BENDIX TCH-003-009 Fascicule

Subject: 

We have recently experienced leakage problems at the exhaust of our dual circuit brake
valves with double check stop light switches installed.  Some OEM manufacturers are
using a double check stop light switch between the two circuits of the dual brake valve to
eliminate the need for two stop light switches.  One inlet to the double check is supplied
from the primary delivery circuit of the dual valve and the other is from the secondary
circuit.  The delivery port of the double check stop light switch is plugged.

In some cases, when a brake application is made and partially released, leakage out the
exhaust of the brake valve occurs.  This leakage is a result of the double check shuttle
centering itself allowing the primary and secondary circuits of the brake valve to cross
feed.  If this application is held for an excessively long period of time both circuits of the
system can be bled down.  Additional application or release of the valve, however, will
stop the leakage.

If this leakage problem occurs, our recommendation is to install a separate stop light
switch in each circuit of the dual brake valve and wire switches in parallel.