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Posted by Chet on August 26, 2008, 5:29 pm
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Hi Guys!
I run a 1/8 scale live steam locomotive.
While testing the vacuum brakes on my tender, I blew out the diaphrams that
activate its brakes.
The original unit was used as a vacuum advance for old-time carburetors and
is now an endangered species.
Anybody have success making their own from scratch?
If so, would you be willing to share the process?
Thanks in advance,
Chet (engineer of ANCR Mogul #9401)
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Posted by Bruce L. Bergman on August 26, 2008, 6:43 pm
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On Tue, 26 Aug 2008 17:29:50 -0400, "Chet"
>Hi Guys!
>I run a 1/8 scale live steam locomotive.
>While testing the vacuum brakes on my tender, I blew out the diaphrams that
>activate its brakes.
>The original unit was used as a vacuum advance for old-time carburetors and
>is now an endangered species.
>Anybody have success making their own from scratch?
>If so, would you be willing to share the process?
>Thanks in advance,
>Chet (engineer of ANCR Mogul #9401)
Haven't built one, but a distributor vacuum advance was expected to
move a few grams of linkage, not transmit enough force to (in concert
with two dozen others) stop several hundred pounds of train and
riders.
You might have to come up with your own design - make two shell
halves that bolt together with 6/32 screws to roughly duplicate the
shell of your vacuum advance, get some fabric reinforced neoprene
gasket material - think fuel pump diaphragm, and two fender washers
sandwiched in the middle on a rod nut for connecting an actuating arm.
Go take apart an old mechanical fuel pump for ideas on how to build
the working section - they transmitted the levels of force you need.
Or look at a truck air brake actuator for ideas. Scale down.
Or see if you can find a miniature air cylinder that is the right
size and shape for the job, and you can just buy them and drop them in
instead of reinventing the wheel. Clippard or Cincinnati or Bimba...
On that note, you can get a lot more power from air than vacuum,
even under "Direct Air" - or duplicate the full WABCO Relay system in
scale, and if the train brake pipe breaks everything stops.
--<< Bruce >>--
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Posted by Jim Stewart on August 26, 2008, 7:19 pm
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Chet wrote:
> Hi Guys!
> I run a 1/8 scale live steam locomotive.
> While testing the vacuum brakes on my tender, I blew out the diaphrams
> that activate its brakes.
> The original unit was used as a vacuum advance for old-time carburetors
> and is now an endangered species.
> Anybody have success making their own from scratch?
> If so, would you be willing to share the process?
> Thanks in advance,
> Chet (engineer of ANCR Mogul #9401)
Look at a cruise control throttle actuator.
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Posted by spaco on August 26, 2008, 7:32 pm
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How about using a vacuum operated windshield wiper motor instead? They
have a lot more power than a vacuum advance would have. This "old
stuff" isn't gone, you just have to know where to look. In Minneapolis
Mn there's a place called "Little Dearborn" where you can get almost
anything for old Fords at least. I didn't say "cheap", though.
I'd also try an outfit like Bimba who makes air cylinders. They make
em pretty small and the difference between air pressure and vacuum isn't
all that great.
Also, there are companies that make vacuum sensing switches. We used
to use several open bellows types. There are your bellows.
Pete Stanaitis
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Chet wrote:
> Hi Guys!
> I run a 1/8 scale live steam locomotive.
> While testing the vacuum brakes on my tender, I blew out the diaphrams
> that activate its brakes.
> The original unit was used as a vacuum advance for old-time carburetors
> and is now an endangered species.
> Anybody have success making their own from scratch?
> If so, would you be willing to share the process?
> Thanks in advance,
> Chet (engineer of ANCR Mogul #9401)
>
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Posted by Lloyd E. Sponenburgh on August 26, 2008, 8:08 pm
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> Hi Guys!
> I run a 1/8 scale live steam locomotive.
> While testing the vacuum brakes on my tender, I blew out the
diaphrams
> that activate its brakes.
> The original unit was used as a vacuum advance for old-time
> carburetors and is now an endangered species.
> Anybody have success making their own from scratch?
> If so, would you be willing to share the process?
> Thanks in advance,
> Chet (engineer of ANCR Mogul #9401)
>
YES! I built my own cruise-control in the 1980s. I built a "sock"
type actuator. It's really simple.
Get an inner tube of the un-inflated diameter about what you want.
Find a piece of metal or plastic tubing into which it will fit
closely.
Find or fabricate a disk that will fit inside the inner tube when it
is doubled over inside itself.
Cement/fasten/clamp the inner tube to the disk. Then turn the whole
assembly inside-out, so the disk pulls the "inner" portion down inside
the "outer" portion.
Now slide the whole tube/disk affair inside your metal tubing, and
fold the free end of the inner tube over and around the butt-end of
the tube.
Seal it with a little adhesive between the outer surface of the metal
tube and the inner tube fold-over. Add over that a cap that fits
tight. Apply vacuum to the cap end.
You may also install a return spring inside, or rely upon an external
return spring.
Mine lasted eight years of daily interstate driving without a leak.
LLoyd
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>I run a 1/8 scale live steam locomotive.
>While testing the vacuum brakes on my tender, I blew out the diaphrams that
>activate its brakes.
>The original unit was used as a vacuum advance for old-time carburetors and
>is now an endangered species.
>Anybody have success making their own from scratch?
>If so, would you be willing to share the process?
>Thanks in advance,
>Chet (engineer of ANCR Mogul #9401)