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Brakes....vacume or pressure????

andrieskeyser

Joined: 1-01-70

Topics: 3

Replies: 4

Posted: Fri 10th Jun 2011, 2:20pm
Brakes....vacume or pressure????

Good day Gentlemen,

I have been a member of this society for not too long so please excuse me if this subject has been discussed before.

I am nearing the completion of my narrow gauge steam locomotive and it is time to think about brakes. Being from South Africa and a third world country, the blokes around here don’t really care for brakes, thus I cannot look at any successful braking systems locally. Up to now it was a case of the biggest feet stops the quickest!

I would like to fit vacuum brakes to my engine and the rolling stock I intend to build for it purely because that is what was used on the South African Narrow Gauge system, however I am sure there are pros and cons when it comes to vacuum and air brakes…. So what system is the best?

Things that I think would be relevant to designing such a system:

- Vacuum/pressure of the system
- Generating of Vacuum/Pressure
- Reservoirs
- Coupling between rolling stock
- Brake cylinder size and how it’s made?

Is there anyone out there that has a successful working braking system that would not mind sharing this valuable information?

Kind regards
Andries (Unstoppable) Keyser
 

Replies To This Post

Xz

Joined: 1-01-92

Topics: 17

Replies: 244

Posted: Fri 10th Jun 2011, 4:42pm

Hi Andries, a well designed system of either type is just as good as the other. One thing about train brakes is that they will never be as good as the ones on your car, it's to do with the friction between wheel and rail, metal wheel on metal rail will never be as good as rubber tyre on tarmac road. With a steam loco, I beleieve it is easier to use vacuum brakes as sufficient vacuum can be obtained for very little steam usage. To provide air pressure you need a compressor which is much easier driven electrically, which of course means carrying, and charging, a battery. Of course there are many people who are quite willing to take that trouble. Several of the companies that advertise with us can provide parts. I suggest that you access a few of their websites to get an idea of what is needed.
 

colinedmondson

Joined: 9-08-09

Topics: 3

Replies: 82

Posted: Sat 11th Jun 2011, 5:34pm

If you are stuck for space to mount the brake cylinder stick with air, you can use up to 50 psi or so whereas vacuum is generally limited to the difference between atmospheric and the vacuum in your system, normally 12 - 13 psi. Hence air brake cylinders can be a lot smaller for the same pull or push. Vacuum lends itself to steam locos, I would prefer air on anything else. It is possible to mount an air pump under a driving truck driven by a chain off the axle, to save carrying a battery around. Hope this helps, Colin Edmondson 4443
 

Peter Beevers

Joined: 9-10-01

Topics: 3

Replies: 134

Posted: Sat 11th Jun 2011, 5:52pm

Andries,
With a steam loco, vacuum brakes are generally easier. Aim for 15" of mercury. I use ejectors from Live Steam Models in Derby to create the vacuum. Ejectors are a bit fiddly - the steam passages are quite small - if it stops working, take it off, blow it though and it will work again. Also keep the exhaust from it (the 1/4" pipe) short and free from tight bends. They also supply vacuum gauges etc.
Reservoirs, cylinders etc. can be obtained from Paul Norman Plastics. His website has a good schematic of how it all works too. He also supplies a vacuum limit valve, and a brake application valve.
Between vehicle couplings - use gas-type oldham nozzles, and push rubber hose on. It's as simple as that.
I think I've answered all your questions, but would be more than happy to explain a bit more if required.
Regards
Peter
 

bruce morgans

Joined: 21-01-05

Topics: 6

Replies: 18

Posted: Sun 12th Jun 2011, 9:23am

Hi. My advise would be to use vacuum braking on the rolling stock only. There are a number of suppliers including Paul Norman. I have used his products and found them to be very good. Normally the weight of the rolling stock and passengers is greater than the weight of the loco so the brakes on the loco are secondary to those on the rolling stock as the stock should provide most of the braking force. I have a Romulus narrow gauge loco and only have the hand brake, which I find totally adequate. An ejector is fitted for operating the train brakes. I'm currently finishing a Tom Rolt, another narrow gauge loco and although I have fitted a steam brake I may not bother to connect it up. The hand brake is all I feel I need. Regards
 

Andries Keyser

Joined: 1-01-70

Topics: 3

Replies: 4

Posted: Mon 13th Jun 2011, 9:26am

Thanks for the info chaps! I will certainly follow up. Seems like Paul Norman is the man to see.

@Xz, about the stopping like a car…. I have a Stannier Black 5 that will disagree with you. On many occasions I have watched it throw the driver over the cab once the steam brake is applied, seat and all! The wheels don’t lock up, how it does it is just not possible to describe in words, you have to see this one
 

Xz

Joined: 1-01-92

Topics: 17

Replies: 244

Posted: Mon 13th Jun 2011, 4:48pm

Gotta be something to do with dry S.A, steel then, without a hint of water or oil.
 

bobbramson

Joined: 23-09-00

Topics: 1

Replies: 3

Posted: Tue 6th Dec 2011, 8:41am

Hi Andries,
I am the author of "Braking for Model Engineers" and can send you a serialised copy of my lecture and article if you wish. In my opinion there is no arguement - fit vacuum brakes. I have developed a range of vacuum ejectors which will allow you to operate at 21" Hg and evacuate at the rate of 3 to 20 cu in per second depending on the size of your loco. Please let me know if you require further information and best wishes for your project.
Bob Bramson Memebr 2945
 

Graham Burhouse

Joined: 1-01-96

Topics: 4

Replies: 13

Posted: Tue 6th Dec 2011, 12:13pm

Hi Andries, I have a Tom Rolt with a dual vacuum and steam brake valve, when the handle of the brake valve is moved 45 dergrees the train vacuum brakes are applied to the driving truck and any coaches connected,a further quarter turn applies both the steam brake to the engine and contunes to apply the vacuum, this gives you the best of both worlds, only in emergency do I need to used the steam brake. Vacuum brakes are more commonly used which is handy when taking your loco to other tracks and using their rolling stock.
 

Andries Keyser

Joined: 1-01-70

Topics: 3

Replies: 4

Posted: Tue 6th Dec 2011, 7:41pm

@Bob, I would greatly appreciate it, how do we go about it? Is it a hard copy or can it be emailed? My address is andrieskeyser@yahoo.com. I look forward to the info.

@Graham, sounds like a good idea, do you maybe have some drawings or even pictures you would be willing to share?

But now a question, one that I hope Bob will cover in his lectures:

How do you adjust the brakes when the train is loaded and unloaded? In our scale and gauge, the weight of the coach must more than double when the very oversized passengers apply their backsides to it. In other words, a brake that will effectively stop a loaded train without skidding would just lock up the wheels and skid past the platform if unloaded?

Is this right, and if so, is there a way to compensate?
 

Mike

Joined: 18-07-06

Topics: 2

Replies: 20

Posted: Wed 7th Dec 2011, 8:09pm

Andries....

I'm not sure how you would do it with vacuum brakes, but our (admittedly standard gauge) Aluminum coal gondolas have a "load and empty" air brake. It's just a valve inserted into the cylinder application line between the air brake control valve and the brake cylinder. The valve is controlled by a lever, connected to a plunger, which is pressed upwards by the top of the bogie frame when the car is loaded. When the car is empty, the valve diverts some of the application pressure to a small reservoir on the car, effectively increasing the volumne of the brake cylinders, thereby lowering the average cylinder pressure from an application. When the loaded car "goes down on the springs", it moves the plunger up, so that all of the air from the control valve goes directly to the cylinder, then it gets a higher pressure from the same amount of brake pipe reduction.

I hope that was somewhat understandable.

Best,

Mike....BN Engine Driver and 7-1/2" gauge Erskine Tramway
 

fireflymaster

Joined: 1-01-70

Topics: 0

Replies: 1

Posted: Wed 15th Jul 2015, 11:04pm

Does anyone actually have a diagram for fitting airbrakes
 

johnnicholson

Joined: 1-01-77

Topics: 12

Replies: 69

Posted: Wed 15th Jul 2015, 11:30pm

For vacuum brakes you will find all the details on REEVES drawing sheets 1 &2 part No. RV1
 

colinedmondson

Joined: 9-08-09

Topics: 3

Replies: 82

Posted: Thu 16th Jul 2015, 10:59pm

This is my diagram for air-air failsafe brakes, with the reservoir built into the bogie and the coach only carrying a through pipe. The compressed air is piped from the loco via a variable pressure valve of my own design. Once the reservoir has been charged any reduction in line pressure results in a brake application.
This is my diagram for air-air failsafe brakes, with the reservoir built into the bogie and the coach only carrying a through pipe. The compressed air is piped from the loco via a variable pressure valve of my own design. Once the reservoir has been charged any reduction in line pressure results in a brake application.
 

Denis Mulford

Joined: 1-01-89

Topics: 4

Replies: 24

Posted: Thu 16th Jul 2015, 11:58pm

For Vacuum brake set up look on the PNP Railway website as there is a working diagram.
 
 
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