2) OPERATION OPERATION 1 1 3 4 2 HYDRAULIC CIRCUIT (3 Electromagnetic locks) Electromagnetic lock 9 10 11 5 4 (1) Hydraulic functional principle Hydraulic functional principle Pilot devices with end position locks operate as direct operated pressure reducing valves. They basically comprise of control lever (1), four pressure reducing valves, housing (6) and locks. Each pressure reducing valve comprises of a control spool (2), a control spring (3), a return spring (4) a plunger (5). At rest, control lever (1) is held in its neutral position by return springs (4). Ports (1, 2, 3, 4) are connected to tank port T via drilling (8).
12 3 7 2 x T 8 P 6 Port 4 Port 2 7707WE12 When control lever (1) is deflected, plunger (5) is pressed against return spring (4) and control spring (3). Control spring (3) initially moves control spool (2) downwards and closes the connection between the relevant port and tank port T. At the same time the relevant port is connected to port P via drilling (8). The control phase starts as soon as control spool (2) finds its balance between the force from control spring (3) and the force, which results from the hydraulic pressure in the relevant port (ports 1, 2, 3 or 4).
Due to the interaction between control spool (2) and control spring (3) the pressure in the relevant port is proportional to the stroke of plunger (5) and hence to the position of control lever (1). This pressure control which is dependent on the position of the control lever and the characteristics of the control spring permits the proportional hydraulic control of the main directional valves and high response valves for hydraulic pumps. A rubber bellows (9) protects the mechanical components in the housing from contamination. 6-21 T P B.D/F B.U IN OUT