jinma HW-03 backhoe filter

[Ronmar]

I added a 10 micron filter assembly to the return line of my backhoe. This is the most basic of Jinma backhoes that uses it's own bolt on hydraulic pump and 5+ gallon resovoir as it is easy to access an unrestricted return path to the reservoir which is a requirement for a return line filter installation. I chose the 7GPM Zinga filter assembly available from surplus center as it is inexpensive, small and will meet the flow of the 5.5 GPM backhoe pump. The filter was small enough that it will fit inside the control console below the valve assembly. The front cover plate will go back in place over the filter. No protruding parts so it is well protected and you don't even know it is there unless you remove the cover. Total cost of mod was about $35 with all the fittings and some welding was required.



I initially thought this was going to be a simple mod, just cut the return line and plumb in the filter using some elbows and hose barbs. There was enough slack in the existing line to accommodate the filter. Unfortunately The backhoe manufacturer didn't chose a traditionally larger return line. It appears that they used an off the shelf high pressure line with a banjo fitting on the end that could be easily interfaced to the reservoir return port. This return line is 10MM or around 3/8", but the actual hole into the banjo fitting at the end right before the tank was barely 1/4" across. This restriction led to pressure spikes in the filter when I just spliced it into the middle of the stock return hose. After the first half hour of operation with the filter, I blew out the "O" ring seal on the filter cartridge and also destroyed the movement on the gauge I had installed immediately upstream from the filter.

My fix for this was to completely replace the downstream half of the return line from filter back to reservoir. I welded a 1/2 Female to 3/8 male NPT street elbow to the boss where the banjo fitting used to be bolted. To this I attached some 1/2" oil compatible hose and ran it to the filter outlet to a 3/8-1/2" 90 degree hose barb. I clamped it on both ends with hose clamps. I now read about 5PSI of back pressure when warm and spikes are virtually non existent with only a slight twitch of the needle when I vigorously work the controls. I replaced the gauge with a bicycle schrader valve as i didn't want to cut a hole in that side of hte panel or have a gauge exposed. Come maintenance time, I can remove the panel and check the backpressure with a small gauge and a air chuck fitting attached(tire gauge).



I also believe the original high velocity flow returning to the reservoir thru the stock return line was agitating and aerating the fluid in the reservoir. Kind of like shooting a straight stream garden hose nozzle into a bucket of water. You can never quite fill the bucket this way because of the boiling air bubles carrying water over the side. This high velocity stream was shooting right across the reservoir toward the suction strainer and rolling this entrapped air right down on top of the suction strainer. In the first few hours I operated my backhoe before starting this mod, I noticed the pump made a little bit of squealing noise when under load. Since the modification, it is absolutely quiet under load, just like the main pump on the engine is when operating the loader.

Ron

[3RRL]

Very interesting Ron,
I like how you figured the high pressure jet perhaps sawing through something and also replacing the return line with a much larger diameter as is commonly done.
I have always wondered about putting a 10 micron filter on the return side. I was afraid it would blow up? I'd actually like to add one to my Kama.
What do you think?
Rob-

[Ronmar]

The return line back to the reservoir MUST be a low pressure path(no valves downstream between filter and reservoir). IF you have a unrestricted return line to the reservoir, blowing up the filter shouldn't be a problem. Most cartrige filters are rated between 100 and 200 PSI. This little 3/8" one is rated at 200 PSI, and the 3/4" 20GPM that they sell at Surplus center is rated to 100 PSI The bypass in the filter should allow fluid around the filter long before there is any problem, provided the filter assembly is rated for the flow and the line downstream of the filter is an unobstructed path(which is what initially caused me problems).

The importer who I bought my backhoe from said the only problem they had had with these things was from crap in the valves... That was why this filter was my first mod for the BH.

As for adding a return filter, I would say go for it, you just need to pick a low pressure point where the filter can be added to flter the oil right before it goes into the reservoir.

On my jinma, the main hydraulic flow goes to the 3PH control valve bolted to the side of the reservoir and directly back into the tank wall with no way to access it after the valve. That is why I made up the maintenance filter I just posted about. It was the easiest way to access the main flow to pass it thru a filter before returning it to the reservoir. When I am using it, the only fluid it isn't filtering is that passing thru the steering system while I am turning the steering wheel. I need to modify it so I can use it with the backhoe on as with the BH in place, it won't fit as pictured. With it not on the system, I am missing a lot of potential filtering while I am using the backhoe and not the 3PH

Ron

[GuglioLS]

Ron,
Nice addition to your hoe. If at all possible I agree that a 10 micron return filter is superior to a 140 micron suction strainer.


The return line back to the reservoir should be a low pressure path, so blowing up the filter shouldn't be a problem.

One word of caution about doing that is the "return" line is actually the Pressure input for the TPH hydraulics and does become pressurized when lifting a heavy load with the TPH.

Rob - lift something heavy with the TPH and watch your pressure gauge. I think you will find it will pressurize way above 1000 psi.
That's why our tractors do not have return filters. they would most likely blow up sooner or later by the back pressure from use of the TPH.

Larry

[Ronmar]

gugliols said:

One word of caution about doing that is the "return" line is actually the Pressure input for the TPH hydraulics and does become pressurized when lifting a heavy load with the TPH.

Rob - lift something heavy with the TPH and watch your pressure gauge. I think you will find it will pressurize way above 1000 psi.
That's why our tractors do not have return filters. they would most likely blow up sooner or later by the back pressure from use of the TPH.

Larry

Larry
I guess I should have worded that differently and used the word "Must" instead of "Should". Just for clarification, ANY filter installation MUST have a low restriction path back to the reservoir. I did some editing above so there is no confusion by anyone else who reads this, Thanks.

Rob I didnt consider the possibility that your backhoe is fed from the tractor hydraulics. If you have a backhoe that is fed by the tractor hydraulics, and the output of the backhoe back to the tractor feeds to the 3PH valve, then the appropriate place for the filter would be AFTER the last valve(3PH) in the system, if you can access that point. That is probably the reason why most of these tractors don't have return line filters as the valve dumps directly back into the reservoir.

I probably confused things by talking about this tractor maintenance filter chinesetractor.proboards66.com/index.cgi?board=hydraulics&action=display&thread=1201836533
in this backhoe thread. On the Jinma 284, There is no way to access the main flow downstream of the 3PH valve(low pressure side) to install a permanent filter. The return port out of the 3PH valve is covered by the valve body itself, as it is on most tractors, where the valve is bolted to the reservoir.

By using the auxiliary pressure outlet on my 284 to feed the Maintenance filter, I am downstream of the 3PH valve. The outlet of the filter is connected to a port that flows unrestricted back into the reservoir. The only way to damage the filter would be to remove the QC connecting the filter outlet back to the reservoir which would deadhead the flow into the filter and cause it to rupture. I tywrap that QC when I am using this filter.

The flow I am feeding that filter with is the fluid that would normally go to lifting the 3PH. With the filter in place, the 3PH will not lift as it can't build any pressure because the flow has a low restriction path thru the filter and back to the reservoir.

On the Backhoe, and this is a backhoe with it's own pump and 5+ gallon reservoir, the filter has a 1/2" hose(red hose) on it's outlet directly back into the reservoir.

Ron