Toro 3020, 5020, 2020 service manual Retract and Extend Lift Cylinder

Retract and Extend Lift Cylinder

The hydraulic lift circuits for the SP 2020/3020 and SP 5020 function identically. Each machine has identical charge pumps, lift valves, and lift cylinders. These com- ponents are the heart of the lift circuit.

In addition to replenishing the closed loop circuit with fluid from the tank, charge pump (P2) flow in excess of replenishment requirements is relieved through the charge relief valve (R2). Fluid returns through the lift valve and back to the tank. This excess flow is used to operate the lift cylinder.

The charge pump is a fixed displacement gerotor pump that is driven directly off the traction pump (P1). It has sufficient output to handle intermittent operation of the lift cylinder under load. The implement relief valve (R1) in the charge circuit allows high enough pressure to op- erate the lift cylinder with attachments, and protects the charge pump.

When the lift lever to the lift valve is in the neutral posi- tion, fluid flow from the charge pump is bypassed around the lift cylinder through the lift valve. Fluid returns to the tank as a normal part of the charge and bleed off circuits.

Moving the lift lever to the lift position allows the lift valve to direct fluid flow from the charge pump into the rod side of the piston. The piston moves into the cylinder pushing fluid out the piston end of the cylinder and to the tank. As the cylinder rod retracts, the attachment is raised. When the lift lever is released, the lift valve returns to the neu- tral position. The attachment is held in its present posi- tion.

Moving the lift lever to the lower position allows the lift valve to direct fluid flow from the charge pump into the piston side of the cylinder. The piston moves out of the cylinder pushing fluid out the rod end of the cylinder and to the tank. As the cylinder rod extends, the attachment is lowered. When the lift lever is released, the lift valve returns to the neutral position. The attachment is held in its present position.

Excessive load on the lift cylinder causes circuit pres- sure to increase and the implement relief valve (R1) to dump directly to the tank. This condition happens in both the lift and lower modes.

Hydraulic System (Rev. A) Page 4 – 12 Sand Pro 2020/3020/5020