Hello All Is it possible to reduce the flow rate to the tool valve for the left pedal? I have just purchased a tilt bucket and the circuit is way too fast to be of any use. I can add flow controls to the bucket but thought I would check to see if the valves flow rate is adjustable. DGT series. Thanks in advance. Phil
From the hydraulic schematic it doesn't appear as though the flow rate is adjustable on the auxiliary circuit in its "as built" form.
I've heard of people shimming the spool in the main valve to limit how much oil gets sent out and returns. I've also seen those needle type flow control valves in other machines. I don't remember there being any adjustable flow settings in the monitor panels on the CR series machines. Most were just a couple of gauges and indicator lights.
Thank you both for the replies. I have purchased two reverse free flow check valves today to install in the lines on the bucket. I think that is easier than shimming the valve and won't affect other tools used on the machine. Regards Phil
I installed the flow control valves but now I have another issue. When I use the valve it stalls the engine. It's like the load sense on the pump is being told to deliver full flow to that circuit despite what the demand is. Maybe I should have looked at limiting the travel of the foot valve.
What exactly did you buy and install? It says "reverse free flow check valves".
Its a valve that has adjustable flow in one direction and full flow in reverse. The Stauff version of the below. https://www.hydac.com.au/products/hydraulic-valves/flow-control/needle-reverse-flow/ By placing one in each line it allows you to control flow in each direction so you can adjust the rod end and the piston end's flow to the same speed.
I've not had to work on the mini exs before but if they are like most of the rest of the Cat machines they are negative control systems. They have some load sensing on the NC line but not much. Generally the pump goes to maximum flow and regulation only comes in when pressure is high.
They are not negative flow control What about serial number
CAT00305VDGT01480
If they are not a negative flow system, then let us know what kind of system they are. Solving a problem with a pat answer doesn't let us know how the system works so leaves us at a loss on how to troubleshoot it.
Here's the hydraulic schematic if it helps.
Thanks Nige! The schematic shows a four pump system with two high pressure piston and barrel groups, one medium pressure pump that supplies house rotation, boom swing and blade up. The last pump is a pilot pump. There is a control system that is not explained but apparently only controls the high pressure groups. My guess is that it is a pressure compensated system and yes it apparently shows the system is at max flow all the time until it reaches and set pressure when it moves to destroke the high pressure pumps. The valves all show as open center parallel passage. Maybe the book explains the control function better that the schematic?
I looked at the SysOp for the hydraulic system. It's all in bits & pieces everywhere - about 50 separate documents. Let me see if I can stitch something together in one document that hits all the relevant points. Edit: It wasn't quite as difficult as I thought.
Thank you very much for the information Nige. Looking through it there appears to be no adjustments that can be made to the hydraulic system to slow the speed down on the foot pedal. Looks like the only option is to shim the spool or put up with it
Hi, I did this same thing to a 312 with a tilt bucket that was jerky. The check valve bypass needles worked great. Are your sure you have the checks going in the right direction? It sounds like they are restricting too much of the flow to the bucket.
If I remember right. Which ever line is putting flow out I made sure to restrict it on the oil coming out of the other line. So I used “meter out flow control” not “meter in”
The flow control valves on a normal load sensing system should not make the pump load up. Cat use a different method to control load on the pump. I used meter in but it should not make any difference to pump load. Normally meter out is used to control loads better but has the possibility of pressure intensification, meter in does not have pressure intensification but does not control the load as well. Regards Phil
This machine does not have a load sensing system.
305 and 312 are totally different
From the information supplied by Nige; The pump regulator changes the angle of the swashplate according to the flow that is required for a machine operation. As the angle of the inclined surface of the swashplate changes, the stroke of pistons changes, and the pump output increases or decreases. The main pump output varies from maximum output to minimum output according to the load on the machine. The angle of the swashplate determines the actual output of the main pump. So it does have a load sensing ability but not in the way you would expect. Regards Phil
Load sensing means the pump changes the amount of flow based on how far you move a control lever. Looking at the schematic then, would you explain to the viewers how that happens?
There's a little more to a load sense system than that. The systems that I worked on have a standby pressure of around 400-450psi and when you use a function the standby pressure is sent to the pump via shuttle valves to the load sense port that signals the pressure compensator on the pump to increase pressure to the maximum system pressure. The pump swash plate moves to suit the flow requirements while keeping system pressure. More advanced systems use electronics to control pump flow and pressure rate. Also some pumps use horsepower limiters. The Cat system works differently in that there is no standby pressure and while no function is used the pump is putting out full flow with little or no pressure. Once a function is used the springs in the pump regulator changes the pumps flow rate to keep the system pressure at a set level which also keeps power requirements constant. To me the Cat hydraulic pump changing to suit the flow and pressure requirements is a load sensing system. Correct me if I am wrong. Regards Phil
On the Cat mini ex the pump swash plate is at max angle for maximum flow when nothing is being used. The only regulation of flow is when hydraulic horsepower becomes more than engine horsepower. The only regulation of flow is in how much you stroke a valve to open. Which means that excess flow is routed back to the tank. This is a waste of fuel and a generator of heat. Load sensing means the pump is at minimum flow when there is no demand. Flow is ramped up as demand is applied but only in the amount necessary to accomplish a task. If I need 5 gallons a minute to raise the boom, my 30 gallon a minute pump only ramps up to produce 5 gallons a minute. In the Cat mini ex, my 30 gallon a minute pump is always putting out 30 gallons a minute until the pressure and flow are too much for the engine to carry. If I need 5 gallons a minute to raise the boom the main control valve sends 5 gallons a minute to the boom and the other 25 gallons goes back to the tank.