The Locomotive - Lighthouse Survival Blog

PUBLISHED BY THE HARTFORD STEAM BOILER INSPECTION AND INSURAN|;^ COMPANY.
Nkw Skkiks—Vol-. XIV. IIAIITFORD, CONN., MARCH, 1893. No. 3.
A Dang-erous Safety-Valve.
We give, herewith, an account of a safety-valve that \va.s condenincfl by one of our
inspectors not long ago. It illustrates a source of danger that happily is not frequently
met with — namely, a disproportion of the parts of the valve so great that the strains
on some of the parts are much greater than they can .safely withstand. Figs. 1 and 2
give a side and top view of the valve, respectively. The lever was about 50 inches
long, from the fulcrum pin to the end, and on it three weiglits were hung. The outer
one, A, weighed 134 lb., and was 49 inches from the fulcrum pin. The other two, B
and C, weighed 45 pounds each, and their distances from the fulcrum pin were 40 inches
Figs. 1 and 2.—A Dangerous Safety-Valve.
p 1
FO
and 33 inches respectively. The lever weighed 17 pounds, and tapered so little that
for practical purposes it could be considered to be of uniform cross section. The
fulcrum pin was ^ inch in diameter, and the distance from its center to the nearest edge
of the flat-ended valve stem was 2| inches.
The disk of this valve was unusually large, and the calculated blowing-off point
was not excessively high, and agreed well with the blowing point obtained by trial
with the steam gauge. The real point of danger was in the weakness of the fulcrum
pin P and the casting supporting it, the dimensions of which are sufficiently indicated
in Figs. 3 and 4.
To calciilate the strain on the fulcrum pin and its casting, let usi first consider what
would happen if either of these gave way. Plainly the lever would turn about the
point F where it touches the valve-spindle, the weighted end falling down, and the
fulcrum end tipping up. The only thing that resists this tendency is the downward