GAS MATCHING FOR CYLINDERS OF DIFFERENT VOLUMES

 

PSIG
Al 80
Steel 95
Steel 104
LP Steel 121
HP Steel 100
HP Steel 120
1000
26
36
43
50
29
34
1100
38
40
48
55
31
38
1200
31
43
52
61
34
41
1300
34
47
56
66
37
45
1400
36
50
61
71
40
48
1500
39
54
65
76
43
51
1600
41
58
69
81
46
55
1700
44
61
74
86
49
58
1800
46
65
78
91
51
62
1900
49
68
82
96
54
65
2000
52
72
87
101
57
69
2100
54
76
91
106
60
72
2200
57
79
95
111
63
75
2300
59
83
100
116
66
79
2400
62
86
104
121
69
82
2500
65
90
108
126
71
86
2600
67
94
113
131
74
89
2700
70
107
117
136
77
93
2800
72
111
121
141
80
96
2900
75
115
126
146
83
99
3000
77
119
130
151
86
103
3100
83
123
134
156
89
106
3200
85
127
139
161
91
110
3300
131
143
166
94
113
3400
135
147
171
97
117
3500
139
152
176
100
120
singles
2.7
3.6
3.9
4.6
2.9
3.4
doubles
5.3
7.2
7.9
9.2
5.7
6.9

CONVERSION FACTORS ARE THE 2 LINES ABOVE

The table above shows the volume of various cylinders at various pressures. For example: a steel 104 contains 82 cubic feet at 1900 psi.

The table below that shows the volume of the various cylinders per 100 psi. For example: a steel 104 contains 3.9 cubic feet of gas for every 100 psi in the tank.

EXAMPLE OF CALCULATING GAS MATCHING

Two cave divers are planning a dive together and have different sized tanks. One set of doubles happens to be 104's filled to 3400 psi, the other set of tanks are aluminum 80's. filled to 3000 psi.

In order to determine each divers time to turn the dive we have to actually calculate thirds based on volume and then convert that volume to pressure. To make an extreme example consider one diver has a tank the size of a waterglass and the other diver a tank the size of a car, both filled to 3000 psi. 3 or 4 breaths and the small tanks will be at 1/3 of the starting pressure. Many hundreds of breaths and the car sized tanks will be at 1/3 of the starting pressure.

The Aluminum 80's have 154 cubic feet of gas in them (77 X 2). 1/3 of that volume is 51 cubic feet. Thus, that diver must turn after s/he has used 51 cubic feet.

The double 104's have 294 cubic feet of gas in them (147 X 2). 1/3 of that volume is 98 cubic feet. We see from these calculations that the Aluminum 80's must be the tanks used to "control" the turnaround.

The turn pressure for the aluminum 80's then is 2000 psi. So, after the diver uses the 1st 1000 psi s/he must turn the dive.

In order to determine the divers turnpoint with the 104's you must calculate that tank pressure when 51 cubic feet has been used up. Each 100 psi = 7.9 cubic feet. So...to determine the psi for 51 cubic feet use the conversion factor & divide 51 by 7.9 and the answer is: 6.46. Then 6.46 X 100 = 646 psi. This answer means that subtract 646 from starting pressure and that is the turn pressure for the 104's. Round 646 up to 700 and subtract 700 from 3400 and get 2700 psi as the turn pressure.

The park bench in Devils' system.

E-mail Jim@cavediveflorida.com

Call Jim at 352-363-0013