Brake Cylinder Dimensions

[Chris RandallParticipant @chrisrandall69004]

I am fitting a steam brake to the loco but I have overdone the size of the brake cylinder! Can anyone devise a formula for the cylinder diameter? I am not sure of the axle load and calculated it from a guess, making the pressure on the brake blocks equal to the weight carried by the driving wheels.

[Chris RandallParticipant @chrisrandall69004]

formula sought

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Chris ,

 

I could show you how to do the calculation that full sized designers used but in truth for a model there are so many indeterminates that the result would not be very accurate .

 

I suggest that you do two things instead of calculations :

 

(1) Get information about steam brake cylinders on successful model designs and adapt and modify to suit your specific needs .

 

(2) Copy the principles and general dimensions of full size steam brake systems .

 

Notes :

 

Typical full size steam brake cylinders usually had bores in the range 4 inches to 9 inches .

 

Taking the larger size that becomes 9/16 to 5/8 inches for a 3 1/2 inch gauge engine and

3/4 to 7/8 inches for a 5 inch gauge engine .

 

Some full size engines had two steam brake cylinders – one each side and these were usually smaller .

 

The success of steam brakes in a model depends very much on the design of the brake valve .

 

MW

Edited By MICHAEL WILLIAMS on 02/02/2012 13:56:03

[Chris RandallParticipant @chrisrandall69004]

Hello Mike

 

Thanks for your helpful post.

 

Scaling down your suggested dimensions for 7.25 inch gauge I see that max size would be about 1.125 inches based on full size practise. I think mine is 1.5 inches. The ratio of all the linkages must be about 4 times increase in pressure.

 

It will be interesteg to see what happens when loco is fully assembled and running and I might have to sleeve the cylinder and make a new piston or else end up with square wheels!

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