Bartz, Paul wrote
"Are there not/were some large trucks that come with
line-lock type system for setting the brakes??
How do they pass the test??"
Trucks with air brakes use 2 different systems. The 1st
applys the brakes with air pressure. The 2nd, as best I
can remember is called "maxi brakes" applies the
brakes with spring pressure and releases them with
air pressure.
It works like this. Most of the wheels use the 1st system
and apply the brakes with air pressue. One of the axles
(if memory serves correctly typically the forward rear axle)
use the 2nd system and RELEASE the brakes with air pressure.
This way if you have air pressure all the brakes work and if
your air system fails then the brakes on 1 axle will automatically
be applied.
When the button or lever is pulled for parking the noise you hear
is the air being released from the system and therefore the
springs apply the brakes.
I suspect that the reason these brakes are considered O.K.
for emergency use is that they will not release if any air or fluid
was to leak out of the system. If line locks are not permitted then
I suspect that it is because they use the same fluid system as
the regular brakes and therefore offer nothing should a failure
develop in the main hydralic system.
Regards
Gary Zingle
1973 GMC 26 foot
"Are there not/were some large trucks that come with
line-lock type system for setting the brakes??
How do they pass the test??"
Trucks with air brakes use 2 different systems. The 1st
applys the brakes with air pressure. The 2nd, as best I
can remember is called "maxi brakes" applies the
brakes with spring pressure and releases them with
air pressure.
It works like this. Most of the wheels use the 1st system
and apply the brakes with air pressue. One of the axles
(if memory serves correctly typically the forward rear axle)
use the 2nd system and RELEASE the brakes with air pressure.
This way if you have air pressure all the brakes work and if
your air system fails then the brakes on 1 axle will automatically
be applied.
When the button or lever is pulled for parking the noise you hear
is the air being released from the system and therefore the
springs apply the brakes.
I suspect that the reason these brakes are considered O.K.
for emergency use is that they will not release if any air or fluid
was to leak out of the system. If line locks are not permitted then
I suspect that it is because they use the same fluid system as
the regular brakes and therefore offer nothing should a failure
develop in the main hydralic system.
Regards
Gary Zingle
1973 GMC 26 foot
