Cat 305CR tool valve flow rate change

[Phil_C]

This machine does not have a load sensing system.

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

 

[John C.]

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?

 

[Phil_C]

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

 

[John C.]

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.