Total Gallons Inside Batch Reactor

Hello,

I'm having diffuculty writing a PE... I'd like to calculate the total gallons of a process, and I am utilizing two tags. I have the current flowrate going inside the reactor reproted in gallons per minute, and I have the pressure inside the reactor in pounds per sq inch. The batch process only starts when the pressure is above 50psi, and from there on I'd like to calculate the total gallons that went into the reactor.

This is what I've come up with so far:

tagtot('FlowTAG','FindGE('PressureTAG','t+6h','*',50)','*')*1440

Any help would be much appreciated!