Hi I have a cat 330b excavator that when the stick is operated in either direction, it carries on going until the full lock position even if the Controls are left alone. If the controls are then pushed in the opposite direction the function still carries on in that same original direction. The machine then has to be shut down and restarted. This occurs in both stick in and stick out. This happens after a few hours for about 10 min then rectifies itself for a few more hours. Thanks for any help.
You have a problem inside the stick cyl. Later Bob
Good day Rodderz Suggest you begin by check pilot pressure at the spool this will define if you have a pilot pressure issue or main circuit issue - work on and check that the spool is reacting correctly according to the pilot signal. If you need more information you can find it at excatech.com Kind regards Uffex
Sounds like a pilot problem or sticky stick spool. Try putting the safety lever down to lock out the pilot system while it's moving the stick on its own. If the stick stops you have a pilot valve problem. If the stick continues to move with the pilot lockout on then you are probably looking for a sticking stick spool in the main control valve. I hope I'm understanding you right that if you start moving the stick out it continues to go out and if you start moving it in it keeps moving in?
Ok the stick issue seems to have sorted it's self out. My next issue has started up on the left hand side of the control valve. The left track is very week. It only moves when you lift that side of the machine off the ground. The swing is also very week. I tried changing pump pipes around and signal lines to the pumps. That dosent seem to help as the right track works fine on both pumps. If I try left track and pull stick or boom, then the left track work which means it's getting pressure from the other side of the control valve via the stick or boom pipes as they have control spool 1 and 2 each.so this means the track motor and pilot control valves are all fine. The only thing I can think of is that somewhere in the left side control valve there is a contamination blockage in the signal gallery that sends the signal to load the pump once the spool moves.the pump is not being told to pump.? I have blown out the signal line from the left side control valve to the pump. And I removed the left track control valve spool and that slides fine. I see there is a small block bolted on the side called a pressure control valve? What is its function ? Thank you.
I believe you have a large piece of debris floating around in the hyd system. First jamming the stick spool open and now minimizing the travel of the LH travel spool. To verify this hook a gauge up to the two NFC lines going to the pumps. Pressure should fall from 500 PSI to 100 PSI when the circuit is fully in. Later Bob
Have you checked the seals for the travel motor lines at the swivel?
Hi Bob I hooked a gauge up to the nfc lines. There is no fall in pressure on the left side which is the side hassling. So this means the pump is not being told to pump. I have checked the negative flow control relief valve. Is there anything else on that side of the control valve that could be supplying pressure and not allowing the nfc port/line to drop in pressure. ?
Yes there is a slow return check valve in the same housing as the cooler bypass valve. It adds a slight back pressure on the return of one pump to provide a head of pressure for the swing anticavitation valve. The check valve's housing/spider has likely backed out and preventing the valve from opening. This restriction is likely building the NFC pressure not the NFC valves. The NFC pressure can't fall since the valve exhausts into the oil flow that the slow return valve is restricting and causing pressure to build. Confusing but hope you can follow. Later Bob
Hi Bob Iv checked the slow return and the cooler bypass. All seems fine. If they were causing a restriction would it not affect both pumps? As the return for the right side valve is a hose that goes around to the left side valve and feeds in just above the slow return check valve housing. The right side with its pump seems fine. It's just the left side that is not dropping the pressure for the nfc on its pump. Anything else you suggest ? Last resort would be to pull the whole control valve out and go through it. Many thanks for your input.
Okay, with all that checked out something is either not cutting off the center flow when moving a spool or the NFC valve is not opening up and letting oil away. I forget which side the slow return affects but I think it's the side of the valve the swing is on, it's to feed the swing motor through the make up valves when the control levers are let go and the motor is coasting. You are sure the slow return was not backing out aren't you? Later Bob
One more thing, if the NFC hoses run through a block with one or two solinoids on it they can raise NFC pressure to slow pump flow for attachments. Unplug them and see. Later Bob
There are no solenoids the nfc lines run through for attachments. They go direct to the pumps from the valve body's. I stripped and re assembled the slow return valve so I'm positive it's ok. Is it possible maybe the anti cavitation on the swing motor is back feeding into the return causing the pressure on the return passages. ? If this was the case would it not affect the right side as the return from both sides of control valve go through the slow return valve ? The only other thing I can think of is that a piece of debris may have scored the bore or spool on one of the 4 spools on that side, allowing constant pressure to the nfc relief valve. Cheers. ,
Pull the NFC valve out of that side and check for debris before it as well as in it. I have seen them full of metal slivers. There wouldn't be much oil coming out of the check valves in the swing motor to cause this problem. Later Bob
Check your pattern change valve if it hasn't creeped over had a very similar fault today lock bolt came out and it start to creep
Solved the problem. On the stick control valve spool there is a check valve that goes between the valve body and the loop pipe which joins the 2 stick control valves. That valve had completely destroyed itself somehow. Changed that out and problem gone. Pressure was obviously being back fed by the other pump. Thanks for all the helps. Cheers.
Sorry what is and where is the pattern change valve ?
Thanks for the feedback, pattern changer is a square block with a lever that turns a core valve inside. Two positions 90 deg apart locked with a bolt. Should be behind the cab with pilot lines to the joysticks (boom and stick) running through it. About 2 1/2" square by 3" long. Later Bob
rodderz Thanks for the feedback on what solved your problem. This may be of help to others someday. Many times a poster disappears after the problem is solved, and the rest of us do not find out what fixed it. Best of luck to you