Re: NT Class again

[Keith Malcolm <kmalcolm@tpg.com.au>]

Aus loco discussion mailing list

I don't know if this would be any help, but the NSW 73 class are similar to 
the QR DH. If the brake cylinder is above 200kPa then the throttle won't 
operate if the transmission is "in".

Dave Malcolm

At 01:18 PM 03-04-00 -0500, you wrote:
>Aus loco discussion mailing list
>
>Peter, I can't help you much here, except to guess at what might have
>happened.
>
>The control system air reservoir is usually fed from the main reservoir
>through a protection valve that will not feed until main pressure is above a
>value like 75 lbf/in2.  Likely the DH class has an air-operated reverser (I
>think that most Voith hydraulic transmissions have an electro-pneumatic
>arrangement.)  So even if the driver reset the direction, the reverser
>itself might not do anything if the control air pressure was low.  The
>reverser can be the heaviest load for the air control system, and so likely
>the first to suffer from non-function from low pressure.   I think that the
>DH might also have an air throttle, so with low control air pressure, it
>might not open very far, but nevertheless enough to move the loco.  And the
>throttles often operate at reduced pressure (e.g. 60 lbf/in2 max for the
>standard Westinghouse system, and even lower for the EE system) so would be
>less affected by low control reservoir pressure.
>
>As far as I know, most locos have interlocks that prevent the application of
>power (or cut off an existing application of power) if there is insufficient
>air pressure in the main reservoir to properly operate the brakes.  So you'd
>think that this would supervene.  But maybe there's a situation when you can
>have enough main reservoir pressure to release brakes, but still be a bit
>low in terms of control air pressure.
>
>Maybe someone familiar with the Walkers DH locos can confirm/refute/modify
>the above guess?
>
>Steve P.
>
>
>----- Original Message -----
>From: Peter Donaghy <PeterDo@als.com.au>
>To: 'Aus loco discussion mailing list' <Ausloco@listbot.com>
>Sent: March 23, 2000 07:00 PM
>Subject: RE: NT Class again
>
>
> > Aus loco discussion mailing list
> >
> > What arrangement exists on the ex-QR DH class units?  When I was in
> > Alice Springs recently, the two operators rearranging pass cars and
> > locos at the Ghan Preservation group invited me onto DH14 with them.
> > The loco had just been re-started, and when the brakes were released,
> > rolled the opposite direction to that which the driver tried to move.
> > He re-braked, and said the compressor hadn't pumped the air up
> > adequately.  After another minute or so, everything was OK.  Is this a
> > throttle matter, or reverser?
> >
> > Peter
> >
> >
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