Questions about low air

[Gregory OConnor]

Mike has the most probable cause with debris in the line but I think
it is your Parkingbrake release valve. Some event removed too much
air to make the alarm go off and it held open and exhausted pressure
just under the buildup pressure of the compressor.

when you set the park brake you release air from behind springs at
the drive axle (double pumpkin maxicam). these springs are always
trying to put the brakeshoes to the drum. Air pressure is required
to compress the spring and push the shoe off the drum. So when you
drive, air must be maintained in the lines and at-axle diaphrams.
The parking brake is completly oppisite of the way service brakes
work. To test the ParkValve, line, and diaphram , do the following

Build up tanks to full pressure
Chock the tires
turn off the engine
release the parking brake (set to drive)
listen for leaks

you will hear air pressureize the spring diaphrams. Then you should
hear no more air passing the ParkBrakeValve. I put an ear to the
yellow handle. It should maintain the tank balance of air pressure
for an hour or so.

As far as your leakdown it sounds like it is good but you should
have someone in the trucking industry check it out. It is
inexpensive to have a CHP checkover of all systems at a certified
location.

GregoryO'Connor
94ptRomolandCa

--- In WanderlodgeForum@yahoogroups.com, "curlesw"
wrote:
>
> We were on the last few miles of our 4,000 mile trip yesterday and
> home was just a few miles down the road when my "low air" light
and
> buzzer decided to go off. We had just finished descending a
4,100+
> mountain and all my gauges were perfect. I immediately checked
all
> three air gauges and all three were well within the normal
operating
> limits. I checked my brakes and all was fine but nervous given
the
> situation. I continued slowly on and watched as the system
increased
> pressure as it normally does once it gets too low.
>
> We were able to make it home just fine but the light and buzzer
never
> went off, even when the system was clearly operating ok (i.e. the
> gauges indicating all was well). Once home, I turned the Bird off
> and walked around listening for leaks but could not find/hear
> anything. Today, I turned the Bird on and light and buzzer went
off
> once the system was fully pressurized. I drove to storage and all
> was normal, go figure. As such, I am thoroughly confused and have
a
> couple of questions.
>
> 1) Has anyone experienced a similar problem?
>
> 2) How long should a properly functioning system stay
pressurized?
> After 12 hours of sitting, my system will require a few moments to
> fully pressurize once I start the Bird. Also, when driving on the
> highway for example, the system goes from full to low and then
pump
> back up to full every 20-30 minutes. Is this normal?
>
> Thanks.
>
> Wayne C.
> San Diego, CA
> 1985 PT-40
>