How to size a pump to your tank

**importracer** · 12-17-2006, 9:08 PM

Originally Posted by TankBuster;604390;

Well, there ya go. Hope your happy. Im off to the hospital to repair blown capilaries in my eyes.

Got room for another TankBuster???sheesh

**IITUFFTOBEATII** · 12-27-2006, 11:17 AM

Originally Posted by TankBuster;604390;

Well, there ya go. Hope your happy. Im off to the hospital to repair blown capilaries in my eyes.

ya kno, if you click on it it will open in a new window and you can resize it so that you can read it

**Potts050** · 01-01-2007, 9:13 AM

Originally Posted by IITUFFTOBEATII;630968;

ya kno, if you click on it it will open in a new window and you can resize it so that you can read it

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?

**sparker18** · 01-21-2007, 8:28 PM

Great info I'm building my sump right now.

***KrAmEr*** · 04-01-2007, 9:38 AM

Thanks for the info, it was very helpful.

**IITUFFTOBEATII** · 04-06-2007, 2:23 AM

Originally Posted by Potts050;636565;

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.

**bigspizz** · 05-12-2007, 6:13 AM

Just a plain out nice thing for you to do for ALL of us! Thx its info like this that makes us all a step ahead of ALL non MFKERS!!!!!

**CHOMPERS** · 05-13-2007, 4:46 AM

Originally Posted by IITUFFTOBEATII;790403;

...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...

And Velocity is the time differential of Newtons Second Law

The force of gravity is not equal to the force of the pump returning the water to the tank. That is why the return plumbing can be smaller than that going to the sump or wet/dry.

Originally Posted by IITUFFTOBEATII;790403;

...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...

Gotta love those textbooks

Since one pipe is pressurized and the other is not, the easy way to size the plumbing is to duplicate the size of the pump outlet for that returning to the tank and four times the cross sectional area for the plumbing going to the sump (rule of thumb but again case by case). A pump with a half inch outlet should use half inch plumbing going to the tank and one inch plumbing going to the sump from the tank. A pump with a 3/4 inch output should use 3/4 inch plumbing going to the tank and 1 1/2 inch plumbing going to the sump. Taller tanks can get away with using smaller plumbing going to the sump.