HYDRAULICS 1.33 Crowd section (28) A Port A - connection to service B Port B - connection to service PP Pilot pressure LS Load sensing T Return to tank P Pressure (35) Shock and anti-cavitation valve - Port A (RV2-175 bar) (37) LS shuttle valve (38) Controller, proportional (39) Shock and anti-cavitation valve - Port B (RV3-265 bar) Function Crowd service is fully proportional and operated electrically to provide oil flow to the crowd circuit. When the spool is moved from the neutral position, oil at P (standby pressure 20 bar (290 psi)) is delivered to the consumer (service). The oil at the consumer meets a resistance (i.e.
to move the piston) and the pressure at P rises to overcome this force. The P line is connected permanently to the LS line; therefore the pump receives a signal to swash to the required position to provide the pressure required to overcome the resistance. The pressure at P will therefore be the LS pressure plus the standby pressure of 20 bar (290 psi). The pump will always react to the highest pressure requested when more than one service is operated by virtue of the LS shuttle valve in each section. When the valve returns to neutral the pressure at P drops and therefore the pressure in the LS line also drops.
The spool is operated by pilot oil pressure delivered by the electrical actuator under the command of the ‘Solo’ joystick and is fully proportional. In neutral the spool is closed’, neither of the consumer ports A or B are connected to the T line. This enables self-levelling operation from the compensator cylinder. To protect the circuit, shock valves are provided in both A and B ports.