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vacuum brakes

paddy

Joined: 11-01-16

Topics: 1

Replies: 1

Posted: Mon 19th Feb 2018, 7:19pm
vacuum brakes

does anyone use the p.n.p vacuum brakes? no matter what I try they just don't seem to brake very efficiently , I'm using around 15 vacuum ,one tender is behind a bagnal with steam ejector and the other is behind a sweet William using a 12 volt vacuum pump, they sort of pull on but not how I feel they should,any thoughts? or should I go back to manual brakes.
 

Replies To This Post

Mick

Joined: 1-01-89

Topics: 9

Replies: 163

Posted: Mon 19th Feb 2018, 8:01pm

All our carriages at Abbeydale are vacuum braked, and they have superb stopping power. If you look at my recent post on track and infrastructure there is a photo of one of our vacuum braked bogies. 15hg is typical and with the correct leverage should work fine. One thing I have found with PNP cylinders is that when setting them up you do need to have them empty of air when you do so, so they can pull the maximum - difficult to explain! You can't set them up just as they come out of the box, i.e. you need a vacuum source to do it, e.g. a pump.
 

Denis Mulford

Joined: 1-01-89

Topics: 4

Replies: 29

Posted: Mon 19th Feb 2018, 9:29pm

At Oxford we use all PNP vacuum products and they work well. I suspect your problem is in the adjustment, do not have the brake blocks too far off the wheel when brakes are off or in the linkage, I was always told to try and get them at 9-1 ratio but have found 6-1 works well. Also from experiance I have found that you do not want the pins in the linkage to be too good a fit, build in a little slop and remember to oil.
Our diesel works happily on 10hg.
 

Peter Beevers

Joined: 9-10-01

Topics: 4

Replies: 154

Posted: Tue 20th Feb 2018, 6:43am

As mentioned above, old fashioned tread brakes can be a nightmare to set up. Far better is the modern equivalent, the disc brake, which is an order of magnitude simpler, and provides significantly more stopping power. Our coaches have one axle per bogie braked and on test, loaded with 300kg, stop quickly from 3mph on the steepest part of our line (1 in 50).
 

paddy

Joined: 11-01-16

Topics: 1

Replies: 1

Posted: Tue 20th Feb 2018, 7:46pm

many thanks for your comments, I take it mick that what you mean is before linking them to your brake linkage you must firstly apply a vacuum source, i.e a 12 volt pump ,(which I do have) and then while its causing a vacuum then set up your linkages to the brakes? am I right?, also I do have the brake shoes set very close, it seems that there is just not enough (pull) when the vacuum goes off, iv'e never had any luck with these brakes so maybe mick I will try what I think you mean, many thanks everyone and will see how it goes.
 

Mick

Joined: 1-01-89

Topics: 9

Replies: 163

Posted: Wed 21st Feb 2018, 8:51am

You have got the idea Paddy, when you have a go with a pump I think you'll find it works! Sorry I couldn't find a better way of explaining it. It also helps if you profile the brake blocks to match the wheel diameters.
 

Little Hunslet

Joined: 8-11-00

Topics: 4

Replies: 32

Posted: Sat 24th Feb 2018, 10:12am

Hi Paddy, Just read through all the posts and I think Dennis probably has the answer with the lever ratios. Wherever I go most clubs seem to use PNP and work fine. I use them on my Romulus and my driving trucks without any problems. Check the lever ratio and don't forget to let us know how it turns out.
Pete
 

Xz

Joined: 1-01-92

Topics: 24

Replies: 296

Posted: Sat 24th Feb 2018, 4:20pm

I would add to all the above, don't go looking for 'car' type brakes, it's a train! It's very easy, even with Vac brakes to lock the wheels and wonder why it isn't stopping too well. You're running metal to metal, not rubber to tarmac.

There's is also an old addage that says a good driver shouldn't need them.
 
 
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