Cat 924G hydraulic problem

[Cmark]

Okay. So if we suspect low power all round, the signal limiter could be a problem. It basicaly takes the resolved signal oil from either valve and limits it to a certain pressure.

View attachment 9SW.pdf

Item 11 on the graphic.

Lee. What format are you using to upload attachments from SIS? .PDFs don't do a great job.

 

[Per Eriksson]

Use the "print format" in SIS and then print using a pdf printer like bullzip, it makes a pdf looking just like when you browse in SIS and scales nicely too.

It would be intersting to see what the LS signal does when operating the lift and then lift and tilt combined.

 

[Lee-online]

The reason I was thinking SL was because if it was weak and dumping the signal then lifting with a full bucket would have the most load and would be the first noticed. Other functions may not be effected unless they go into a stall.

Without checking pressures, it is just trial and error. That takes time and can get expensive.

I save the pics, then use MS paint, resize and change to Jpeg.

 

[MGW]

Ok guys, where is the port for the SL so I can get some pressure readings for you?

Many thanks,
Marv

 

[maytag]

terms mobile vs heavy industrial

I've been following this thread with a little interest, looking to learn from the mobile world of hydraulics-the terms "resolver" and "signal limiter" are foreign to me.
Looking at the valve body and following the thread I think a resolver would be a "shuttle valve" and a signal limiter would be a "pressure compensator" that runs in parallel with a load sense control on a variable displacement pump.
Can someone clarify?

TIA
Tom

 

[Cmark]

I've been following this thread with a little interest, looking to learn from the mobile world of hydraulics-the terms "resolver" and "signal limiter" are foreign to me.
Looking at the valve body and following the thread I think a resolver would be a "shuttle valve" and a signal limiter would be a "pressure compensator" that runs in parallel with a load sense control on a variable displacement pump.
Can someone clarify?

TIA
Tom

I think that sometimes Caterpillar designers make their own names up for components, to suit the applicatin that they're in. Because these made up names then go in to the service literature which lots of people read and are trained by, they become part of everyday language for heavy equipment mechanics.

In caterpillar land, a resolver will receive two different pressures and deliver the higher pressure, (a logical "OR", if you like). In this case it's the signal (load sensing pressure) to the pump compensator valve which controls the swashplate angle. The signal limiter is just a pressure relief valve in this signal line, but,

"hey, boss, seeing as how it's job is to limit the pressure in the signal line, why not call it a "signal limiter"?"

"Yup, looks good to me. go for it!"

HOWEVER,

Marv, it looks like your machine doesn't have a signal limiter. I gave you the wrong graphic in post #21. The schematic with a signal limiter starts at serial #2026. I think you'll find just one valve in the end manifold of the bank-valve. This is a flow control valve which allows the signal pressure to drain to tank when the controls are returned to neutral. This could potentially be causing your problem.

The pressure tap for the signal line is on the pump compensator valve, which is bolted to the top of the pump. Attach a 5000psi gauge and compare what you get with bucket tilt and lift. The pressure tap on the bank-valve manifold is for pump pressure, if you want to take a look at that as well.

 

[Nige]

"Resolver" my ass ................... it's a double check valve ..............!!!!

 

[maytag]

mobile vs industrial

I'll admit I'm not the most computer proficient but the adding attachments is a daunting task-anyway maybe I got it resized and attached. This is a typical industrial print of 2 circuits with load sense control for the pump. Items 23 and 24 are shuttle valves (your resolvers/double check valves)- shuttle valve 24 insures that the pump will see the highest pressure if the two circuits are operated at the same time. Variable dispalcement Parker piston pump, the load sense line feeds the load sense control with the pressure compensator (maybe your signal limiter)in parrallel.
BTW items 23 are stacked under the DCV and 24 is threaded and tied into pilot lines.

Tom

 

[MGW]

Figured I would give you an update on this machine.

I installed two new resolvers and nothing has changed. I installed a pressure gauge into the tap for main pump pressure, and am seeing the pressure max out at about 1500 psi when activating only one function. When activating 2 functions at once, I'm seeing about 2200 psi. I guess there is no signal limiter, but there is that little valve at the top of the main bank to bleed off signal pressure when no function is activated. Is it more likely to be in the pump compensator itself? Is it possible that the margin spring in the compensator has weakened slightly and that the margin pressure is too low? I'm thinking if the margin is too low there will not be enough signal pressure to upstroke the pump??? Not sure why it's picking 1500 or 2200 to cut off though. Maybe there is enough internal leakage in that compensator spool to become an issue at those points.

Ideas welcome!

Thanks,
Marv

 

[Cmark]

If your pump/compensator is capable of making pressure with two functions, it should be able to make it with one. I would say it's unlikely to be your problem.

You really need to check the signal pressure instead of the pump pressure. Now you've changed the resolvers, If you have low signal pressure then the flow control valve mentioned earlier is (as far as I can make out) is the only other component which can be at fault.

 

[MGW]

You're probably right Cmark. It might be easier if I had a gauge on both signal and main pressure at the same time, since it's kind of a chicken vs egg situation. If the main pressure is holding steady at 1500 with one function activated, then I think I couldn't see any more than 1500 signal pressure at that moment, according to the schematic. I can't quite grasp how just watching signal pressure alone can lead one to the problem. On a normally functioning system, if I dead-end a function, would one expect to see both signal and main pressure come up to the high pressure cut-off point of 3600 or so? With my current situation, what would you expect the signal pressure to be at when the main pressure is stalled at 1500?

Thanks again,
Marv

 

[Per Eriksson]

signal pressure + margin pressure (300psi) = pump pressure.

Did you have the sectioned or one piece valve on it? apparantly there was a retrofit program to install new type of valve on older machines.

I've had a similar issue on a 950H, couldn't lift for **** but just touch the tilt and the bucket went for the moon, the bore for the compensator spool in the tilt section was worn just enough to let signal pressure leak by, hard to spot with the valve installed in the machine but it was easy to see when it was pulled and looked at on the bench with good lighting.

 

[Nwufor]

hello everyone. I've read all through but i still can't get it. my 924G has a lifting failure , the controllers are acting void.

 

[Caincon]

I know this post is 15 years old. My machine is having almost exact same symptoms . Any fixes ?