Air brakes

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Glenn Brooks
Posts: 2930
Joined: Mon Nov 10, 2014 1:39 pm
Location: Woodinville, Washington

Air brakes

Post by Glenn Brooks »

Hello All,

Iam restoring the original air brake system installed on my 1950 Ottaway steam engine. The original plumbing has been disconnected for years, and some components long since disappeared.

The air pump is a double acting pump running off a mechanical arm that connects to the cross slide. So it runs continuously.

My question is: should I install a simple inline cut out valve to divert the continuous flow of air to the atmosphere, once my reserve tanks reach operating pressure? Or would a small pop value somewhere in the line, suffice?

I am thinking a simple two way diversion valve would ease back pressure on the engine, hence increase draw bar tractive effort, during those times when I don’t need to replenish reserve air...

Also, wondering what max air pressure I should expect? The existing, original air pressure gauge goes up to 150 PSI. Iam thinking perhaps the intended operating pressure was designed to be somewhere from 80 to 100 psi? Does this seem reasonable for an airbrakes system equipped with 2.5” diameter brake cylinders?

Thanks
Glenn
Moderator - Grand Scale Forum

Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....
Soot n' Cinders
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Location: Marietta, Georgia

Re: Air brakes

Post by Soot n' Cinders »

A simple safety valve would be the simplest solution I think. It’d automatically relieve any excess pressure and seal on its own when needed. The downside like you said would be the excess back pressure robbing the locomotive of power. A diverter valve, such as a 3 way ball valve would do well also I think, but it will have to be manually actuated.
-Tristan

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-2.5" scale Class A 20 Ton Shay

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K. Browers
Posts: 94
Joined: Wed Mar 21, 2007 11:57 am
Location: Philippines

Re: Air brakes

Post by K. Browers »

Hello Glenn,
Some air compressors have a exhaust valve pressure switch. Perhaps you could use one of these to serve as your relief of the air pressure when you reach a set pressure point. the air relief mechanism of one of these switches is mechanical in its function. The relief valve is rather small so I do not know if it will pass enough volume of air for your purpose. A larger relief valve could be made though.
https://www.mcmaster.com/air-compressor-switches/
Happy stopping
Karel
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NP317
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Location: Northern Oregon, USA

Re: Air brakes

Post by NP317 »

Those are electric-powered air switches.
Glenn's pump is purely mechanical, if I correctly understood his description.

Perhaps set up a pressure-operated recirculation valve right at the pump allowing the air to be cycled back and forth through the pump when max pressure is reached.
RussN
Glenn Brooks
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Joined: Mon Nov 10, 2014 1:39 pm
Location: Woodinville, Washington

Re: Air brakes

Post by Glenn Brooks »

Yes, the pump is entirely mechanical- runs off the cross slide.

Should be able to fire up and test out the new plumbing in a day or so. Still no idea what the Ideal operating pressure should be. Thinking about just pumping air into the stands and determining how much is needed to activate the brake cylinders.

Still hoping to hear what operating pressures people might be running in our our scale...have some known PSI to compare to...

Thanks,

Glenn
Moderator - Grand Scale Forum

Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....
STRR
Posts: 469
Joined: Thu May 24, 2007 9:01 pm
Location: Westminster, CO

Re: Air brakes

Post by STRR »

Glenn,

Think gas engine powered air compressor. When the tank reaches design pressure, there is a cut out that allows the engine to continue running, AND the compressor still compressing but now the air is just discharged and not put into the tank until the tank pressure decreases enough to kick in the compressor again.

I'm sure you could get one of those dump valves and fit it to your compressor discharge just before the storage tank(s).

Good Luck,
Terry
K. Browers
Posts: 94
Joined: Wed Mar 21, 2007 11:57 am
Location: Philippines

Re: Air brakes

Post by K. Browers »

Hello Friends,
Yes of course the switches have an electrical application. They work by a mechanical diaphragm and that diaphragm mechanically releases the pressure on the compressor head by actuating a small valve on the side of the switch. I have had them apart many times. I do realize electronics and steam engines are anathema... He He He.. The link was to give an example of the type usually they can be found on a surplus compressor. Heavy trucks used to use a similar system to stop the air compressor from over filling their reservoirs called a governor. Perhaps you could find an old one of those. I have an electrical switch I could take photos of if you would like. The switches could be cut down to just the mechanical parts what would be left would be small enough to hide between your frames.
Cheers
Karel
K. Browers
Posts: 94
Joined: Wed Mar 21, 2007 11:57 am
Location: Philippines

Re: Air brakes

Post by K. Browers »

Hello Again.
The electrical pressure switches work on the same principal as the gasoline compressor head un-loader switches, good to think of them they totally slipped my mind. He He He
Karel
tetramachine
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Re: Air brakes

Post by tetramachine »

A govenor type unloaderWill not work as you think. At cutoff pressure the valve opens and tank air pressure is fed to the unloader valves on the compressor, those valves open the two cylinders to each other. So as one piston goes up the other goes down. The air goes from on cylinder to the other. none is pumped to the tank.
My wheels don't slow me down
6175
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Joined: Mon Aug 10, 2020 5:09 pm

Air governor

Post by 6175 »

I though I would post this link in case you were going to try to build a governor to control the pump. It is used for a regular design air pump, but I imagine you could adapt it over to your application.
The whole website is awesome though and full of great ideas.
http://nelsonslocomotive.com/Heisler/Br ... essorV.htm
http://nelsonslocomotive.com/Heisler/Br ... dConIV.htm
Glenn Brooks
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Joined: Mon Nov 10, 2014 1:39 pm
Location: Woodinville, Washington

Re: Air brakes

Post by Glenn Brooks »

Thanks all, for the great information in this thread. My near term approach is to replace the two brake cylinders at the drivers and find out if the existing cross head air pump works. The old cylinders were rusted shut and inoperable. It appears they are original equipment- installed in 1950 or thereabouts. Interestingly the casting marks show them to be original Delco rear brake cylinders. Dr Google reports they were used as OEM equipment on INternational Harvester Farmall tractors, and 1959 1/2 ton Chevy pickups.

My two replacement cylinders are 1/4” to wide. They don’t fit in between the drivers properly. So in process of cleaning up the old dust caps off the old castings to make them fit.

Also ordered an adjustable 1/4” pressure relief valve. This might allow overpressure to pop off the storage tanks. Simplest way to maintain pressure and still hopefully have an operable brake system.

Playing around with the idea of buying a small little racing kart hydraulic master cylinder and converting the whole kit and kaboodle to a hydraulic brake system... not authentic steam power for sure. but I suspect Herb Ottaway would would have gone for it in a hearbeat if these new high performance gadgets were available to him in 1950.

But first I need to know if the existing air pump and system does what it is supposed to do. Could be usefull for latter putting air brakes on the rolling stock.

Here’s a shot of the old and new replacement brake Cylinders.
1EF87EBC-0C61-4CA3-848A-19D389A29775.jpeg
Glenn
Moderator - Grand Scale Forum

Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....
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NP317
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Joined: Tue Jun 24, 2014 2:57 pm
Location: Northern Oregon, USA

Re: Air brakes

Post by NP317 »

Glenn:
Will you have a way to pre-charge the brake reservoir prior to running the locomotive?
Like a simple Schrader valve somewhere?
RussN
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