QUICK RELEASE VALVES AND DIFFERENTIAL QUICK RELEASE VALVE
Quick release valves are used to release air from air
brakes at the brake chamber. This makes the release of
brakes quicker than a system where the chamber air has
to flow back through the brake piping to the foot valve.
There are two types of quick release valves, the basic
type and the differential type.
These valves are usually mounted on the frame close to
the brake chambers they control. The line connected to
the top port is the delivery line from the brake valve. The
two side ports are the brake chamber connections, and
the bottom port is the exhaust. In most cases it also
functions as a tee and connects two air brake chambers
to the line from the foot valve.
The valves that are used by International Harvester are
supplied by Bendix and by Midland.
BENDIX QR-1 TYPE QUICK RELEASE VALVE
The Bendix valve can be distinguished by having a cast
body and cover (Figures 1 and 4).
Figure 1 - Bendix QR-1 Quick Release Valve
The brake foot valve port is in the body and the other
ports are in the cover.
MIDLAND TYPE QUICK
The Midland valve can be distinguished by having a cast
or plastic body and stamped cover (Figures 2 and
5). The brake foot valve port and the brake chamber
ports are in the body. The exhaust port is a set of holes
pierced in the center of the stamped cover.
Figure 2 - Midland Quick Release Valve
QUICK RELEASE VALVE
The Midland differential quick release valve can be
distinguished by having a cast or plastic body and cover
like the Bendix valve, but having the brake chamber
ports in the cover (Figures 3 and 6).
QUICK RELEASE VALVE
When a brake valve application is made, air pressure
enters the top (brake valve) port of the valve (Figures 4
and 5). This will move the diaphragm down closing the
exhaust port. At the same time, the air pressure forces
the edges of the diaphragm down. The air will then flow
to the brake chambers.
diaphragm equals the air pressure being delivered in the
brake valve, the outer edges of the diaphragm will seal
against the cover seat. The exhaust port is still sealed
by the center portion of the diaphragm.
When the brake valve is released, air pressure above
the diaphragm is exhausted. This will allow the
diaphragm to raise, opening the exhaust port. It will then
allow the brake chamber pressure to release through the
CTS-4079A-CHAPTER V - Page 2