Re: Flat Wheels in Sydney

["Rod" <berlina@bigpond.com>]

Rob McKiernan wrote in message ...
>Excues my ignorance but what is the difference between hand and park
brakes.
>Cheers,
>Rob
>
in general a hand brake is cranked, or wound on, if a wheel, till tight,
thus mechanically holding the brakes to the wheel or disk.
Park Brakes are now becoming more common, and in Victoria we came across
them first on 81 Class diesels that ran on the NE SG. [ and later on the
Comenge Sparks} A gauge showing on and off positions is installed at some
convenient place in the Locomotive cab, and a pneumatic switch forces air to
the brake cylinder, forcing the cylinder to release against a "parking "
spring...Release Position.
When the switch is reversed the air drains away and the Park brake applies.
This is a very safe way of applying the brake, because the brake
automatically applies if the air is lost.
As an example, the driver might forget to apply the handbrake, Shuts down
the loco and it is held still by the applied engine brake. As the Main Res.
air leaks away, the engine brake releases, and could allow the Engine to
roll away!
but the air holding the Park brake off also leaks away, allowing the Park
brake to apply via spring pressure.
There you go....should not be any 'driver' speak there to confuse you,
simple.
The ratchet style hand brake would of course still remain off and the loco
would roll when the air pressure dropped far enough to release the brake.
Rod