Throttle inspiration?

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DianneB
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Throttle inspiration?

Post by DianneB » Thu May 24, 2018 10:00 am

My LE American was built around 1962, about 56 years ago, and has been with me since 2012. One problem that has bugged the heck out of me since I got it is that the throttle LEAKS! It leaks to the cylinders no matter how tightly it is closed. It also leaks around the stem when under way.
Throttle 1.jpg
Throttle 2.jpg
Here is a sketch of the 'internals'. (Should have taken a picture but didn't!)
Throttle3.JPG
Problem #1 with leaking to the cylinders (I think) is that the face on the stem is PART of the stem (stainless, I think) and can not float to make a perfect seal to the seat, which is brass. It is also a 'hard face' and relies on two hard flat surfaces coming together to for a steam-tight seal.

Problem #2 with the steam leak underway is (I think) that the thread on the stem moves into/through the packing as the throttle is opened and that distorts the packing.

I could make another stem (also from stainless) with a half-ball on the end, maybe free-floating, to seal against the seat. Or, I'd use an O- ring but I don't think an O-ring would stand up to the heat and erosion on live steam. Or maybe I could fit a red rubber gasket between the seat and the body and have the present steam seat against the gasket.

For problem #2 I can't see any solution except to make the packing nut longer so the thread on the stem doesn't cut into the packing.

I'd sure appreciate some suggestions from those of you who have built throttles (that work) and how you would tackle this?

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Bill Shields
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Re: Throttle inspiration?

Post by Bill Shields » Thu May 24, 2018 12:31 pm

suggest you forget the 1/2 ball and make it a cone.

you may need to make a new back head and move the packing further away from the thread instead of shortening the thread...otherwise you may end up with no thread engagement when fully closed...

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Builder01
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Re: Throttle inspiration?

Post by Builder01 » Thu May 24, 2018 3:32 pm

Dianne,
what you have is a simple screw down throttle. As Bill has suggested, a cone will work just fine and is easier to make. All of the throttle pieces/parts must be truly concentric in order to work well.

One thing you mentioned that is troubling, is the age of the loco and that the seat for the throttle valve is brass. The brass is now old enough that is may be leaking through. Brass is considered less than optimal for use inside a boiler because of the zinc leaching out and becoming porous.

A screw down throttle is just fine, I have that type and it seals perfectly. The valve cone is stainless and the seat is aluminum bronze. Any sort of bronze would probably work fine for the seat. Stainless on stainless may gall.

Any valve spindle that can be unscrewed far enough such that the thread cuts into the packing, has not been engineered correctly. Proper captive spindles bottom out on the thread and stop long before they can ever touch the packing. A screw down throttle usually hardly ever needs to be turned open more than about 1/2" a turn.

Here's the drawing for the screw down throttle in my loco:
Super Simplex Regulator - JPG.jpg
Here's the pieces that form the nut, valve cone, seat, and the tube that they fit into. The large hole in the side of the tube is for the dry tube that goes up into the steam dome. This is not exactly like your throttle, but, you get the idea. The nut, like the seat is aluminum bronze. It has "lots of holes" drilled and tapped into it so it can be rotated in the tube for correct orientation of the throttle handle:
DSCN1369 - reduced 8.jpg
Here's a photo of the "handle" end of the throttle. The fitting that goes into the backhead of the boiler is aluminum bronze, the packing nut is bronze. The shaft that fits into the packing nut does not have any threads anywhere near where the packing and nut fit, it's all smooth. No leaks here:
DSCN1367 - reduced 6.jpg
If you want to see more photos of this screw down throttle assembly, here's a link, scroll about 1/3 down the page:

https://supersimplex.yolasite.com/Makin ... ttings.php

David

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Bill Shields
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Re: Throttle inspiration?

Post by Bill Shields » Thu May 24, 2018 3:42 pm

good luck finding a 1/2" whitworth tap and die set....giggle..

I am building something very similar for a 1" loco right now...except I am using slightly different threads...

I repaired one (very similar) 4 years ago that was 50 years old and still running...the only problem was that the soft solder used to assemble it had deteriorated....

the big problem that I believe DB is having is that the entire throttle appears to be RIGHT THERE mounted on the back head of the boiler.

The 'dry pipe' comes out of the side of the throttle then travels forward through a tube to the smokebox...

or am I viewing this all wrong???

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DianneB
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Re: Throttle inspiration?

Post by DianneB » Thu May 24, 2018 3:49 pm

You have it right Bill

I like the idea of a cone or truncated cone - easy to make as well. I figure I should strike off the sharp edge on the seat with a tapered reamer to remove the sharp edge. I'd let the cone float a little if I could figure an easy way to mount it to the stem.

If I re-do the stem, which I will, there is plenty of depth in the body to put the threaded section deeper and extend the smooth part of the stem through the packing so it will bottom out in the open position without hitting the packing.

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Bill Shields
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Re: Throttle inspiration?

Post by Bill Shields » Thu May 24, 2018 3:54 pm

suggest that you not use a tapered reamer...you want a much steeper angle than that or the cone WILL get stuck..

note that the cone shown in the photo is darn near to 90 degrees (might be 82)…..

you don't want the cone to 'float'...asking for trouble...

just be sure all is CONCENTRIC when assembled...maybe you will want to use some lapping compound to seat the cone...but NOT by driving it with the handle and / or thread...set it up in the lathe..

Capice??
Last edited by Bill Shields on Thu May 24, 2018 3:56 pm, edited 1 time in total.

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Builder01
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Re: Throttle inspiration?

Post by Builder01 » Thu May 24, 2018 3:56 pm

Hi Bill,

Yes, good luck with the 1/2" Whitworth thread! I single point cut it with a a "normal" 1/2-13 thread, no problem. Whitworth is certainly not necessary!

The valve "seat" is a straight sided hole, not tapered. If you leave the corner of the valve seat sharp, the cone will make it's own "flat" on the corner and will probably seat better this way.

David

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DianneB
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Re: Throttle inspiration?

Post by DianneB » Thu May 24, 2018 4:41 pm

Good points gentlemen - thank you.

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gwrdriver
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Re: Throttle inspiration?

Post by gwrdriver » Fri May 25, 2018 5:12 pm

Have you considered a rotary throttle, using a rotating disk drilled for incremental steam passage?
The body would be a "biscuit" shape as you have now. The stem wouldn't be threaded at all so an O-ring gland would do fine and what you might gain in throttle body thickness could be compensated for with a compact gland. The photos are of the throttle plate (and then the dome throttle assembly) I made for my current loco project. Unlike mine your disk would be driven directly by the stem, and IMHO I would want to put stops, or a quadrant, on the back head of the throttle to limit handle rotation. You wouldn't have to have three holes, one might do, but the three virtually eliminate jackrabbit starts.
Drawbacks, . . . the body would probably be thicker (deeper) than the present one, and you might have to adjust the steam supply line to make the connection.

Food for thought.
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SteveM
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Re: Throttle inspiration?

Post by SteveM » Sat May 26, 2018 7:57 pm

gwrdriver wrote:
Fri May 25, 2018 5:12 pm
Have you considered a rotary throttle, using a rotating disk drilled for incremental steam passage?
Nice. Never thought about using graduated holes, but it makes a lot of sense.

Steve

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Bill Shields
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Re: Throttle inspiration?

Post by Bill Shields » Sat May 26, 2018 8:57 pm

Steve:

Get a copy of LBSC's book....good browsing...lots of 'old ideas' that are still workable today

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DianneB
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Re: Throttle inspiration?

Post by DianneB » Mon May 28, 2018 1:03 pm

Throttle parts.jpg
A friend of mine has a different LE engine of the same vintage and has no problem with his throttle so I took my throttle apart to have a close inspection. you can see the ring around the opening for the steam from the boiler - turned out the face was scored. There were also some barely-perceptible nicks in the face of the stem as well so I sanded the base on a surface plate until all the marks were removed and turned the stem in the lathe to restore that surface as well. I will give it a steam test when I get a chance but hopefully that will greatly reduce the steam leakage.

Someone must have closed the throttle with some grit in there - looks like they closed it HARD as well.

It was suggested that I make a new stem with a brass "tapered plug" to seat for a seal and I will try that if this doesn't work. The trouble is I have LOTS of bronze but precious little brass LOL!

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