Hyraulic motor circuit

A hydraulic motor circuit for driving an auger, including:

• a bi-directional hydraulic motor that receives oil from an oil supply via a supply line and returns oil to the oil supply via a return line;
• a main stage pressure relief valve;
• a first pilot stage relief valve openable if pressure in the return line exceeds a predetermined value corresponding to an allowable inertia load acting on the motor, opening of the first pilot stage relief valve causing the main stage pressure relief valve to open, allowing flow to be diverted from the return line to the supply line and back to the motor;
• a second pilot stage relief valve openable if pressure in the supply line exceeds a maximum working pressure, opening of the second pilot stage relief valve causing the main stage pressure relief valve to open, allowing flow to be diverted from the supply line to the return line;
• and
• a spool valve configured to block flow to the first pilot stage relief valve when pressure in the supply line is greater than pressure in the return line,
• wherein, a pressure differential set up in the return line is used to open the spool valve when pressure in the return line exceeds pressure in the supply line thereby exposing the first pilot stage relief valve to pressure in the return line and enabling an inertia load acting on the motor to be absorbed.

A drilling apparatus, including:

• an auger for performing a drilling operation;
• and
• a hydraulic motor circuit for driving said auger, said circuit adapted for use with either an open or closed centre hydraulic system associated with equipment that the auger is attached to, the hydraulic motor circuit including:
• a hydraulic motor that receives oil from the hydraulic system via a supply line and returns oil to the hydraulic system via a return line;
• a main stage pressure relief valve;
• a first pilot stage relief valve openable if pressure in the return line exceeds a predetermined value corresponding to an allowable inertia load acting on the motor, opening of the first pilot stage relief valve causing the main stage pressure relief valve to open, allowing flow to be diverted from the return line to the supply line and back to the motor;
• and
• a control valve configured to block flow to the first pilot stage relief valve when pressure in the supply line is greater than pressure in the return line;
• wherein, if pressure in the return line exceeds pressure in the supply line, the control valve shifts open and exposes the first pilot stage relief valve to pressure in the return line.