elenms,
If you don't begin adding some precision to your language now, then you will spend a career confused and confusing other people. Never ever ever say "flow rate". Never. It is either "volume flow rate" or "mass flow rate". If you are interested in volume flow rate then it is much more precise to say either "volume flow rate at standard conditions" or "volume flow rate at actual conditions".
The first volume flow rate is very common because two gas volumes must be at the same pressure and temperature to be able to add them (e.g., the volume flow rate at standard conditions at the suction of a compressor is identical to the volume flow rate at standard conditions at the discharge of the compressor).
The second volume flow rate is necessary to calculate velocity (e.g., the volume flow rate at standard conditions through the compressor might be 1000 MSCF/day, but if the suction is 32 psia and 60F then the volume flow rate at actual suction conditions is 460 MACF/day and if the compressor gets the gas to 200 psia and 120F then the volume flow rate at actual discharge conditions is 82 MACF/day, if the suction pipe is 6 inch and the discharge pipe is 4 inch then the velocity is 27 ft/s on the suction and 10.9 ft/sec on the discharge).
Finally the only way that your velocities are required to be equal is if the flow is choked (i.e., limited to exactly sonic velocity), other than that the velocity through the two pipes is dependent on where the lines are going and what resistance to flow exists in both lines. You said "supplies air to two systems" which implies that the flow is not choked, but is supplying air to pneumatic devices--velocity is dependent upon the air load of that equipment.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
