wheel loader lift high speed only

[maxpax]

So, i went bananas with the chinese machine and tried some more with the lift/tilt. With the tilt I can fether but the range with the lever is very tight although the lever itself moves a lot before reaching the fethering spot so to speak. The "lift" is a bit worse, I move the lever, more, more, more, and next thing it starts hissing and the next thing it takes off. I can find a spot where it moves little but it is raising in steps, not slowly and controlled.

Maybe I can take the valve apart and change springs or something? And, does anyone know what the screw in the last picture is for?

 

[bigdeano]

The black hex adjustment at the bottom of the valve must be for the pressure relief.

Possibly the valve could be made to meter smoothly by machining just the right place on the spool. It's a matter of the grooves on the spool lining up with the ports in the valve casting at just the right place. It could easily ruin the valve if not done correctly though.

 

[jb1390]

Hi.

I am close to buying a chinese changlin zlm15b from around 2008. The loader on it is a bit annoying when lifting, it's not possible to lift slowly by pulling the lever a little bit, pulling it and coming 'bout half way suddenly it jerks up in high speed. Same with raising the tilt. However, when lowering the loader (and/or tilt) it's perfectly controllable and possible to lower slowly och fast by choice. Everything else in the hydraulics works good.

So, the question for people who are experienced with hydraulics is what comes to mind first? I have just started to learn about hydraulics and my thought would be maybe a wrongly mounted flow control valve or something. Any ideas on how to achieve a controlled lifting motion?

/MaxPax

In all open-center hydraulic systems, there is a check valve that prevents loader drop when the valve is partially opened. There is no check valve when lowering. So, when lowering you gently crack the valve, and oil is allowed to slowly seep out and loader movement is easy to control.

When lifting, there is already residual pressure in the lines and cylinders from holding the weight of the loader. Since it is an open center system, the pump circuit has essentially 0 psi. Without the check valve, as soon as you open a port the loader would drop until you continue to open the valve and force the oil flow from the pump to build pressure and lift the loader. Don't bother reversing the lines as it won't work correctly without that check valve.

Essentially when feathering the valve, you are trying to get the pump pressure to match the residual pressure in the loader, at which point it will start to move. That point on the loader valve is different depending on where the loader is in its travel, and how much weight you have in it. Some valves make it easier to control than others, but all open center systems are subject to this kind of limitation. This is a large part of the reason why closed center systems are used on larger machines. You can apply full pressure very slowly with closed center systems pretty easily. It's a hard thing to do on open center setups.

Ensure you don't have any binding or worn linkages, as that will make it more difficult - but you won't ever get this problem to go away completely with an open center hydraulic system.

 

[maxpax]

Wow thanks for the informative answers!

So, could it be rebuilt to a closed center system easily? Like changing the directional valves etc. or would it be a too big project to be justified on a $6000 machine?

 

[jb1390]

Wow thanks for the informative answers!

So, could it be rebuilt to a closed center system easily? Like changing the directional valves etc. or would it be a too big project to be justified on a $6000 machine?

Nope. Closed center pumps are a completely different setup. Variable displacement, but constant pressure. More costly, which is why they aren't used on smaller machines. They are nice to use though.

Best thing to do is ensure the linkages are clean, lubricated, and tight. There's also a possibility that the controls don't allow enough of a "throw", which would make it more difficult to find that middle ground. Some modification in the linkage adjustment might help that, but I doubt it's worth the hassle. Operationally, when I need to feather something gently off the tip of a fork or the bucket, I will use the curl function instead of up/down. Generally it's easier to feather.

 

[maxpax]

Ok thanks a bunch. Guess my machine have a gear pump then and a closed-center usually have a piston pump with swash plate and such.

Trying around with it today I think I can live with this and just learn to handle the levers.

 

[Tx Jim]

maxpax
You could install an adjustable flow control valve in boom hose circuit. I did just yrs back that on a Kubota frt end loader for handling large rd bales.

 

[GLyford]

I also did that on a homemade loader on a garden tractor. Made a big difference in how much control I had of the machine.

 

[maxpax]

Thanks for that tip, I think I will do that. Seems simple enough.

 

[maxpax]

Update on this old thread then.

I acquired a brand new valve pack, it had been sitting on a shelf for about ten years but very high quality (nimco) and very cheap b/c the owner wanted to get rid of it.

The connections on the bulky chinese pack is M27/2 thread, not very common so I cut and welded 1/2" BSP's, put it together an violà!

It's fethering perfectly now! Super precision, and since the new pack had three sections I put 2 new hoses in with a couple of 6/2-valves and put a cylinder on the attachment mechanism so now I jave 3rd & 4th function plus hydraulic tool change without having to go out of the machine (if no extra functions are used anyway)

So satisfied with this. Happy!!