Header height valve

A hydraulic valve in a load responsive system supplied by a pressure flow compensated variable displacement pump having a flow compensating means, said valve raising and lowering a header height cylinder under load on a machine, the improvement comprising:

• a valve body;
• a first bore in the body;
• a valve spool means having lands and grooves to control flow to and from the header height cylinder, said spool means positioned in the first bore;
• a pump pressure cavity intersecting the first bore and connected to the pump discharge;
• first and second motor port cavities intersecting the first bore on opposite sides of the pump cavity with the first motor port cavity connecting to the header height cylinder;
• a drain cavity adjacent the first motor port cavity;
• a signal passage intersecting the first bore intermediate the pump cavity and each motor port cavity, the signal passage connecting with the flow compensating means of said pump;
• a lockout check valve positioned in the first motor port cavity blocking flow from the header height cylinder to the bore;
• servo means actuated by pressure in the second motor port cavity acting against the lockout check valve, whereupon pressure in the second motor port cavity actuates the servo means and opens the lockout check allowing backflow into the first bore due to the load on the header height cylinder;
• low pressure relief valve means in the second motor port cavity connectible to drain;
• the valve spool means having:
• a first neutral position, blocking flow to or from the pump cavity and blocking flow to or from the motor port cavities;
• a second position of the valve pool, opening the signal passage to the second motor port, and metering the flow from the pump pressure cavity into the signal passage thereby actuating the servo means and passing flow over said relief valve means whereby the flow compensating means of the pump maintains a relatively low pump discharge pressure level;
• and
• a third lowering position of the valve spool metering flow from the first motor port cavity to drain while continuing to meter flow from the pump across the signal passage and over said relief valve means.