Patent ID: 8353157

Claim:
An open center hydraulic system comprising: a variable displacement pump having an inlet, an outlet and a sensing port, the pump configured to provide reduced fluid flow in response to a predetermined fluid pressure differential between the outlet and the sensing port; a first fluid circuit and a second fluid circuit in selective fluid communication with the pump; a first controlled pressure reduction device in fluid communication with the pump outlet and each of the first fluid circuit and the second fluid circuit; a flow regulating device in fluid communication with the sensing port in each of the first fluid circuit and the second fluid circuit; the first fluid circuit comprising: a second controlled pressure reduction device; and a first maximum pressure limiting device; wherein the second controlled pressure reduction device and the first maximum pressure limiting device in fluid communication with the pump sensing port during operation of the first fluid circuit, the first maximum pressure limiting device configured to permit up to a first predetermined fluid pressure value between the pump sensing port downstream of the second controlled pressure reduction device and the first fluid circuit during operation of the first fluid circuit; and the second fluid circuit comprising: a third controlled pressure reduction device; a fourth controlled pressure reduction device; and a second maximum pressure limiting device; wherein the third controlled pressure reduction device, the fourth controlled pressure reduction device and the second maximum pressure limiting device in fluid communication with the pump sensing port during operation of the second fluid circuit, the second maximum pressure limiting device configured to permit up to a second predetermined fluid pressure value downstream of the fourth controlled pressure reduction device between the pump sensing port and the second fluid circuit during operation of the second fluid circuit; wherein the first controlled fluid pressure reduction device is configured to introduce a first induced fluid pressure reduction between the pump outlet and the first fluid circuit during operation of the first fluid circuit; wherein the first controlled pressure reduction device is configured to introduce a first induced fluid pressure reduction between the pump outlet and the second fluid circuit during operation of the second fluid circuit; wherein the fourth controlled pressure reduction device is configured to introduce a second induced fluid pressure reduction in the second fluid circuit during operation of the second fluid circuit; wherein during operation of the second fluid circuit, reduced fluid flow from the pump outlet is achieved as a result of the sum of the first induced fluid pressure reduction of the first controlled pressure reduction device and the second induced fluid pressure reduction of the fourth controlled pressure reduction device approaching the predetermined pump fluid pressure differential.