Cooling System Valve - Fig. WH 210
The auxiliary pump is connected to Connection P. Oil is flowing through the covering plate from P to T1. The fan motor for the cooling system is connected to T1. The protection valve function is adopted by the pressure relief valve (represented in sectional drawing WH 210). This relief valve is electrically controlled and is inoperative when de-energized. The pressure applied to T1 enters Connection A of the relief valve. The pressure applied to A goes behind the cartridge through a nozzle, Item 1. As long as the magnet coil, Item 2, is not excited, the valve cone, Item 3, is prevented by the spring, Item 4, from closing the cone seat of the member Item 5.
This means that no pessure is building up in the spring area of spring 6, since the oil arrives without pressure at Connection b through the cross hole. The flow resistance only corresponds to the preload value of the spring, Item 6. When the magnet coil, Item 2, is excited, the magnet armature (as represented in the drawing) is displaced against its stop and pretensions the spring, Item 7. The valve cone, Item 3, is pressed against the cone seat. The piston, Item 8, closes, and the oil flow from A to B is cut. The supplied oil flows to the fan motor. As soon as pressure is rising above the set value of this valve, the valve acts as a normal pilot controlled pressure relief valve.
The operating pressure for the cooler motor [approximately 20 bar (2000 kPa)] is substantially below the set value of the valve. Should the protection valve function be released, some failure must exist in the fan drive.
The valve is designed in such a way as to allow emergency actuation with a small cylindrical pushrod, through the plunger, Item 9. In case of power failure of the complete system, the magnet armature can be strongly pressed against its seat, also through the adjusting screw, Item 10, thus permanently releasing the protection valve function. Care should be taken to ensure that under normal conditions this actuating screw has not been turned out so far that no pressure can be built up due to insufficient return stroke of the magnet armature.
Assembly and Troubleshooting
It must absolutely be ensured that the preset screw-in cartridges are tightened only with a maximum torque of approximately 25 N·m (18 lb. ft). Tightening in excess of this value can result in distortion of the cartridge, thus causing malfunction. If no pressure is built up and therefore the fan motor is not driven, the magnet being energized, it must be checked whether the current supply through the plug, Item 2, is correct. Function of the cartridge can already be checked, as had been described, through manual emergency actuation. If both actions are not successful, the cartridge may be turned out of the basic block for functional test; care should be taken in this case that this should be done only using the wrench flats of the cartridge head, Item 12. On the unturned cartridge it should be checked whether the piston, Item 8, reaches its foremost position. The function of this piston can be checked by pushing it backward: it must always smoothly come back to its seat in the cartridge neck, Item 13. At the same time, it should be checked whether the nozzle, Item 1 (0.8 mm), is not clogged by dirt. When this has been done, the cartridge can be turned back, carrying out another functional test on the block. The maximum pressure setting is pin locked on the setscrew, Item 14, and can not be changed.
It can be checked whether the magnet coil is still in perfect condition by unscrewing the union nut, Item 15, and testing the flux of the magnet in energized condition. It can clearly be noticed whether current is flowing in the magnet since this magnet tries sticking on the magnet coil tube; if no current is flowing, it will not oppose to being withdrawn to the rear. The magnet coil can be changed by removing the union nut, Item 15. Care should be taken to reinsert the O-ring, Item 16, each time a magnet is reassembled.