Gas Matching For Cylinders Of Different Volumes

 

The Chart Below Shows The Volumes of Different Tanks At The Pressures Shown On The Left

PSIG Al 80 Steel 85 Steel 95 Steel 104 LP Steel 121 HP Steel 100 HP Steel 120
1000 26 32 36 43 50 29 34
1100 38 35 40 48 55 31 38
1200 31 39 43 52 61 34 41
1300 34 42 47 56 66 37 45
1400 36 45 50 61 71 40 48
1500 39 48 54 65 76 43 51
1600 41 52 58 69 81 46 55
1700 44 55 61 74 86 49 58
1800 46 58 65 78 91 51 62
1900 49 61 68 82 96 54 65
2000 52 64 72 87 101 57 69
2100 54 68 76 91 106 60 72
2200 57 71 79 95 111 63 75
2300 59 74 83 100 116 66 79
2400 62 77 86 104 121 69 82
2500 65 80 90 108 126 71 86
2600 67 84 94 113 131 74 89
2700 70 87 97 117 136 77 93
2800 72 90 101 121 141 80 96
2900 75 93 104 126 146 83 99
3000 77 97 108 130 151 86 103
3100 83 100 112 134 156 89 106
3200 85 103 115 139 161 91 110
3300 106 119 143 166 94 113
3400 109 122 147 171 97 117
3500 113 129 152 176 100 120
singles 2.7 3.2 3.6 3.9 4.6 2.9 3.4
doubles 5.3 6.4 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.  The numbers are derived by dividing the cubic inch capacity by the rated pressure.   For example: a steel 104 contains 104 cubic feet at 2640 psi because 104 / 2640=.039 for 1 psi of gas so .039 X 100 = 3.9 cu ft of gas.

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.

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.