Q=D² × L × n × N × π ÷924
Q : flow rate in gpm(gallons per minute).
D: Plunger diameter in inches.
L:Stroke in inches.
n:Number of plungers.
N:Speed of pump in rev. per min (revelution per minute).
π=3.14159
1 barrel per minute(bpm)=42 gallons per minute(gpm)
Assume a single acting pump with L=D , pump speed =100 rpm.
Then D =1.1 inch approx.
Otherwise you leave L,N undefined then make a selection from a specified company catalougue.Inside the catalogue N is given ,D and L are related to Q.