line is which or can you give me some tip to identify which is which?

Again thanks!

 

[ray66v]

Where I have been working, we use compressed air to remove oil from cylinders, before, and after, rebuilding them. As well as, compressed air to initially test them.

A blow gun with a rubber tip, and a rag, usually works fine, on the inlet, or outlet threads.

Yes, you would have to break a lot of lines loose. But, everything is pipe thread once you remove the couplers, and hoses, just like air fittings, so it's not hard to cobble up something that you can couple up to.

Low pressure is recommended. This is due to the fact that it will cause rapid piston movement, and lots of flying oil.

 

[Luke'sScreenName]

Where I have been working, we use compressed air to remove oil from cylinders, before, and after, rebuilding them. As well as, compressed air to initially test them.

A blow gun with a rubber tip, and a rag, usually works fine, on the inlet, or outlet threads.

Yes, you would have to break a lot of lines loose. But, everything is pipe thread once you remove the couplers, and hoses, just like air fittings, so it's not hard to cobble up something that you can couple up to.

Low pressure is recommended. This is due to the fact that it will cause rapid piston movement, and lots of flying oil.

Ok cool. Rubber tip seems simple. What's the rag for? What do you consider low pressure?

 

[dfkrug]

What are the proper names for these lines? Sump return and.. ?

Woods hoes and all other CUT hoes I have seen have only 2 lines, IN, and OUT. AUX valves
sometimes have a third line call Power-Beyond. Industrial hoes usually have more lines cuz
they use 2 pumps (swing, and boom/dipper/bkt). Except the B21 hoe, it has only 2.