Author Topic: Locomotive question  (Read 787 times)

Offline Grant Jones

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Locomotive question
« on: April 28, 2020, 08:40:34 PM »
I am building an early American Baldwin engine. The original full size engine exists in a museum. I noticed that the steam chests each had a snifter valve on the top of the chest. The valves are the slide valve style. Can anyone tell me the reason for the snifter valves? All the plans and models I have seen do not have these.

Online Admiral_dk

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Re: Locomotive question
« Reply #1 on: April 28, 2020, 10:00:15 PM »
As this came up a few days ago in another thread - I believe that I can recall  :old:

It's there to protect the engine when going downhill with the throttle / steam valve closed - so the links and rods aren't bend ....

Offline crueby

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Re: Locomotive question
« Reply #2 on: April 28, 2020, 10:17:25 PM »
Thats right, keeps cylinders from drawing a vacuum when throttle is closed but wheels are turning.

ChuckKey

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Re: Locomotive question
« Reply #3 on: April 29, 2020, 12:17:25 AM »
Without them, the cylinders would act as a brake when coasting, and ash would be drawn into the cylinders from the blastpipe. Sometimes the snifting valve is arranged to draw through the superheater tubes to prevent their overheating, but the hot air tends to carbonise the cylinder oil.

Offline Grant Jones

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Re: Locomotive question
« Reply #4 on: April 29, 2020, 08:14:43 PM »
Thanks for straightening this out for me. This engine saw considerable use in the mountains where this would be important

Offline PJPickard

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Re: Locomotive question
« Reply #5 on: April 30, 2020, 11:56:50 AM »
see this discussion for more info:

http://ngdiscussion.net/phorum/read.php?1,394453

Offline Grant Jones

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Re: Locomotive question
« Reply #6 on: May 02, 2020, 01:04:48 AM »
One more related question...the rocket shaft has what I believe to be a helical spring, the purpose of which was to reduce the force required by the operator to move the forward/reverse lever. Can somebody shed some ligjt on how these were made. I would like to incorporate this in my build.

Offline crueby

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Re: Locomotive question
« Reply #7 on: May 02, 2020, 01:20:16 AM »
Rocket shaft? Don't know that term, but I have seen machines that had counterweights on linkages to balance them to lower the force needed on the operator lever. Do you have a picture or drawing?

Offline 10KPete

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Re: Locomotive question
« Reply #8 on: May 02, 2020, 02:41:40 AM »
It's a rocker shaft. Also called a weigh shaft. The ends have links for moving the cut off link. The center has a lever sticking out that the rod from the Johnson connects to. The valve gear is very heavy so arranging the links and levers for best advantage to the engineer makes him happy.
Springs in various forms and attached in various places is an easy way to do this as it allows greater freedom in routing the rods and things.

So it's functionally a rocker, and holds the weigh(t) of the valve gear.

Respectfully,
Pete
Craftsman, Tinkerer, Curious Person.
Retired, finally!
SB 10K lathe, Benchmaster mill. And stuff.

Offline crueby

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Re: Locomotive question
« Reply #9 on: May 02, 2020, 02:46:36 AM »
Thanks for the explanation Pete!  :cheers:

Offline Grant Jones

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Re: Locomotive question
« Reply #10 on: May 02, 2020, 04:59:29 AM »
That was a typo on my original meassage...hit a t instead of an r and ended up with rocket instead of rocker.
The full size device is a drum about 10” in dia. with 12 holes in the end. A bolt appears to be inserted into one of the holes. My suspicion is that the drum us rotated until the desired tension is put on the helical spring then the bolt is inserted to lock the position.

Offline 10KPete

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Re: Locomotive question
« Reply #11 on: May 02, 2020, 05:04:15 AM »
You have it surrounded, sir! I'd love to see some pics of it as it's hard to find the larger designs.

Thanks,
Pete
Craftsman, Tinkerer, Curious Person.
Retired, finally!
SB 10K lathe, Benchmaster mill. And stuff.

Offline Grant Jones

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Re: Locomotive question
« Reply #12 on: May 02, 2020, 07:20:12 PM »
I will search through my large photo file and send the best pictures I have.

Offline Grant Jones

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Re: Locomotive question
« Reply #13 on: May 03, 2020, 04:49:22 AM »
Picture of unit