Owner's manual

3
Bendix
®
SV-3
™
Trailer Release Valve
While originally designed for automatic operation to
accomplish brake release on trailers without spring brakes,
the Bendix
®
SV-3
™
valve can be used in any installation
where its single automatic pressure setting is advantageous.
The SV-3 valve is very similar in appearance to the Bendix
®
SV-4
™
valve but can be distinguished by measuring the
length and diameter of the supply hex cap nut (1/4" PT
supply port). See the comparison chart for the dimensions.
Bendix SV-4 Trailer Release Valve
The SV-4 valve was designed primarily for use on trailer
converter dollies to minimize the possibility of false
charging. Like the SV-3 valve, it can be used in other
applications. The SV-4 valve is the combination of two
valves — an SV-3 valve and a single check valve. A typical
installation is illustrated in Figure 4. The SV-4 valve can
be distinguished from the SV-3 valve using the dimensions
given in the comparison chart below. In addition, the tip of
the check valve contained in the SV-4 valve is visible at
the bottom of the ¼" PT supply port.
OPERATION
GENERAL
The SV-1, SV-3 & SV-4 valves all operate in a similar
fashion. All can be connected in the air system so that
other valves control them. When connected in this non-
automatic mode, the valve serves as a remote-mounted,
on-off control. They can also be installed so that they
function automatically, or self-actuate, at a preset pressure.
Automatic operation is the most common application.
Regardless of how they are connected, the internal valve
operation is the same.
NON-AUTOMATIC (valve controlled remotely by
another valve)
With no air pressure present at the control port, supply port
air pressure and the inlet/exhaust valve spring hold the
inlet valve on its seat in the body. The piston is held away
from the inlet/exhaust valve by the piston spring, and the
delivery line is vented to atmosphere through the hollow
exhaust stem of the piston.
When suf! 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 exhaust
valve portion of the inlet and exhaust valve (which seals
the hollow exhaust passage in the piston stem). Continued
piston movement drives the inlet valve from its seat and
allows supply air to # ow through the body and out the
delivery port.
FIGURE 4 - TRAILER CONVERTER DOLLY
SV-1
™
SYNCHRO
SINGLE CHECK VALVE
Note: A Bendix
®
SV-4
™
valve can be used in place of the
Bendix
®
SV-1
™
valve and single check valve shown here.
Bendix
®
SV-3
™
/SV-4
™
Valve Comparison
Supply Cap Nut Dimensions
Valve Diameter Length
SV-3 .81" 1.162"
SV-4 .94" 1.062"
When air pressure is removed from the control port, the
piston return spring and delivery port air pressure move
the piston away from the inlet/exhaust valve. As the piston
moves, the inlet valve re-seats itself, preventing air # ow to
the delivery port. Continued movement unseats the hollow
exhaust passage in the piston stem,n allowing delivery air
to # ow through the stem and out the exhaust check valve.
AUTOMATIC (self actuating at a pre-set pressure)
There are two methods for accomplishing automatic
operation of an SV valve.
1. One method for affecting automatic operation is to
connect the SV valve control port to its supply port using
a pipe or tubing tee. This is referred to as “common
control and supply” since the pressure at the supply
and control port is the same.
With common control and supply, the valve opens
(delivers air) on ascending supply air pressure and
closes (and exhausts) on descending pressure. The
pressure at which delivery and exhaust occurs differs
for various part numbers. Opening and exhaust
pressure is speci! ed for the various part numbers.
2. SV valves can be made to operate automatically even
when the supply port and control ports are separate
(not connected as described in $1 above).
The SV valve will open (deliver air) and close (exhaust)
when control port pressure is increased or decreased.
Consult with Bendix Engineering for speci! c control port
pressure for valve opening and closing when this type
of automatic operation is used. When using the SV-1
synchro valve in this manner, the control signal ramp
rate should be limited by ori! cing or other methods.
Please contact Bendix Engineering with specific
application requirements.