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.
Email Jim@cavediveflorida.com
Call Jim at 3523630013