BENDIX SS-1 SHUT OFF VALVE Manual - Página 2

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OPERATION

GENERAL

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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.

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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

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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

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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

CONTROL VALVE

SS-1

RESERVOIR

Pilot Operation

TRACTOR PROTECTION

CONTROL VALVE

SS-1

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DOUBLE

CHECK VALVE

BRAKE VALVE

Pilot Operation - Tractor Protection Application

SS-1

VALVE

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RESERVOIR

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

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valves will "trap" approximately 10 psi.

AUTOMATIC (self actuating at a preset pressure)

Automatic operation of the SS-1

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

Engineering for speciﬁ c opening and closing control

pressures when the SS-1

CON

DEL

VALVE

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SUP

RESERVOIR

CON

VALVE

DEL

HOSE COUPLING

SUP

"GLAD HAND"

CON

DEL

SUP

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shut-off valve occurs

cataloging and/or Bendix

valve is used in the automatic

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