Same size barb for pump inlet and outlet?

[gungeek]

There was a statement made in the discussion of the CSP750 pump about barb sizes. The statement was essentially that having a larger inlet barb than outlet barb would increase flow in an open loop system but not a closed loop. I was under the impression that it did make a difference.

In my case, I'm changing the watercooling system and was going to use 3/8ID tubing everywhere except for the tube that feeds the pump inlet; that would be 1/2ID. The only reason for the planned 1/2ID section was to help the pump make a little more pressure due to the inlet not being restricted. The stock barbs on my Eheim 1250 pump are not the same (1/2OD outlet, 5/8OD inlet) which helped confirm the bigger inlet theory. I'll be using a Hydor L30 in the new setup and it comes stock with 1/2OD barbs for the inlet and outlet.

What is the truth? :shrug:

[killernoodle]

It probably wont matter much for a small pump like the 750, but on larger pumps there is sometimes a problem with cavitation if the inlet is restricted more than the outlet.

[Cptn. Foo Foo]

I read somewhere that having the bigger inlet does indeed help the pump move more water. I thought it was because the pump's impeller shaft is supported at one end right where the inlet is...making the inlet somewhat restricted. And if the inlet was the same size as the unrestricted outlet then there would be a difference of internal volume between the two. So having the bigger inlet allows the slightly bigger overall volume to account for the support structure for the impeller shaft.

Maybe I'm just crazy :shrug:

Side note...my pump has a 1.25" inlet and 1" outlet. I have the pump running un-submerged (it can run submerged if needed). It is hooked up to my 4" diameter ABS pipe reservoir.

[gungeek]

thanks for the clarification.