Jump to content
 

air braked rolling stock


sej

Recommended Posts

I was wondering what would show in an ordinary view of a 7mm model coach with air brakes. From photos there doesn't seem to much at all going on underneath! How do air brakes work? Is there a reservoir/cylinder? What is the difference with vacuum braking and how can you tell from an end on view? Thankyou for your patience with my ignorance.

Cheers

Simon

Link to post
Share on other sites

Hi, that's really helpful, thankyou. These are vintage coaches from around the turn of the last century, with one air hose, so very likely to be the rather dodgy, original air braked system you describe.

Do you have any idea where the air cylinder might be situated, I'm hoping it would not be visible!

Many thanks again,

Simon

Link to post
Share on other sites

Hi, that's really helpful, thankyou. These are vintage coaches from around the turn of the last century, with one air hose, so very likely to be the rather dodgy, original air braked system you describe.

Do you have any idea where the air cylinder might be situated, I'm hoping it would not be visible!

Many thanks again,

Simon

 

 

Simon.

 

Would you like to tell us more about your project ?

You might get a more detailed response if we know what type / era / area your model represents.

 

Cheers

Link to post
Share on other sites

Simon, you don't say what sort of era or line you are modelling, as this will make a difference. Up until grouping in 1923, the use of Westinghouse (airbrake) and vacuum brakes varied between the different companies. The majority adopted the vacuum brake, as it was cheaper, but some of the better(!) lines, like the London Brighton & South Coast, selected the superior Westinghouse brake (with its triple valve), after a series of comparative trials at Newark in the 1880's showed the advantages. The vacuum brake is limited in power between normal air pressure and the best vacuum that can be achieved, whereas an air brake is as powerful as the pressure that can be applied in the system. Both ended up being fail-safe - a break in the pipe would automatically apply the brakes. Despite its advantages, the air brake was generally phased out following grouping, really for simplicity, as the two systems are completly incompatible, requiring expensive provision of through pipes or second sets of brake gear to accommodate through runnng between different companies, although it has recently made a comeback. (Westinghouse air pumps were used for Southern pull-push units, although only for the controls - the coaches were vacuum braked)

The twin-pipe system is a modern development, and not applicable, as far as I am aware, to older rolling stock.

What you might see under a coach will depend a lot upon the individual design, and how far you want to go in detailing. It would be best to track down a good drawing of the type of vehicle you are building, and you can then decide how much of the under-gubbins would be visible from the side elevation. On many coaches the provision of substantial battery boxes for electric lighting obscures much of the brake gear, which is mainly located closer to the centre line and thus less visible from normal angles anyway.

On the ends of coaches and fitted locos you might find up to three hoses, although only one is absolutely necessary if the vehicle is not expected to travel on another line - i.e. a Westinghouse brake connection or a vacuum brake one. The third possibility would be for steam heating, which was introduced gradually from around the turn of the century. On many vehicles it is possible to tell whether it is air-braked or vacuum fitted, as a vacuum hose has to be reinforced with wire to prevent the casing collapsing as the vacuum is created, whereas this is not absolutely necessary for air-brakes, so a smooth pipe would indicate Westinghouse brakes.

Really you need a good drawing, some clear photographs, and a bit of history to sort these things out for each vehicle you're doing.

Link to post
Share on other sites

Thankyou for all of your replies and interest. The coaches are NER 4-wheelers, from lovely little 7mm kits produced by Connoisseur, built around 1900's. None of the drawings I have show up anything under the floor. They were reportedly air-braked and I think, oil lit. I can't see anything on any of the photos I have and was wondering how the brakes were actuated.

Cheers

Simon

Link to post
Share on other sites

Had a look at the few NER drawings/books I could find and they weren't too helpful. As a stop gap, scrolling down this website page http://www.lner.info/forums/on-my-workbench-before-the-grouping-t937s30.html-st=0&sk=t&sd=a shows the udnerside of a four wheel van, albeit vacuum braked, which may help. The NER coaches would probably not have had the crossbar the full width of the carriage, as I think this is more appropriate for NPCS stock which would have had an external handbrake, but the location of the brake cylinder just off-centre is typical. Looking at the Connoisseur's instruction leaflet shows how the etched brake bits fit. One great advantage of NER stock would appear that they all had continuous footboards at axle-box level, which means that there is very little to be seen once these are in place!

Link to post
Share on other sites

  • RMweb Premium

I was wondering what would show in an ordinary view of a 7mm model coach with air brakes. From photos there doesn't seem to much at all going on underneath! How do air brakes work? Is there a reservoir/cylinder? What is the difference with vacuum braking and how can you tell from an end on view? Thankyou for your patience with my ignorance.

Cheers

Simon

 

Dutch Master answers it very well. As he says, you need a large brake cylinder for vacuum systems, as the "available" negative pressure is approximately 1 bar (14.4 psi)

With air brake systems, the pressure used is much higher (70-80psi?), therefore a smaller cylinder is required for the same mechanical braking effort. And a smaller cylinder is much easier to tuck away on an underframe!

 

Cheers,

Mick

Link to post
Share on other sites

Found this site http://www.1902encyclopedia.com/R/RAI/railway-40.html which shows a typical Westinghouse brake arrangement in both plan and elevation. From it you can see that very little is visible beneath the solebar level.

As Mick notes, because of the different pressures involved the vacuum cylinder has to be around 18 inches in diameter, which makes it very difficult to position horizontally, and also, due to its relative weakness, I believe the moving part (normally the piston) is made as heavy as possible, so that gravity can help. (Some versions had the piston fixed, with the cylinder moving instead) The air brake cylinder can be around 8 inches in diameter to achieve the same braking force, and doesn't need assistance from gravity, so can be set horizontally, working in both directions. (See also page 43 of Historic Carriage Drawings Volume 3 NPCS)

Link to post
Share on other sites

Thankyou everyone, and Nick, that webpage is perfect! I could see some small part of a cylinder in one picture and the diagram you found explains it all! Brilliant!

I've not used RM web before and I really appreciate the time and effort you've all taken, what a fantastic resource!

I'll try to post my coach-build pictures on the scratch/kit build section, when I've wrestled with the computer technology.

Many thanks again.

Simon

Link to post
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...