vacuum brakes, how do they work?

[E.M. Bell]

OK, here is a question for the Tecnical types across the great pond.. or maybe even here in the Good OL USA. I have often wondered how the British vacuum brakes functioned, and the components of the system. I am studied in the various forms of pheumatic braking systems inuse in the USA, and have been through all the classes to inspect, rebuild clean....blah blah blah.... air brakes, but the thought of a brake system the sucks instead of blows is truly foreign..

Specific questions..

1. How exactly do they create the vacum?? I assume that each locomotive has a vacum pump just as here in the US, each loco has a air comp. . When two or more locos are MU'ed, does the vacuum system MU as well?

2. what is the standard operating pressure? or is that negitive pressure....

3. Hoses and connections. What are the hoses and conncetitions between equipment made of? It would stand to reason they are not rubber (I could be wrong), as the negitive pressure would suck the hose into...so, metal or metal shielded?

4. Locomotive brakes. Does each loco have a seperate brake system, either vacuum or air....

5. operation....in simple terms. I assume that when the brakes are released, the brake pipe has at least normal atmosperic pressure. To apply, the pressure is reduced by the vacuum pump, pulling out the cylinders to apply the brakes aganst the wheels. are there a number os resivors and valuves on each car to help this along?

6. is this style of brake system still in common use? and if so, in what countries?



any answers would be great..or a point to a web site that might help.. if I get good answers, I might have more questions :)

[Dutch Steam]

I only know that vacuum pomps are used a lot at ( British ) steamengines.
And i know that this system is forbidden in the rest of europe.

a british engineer told me that Britain choose for this sytem becaus this system don`t have so much meachincal wear, likethe westinghouse system has.

I know it`s not much, but maby it will help you...


And sorry for my bad english,

Kind regards,

[Rod Williams]

I don't know where and if these brakes are still being used much but simply.......they work much the same way as an air brake but do not need an auxilliary reservoir on each vehicle to provide air to the brake cylinders when the brake pipe pressure is reduced by the driver. Instead the loco pump creates a vacuum in the entire system. To apply the brake some positive pressure is allowed to occur which causes an imbalance of pressure and vacuum in valves on each vehicle. This imbalance then allows atmospheric pressure in to the system which works on the brake piston ( the piston has vacuum on the other side ) thus the brakes are applied. The brake pistons/cylinders are very big because because atmospheric pressure is as you should know only about 14lbs whereas with an air brake brake cylinder pressure is up around 50lbs. Drivers that worked with this system liked it because unlike the Westinghouse brake it was impossible to run out of auxilliary reservoir air and lose the brakes. The system obviously had shortcomings or it would have survived. Personally I have never used it, my company always had Westinghouse brakes. I have seen it used in the UK and Tasmania ( Australia ) but never had a go at it myself. All fixtures and fittings were the same type as used with air brakes. Atmospheric pressure will not crush strong rubber flex the same as a 70-90lb brake pipe will not blow it.

[rahul.v.rao]

Some of the older Indian locomotives WDM series 1957 to 1979 have vacuume brakes. Now a days most have been retrofitted with air-brakes with a rare few still having both kits so that they can be used with both older and newer rakes. Indian railway shifted from vacuume to air brakes gradually from 1979 onwards.
Rod has explained the operation perfectly.
A vacuume braked train gets locked or immobilised if there is a leak in the system.
A lag in releasing the brakes is one of the main reason why they were discontinued

[Tåg]

So these were only used in the Commonwealth countries? Did the Canadians ever use the system? Is it a failsafe system like the Westinghouse system? (Loose your air and go into emergency)

[rahul.v.rao]

It is falesafe. The train just cannot moove if the vacuume is low or the circuit leaking. Only thing is that the brakes release a few seconds after the driver releases them and that too gradually When stopped on a gradient the engineer has to apply some power to prevent roling back. This is not sutable for today operating conditions where a Train follows another at a frequency of less than 2 minutes in most high traffic zones.
Stand next to one of the older trains and you can see that the brake shoes are gradually releasing and scraping for about half a minute even after the train starts moving.
I expect that the locomotive must be consuming more energy as well as brake lining.

You can see a few ancient(1950s) ALCO locos with vacuume brakes in India that means even US might have used or atleast manufactured and exported them years ago.

[Benbe]

Hi,

I recommend you two articles:
http://en.wikipedia.org/wiki/Vacuum_brake
http://www.midcontinent.org/rollingstock/dictionary/eamesbrakes.htm
The latter mentions mainline usage of vacuum brakes in the US.

Here's a transscript from Google Books:
http://www.google.com/url?sa=t&source=web&ct=res&cd=9&url=http%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3Dd asMbOShnJEC%26pg%3DPA548%26lpg%3DPA548%26dq%3Dvacu um%2Bbrake%2Bwestinghouse%26source%3Dweb%26ots%3DF-PY-CyJJl%26sig%3Dn4bBBw3ikIAX_yCfAKgfl2lj7GU%26hl%3De n%26sa%3DX%26oi%3Dbook_result%26resnum%3D9%26ct%3D result&ei=KAK7SMyFLomg0gXbp7WwDA&usg=AFQjCNFFSaiQuDcZvZPn0BGFTwUu7HSsUQ&sig2=5Y3tQhTLIS4_gchb0U3RXg





B