Charge pumpThe charge pump is necessary to supply cool fluid to the system, to maintain positive pressure in themain system loop, to provide pressure to operate the control system, and to make up for internal leakage.Charge pressure must be at its specified pressure under all conditions to prevent damage to thetransmission.The charge pump is a fixed-displacement, gerotor type pump driven off the main pump shaft. The chargerelief valve limits charge pressure.Pump charge systemCasedrainline Charge relief valveChargepumpSystemcheckvalvesInputInlet filterTankPV PFP104 121ECharge relief valveThe charge relief valve on the pump maintains charge pressure at a designated level. A direct-actingpoppet valve relieves fluid when charge pressure reaches a certain level. This level is nominally setreferencing case pressure at 1500 rpm. This nominal setting assumes the pump is in neutral (zero flow). Inforward or reverse, charge pressure is lower. The pump model code specifies the charge relief valvesetting.Charge pressure relief valveCharge pressure P106 157EMulti-function valvesThe multi-function valve incorporates the system check valve, the pressure limiter valve, the highpressure relief valve, and the bypass valve in a replaceable cartridge. These functions are describedseparately. There are two multi-function valve cartridges in each Series 90 pump to handle functions ineither direction. See corresponding sections for adjustments and repairs.Service Manual Series 90 PumpsOperation520L0818 • Rev 0101 • August 2015 11
