A conventional cylinder can exert a larger force extending than retracting because of the area difference between full bore and annulus sides of the piston. The system in Figure 5.41 employs a cylinder with a full bore/annulus ratio of 2:1, and is known as a differential cylinder.
Upon cylinder extension, line pressure P is applied to the right hand side of the piston giving a force of P x A, while the left-hand side of the piston returns oil via valve V 3 against line pressure P producing a counter force P x A/2. There is thus a net force of P x A/2 to the left. When retraction is called for, a force of P x A/2 is applied to the left-hand side and fluid from the right-hand side returns to tank at minimal pressure. Extension and retraction forces are thus equal, at P x A/2.
