Apparatus and method for recirculating hydraulic fluid

A method for recirculating hydraulic fluid in a hydraulic system, the hydraulic system including a hydraulic pump, a bypass valve, a sub-circuit and a controller, the hydraulic pump pressurizing hydraulic fluid for circulation through the hydraulic system, the sub-circuit comprising a fluid switching valve, a piston-bypass valve, a cylinder and a piston reciprocating therein between first and second cylinder heads, the piston dividing the cylinder between a first chamber adjacent the first cylinder head and a second chamber adjacent the second cylinder head, first and second hydraulic lines fluidly connecting the first and second chambers to the fluid switching valve, respectively, hydraulic fluid entering and leaving the sub-circuit through entry and exit ports on the fluid switching valve, respectively, the piston-bypass valve selectively fluidly connecting the first and second chambers, the controller operatively connected to the fluid switching valve and programmed to command first and second actuating positions, in the first actuating position the entry and exit ports are fluidly connected to the second and first chambers through the second and first hydraulic lines, respectively, in the second actuating position the entry and exit ports are fluidly connected to the first and second chambers through the first and second hydraulic lines, respectively, the controller operatively connected to the bypass valve and programmed to command the bypass valve to a bypass position where pressurized hydraulic fluid bypasses the sub-circuit, the method comprising:

• supplying pressurized hydraulic fluid to the second chamber and closing the piston-bypass valve to move the piston towards the first cylinder head;
• detecting when the piston has completed a first stroke and is adjacent the first cylinder head;
• delaying:
• supplying pressurized hydraulic fluid to the first chamber and closing the piston-bypass valve to cause the piston to move towards the second cylinder head,
• bypassing the pressurized hydraulic fluid from the sub-circuit, or
• stopping the hydraulic pump that pressurizes the hydraulic fluid through the piston-bypass valve,
• the piston-bypass valve being open such that hydraulic fluid is fluidly communicated into the sub-circuit through the entry port and through the piston-bypass valve wherein a quantity of hydraulic fluid is flushed out of the sub-circuit through the exit port;
• and
• performing after the quantity of hydraulic fluid is flushed out of the sub-circuit:
• supplying pressurized hydraulic fluid to the first chamber and closing the piston-bypass valve to cause the piston to move towards the second cylinder head,
• bypassing the pressurized hydraulic fluid from the sub-circuit, or
• stopping the hydraulic pump from pressurizing the hydraulic fluid.