The Use of Multiplied Pressures for Automatic Altitude Adjustments Page: 4 of 10
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Approximate Barometric (2-1) Atmospheric (10-1) Atmospherio
Altitude. Pressure Pressure. Pressure.
feet Cm. Hg. lb./ sqin. lb./ sq. in.
Sea level 78 14.7 132
5,000 63 12.2 110
10,000 52 10,1 91
15,000 44 8.5 77
20,000 33 7.0 63
25,000 30 5.8 52
Using 2 as the multiple gives a force for operating the ad-
justment equal to that which would be obtained in the conventional
devi-ce if the sealed chamber were completely evacuated. With the
higher multiples sufficient pressure is obtained to make it un-
necessary either to provide a relay or to make the unit of large
dimensions to care for adjustments whose operation requires con-
The accompanying drawing shows a possible device based on
this method of altitude compensation. The multiplication of
pressure is obtained with a pump comparable in size to those now
used for supplying pressure to fuel systems. For a pump of this
type the following relaticn is true:
Pg= Pl )n
P= absolute pressure at beginning of compression stroke
V1 = volume at beginning of compression stroke.
P2 = absolute pressure at end of co Tress on stroke.
n-= exponent having a value between 1.3 and 1.4,
V2 volume at end of compressicn stroke,
V1, V2, and n are constant for any given pump and hence the quan-
aity (9v)n is also constant. This relation can be chosen to give
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Sparrow, Stanwood S. The Use of Multiplied Pressures for Automatic Altitude Adjustments, report, August 1922; (digital.library.unt.edu/ark:/67531/metadc53798/m1/4/: accessed January 23, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.