if it is a normal buffer tank (they may have baffles), pressuredrop should be low if you stay within allowable flow rates. Maybe 0.1 psi or less. If that manufacturer doesn't have the information, look for a similar product that provides that information. but make sure the internals and pipe size are similar.
What is the "inline tank" - very vague description - it could be minimal but on the other hand a considerable pressure loss.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
