Patent ID: 6955045

Claim:
In an oil pumping system ( 1 ) for a riding lawn mower, receiving oil from an oil reservoir ( 6 ) and pumping oil under pressure to an external load ( 16 ), having an input shaft ( 3 ) rotated by an external source of power, a cylinder block assembly ( 4 ), a variable displacement swash plate ( 2 ) inside said cylinder block assembly ( 4 ) secured to and rotated by said input shaft ( 3 ), a charge pump ( 5 ) secured to and operated by said input shaft ( 3 ), a first oil line ( 15 ) communicating between said variable displacement swash plate 2 and said external load ( 16 ), a second oil line ( 17 ) communicating between said variable displacement swash plate ( 2 ) and said external load ( 16 ), said first oil line ( 15 ) carrying oil under high pressure at a first point in the cycle of operation of the system from said cylinder block assembly ( 4 ) to said external load ( 16 ) or alternately carrying oil under low pressure at a second point in the cycle of operation of the system from said external load ( 16 ) to said cylinder block assembly ( 4 ), said second oil line ( 17 ) carrying oil under low pressure at said first point in the cycle of operation of the system from said external load ( 16 ) to said cylinder block assembly ( 4 ) or alternately carrying oil under high pressure at said second point in the cycle of operation of the system from said cylinder block assembly ( 4 ) to said external load ( 16 ), a third oil line ( 10 ) carrying oil from said charge pump ( 5 ) through an oil line ( 11 ) and a check valve ( 13 ) to said first oil line ( 15 ) and through an oil line ( 12 ) through a check valve ( 14 ) to said second oil line 17 , the combination comprising: (a) a fourth oil line ( 26 ) communicating between said said third oil line ( 10 ) and said reservoir ( 6 ) and carrying oil from said third oil line ( 10 ) to said reservoir ( 6 ), (b) a fifth oil line ( 19 , 21 ) communicating directly between said third oil line ( 10 ) and said cylinder block assembly ( 4 ) without the interposition of a check valve therein.