TM 5-3805-258-24-1
S T E E R I N G S Y S T EM
S Y S T E M S O P E R A T I O N
A M P L I F I E D S T E E R I N G S Y S T EM
The oil for the steering system is sent from the
NOTE: The hand metering unit will not give manual
steering section of the pump to the control valve. If
steering when the engine is stopped. Steering with a
the pilot oil has moved the valve spool to either the
dead (stopped) engine can be done only when the
right or left turn position, the oil from the pump
Supplemental Steering System is installed.
section will flow to the steering cylinders. The pres-
sure of this oil moves the cylinder rods and causes the
machine to turn.
HAND METERING UNIT (HMU)
HAND METERING UNIT (HMU)
A. Control section.
3. Outlet (to tank).
B. Metering section.
4. Inlet (for pump oil).
1. spool.
5. Internal pump gear.
2. Sleeve.
6. External pump gear.
The hand metering unit (HMU) has two main
sections: control section (A), and pump or metering
section (B). These two sections work together to send
pilot oil to the steering control valve.
Oil from the pilot pump section goes through inlet
(4) into the control section of the HMU. When the
steering wheel is turned, the control section sends the
oil to and from the metering section and also to and
from the steering control valve.
The metering section is a small hydraulic pump. It
controls (meters) the pilot oil that goes to the steering
control valve. As the steering wheel is turned faster,
there is an increase in the flow of pilot oil to the
7. Centering springs.
10. Right turn port.
6. Pin.
11. Body.
9. Left turn port.
12. Drive.
steering control valve. This increased flow causes the
main valve spool to move farther. As the spool moves
farther, more oil can flow from the steering pump
section to the steering cylinders, and a faster turn is
made.
Oil Flow
The control section of the HMU is a closed center
type valve. The oil from the pilot pump section flows
through inlet (4). When the steering wheel is station-
ary (NEUTRAL), the oil is stopped by spool (1).
The pump oil can not flow through the HMU until
the steering wheel is turned.
3-62
