Calling all CAT gurus, I need your help. Which relief on a CAT 312CL s/n CBT00342 adjusts the pilot pressure? I have a schematic that I cannot see clearly enough to decipher and I was hoping someone here has adjusted it previously and could direct me as to which relief it is and what section of the valve. Your help would be greatly appreciated!
It's the relief valve built into the pilot filter head. Pressure should be 4100kPa+-200 with the oil at 55C, engine speed control at 10.
Thanks for the reply. Would that be a system wide pressure adjustment? I was looking to increase the pilot pressure for the travel circuit. There is not enough pressure to shift the travel motor into high speed on both sides. We need to increase the pressure 250psi in order for it to be within the proper specs.
Yes, that is for all of the pilotsystem.
So what exactly is the problem? Reading between the lines, do you have one motor that won't shift into high? Where are you currently reading pilot pressure to know that you are 250psi low?
I am a distributor the brand of travel motor in this machine and the pressure AT the travel motor on the two speed line is 250psi less than the recommended Minimum pressure required to shift it. Pressure has been checked at pump, at valve and at travel motor. All consistent, just too low at the travel motor. (now that I'm typing I'm curious as to the other functions and why they are normal...) Not much history on the machine, nor am I directly working on the machine. I'm helping a customer of mine. I'm not very well versed in CAT, I know Kobelco and Korean machines very well though. On those we would adjust the relief valve on the travel motor section of the main control valve. It would increase pressure to the travel motor only, not the entire system. I'm not sure why it is set below spec, someone must have worked on the machine before my customer bought it. We've checked all possiblities and we quickly found that the pressure was too low to shift the motor. So we're stuck until I can figure out where to tell him to adjust the pressure at. Again, I'm not directly working on this machine. My customer does not have email or a fax. I've printed schematics and FedEx'd them to him.
Yes. As mentioned before, there's only one pilot pressure adjustment and that's at the pilot filter. The whole pilot system runs at this pressure. So you're saying that pilot pressure is 250psi low at the test port on the filter head? If so then try adjusting the relief valve on the filter head. If you can't make spec then either; A. There's a problem with the relief valve, O rings, seals etc Or B. The pilot pump is faulty Hope this makes sense
It makes sense, thank you for your reply. Again, without working on the machine myself I'm taking all of this on my customers word. It's difficult to help when I cannot email or fax. No digital photos to send or receive and shrunk down schematics to snail mail. It doesn't make sense that you cannot "fine tune" the pressures from the main control valve. I understand system pressure be sent out the same, but once the pilot line goes to the spool on the MCV, you should be able to adjust relief settings on some of the sections. In my experience some operate at system pressure, while others require adjustments and use the reliefs to protect the circuit. So I do understand you, but I think I'm not explaining correctly what we're trying to accomplish. Then again, maybe CAT is just that different and I can add it to the list of things I don't understand about CAT
I don't understand what there is to fine tune? At low travel speed the pressure to the motor displacement change valves is zero. When you hit the rabbit button, a solenoid dumps full pilot pressure to the displacement change valves and the motors shift to high speed. This circuit doesn't effect and isn't affected by the main control valve. Is your problem that the ECM is downshifting the motors too early?
I find it is very frustrating sometimes to have to troubleshoot problems over the phone, especially with people that do not fully understand how their system works. I feel for you. Pilot system pressure only operates control type items. Joysticks, solenoid controls and some pump controls. If pilot pressure is set at the proper spec on the relief valve, that is what you should see anywhere in the system. I would think there is a problem with internal leakage somewhere that is letting flow go out of the circuit. My first suspicion would be that the seals for the circuit in the swivel are leaking into the drain circuit and pressure will not build high enough to shift the spool. The second place I can think of is in one of the motors. Link-Belts used to have the problem all the time. The pistons that change the swash plate angle in the motors would get loose in their bores and not let pressure build enough to shift them. All the oil would bypass into the case drain and back to the tank. As far as fine tuning pressures in the main control valve the load sensing systems do that in the pump. The pump will stroke and destroke by the load placed on it from the operator and the pressure sensed in each circuit. There are reliefs in each circuit but they are set higher than the pump. They only relieve when an outside force causes a high pressure with the control valve spool closed.
Thanks for the input. I'll see if I can get some more accurate data from him. I had not thought of the ECM, this machine might just be a basket case...he didn't buy it new. You never know what sins it carries. Thanks again, I'll report back next week.
You're right. The main drive circuits are protected by the crossover relief valves which are part of your motor. It looks like they're non-adjustable though. BUT, they should not affect the two speed travel.
finaldrive, you said the pressure is 250 psi less than is needed "At" the drive motor. What does the pressure read at the upper part of the machine in the pilot circuit? Is it the same pressure (250 psi low) there?
I can't find what the Bar was in my notes (of course) I did the conversion to psi and found that it equated to 250psi low. And, from what I was told the pressure was the same from the pump down all the way to the motor.
What? You mean the whole pilot system pressure is low? If that's the case, sounds like you have a problem with either pressure regulator of pilot system or a failed pilot pressure pump. Still not enough info for us to say for sure. Just what is the pressure you are reading on the pilot system? Not the pressure for the hi drive for the motors, we'll get to that later, the pressure of the pilot system of the machine?
I'm going to clarify the pressure and now with the data given by Cmark, I'll make sure that the system pressure is correct. Now I just have to figure out how to explain this to my customer (which has been challenging) Thanks for the insight