cylinder cock design from latest live steam mag...

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10 Wheeler Rob
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Re: spring loaded check ball vavels

Post by 10 Wheeler Rob » Fri Mar 06, 2009 12:03 pm


That is a slick machanical design, I like the way it can be built in a very small size, and that it lets a water filled cylinder self releive. Very neet!

The great, elagant, and pratical machanical solutions to the may complex things on steam locomotives and the execution of it in detail in the models is what attracted to me to this hobby.


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Post by ccvstmr » Fri Mar 06, 2009 12:33 pm

Question...(for anyone that might want to provide an answer)...

If the relief valve Bill provided a drawing for is "self-relieving"...why would you want (or need) a mechanical lever to open the valve? Carl B.
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Post by bcody » Fri Mar 06, 2009 12:57 pm

I have seen a set of very small relief valves installed as cylinder cocks. Just build a small relief valve and set the relief pressure at slightly higher than the boiler relief valve setting. The relief valve type cylinder cocks will protect the cylinders from liquid lock and normal running will quickly warm the cylinders. They require no activation levers/linkage or steam lines to close the cylinder cock. Just install and go run.

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Post by cbrew » Fri Mar 06, 2009 4:42 pm

ccvstmr wrote:Question...(for anyone that might want to provide an answer)...

If the relief valve Bill provided a drawing for is "self-relieving"...why would you want (or need) a mechanical lever to open the valve? Carl B.

because, at slow speed, the pressure will not get Hi enough to open the valve
(at all on a slide valve because the valve will left off the seat)
(until the piston valve closes the exhaust port)
the water will shoot out the stack and you and anyone near by will get a hot shower

Also one more thing, if the opening pressure is greater then the boiler pressure, then at startup, the chance of locking the engine up is present.

Nothing beats cylinder drains that open manually.
Just my 2 cents
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Cylinder drains

Post by steamingdon » Tue Mar 10, 2009 8:22 pm


Lets not forget B.VanBrocklins AUTOMATIC cylinder drains.No fuss a tee or elbow with a small s.s. ball make a cap with small hole,attatch to the cylinder presto done. The word AUTOMATIC is very misleading on some designs,this means it works by itself,not mechanical or you have a network of plumbing to install and YOU have to activate this drain.The less parts you have to make,the less parts you will have break. Who sees these anyways? they are buried beneath the cylinders. :D

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Bill Shields
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Bill Van B's

Post by Bill Shields » Tue Mar 10, 2009 10:41 pm

Yes, they are a nice, simple design.

The only drawback is that you cannot manually open them when you want - and if you get a big slug of water, they may not always open (been there - done that on my 3/4" Hudson).

I like the relief valve type since I am not always the most diligent at keeping boiler water level below the top of the steam dome! :shock:

As for manual opening, I like the ability to open a drain valve to wash cylinders out after running and at other times where I may think it appropriate to 'steam clean' objects along the right-of-way. :wink:

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Post by Fender » Wed Mar 11, 2009 6:32 am

ccvstmr wrote: If the relief valve Bill provided a drawing for is "self-relieving"...why would you want (or need) a mechanical lever to open the valve? Carl B.
Another reason for manually opening the valve is to avoid slipping the drivers when starting a heavy train. The full-size loco engineers did this too. Having the cylinder cock valves open reduces the pressure in the cylinders enough so that you can start without so much slipping. You put the loco in full forward gear, open the cylinder cocks, and pull the throttle back, further than if they were closed. Once you have it moving, reduce throttle and close the cylinder cocks.
Dan Watson

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Or worn piston rings...

Post by Kimball McGinley » Wed Mar 11, 2009 2:27 pm

Cylinder cocks can be usefull in starting if the rings are leaking a bit. Sitting still, with the throttle slowly opened, the steam pressure can equalize on both sides of the piston, and the loco can't move. Open the cocks and she will build pressure on the correct side of the piston only.
I read of an SP Daylight 4-8-4 that just would not leave the station one day, until the Road Foreman of Engineers called out for the engineer to open the cylinder cocks, even if the cylinders were good and hot!

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Post by gnsteam » Thu Mar 12, 2009 12:35 pm

Mr Sheilds,

I too would like to see your steam operatied cylinder cock design. I have a friend in need of a set for a 1" scale LE Atlantic. He would prefer to use steam for actuation rather than build and install all the linkages nessasery for the manual type.


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Post by xo18thfa » Fri Mar 13, 2009 2:40 pm

alanstepney wrote:Almost all the cylinder drain cocks made (and used) over here, as sold by Reeves and others, and very basic, with a tapered plug, and no O rings or other seals.

They work, dont leak, and last for many years.
Equally as important, they are simple, to make and to maintain.

The only "secret", is to ensure that the taper of the plug is EXACTLY the same as that of the bore.
To do that, I set the lathe cross slide over by the correct amount, make the plug (s), and also, at the same setting, make a taper reamer (actually a tapered D bit) to open out the hole in the bore.

An old idea, but it seems to be the only way to ensure that both tapers are identical.
(I guess CNC would work as well, but trying to set to a standard reamer certainly doesnt!)
Alan: Does this technique produce a good fit with just the D-bit, or do you lap the plug and hole in anyway?

I like the simplicity part. Harry Wade's drawing looks the way to go.

Thanks, Bob

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Post by gwrdriver » Fri Mar 13, 2009 2:55 pm

I made mine as a raw beginner, a first attempt at plug cocks, a first D-bit, following closely the instructions in ME, etc, and they really came out very well, and yes I did choose to grind them in with a little Bon-Ami although I don't know if I HAD to do it. At that time Bon-Ami was made of diatomeceous earth and was just the thing for seating model parts. I don't know what it's made of now, but I've no doubt it has been "improved" to the point where it's useless.
Nashville TN

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Post by Fred_V » Fri Mar 13, 2009 10:46 pm

just don't use valve grinding compound. don't ask how i know.
Fred V

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