Potts050;636565; said:
Thanks for that post dude.
Very informative. Takes a lot of the black magic out of pump sizing. It also shows how important pumbing is in the system when selecting pumps. Any sugestion on the ratio of diameters on pressure side and drain side pipe?
I must apologize for not returning to respond for so long, dont know how that happened.
to answer the question; it really needs to be looked at on a case by case basis. Flow (Q) = Velocity (V) * Cross-sectional Area (A)-> for all cases you want Qin to equal Qout, otherwise your tank/sump would overflow
For simple cases where neither the inlet nor the outlet is pressurized the ratio should be 1:1. This is because the velocity should be nearly the same and drops out of the equation, therefore to get the same flow you must have equal size pipes.
For more complex systems, the math gets a little harder, though its not that difficult, (i'll let you borrow my fluid mechanics textbook and you can do it for yourself
). If you know what your pump is putting out than that is your Qin, we know that Qin must equal Qout, but we don't know the velocity or the diameter. We only have one equation and two unknowns so its not an easy answer to find, gotta do the book work. There are tricks to simplify this, and you could guess and check experimentally, but the convention around here is just to size the outlet to have a larger capacity than the inlet. This is a good practice for the average hobbyist as the additional capacity on the outlet usually doesnt blow the budget.