Verified answer

Capacity. Pressure is only pressure, that does not cover the volume. You can have 1 cubic feet reduced to ten cubic inch at 170 atmospheres (or 3000 psi) but that is still 1 cubic feet of oxygen.

Now, have 20 cubic inches, and you have 2 cubic feet of oxygen in that tank.

The psi figure is not the capacity. The difference between the large bottle and the small bottle is the volume. The storage capacity of oxygen is equivalent to Volume times Pressure.

So the large bottle will hold about seven times the volume. With the same pressure in psi there is the seven times the capacity of the small one.

The answer is volume. The larger tanks contain a greater volume of O2 - this translates into being able to keep the patient on that cylinder; or multiple patients on that cylinder for a longer perriod of time (without having to change the bottle.) A small bottle empties out quite quickly.

The difference is in the Volume of O2 that the tanks can hold.

Ok...the small tanks are probably about one third the diameter of the large ones by estimation right?

Vsmall = h*pi*r^2

Vlarge = (5*h/2)*pi*(3*r)^2

= (5/2)*h*pi*9*r^2

= (45/2)*h*pi*r^2

= 22.5*h*pi*r^2

= 22.5*Vsmall

So, given equal pressure in either tank, the large tank would hold roughly 22.5 times more oxygen (by volume) just by estimating

the difference is the cubic foot of liquid they contain, this accounts for there performance. a small bottle may only contain 2 cubic feet of liquid and it will convert into 1700 gallons of gas per gallon of liquid. the large bottles contain approximatly 160 gallons of liquified gas, so compair the difference in endurance