Pressure Compensated Pump Control for Forestry Log Skidders

Pressure compensated pump control ensures maximum pump flow until the hydraulic system reaches the control's preset pressure setting. This control then regulates the pump's output flow to match the flow requirements of the hydraulic system while maintaining a preset output pressure. This type of pump control assists in reducing hydraulic system loads on the engine and eliminates engine stall when maximum engine horsepower is required.

John Deere (Industrial Div.) produces a forestry log skidder (Fig. 1) that uses this type of pump control to maximize overall machine efficiency. This type of pump control allows them to drive their transmission directly from their engine, eliminating an inefficient torque converter.

This paper will describe how an Oilgear pressure compensated pump (Fig. 2) operates and interacts with each hydraulic function on a forestry log skidder. Diagrams illustrating a pump and control will be explained in detail. Pressure-flow curves will be explained in detail to assist in describing how a pressure compensated pump is a practical way to efficiently use power on a log skidder. A hydraulic circuit will also be shown to assist in the explanation of the interaction of the hydraulic pump and each function of the log skidder. This paper will conclude by explaining how a pressure compensated pump control assists John Deere in eliminating an inefficient torque converter.