Convert Welch Duo-Seal Hose Nipple to KF-25

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Rex Allers
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Location: San Jose CA

Convert Welch Duo-Seal Hose Nipple to KF-25

Post by Rex Allers »

The old Welch Duo-Seal vacuum pumps are still among the best.
The 1402 that I have still gets down to below 5 micron vacuum at the inlet port.

Here's a way to modify the hose inlet adapter to a KF-25 (or whatever -25)

It does require a metal lathe and some bravery to destroy the original port device.

Being 1960's vintage, the default input port is a big hose nipple.

hose nipple.jpg

For most of my vacuum pumps that get into this 20 micron range or less, I prefer the KF-25 fitting as a standard. (Or the equal NW-25, etc.)

I modified the input of my 1402 from hose to -25 fitting.

This mod required a metal lathe and some bravery to cut and shape the original inlet fitting. After this turning, the newly shaped Welch adapter fit inside of a KF-25 butt nipple and they were joined with JB Weld metalized epoxy.

Here is the final result.

New Intake port.jpg

And some detail of the joined part.

full mod_.jpg

I didn't take any pictures from my lathe work on the original hose input, but here is an image I created showing what the modified Welsh part looked like.

mod_wrk2.jpg

Here's one more pic showing an inside view of the end of the turned Welsh part with a bit of JB Weld at the end of the joint.

inside joint.jpg

So now, a bit of description. The inside diameter of the KF-25 nipple is 0.875 inch.
the inside diameter through the Welsh hose part is 0.75", which gives a 0.125" difference. So the Welsh part can be turned down to a bit less than 0.875 OD and fit into the KF-25 nipple, giving a remaining wall thickness of the turned down Welsh part of the vicinty of 0.060.

This ~ .050 to .060 thickness, after turning down, should be strong enough especially after joining with the KF-25 flange and JB Weld.

As noted in the above picture dimensions, the newly shaped Welch part fits into the KF-25 flange about 1/2 inch. The turned down diameter is shown in one picture as ~ 0.870". This is approximate. The fit of the KF-25 flange ID should be tested as the turning is progressing. The turning should progress until the fit is a bit sloppy, allowing for a bit of JB Weld in the radial gap to seal along the joint.

JB Weld is good for vacuum applications, especially at these realms in the vicinity of 1 to tens of microns.
Rex Allers
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