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DianneB
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Thread ending positon

Post by DianneB »

I need to replace the drain cocks on my 1-1/2" American. The originals were "automatic" and it didn't matter what position they ended up in when the thread snugged up. The steam-operated replacements only mattered within 1/4 turn but I want to install manual drains that will have to end up in a fairly accurate direction.

Is there a way to get all 4 drain cocks to tighten up in the same position without designing a swivel into the body? I would like to avoid having each drain matched to a particular hole but maybe that is the easiest way?

Thoughts? Streaks of inspiration? Flashes of ingenuity?

(Thanks!)
Magicniner
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Post by Magicniner »

Banjo fitting design with a central bolt & the valve integrated into the sleeve allowing exact orientation in any hole.
pete
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Post by pete »

In drag racing and in some classes they do what's called spark plug indexing Dianne. All that means is the elecrode tips and gaps are indexed in the cylinder head to the optimum position for the best ignition. It's accomplished by using different washer thickness so when the spark plug is torqued to final specification the electrode tip is in that correct position. Likely your drain cocks will have a pretty fine thread and with a known pitch and a trial washer of known thickness it's pretty easy to calculate what each will need for it's own washer thickness to position them correctly. That method obviously means if the drain cocks are removed during maintenance they'd need to go back in the same spot each time. But it should work. Fine positioning can be done with a washer just a hair oversize and stone or sand the washer face until you get exactly what you want.
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DianneB
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Post by DianneB »

Thanks Pete - that sounds like a fine solution.

The threads are 1/4-32 so those will be some thin washers!
pete
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Post by pete »

Magicniners banjo idea might be a bit more elegant solution Dianne but I guess it depends on what fittings the full size had.
Russ Hanscom
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Post by Russ Hanscom »

The washers do not have to be thin - they can be a multiple of the thread pitch - just have to be different thicknesses.
epanzella
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Post by epanzella »

You can machine the shoulder to size just like headspacing a rifle. See where it ends up, then take small cuts on the shoulder to dial in the drain location.
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larry_g
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Post by larry_g »

To do this with precision you can figure the the cut to make. If you have a 32 pitch thread divide 1/32 and this will give you the the movement one turn will give you. 1/32=.03125.. if you divide this by 360 degrees you will have distance per degree. .03125/360= .00009 in/degree. Once you get how many degrees additional you need to turn to get it straight then multiply degrees additional * .00009" and you will have the amount needed to be removed from the shoulder or spacer.

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prlawiii
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Post by prlawiii »

When I needed to do this on a boiler gauge glass fitting, I used the red fibre washers. You can sand them thinner with finger pressure on sandpaper on any flat thickness. Sand a bit, then check, and repeat. Trial and error gets you into the range, and because they have some compressability, they seal and still give you some wiggle room to fine tune the orientation of the fitting.

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Bill Shields
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Post by Bill Shields »

In reality, if you just dope the threads and forget about 'seating' you won't have any problem.

I have several locos with straight threaded fittings on drains that are put together that way. They may weep a bit for a few weeks, but after that, they seal up and you don't have to worry about washers etc:

Tapered pipe threads are another matter...
Too many things going on to bother listing them.
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