The pressure switch monitors the hydraulic pressure to the brake. The switch closes when the STCM sends hydraulic pressure to release the brake. The discrete brake release signal goes to the ACE.
Brake Bypass Valve

Maintenance personnel use the brake bypass valve to periodically test the operation of the hydraulic brake. When you push on the brake bypass valve button, the valve shuts off hydraulic pressure to the brake. While you hold the button, you verify that the brake stops and holds the hydraulic motor. When released, a spring moves the brake bypass valve back to the open position.
Training Information Point
These are the LRUs on the STCMs:
*
Rate control solenoid

*
Nose up and down arm solenoids

*
Nose up and down control solenoids

*
Pressure switch

* Motor operated shutoff valve.

EFFECTIVITY BEJ ALL  27-41-00 
Page 30 
D633W101-BEJ  Sep 05/2002 

HORIZONTAL STABILIZER CONTROL -STCM -PHYSICAL DESCRIPTION

EFFECTIVITY BEJ ALL  27-41-00 
Page 31 
D633W101-BEJ  Sep 05/2002 

HORIZONTAL STABILIZER CONTROL -STCM -FUNCTIONAL DESCRIPTION

General

The STCM controls hydraulic power to the motor and brake of the stabilizer ballscrew actuator. It operates in two different modes of operation:
*
Electrical

*
Mechanical.

An inlet filter and check valve are in the hydraulic power supply line to the motor operated shutoff valve. In either mode of operation, the shutoff valve normally controls hydraulic power to the trim rate solenoid valve. The cutout switches on the control stand and the PFCs control the motor operated shutoff valve.
The PFC commands, through the ACE, the trim rate solenoid valve to high or low flow based on airspeed and flap position. A spring returns the trim rate solenoid valve to the high flow position when the solenoid is de-energized.
Arming and Control Valves
The arming and control valves have three positions:
*
Null

*
Trim up

*
Trim down.

Hydraulic pilot pressure controls the position of the arming and control valves. This pilot pressure comes from one or both of these sources:
*
The trim up and down, arm and control solenoid valves

*
The arm and control manual valves.

Springs in the arming and control valves center and hold them in the null position when there is no hydraulic pressure. With the two valves in the null position, they stop hydraulic pressure to the brake and motor of the stabilizer ballscrew actuator.
The arming and control valves must move together in the same direction to permit hydraulic pressure to the hydraulic brake and motor.
When both arming and control valves move to the trim up position, hydraulic power goes to release the brake and drive the hydraulic motor in the nose up direction.
When both arming and control valves move to the trim down position, hydraulic power goes to release the brake and drive the hydraulic motor in the nose down direction.
Two anti-cavitation check valves supply hydraulic fluid to the motor. They prevent motor cavitation in the unlikely event of brake slip and backdrive of the motor.

EFFECTIVITY BEJ ALL  27-41-00 
Page 32 
D633W101-BEJ  Sep 05/2002 

HORIZONTAL STABILIZER CONTROL -STCM -FUNCTIONAL DESCRIPTION

Electrical Operation

When the trim up and trim down, arm and control solenoid valves are de-energized, they allow hydraulic pilot pressure on both sides of the arming and control valves. The two valves are in the null position.
When their solenoids are both energized, the trim up arm and control solenoid valves operate. They stop hydraulic pilot pressure to the trim up side of the arming and control valves and port it to the system return line. Both arming and control valves move to the trim up position and permit pressure to the brake and motor.
When the solenoids of the trim down arm and control solenoid valves are both energized, the same process occurs. But in this case, the arming and control valves move to the trim down position and permit hydraulic pressure to the brake and motor.
Mechanical Operation

The arm and control input cranks connect to the arm and control manual valves. These valves control hydraulic pilot pressure to the arming and control valves.
The arm and control manual valves have three positions:
*
Null

*
Trim up

*
Trim down.

EFFECTIVITY
BEJ ALL

Springs in the arm and control manual valves center them in the null position when there is no force on the input cranks. With the two valves in the null position, they permit hydraulic pilot pressure to both sides of the arming and control valves.
　
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