HYDRAULICS 1.35 1st service (30)/2nd service (31) section A Port A - connection to service B Port B - connection to service PP Pilot pressure LS Load sensing T Return to tank P Pressure (37) LS shuttle valve (40) Controller, non-proportional Function 1st service/2nd service is non-proportional and operated electrically to provide oil flow to the 1st service/2nd service 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.
These sections, although electrically controlled, are non-proportional. Operation of the buttons on the ‘Solo’ joystick operate these sections as an on-off switch. In neutral the spool is closed, neither of the consumer ports A and B are connected to the T line.