27 Jul 12 22:04, Richard Webb wrote to Roy Witt:

 RW> * Reply to a message in fidonews.

 RW> On Fri 2012-Jul-27 05:39, Roy Witt (1:387/22) wrote to mark lewis:

 ml>> i can't say that i've ever known an air horn to work on a vaccum
 ml>> system... or air brakes, for that matter... everything i've seen has
 ml>> been under pressure...

 RW>> Yes, air horns require a compressor, but there are also electronic
 RW>> horns that can wail at 108db that sound like the old air-horn you're
 RW>> talking about.

 RW> I'm not sure this is electronic, large air tank, with a
 RW> fitting that can be used to pressurize it.  This is one
 RW> reason I wonder if at one time there wasn't air brakes with
 RW> hydraulic assist as well as the hydraulic.

I was thinking it was a vacuum tank, but you mentioned 'air gage' which
would mean to me that it is a pressurized tank. If you had mentionedd
'vacuum gage' I wouldn't have to assume anything. If you can, checking the
cab-mounted horns for hoses or wires would give us an idea of what they
are. Or a pull-chain air valve in front of the driver...

 RW> There is a regular electric horn though under the hood, but
 RW> air horn is atop the cab, at least the "trumpet" part, tank
 RW> mounted down low, usual configuration as would be seen in
 RW> your usual Freightliner or Kinworth.

Is there an air-valve in the cab with a pull-chain attached?

                R\%/itt

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