Compressed Air Work And Diving 1909
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DIVING PUMPS.
35
returned during the second half of the stroke. In the
case of single-action pumps, the work done will be entirely
lost. Out of twelve ordinary service pumps tested by the
Aclmiralty Committee,* the average loss was 11.3 per
cent, at atmospheric pressure, 34.6 per cent, at a depth
of 100 ft., and 57.0 per cent, at a depth of 200 ft.
Afterwarcls improveel pumps were supplied, and gave
results rather better than 25 per cent, at 200 ft.
The loss from cushioning is to a great extent inevit-
able, as there must always remain a small amount of
highly compressecl air due to the valve clearance and
also in the space occupiecl by the springs on the pistons.
I'his loss inereases with any wear or slackness which
would tenel to shorten the length of the stroke.
In Table X. two columns have been workeel out, one
for pumps with an efficiency of 75 per cent, at a depth of
198 ft., and the other for pumps with an efficiency of
50 per cent, at a depth of 198 ft. By dividing by the
capacity of one cylinder per revolution and the result by
the number of revolutions per minute, the numbers of
cylinders for any particular depth will be obtained.
Ihus at a depth of 231 ft. and cylinders with a
capacity of o. 10 cub. ft. per minute, and the number of
revolutions thirty per minute, the number of cylinders
required would be — — 5-7- This necessitates
o. 10 x 30
three two-cylinder pumps and the number of men
required will be six to a pump, and in order that they
may be able to work them comfortably the handles of
the pumps will have to be made rather longer than is
usual. From the last column it will be seen that the work
that will have to be done is rather beyonel the ordinary
* “Diving Report,” p. 25.