LW-6 pressure relief valve

[jezorek]

Ron,

Thank you for you your excellent explaination. I purchased this Jinma LW-6 from a vendor on Ebay who has been totally unresponsive to my questions. I looked through the user manual that came with the machine but it has absolutely no useful information let alone a maximum working pressure.
Perhaps one of the forum members might know what the max operating pressure is. Anyone?
One further point about the squeeling. I still don't understand why the valve block pressure relief valve would relieve at 1500 psi and at 2100 psi after I adjusted the Prince valve. Shouldn't it have continued to release at 1500 psi?

 

[dfkrug]

Ron,

Thank you for you your excellent explaination. I purchased this Jinma LW-6 from a vendor on Ebay who has been totally unresponsive to my questions. I looked through the user manual that came with the machine but it has absolutely no useful information let alone a maximum working pressure.
Perhaps one of the forum members might know what the max operating pressure is. Anyone?
One further point about the squeeling. I still don't understand why the valve block pressure relief valve would relieve at 1500 psi and at 2100 psi after I adjusted the Prince valve. Shouldn't it have continued to release at 1500 psi?

If changing the relief valve setting on the Prince changes the system
pressure seen at the guage, it is set at lower relief pressure than the
main relief on the left lower side of your LW-6 control vlave stack. The
noise you hear on the latter may not actually be the stack's main
relief. Also.....I can not tell from your pix (they are so big, I only looked
at 2 of them) if you have additional "shock relief" valves on one or
more of your individual valves. Have you opened the relief valve on the
stack yet?

Squealing can also be caused by air in the system due to not enough
hyd fluid or cylinders have not yet been purged.

As for what is recommended max press for the Chinese hoes, I wonder
about that myself. If it is recommended to be say 1500psi, then that
says a lot about how weakly-built its structure is.

 

[jezorek]

dfkrug,

What would the shock valves look like? All of the spool valves look the same to me so if one has a shock valve they all do. If you look at the last picture this shows the return line from the stack and you can just see some detail of the last spool valve.
The resivoir is full and I think that I have enough time on the hoe so that the air should have been purged. Is there a procedure other than cycling the cylinders to purge them?
I have not yet attempted to adjust the relief valve on the stack. Since it would seem that the Prince relief valve is the one relieving and is rated at twice the the PTO pump volume do you think it is worth messing with?
Regarding your comment about quality- I am not sure that the words quality and LW-6 backhoes should be used in the same sentence. This unit reminds of some of the stuff that came out of Taiwan in the early 70's

 

[RonMar]

Ron, One further point about the squeeling. I still don't understand why the valve block pressure relief valve would relieve at 1500 psi and at 2100 psi after I adjusted the Prince valve. Shouldn't it have continued to release at 1500 psi?

The main block relief was not relieving... The prince relief was opening at 1500 and the pressure at the main valve block inlet was never getting above 1500 so the relief located there was never opening.

The relief valve consists of a plunger covering a hole in the high pressure line. This plunger is held in place by a spring. The ammount of compression of the spring determines the ammount of fluid pressure in the HP line required to lift it off the hole and vent fluid/pressure from the HP line. Kind of like holding your finger over a hole in a garden hose. The harder you hold your finger on the hole, the higher the pressure in the hose can get. With the flow control having a safety, you have 2 of these in the system and if one is open at 1500, and the other is set at a higher pressure(2100?) the other was never reaching it's release pressure.

The china best website specs the same hydraulic pressure for all the LW series backhoes.
Valve standard pressure (MPa/psi) 16/2320
hydraulic input(L/m or GPM) 28/7

With that main relief lifting at what appears to be 2100 PSI, based on these specs, I would not adjust that valve as it appears to be pretty close to what the LW specs say is proper. I would adjust the relief on the prince valve back down till you just start to see a drop in pressure from that 2100 you mentioned earlier and lock the adjuster at that point.

 

[dfkrug]

What would the shock valves look like? All of the spool valves look the same to me so if one has a shock valve they all do. If you look at the last picture this shows the return line from the stack and you can just see some detail of the last spool valve.
The resivoir is full and I think that I have enough time on the hoe so that the air should have been purged. Is there a procedure other than cycling the cylinders to purge them?
I have not yet attempted to adjust the relief valve on the stack. Since it would seem that the Prince relief valve is the one relieving and is rated at twice the the PTO pump volume do you think it is worth messing with?
Regarding your comment about quality- I am not sure that the words quality and LW-6 backhoes should be used in the same sentence. This unit reminds of some of the stuff that came out of Taiwan in the early 70's

The shock valves on my Prairie Dog hoe look like extensions on the back
of each valve. If each spool looks the same, you do not have them.
If you have cycled your hoe's cylinders numerous times, they should
be purged of air, assuming plenty of fluid. I know I can get my Kioti's
main relief to squeal using my hoe when I am on unlevel ground or fluid
gets low. I set my hoe relief at near the same press as tractor's (2500).

A high-volume pump can cause back-pressure thru narrow orifices, as
noted by Ronmar. If squealing happens when running the pump slower,
then it is unlikely that a relief valve on the hoe, set higher than the
Prince's is making the noise. Why not remove the hoe's relief valve and
see if it is put together properly? There may be broken or missing parts.
Your description DOES sound like a relief valve, so I am puzzled, too.

I have seen the LW-7 hoes offered for as little as $1800. I have not
seen one in person. I think the Chinese are going to make a much
better unit as they ride the learning curve.

 

[tat2z1969]

If your pump can handle it the LW BH's are or should be set at 2250 psi. The seperate relief valve for left and right swing is set: tighten the screw and back off 1/2 turn.Those are single acting cylinders and you can't get pressure up to main pressure setting, They do not want anyone to flip a tractor over using the side swing wrong.
The relief valve on the LW's will moan or squeal or buzz depending how well Hop Sing finished the valve plunger face, no big deal.
A word of caution, if you use a after market pump like say a Koyker type pump(webster) they are only good for 2000 psi and at 2250 set pressure in cold weather you will blow the side out of the pump.

if in doubt about the pump pressure rating set the relief valve for 2000 psi

 

[Stimw]

I have the YW-6 backhoe and I see nothing wrong with the quality or the design. The Chineese tractors that I looked at were crude and simple but the hoe is solid and I would not hesitate to buy another one. The subframe was too light but I had to modify it anyway to fit my Branson.
I worked on Semi's for 30 years (suppervised 3 shops) and now have my own business selling and repairing construction equipment, I'm a dealer for 3 lines. I know a little bit about equipment.
If you can find a Jinma hoe for $1800. you better jump on it!