TUBE AS 4208581 - Caterpillar

Solenoid Valves (Machine Travel)
These solenoid valves (Forward EDC / Reverse EDC) control the speed and the direction of the machine. Based on the operator's request (propel lever / engine speed dial / parking brake switch), the ECM applies current to the appropriate solenoid valves.The valves are proportional solenoid valves. The ECM uses the PWM signal from the sensors to vary the current that goes to the solenoid valve. The distance that is travelled by the plunger is proportional to the current that is output from the ECM. The solenoid valves control the direction of the motor and the swashplate angle of the pump.Note: The solenoid windings are not designed for operation at 24 DCV. The ECM sends a 24 volt PWM signal with a duty cycle that is less than 100 percent. The signal provides an average voltage of about 12 volts to the solenoid windings. Do NOT activate the windings with a source (battery) that is 24 DCV. Otherwise, the life of the coils will be drastically reduced. If you are not using the ECM as a power source, then use a source that is 12 DCV.Solenoid Valve (Parking Brake)
This solenoid valve engages the parking brake, and the valve disengages the parking brake. The brake is spring applied, and the brake is released hydraulically. When the parking brake is applied, the ECM de-energizes the solenoid valve. The hydraulic pressure is reduced, and the brake is engaged by the springs. When the parking brake is released, the ECM energizes the solenoid valve. The hydraulic pressure is added, and the brake is disengaged. The ECM