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.
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.
"Chet" fired this volley in news:DfWdnb4oPJBS6CnVnZ2dnUVZ firstname.lastname@example.org:
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.
"Chet" wrote in message news:DfWdnb4oPJBS6CnVnZ2dnUVZ email@example.com...
Dodge K cars use a vacuum actuator on the heater/defrost door that is just a little bigger than an old vacuum advance, and it has a rod sticking out of it that is attached to the diaphram that's easy to adapt to whatever.
What size is the old one? I could bet a cruise actuator or the 4X4 actuator from an S series GM would work. Or you could find a dashpot from the HVAC controls of 99% of the cars out there, just look behind the dash on the heat ducting.
Holley carbs with vacuum secondaries used a bolt-on cast body with replaceable diaphragm. Same unit for 50 years and counting. Get the body off any old Holley 4-bbl, including the truck models. Easy to adapt mounting, add a nipple for the vacuum port. Diaphragms available at any store that sells speed parts.
Lloyd, Many thanks for the info on your DIY vacuum actuator. I'm sure if I were looking at your unit your description would match perfectly. BUT not having one in my hand, I must confess the description leaves me a bit confused : - ( Any chance you could e-mail a drawing or equivalent??? This is clearly a case of needing to see the 'picture' before I can see the 'light' : - )
And thanks to all the others who offered great suggestions for obtaining a commercial substitute! I'll keep them on file in case my DIY version fails to perform...
Just by chance, I saw the open hood of a Chrysler today with a 3.5 Litre engine, and there right at the front of the intake manifold was a 2" or so vacuum levered gadget that apparently opens some sort of air shutters when you stomp down on the gas. Probably work for you.
On Wed, 27 Aug 2008 21:14:45 -0500, Lloyd E. Sponenburgh wrote: ...
As you've drawn it, it looks like pulling a vacuum would tend to collapse the membrane. Conversely, it looks like a proper setup for pneumatic operation.
If the push rod and vacuum inlet had their positions swapped, pulling a vacuum would pull the membrane out against the cylinder, improving the seal. Conversely, pneumatic operation would tend to collapse the membrane.
In short, from your earlier description I had envisioned the membrane being on the other side of the vacuum, ie, with the vacuum inlet on the left and push rod entering on the right. So, have I got things backwards, or maybe the direction doesn't matter?
Hi Lloyd! You bet I'm listening!!!!! And I must confess to being a bit confused. Both ways seem to have the potential to work correctly. Guess I'll have to plan on making a couple and see which one works best! I'll let everyone know which one won the competition. ; - )
"Chet" fired this volley in news:b5ednThL2f2TASvVnZ2dnUVZ firstname.lastname@example.org:
No.. the way I drew it, it would only work under positive pressure. Reversing the end the rod works through will allow it to work under vacuum. Otherwise, when vacuum is applied (to the end I drew), the sock would simply collapse inward.
Looks like it would work fine to pull the actuator bar in to the device, it just needs an external spring or such to pull it back out. But, it also looks like the sock would collapse on itself, so pulling vacuum such that the sock is expanded against the walls (from the other end) would probably be better for smoothness and longevity.
I knocked together a quickie version of the modifications suggested for Lloyd's sock-type actuator. I was blown away by it's power. I used some 1.5" pvc with caps and a bicycle inner tube. Hooked up a small vacuum pump, and couldn't not believe the amount of 'pull' on the rod!