PDP-11/44 gas struts

Alan Frisbie Flash688 at flying-disk.com
Sat Dec 25 17:37:46 CST 2021

Mark J. Blair <nf6x at nf6x.net> wrote:

 > When I need gas struts and cannot identify a source for exact original
 > replacements, I usually look at McMaster-Carr first:
 > https://www.mcmaster.com/gas-struts/

Thanks for the McMaster-Carr suggestion, I should have thought of that.

I removed the gas struts from my PDP-11/44 and found the following

Gas Spring Corp.
Colmar, PA
22/81/3  (the "1" might be an "I")

I measured them, and found a compressed length of about 9.8" and an
extended length of 15.25".   The threaded studs are 5/16"-24.

I can't find the company, and Google turns up nothing with either
of the number strings.  Nor do the numbers seem to indicate what
the specifications might be.  Perhaps someone with better Google
skills than I have might find something.

It is, however, an almost perfect match for McMaster-Carr P/N 4138T55.
The big unknown is the extension force.  After cleaning and oiling them,
one of the bad ones measures about 12 pounds, and the other is about 23
pounds.   The 4138T55 is available in 15, 20, 30, 40, 50, 60, 90, and
120 pounds.

I made a wild random guess and ordered two of the 30 pound struts,
which should be delivered Wednesday (12/29/2021).  The 40 pound
ones have a seven week lead time, and a pair of 50 pound ones seem
way too high.  When they arrive, I'll let you know how well they work.

Worst case, I will have wasted $20.29 each, plus shipping, and have
to wait seven weeks for the 40 pound units, or go whole hog and try
the 50 pound ones.

Thanks for the help and suggestions.

Alan Frisbie

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