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

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

What Mark was talking about is the Vaccum powered air compressors. They
have a very long pressure recovery time so use with an air horn would be
limited. They work great for Air bag assist on suspensions though.

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 þ SLMR 2.1a þ 0