Bendix Commercial Vehicle Systems SS-1 SHUT OFF VALVE - Manual (Page 2)

2
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 ™ valve can either be connected in the
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.
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
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
FIGURE 3 TRACTOR PROTECTION SYSTEM
RESERVOIR RESERVOIR
SS-1 ™ VALVE
CONTROL VALVE
SS-1 ™ VALVE
BRAKE VALVE
TRACTOR PROTECTION
CONTROL VALVE
DOUBLE
CHECK VALVE
HOSE COUPLING
"GLAD HAND"
SS-1 ™ VALVE
Automatic Operation - Common Control & Supply
Pilot Operation - Tractor Protection Application
Pilot Operation
CON
SUP
DEL
RESERVOIR
CON
SUP
DEL
CON
SUP
DEL