Bendix Commercial Vehicle Systems SS-1 User Manual

Bendix® SS-1™ Shut-Off Valve

SD-03-4010

CONTROL

PORT

VENT PORT

MOUNTING

HOLES

SUPPLY

PORT

FIGURE 1- SS-1™ SHUT-OFF VALVE

CONTROL PORT

CAP NUT

DELIVERY

PORT

SUPPLY PORT

CAP NUT

DESCRIPTION

The SS-1™ shut-off valve (fi gure 1) is a pilot operated,
air controlled, on-off, non-graduating, non-exhausting
pneumatic control valve. The valve is primarily used to
delay, sequence, or control airfl ow from various devices in
the air brake system. It can be operated either in a pilot or
automatic mode using different air connection methods.

1/4" P.T.

CONTROL PORT

PISTON

PISTON O-RING

VENT PLUG WITH

1/8" P.T. VENT

MOUNTING

HOLE

INLET VALVE

CAP NUT O-RING

1/4" P.T.

SUPPLY PORT

CAP NUT O-RING

PISTON RETURN

SPRING

PISTON O-RING

1/4" P.T.

DELIVERY

PORT

INLET VALVE

SPRING

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. All air connection ports contain pipe
threads. Lettering embossed in the valve body identifi es
two of the four ports in the valve. Refer to the chart below
and fi gure 1.

The SS-1™ valve is a general purpose valve used in a
variety of applications on trucks, buses, tractors, trailers
and converter dollies. It is offered in a variety of pressure
settings to accommodate applications where automatic
operation is required. The most common application of
the SS-1

™

valve is in the tractor protection system of a

truck tractor.

™

Important Note: The SS-1

shut-off valve is
application specifi c due to its pressure settings. It is
therefore important to use the proper part number
when replacement is required. IN ADDITION: The

SS-1™ shut-off valve and SV-1™ synchro valves are
identical in appearance and similar in operation but
have substantial internal differences and must not
be confused or used interchangeably. The SV-1™

synchro valve incorporates an internal exhaust passage
through its piston, which allows delivery pressure to
be vented to atmosphere while the SS-1™ does not.
Refer to Service Data Sheet, SD-03-4020, for more
information on the SV-1™ synchro valve. Service Data
Sheets can be obtained by calling 1-800-AIR-BRAKE
or by visiting www.bendix.com on the Internet.

Air Connection Body Ident. Thread Size

Supply SUP 1/4” P.T.
Delivery DEL 1/4” P.T.
Control NONE 1/4” P.T.
Vent NONE 1/8” P.T.

IMPORTANT: A vented, socket head vent plug is
installed in some SS-1

™

valves, however, an exhaust

check valve should be installed in the threaded vent

™

port when the SS-1

valve is mounted outside the cab

in unprotected environments. See Figure 2.

1/8" PIPE THREAD

Note: Either style may be installed in the SS-1™ valve

FIGURE 2 - EXHAUST CHECK VALVE STYLES

1

OPERATION

GENERAL

Because the SS-1™ shut-off valve is a general purpose
valve, it can be connected in the air system in a variety of
ways to accomplish its intended function. Figure 3 displays
only three of the many different connection methods that
can be used.

™

In general, the SS-1
system to function as a pilot operated, remote mounted,
on-off valve or it can be connected in a manner that allows
the valve to operate automatically at preset pressures as
system pressure increases or decreases. Figure 3 displays
examples of air system connections. Two examples of
connections that result in pilot operation are shown and one
that illustrates automatic operation. It should be noted that
since the SS-1™ valve is a pressure sensitive valve, under
certain air system conditions it might temporarily operate in
an automatic fashion even in a system where its intended
function is that of a pilot on-off valve. Regardless of how
the SS-1™ shut-off valve is connected, the internal valve
operation is the same.

valve can either be connected in the

CONTROL VALVE

CON

DEL

SUP

RESERVOIR

SS-1

™

VALV E

RESERVOIR

Pilot Operation

TRACTOR PROTECTION

CONTROL VALVE

CON

DEL

SUP

HOSE COUPLING

"GLAD HAND"

BRAKE VALVE

™

VALV E

SS-1

DOUBLE

CHECK VALVE

Pilot Operation - Tractor Protection Application

PILOT (controlled remotely by another valve)

With no air pressure present at the control port, supply port
air pressure, if present, along with the inlet valve spring hold
the inlet valve on its seat in the body. The piston is held
away from the inlet valve by the piston return spring.

When suffi cient air pressure is applied to the control port,
the control piston moves against the resistance of its return
spring. As the control piston moves, it contacts the valve
and continued piston movement drives the inlet valve from
its seat and allows supply air to fl ow through the body and
out the delivery port.

When air pressure is removed from the control port, the
piston return spring moves the piston away from the inlet
valve. As the piston moves, the inlet valve re-seats itself
preventing airfl ow to the delivery port.

If air pressure at the supply port remains constant (is not
reduced) then delivery port pressure remains equal to
supply port pressure provided that devices connected to
it do not dissipate delivery port pressure.

If supply port pressure is removed (after control pressure
is removed), then delivery port air pressure will hold the
inlet valve away from its seat against the force of the inlet
valve return spring. Air present at the delivery port will fl ow
through the valve body in the reverse direction, from the
delivery port, past the inlet valve, and into the supply port.
Flow will continue until the delivery port pressure (which
acts upon the area of the inlet valve) is reduced and equal
to the force exerted by the inlet valve spring. When delivery
port pressure and spring force are equal, the inlet valve
re-seats in the body and air pressure remaining in the
delivery line is “trapped” between the closed inlet valve and
air devices connected to the delivery port. The amount of

2

CON

SS-1™ VALV E

RESERVOIR

DEL

SUP

Automatic Operation - Common Control & Supply

FIGURE 3 TRACTOR PROTECTION SYSTEM

air pressure “trapped” is dependant upon the specifi c part
number of the valve. Valves used in a tractor protection
system application will “trap” less than 5 psi while other
SS-1™ valves will “trap” approximately 10 psi.

AUTOMATIC (self actuating at a preset pressure)

Automatic operation of the SS-1™ shut-off valve occurs
when the pressure at the supply and control port is the
same. This is referred to as “common control and supply”
and can be accomplished by connecting the valve’s control
port to its supply port using a pipe or tubing tee. With
common control and supply pressure, the valve opens
(delivers air) on ascending air pressure and closes on
descending pressure. The pressures at which delivery
and closure occur differ for various part numbers. Opening
and closing pressures are specifi ed for the various part
numbers. It should be noted that as supply and control
pressure descends delivery pressure will also decrease
but will not be completely removed. Refer to the “Pilot”
operation in this section.

Important: Consult Bendix® cataloging and/or Bendix®
Engineering for specifi c opening and closing control
pressures when the SS-1™ valve is used in the automatic