Possible pump failure on Mitsubishi 2050

[rback33]

Marcus.. you can't just plug the gauge into the pump and fire the engine up.. it will blow the gauge out.

Typically, you chain the lift arms down, and then plumb the gauge into the pressure line, and then operate the lift.. the needle will move to the mas pressure generated.. the relief will kick in at some point and the pressure will go no higher.

To Rback 33... sticky relief valves can and do happen.. they are suposed to be seated and allow no flow to sump unitll their pressure rating is overcome, then they vent pressure and flow to the sump. There will be a limit as to how much flow can be diverted thru the relief.. I would generally think that the relief should be rated for the full flow of the system, for safety. Sometimes the relief does not fully seat.. and some of your oil pressure can be diverted to sump.. giving you less developed pressure and flow.

More than likely, there is damage to the pump and there is internal bypassing taking place now..

Hyd QD's betweent he pump and the relief are such a poor design idea.

Soundguy

Yes, sticky reliefs can and do happen. We have had a few problems with some in the past (poor design by our Supplier). On all of them, when they stick, you lose ALL function, not most. I have never seen any with a PARTIAL loss of function. I don't think there is any way to "split" the pressure (which is an over-simplification of what I am hearing from you)and make it up through flow. No pump on this size of a machine is capable of this in my estimation.

BTW.. get over to the "will it take off thread" It's a fun and completely theoretical discussion....

 

[Doc_Bob]

Can you measure the pressure in the system?
Bob

 

[Doc_Bob]

Marcus.. you can't just plug the gauge into the pump and fire the engine up.. it will blow the gauge out.

I asked about measuring pressure before I saw your post. Now, why would it blow out the gauge? Can't you just T into a line and measure?
Bob

 

[Soundguy]

The relief valve in my 8n hydro pump had some debri in it ( actual threads.. like from a hose or belt! ) The threads were holding the valve open, allowing the relief valve to always divert a small amount of oil . I didn't even try to clean it up.. I just dropped a new one in.. they were real cheap.. like 20-30$.. no need to dink with one for that price.

Soundguy

Yes, sticky reliefs can and do happen. We have had a few problems with some in the past (poor design by our Supplier). On all of them, when they stick, you lose ALL function, not most. I have never seen any with a PARTIAL loss of function. I don't think there is any way to "split" the pressure (which is an over-simplification of what I am hearing from you)and make it up through flow. No pump on this size of a machine is capable of this in my estimation.

BTW.. get over to the "will it take off thread" It's a fun and completely theoretical discussion....

 

[Soundguy]

I asked about measuring pressure before I saw your post. Now, why would it blow out the gauge? Can't you just T into a line and measure?
Bob

Yes, you can T a line and measure... What you can't do is screw the gauge into the out put port on the pump, with no relief in line.. etc.. ( it will deadhead the pump.. probably killing the gauge... )

Soundguy

 

[Soundguy]

BTW.. get over to the "will it take off thread" It's a fun and completely theoretical discussion....

My eng degree isn't in aerospace.. so I'm leaving that one well enough alone..

Soundguy

 

[MarcusCarr]

I did a few tests last night. Here are the results.

I pulled the pump and turned the shaft on the pump, it was easily turning gears inside the pump. No idea if that means anything.

I started the tractor for a few seconds to see if the place that the pump shaft connects to turns...it does...fast.

I put the pump back on and attached the high pressure line. Then, I attached the input line with a slight gap. I used the air compressor on the hydraulic fluid case until the air was out of the input line and the fluid was pouring out the loose connection. I tightened the connection. I was trying to prime the pump.

I then connected the 5000psi guage to one side of my auxillary valve that is used for the cylinder on my backblade. This way, I could push the valve handle and immediately let go if anything odd happened.

I started the tractor, 2000 RPM, and opened the valve to the guage...1000 psi. I raised the RPM to 2500 and opened the valve to the guage...1200 psi.

I closed the valve and moved to the loader, set the RPM back to 2000, tried to lift the loader, nothing. Set the RPM to 2500 and tried to lift the loader, very slow, smooth response.

Set the RPM back to 2000. Maybe the pump isn't primed. I applied 100psi of air to the hydraulic case through the breather tube. WOW! Full hydraulic speed on the bucket lift and tilt! Stopped applying air pressure...and back to the original problem statement. I cannot possibly imagine that 100psi of air could lift that bucket, so the air must have pressurized the case, which forced oil to the pump, which then pumped the oil.

If this holds true...then the pump is not able to create suction on it's own.

Does this indicate a bad pump?

 

[Soundguy]

Bad mounting gasket, or vacume leak on the suction side. Could be anything from a shaft seal, to a mating surface deformed, to a gasket... could be excessive clearance in the pump.. etc.

Soundguy

 

[MarcusCarr]

I am going to go ahead and purchase a new pump, gasket, and o-rings for the entire pump system.

I believe you are dead on with the clearance in the pump and the gaskets and o-rings are cheap, so i might as well replace them too.

Thank you for all your help as I worked through this. I will respond when it is up and running.

Marcus

 

[rback33]

I must say that was a good series of tests that found the answer. I would have never gotten that farm myself.

Hey soundguy... As I stated in the other thread, I don't have an engineering degree, but it's still fun to discuss. The impossibility of it all is what's great.