# how to calculate the gas volume per purge when I change the cylinder?

I have some gas cylinders in a gas cabinet. Every time I change the cylinder, I use N2(100%v/v, 60L/min) to purge the residue gas in the pipe to a local scrubber. I want to know how many gases I should treat per purge?

follow is my customer give me the condition： gas name flow rate pressure(MPa) F2(5%F2, Blance Kr/Ne 95%) max 4.4L/min 14.8 BCl3 same↑ 0.0627
WF6 same↑ 0.04 ClF3 same↑ 0.0588 N2 60 ─

Here is someone give me the solution： 100% gas volume (L/purge)= 0.07(L)*[pressure (pa)/98066.5(pa)]*1(cylinder/purge)*concentration%

How come? In my thought, it use the formula P1V1=P2V2, where V2 is what we want to calculate. P1 is the gas pressure in the cylinder, P2= the pressure in the pipe. But 0.7(L)? Why? And why P2 is not 1 atm = 101325 (pa) but use 98066.5(pa)=1kgf/cm^2

BTW, the pressure(MPa) value let me confused. Generally, how much pressure is the gas cylinder for each kind of gas above? The value is closed to the pressure of a new cylinder or to a used-up cylinder?