7-16 Change A
U.S. Navy Diving Manual—Volume 2
Va
=
Capacity available, scf
C
=
Consumption rate, scfm
Sample Problem. Determine the duration of the air supply of a diver doing
moderate work at 70 fsw using twin 72-cubic-foot steel cylinders charged to 2,250
psig.
1.
Calculate the diver’s consumption rate in scfm. According to Figure 7-6, the
diver’s consumption rate at depth is 1.4 acfm.
2.
Calculate the available air capacity provided by the cylinders. Table 7-1
contains the cylinder data used in this calculation:
Floodable Volume = 0.420 scf
Rated working pressure = 2250 psig
Reserve pressure for twin 72-cubic-foot cylinders = 250 psig
3.
Calculate the duration of the available capacity.
The total time for the dive, from initial descent to surfacing at the end of the
dive, is limited to 26 minutes.
7-4.2
Compressed Air from Commercial Sources. Compressed air meeting the estab-
lished standards can usually be obtained from Navy sources. In the absence of
appropriate Navy sources, air may be procured from commercial sources. Usually,
any civilian agency or firm which handles compressed oxygen can provide pure
C
D
33
+
33
----------------
RMV
=
70
33
+
33
------------------
1.4
=
4.37 scfm
=
Va
Pc
Pm
–
14.7
--------------------
FV N
=
2250
250
–
14.7
---------------------------
0.420
2
=
114 scf
=
Duration
Va
C
------
=
114 scf
4.37 scfm
--------------------------
=
26 minutes
=
