Hydraulic Oil Filter... Why?

[BigJohn]

Pick your farm equipment, any equipment and answer this question....

Why is a filter necessary for a hydraulic system?

Say a guy has a front end loader on his tractor and there are only four hydraulic cylinders. The fluid runs from the tank to the pump to the controls to the cylinders and back to the tank. Where in that system is a filter necessary? No combustion.... no gears, no valves, no rods, no crank shafts..... nothing like that to create wear metals to filter out.

Why? Just curious???

 

[ctechbob]

The pump probably creates small amounts of metal over time. Plus you get a little dirt past the seals.

 

[DemoFly]

This should help you visualize.

 

[Chris142]

Huh? A hydraulic pump makes lots of pressure and 1 spec of whatever will cause damage to the pump. A used hydraulic filter will be plugged full of junk.

 

[4WD]

Huh? A hydraulic pump makes lots of pressure and 1 spec of whatever will cause damage to the pump. A used hydraulic filter will be plugged full of junk.

Indeed - seen major systems down over dirty HF - then you bring in a portable filtering system to get it back clean again …
When a pump fails - metal invades and things cascade quickly

 

[dlundblad]

Wear metals, left over metals from manufacturing, and contaminants from the atmosphere.

 

[DriveHard]

@BigJohn
Former Hydraulics engineer and hydraulic system designer...

Several good answers here, pumps (especially gear pumps) do make some contamination. There is some left over from machining, that is also correct. There are some wear metals in the "clean" oil added to the system. The hoses are a pretty big contributor both when they are first put on dirty, and as they slowly erode due to fluid flow. But...THE MOST MAJOR source of contamination was right there in your statement...

"controls to the cylinders"

Those cylinders are exposed to dust, buried in water, shoved into the dirt, etc. The seals on those cylinders are not perfect. Cylinders are the #1 contributor to system contamination. Clearances in low leak valves and axial piston pumps range in the 5-30 micron range...these are precision machined components. ANY contamination can cause wear and damage.

 

[Urshurak776]

I spent 23 years in the US Navy Submarines changing out Hydraulic oil filters . Never found a spec of anything and samples always came back awesome. Often wondered how necessary the frequency was that we did it. Some of them were a MESSY job and everyone hated it.....

 

[KGMtech]

I spent 23 years in the US Navy Submarines changing out Hydraulic oil filters . Never found a spec of anything and samples always came back awesome. Often wondered how necessary the frequency was that we did it. Some of them were a MESSY job and everyone hated it.....

However the salesman for those filters put all his kids through college and retired to Boca, so there's that.

 

[Chris142]

@BigJohn
Former Hydraulics engineer and hydraulic system designer...

Several good answers here, pumps (especially gear pumps) do make some contamination. There is some left over from machining, that is also correct. There are some wear metals in the "clean" oil added to the system. The hoses are a pretty big contributor both when they are first put on dirty, and as they slowly erode due to fluid flow. But...THE MOST MAJOR source of contamination was right there in your statement...

"controls to the cylinders"

Those cylinders are exposed to dust, buried in water, shoved into the dirt, etc. The seals on those cylinders are not perfect. Cylinders are the #1 contributor to system contamination. Clearances in low leak valves and axial piston pumps range in the 5-30 micron range...these are precision machined components. ANY contamination can cause wear and damage.

plus a piece of equipment blows a hose out at a job site. The new hose is dragged through the dirt by the crew while installing it. Then they fill the system with a funnel thats been riding around in the bed of bobs truck without even wiping it out.

 

[BigJohn]

All good answers..... Thank you.


......

 

[4WD]

I spent 23 years in the US Navy Submarines changing out Hydraulic oil filters . Never found a spec of anything and samples always came back awesome. Often wondered how necessary the frequency was that we did it. Some of them were a MESSY job and everyone hated it.....

I saw a D9 working today where it had not rained in 2 weeks - prolly a bit dusty by comparison …

 

[burbguy82]

no gears, no valves,

There are definitely valves. Complex ones. I change my pilot filter on my Kubota excavator every 100 hours, cheap insurance. It is what filters the fluid that gives the controls their control over which way the arm goes.

 

[RooflessVW]

nothing like that to create wear metals to filter out.

 

[BigJohn]

I baited all of you into a conversation, where I wanted your opinion without bias... Now here is my situation, and if I would have started with this... bias would have run wild.

I just purchased a mini-excavator..... yep, of the Chinese variety. Yep, at the $5,000 amount or so.

It did not come with a hydraulic filter.

Since I started this thread, I have learned that I can probably add a full filter setup for about $100-$120.

What you have convinced me of is.... I absolutely need to add the filter.

Thank you.


.........

 

[dlundblad]

I baited all of you into a conversation, where I wanted your opinion without bias... Now here is my situation, and if I would have started with this... bias would have run wild.

I just purchased a mini-excavator..... yep, of the Chinese variety. Yep, at the $5,000 amount or so.

It did not come with a hydraulic filter.

Since I started this thread, I have learned that I can probably add a full filter setup for about $100-$120.

What you have convinced me of is.... I absolutely need to add the filter.

Thank you.


.........

I’ve read these can run very hot. Have you had any issues with this? What kind of engine does it have?

Good idea adding a filter. A log splitter, which is the most basic setup ran in somewhat clean conditions, has a filter. Perhaps you can add a cooler in the return too?

 

[burbguy82]

I baited all of you into a conversation, where I wanted your opinion without bias... Now here is my situation, and if I would have started with this... bias would have run wild.

I just purchased a mini-excavator..... yep, of the Chinese variety. Yep, at the $5,000 amount or so.

It did not come with a hydraulic filter.

Since I started this thread, I have learned that I can probably add a full filter setup for about $100-$120.

What you have convinced me of is.... I absolutely need to add the filter.

Thank you.


.........

Is there no filter on the suction side in the tank? Should be near the bottom of the tank?

 

[Chris142]

I saw a D9 working today where it had not rained in 2 weeks - prolly a bit dusty by comparison …

2weeks? Oh the horror! Here its doesn't rain for months/ year. lol

 

[Astro14]

Is there no filter on the suction side in the tank? Should be near the bottom of the tank?

I would think a filter belongs in the return line. Dust/debris/etc. are created in the system, and this catches it before the reservoir, where system pressure is lowest, but it still positive pressure. A filter in the suction line would inhibit the pump drawing fluid in. A filter on the output side of the pump would have to deal with very high pressure.

So, return line.

 

[DriveHard]

I would think a filter belongs in the return line. Dust/debris/etc. are created in the system, and this catches it before the reservoir, where system pressure is lowest, but it still positive pressure. A filter in the suction line would inhibit the pump drawing fluid in. A filter on the output side of the pump would have to deal with very high pressure.

So, return line.

@BigJohn

Astro is right on this one, but there is more to it than just popping an in-line filter on the return line. You need to take a look at the schematic. Often times the pumps and motors will have a case drain back to tank. This relieves the oil in the cases of the pumps or motors back to tank at a low pressure. The cases aren't made to take pressure. Any back pressure on the return line for those can pop shaft seals, or even crack cases. You will also need to add a filter bypass to allow COLD oil to bypass the filter, or oil to bypass when the filter loads up. Excess back pressure is not only wasteful in terms of energy, but also can effect performance and increase wear on the system. If you add too much back pressure on your pilot lines you can also effect the joysticks (I doubt this is an electrohydraulic machine at this price point) Ideally you filter the return oil from the main control valve, and that is enough. You might also think about adding a cooler as well...same thoughts apply.

If you can find a schematic, I would be happy to take a look.