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   
      
   --- Twit(t) Filter v2.1 (C) 2000-10   
    * Origin: Roiz Flying \A/ Service * South Texas * USA * (1:387/22)