1
DESCRIPTION
The TW-12
™
control valve is a manually operated, non-
graduating, on-off valve. It is extensively used in hydraulic
braking systems to control devices that are responsible for
the application and release of the parking brakes.
Note: The TW-12
™
control valve can also be
used in air brake system applications.
The most common configuration of the TW-12
™
control valve
uses a levered cam that is manually, remote controlled. A
dash mounted lever or button may be connected to the
aluminum lever cam via Bowden cable control or connected
directly to the transmission selector.
Two .28 inch mounting holes are provided in the die cast
zinc body for panel or frame mounting. Two steel hex cap
nuts at the ends of the cylindrical valve body retain the internal
components and provide attachment for the lever cam. All
connection ports are pipe threads. Lettering embossed in
the valve body identifies two of the three ports in the valve.
Refer to the following chart and figure one.
Connection
Body Ident. Thread Size
x
Supply
SUP
1/4" P.T.
xx
Delivery
DEL
1/4" P.T.
xx
Vent
NONE
1/8" P.T.
xx
OPERATION
SYSTEM CONNECTIONS
Although the TW-12
™
valve can be used in a variety of different
systems and connected in different ways, figure 2 illustrates
a typical hydraulic parking brake system. In this system
the TW-12
™
valve controls an HR-1
™
hydraulic relay that in
turn applies and releases hydraulic spring brakes.
VALVE OPERATION
Parking Brakes Applied
With hydraulic fluid flowing to the supply port (Figure 1) and
the piston in the upward position, fluid flow into the TW-12
™
control valve is stopped at the closed inlet valve.
FIGURE 1- TW-12
TM
CONTROL VALVE
PLUNGER
1/4" P.T.
DELIVERY
PORT
1/4" P.T. SUPPLY
PORT
LEVER CAM
INLET VALVE
LEVER
PIVOT
INLET VALVE SPRING
PISTON RETURN
SPRING
LEVER
YOKE
DELIVERY PORT
SUPPLY PORT
RETURN PORT
MOUNTING
HOLE (2)
1/8" P.T.
RETURN
PORT
LEVER
CAM
PISTON RETURN
PASSAGE
SUPPLY PORT
CAP NUT
CAP NUT O-RING
CONTROL
CABLE
CONNECTION
LEVER
YOKE
CAM
FOLLOWER
LEVER CAM
PIVOT
PISTON
PISTON O-RING
CAP
NUT
SD-03-3625
Bendix
®
TW-12
™
Control Valve
