CAUTION Jinma 284 Hydraulic failure

[RonMar]

Caution! DO NOT USE the knob/valve in front of the seat to regulate 3PH raise/lower speed untill you have examined it throughly and checked that the saftey/bypass valve on the 3PH control valve opens at the correct pressure.

I was brushhogging blissfully along on my Mar05 production Jinma 284, turning jungle into pasture at a fantastic rate(4 hours worth of run time over 3 days), when on the 3rd day after about 1 1/5 hours of mowing I look down and discover that the loader valve is pissing hydraulic fluid onto my right boot. Dam! I cool the tractor down and take her back to the barn to discover that the oil is coming past the forward "O" ring of the left(lift) spool on the loader valve. I also notice some fluid has leaked around the auxilliary quickconnect(dump trailer?) fitting at the rear of the tractor. In my fact finding I also notice it is only an occasional drip from the loader valve unless I am lifting the three point hitch, then it is nearly a steady stream.

When I rigged the mower this time, I set the rate valve located just behind the gearshift, so the mower lowered at a reasonable rate. This was a tricky adjustment. If I went too far closed on the knob, the mower would not come down. With the mower stuck in the up position, I was unable to turn the knob to lower the mower deck and had to get a jack under it to take the pressure off the valve to allow me to turn it. The difference between being able to lower the impliment and it being stuck in the air is a fraction of a turn on my valve. I also noticed that it raised at a slower rate but I thought this OK since it now went up and down at about the same rate.

What was actually happening was that the control knob has a valve assembly on it that is supposed to act like a check valve. If you unscrew the knob(loosen the setscrew first) and remove the valve assembly, you will find a shaft with threads at the top, a O-ring in the middle and a tapered valve plug at the end. This tapered plug has a little travel up and down the shaft due to a pin that rides in a slot in the shaft. The pressurized fluid comes up from the bottom of the threaded hole that the shaft/knob screws into. It pushes up against the valve assembly, which is supposed to slide up the shaft and allow the fluid to easilly flow past and into the 3PH cylinder to raise it. When lowering, the fluid in the 3PH cylinder must pass between the tapers of the valve seat and the cone, which is now hanging down in the lower position. This restricts flow and slows the impliment down speed.
The tapered end of my valve assembly has very little travel and it restricts flow in both directions and I can easilly seat it against the bottom of the hole and completely stop the flow into the 3PH cylinder.
THIS can be bad!

The majority of fluid flow in this Jinma hydraulic system is through the 3PH control valve. In the lower/float position and the neutral position, the hydraulic inlet is connected back to the return resevoir. When in the lift position, the hydraulic pressure is sent to the 3PH cylinder and the rear quickconnect. If that control knob valve is seated firmly against the bottom valve seat, the pressure only goes to the rear quick connect. If nothing is connected to that rear quick connect(or your tractor dosn't have one), you have just deadheaded most of the hydraulic flow. The same symptom could also come from too much weight on the 3PH.

There are 2 small pressure relief valves on these tractors. One is on the flow divider valve near your right foot but it is connected off the steering circuit(to protect the steering valve and cylinder when you hit the steering limits or overload the steering). The other is in the 3PH control valve to protect the cylinder from excessive load on the hitch when the valve is in the lift position. My 3PH saftey valve was set WAY too high and was incapable of dealing with system flow with the raise/lower regulator knob was set to give good 3PH lift/lower speed.

THIS IS VERY BAD!

I plummed a 0-3000 PSI gauge to a male quick connect fitting and connected it to the rear aux quick connect on the tractor. With the rate control knob set where I had it while mowing, I saw 2500 PSI at 1500 RPM while lifting the mower and decided not to go any higher as it was raining hydraulic fluid under the loader valve again. While mowing, I was running at 2300 RPM in the green PTO range so it is a wonder that I only lost some loader valve O-rings and not the pump or blew a hose or fitting. With the knob opened up, I see less than 1000 PSI on the gauge at the same 1500 RPM while lifting the mower.

I do not think the cone assembly on my valve has enough vertical play, mine is about 1/32". Could someone unscrew their valve and measure the ammount of vertical travel the end cone has? I don't think it should limit flow INTO the 3PH cylinder when set to give a good lowering speed.

I disassembled the saftey valve on the 3PH control valve. I found the valve, a spring and 4 thick washers that were shimming the spring. I kept experimenting, removing washers untill they were all gone. Then I loosened the plug about 1 1/2 turns. untill I got the valve to flow enough fluid to keep the pressure below 2000 PSI at full RPM at the rear quick connection even with the regulating knob closed down all the way. The 3PH functions normally as it requires much less than this pressure to lift, even a heavy mower like mine. I am now looking into a lower rate spring to allow me to tighten the plug fully and use a shim to get proper relief pressure as designed.

I believe on tractors with this rear port option that the regulator knob/valve is designed to bottom out to force fluid to that rear aux port to operate a dump trailer cylinder or some other accessory without raising the 3PH. However, if nothing is connected to this port and the regulator valve is closed too far, the only thing protecting the system is the 3PH saftey valve. IF it isn't set right, something else is gonna give.

 

[greg_g]

Two things Ron; first, never adjust the flow control valve on a pressurized system. TPH implements, FEL and the like should be on the ground before you turn that valve. Set it, test the setting, and release the pressure again if any fine tuning is required.

Second, the lack of movement. It sounds like you've turned the set screw in too far. The only reason it's there to keep vibration from rotating the valve past its rotational limits. Too tight, it will impede valve rotation. Too loose, the valve may eventually pop out.

If you examine that valve body again, you'll see a groove - into which that set screw extends. The valve movement should be equal to the distance between the ends of that groove when the set screw is inserted to the correct depth. Remove the set screw while you're at it. I'm guessing you'll find the tapered end isn't tapered any more either.

//greg//

 

[RonMar]

Thanks for the reply Greg.
As for setting the flow control setting unpressurized, that is fine unless you have set it too far closed. On this particular design, The impliment rises but won't come back down. The impliment weight applys too much pressure to the back side of the tapered plug on the end of the regulating valve to be able to turn the valve. Oh and this was with the set screw completely removed. I had to jack up the impliment to relieve the pressure to open the regulating valve and be able to release the pressure and lower the impliment. The threads were dry and had some rust on them. Once I lubed them up, it could be turned with the impliment stuck in the air, but it is very difficult. It almost seems like the tapered plug needs a small weep hole to equalize pressure when the 3PH control valve is set to neutral. This would solve the hydraulically locked knob problem.

Actually the setscrew is not in the picture at this point. it is backed out far enough to not impede knob rotation. The question I had was how much travel does the tapered plug on the end of the valve assembly(approx 5/8" dia tapered plug with a pin driven through it at the opposite end from the plastic knob) have on others machines?

This tapered plug acts like an adjustable check valve. Fluid comming into lift the 3PH pushes the plug up out of the way and flows by easilly to lift the hitch. Once the hitch is up and fluid is no longer flowing into the 3PH cylinder, that tapered plug hangs back down at the end of it's shaft to restrict the flow out of the 3PH cylinder and restrict it's lowering speed. The problem I encountered is when set to give a good lowering speed, that plug on my valve dosn't have enough movement to act as a checkvalve when lifting and restricted the flow INTO the 3PH cylinder. When the saftey valve didn't lift at a reasonable pressure, the rest of the system was exposed to greater than 2500PSI while lifting the mower.

 

[greg_g]

I think the setscrew should be in the picture at this point. Without it, it's wholly possible for you to turn the valve body too far into the hole - which almost certainly will produce the symptoms you describe.

One of my JM254s had a flow control valve so badly rusted as to make it almost useless. But once removed/cleaned/replaced, it worked fine from that point on. This is how I discovered how easy it is to blunt the tip of the set screw. The technique that proved to work best was to turn the valve all the way closed, then insert the set screw only to the point where it barely touched the face of the valve body. Then back the valve body out while maintaining light pressure on the set screw. When the valve body rotates into the correct position, it will be reflected in reduced pressure on the set screw. At that point turn the set screw in till it once again touches the valve body - but this time it will be in the groove. For a final adjustment, I backed the set screw off one quarter turn. That permitted the valve to rotate between the limitations of the groove, while minimizing wear and tear on the set screw tip.

Having said all that, there's a chance you have a defective valve body - groove cut in the wrong location perhaps? Conical section too long?

//greg//

 

[RonMar]

Greg
When I said the screw was out of the picture, I was refering to the problem with the knob frozen with the 3PH holding the mower in the air. The screw was backed out far enough to not interfere with the rotation of the shaft.

The valve head on mine closes firmly against the valve seat with the setscrew adjusted as you described. I think this is normal as it must be able to be locked down to force fluid pressure to be sent to the rear auxilliary hydraulic quick connect. If it couldn't, the 3PH would just raise untill the linkage kicks the control valve back into neutral and you would never get any pressure back to the aux port. This would not allow a dump trailer cylinder or outher accessory connected to that port to function. On the newer LE's I have seen recently, there is also a male quick connect return line that feeds right back into the resovoir so you have a complete circuit to operate other accessories such as a log splitter or a hydraulic feed on a woodchipper(within the limits of the pump of course). I don't think the check valve/conical valve tip section of my 3PH regulator valve has enough travel so I was curious if others could take a measurement for me to see if mine is the norm.

My warning was also for others to check their relief pressure on the 3PH control valve saftey. Mine was so far out of wack that it caused damage elsewhere in the system.