Straight pipe before pump

It is certainly advisable; inlet more so than outlet. I'd try to hold 10 diameters if possible.

The problem -- particularly on the inlet side -- is that if there is a bend closer to the inlet, you can get unbalanced pressure on the rotor. If the inlet pressure is low -- getting down to the required net positive suction head -- this can cause cavitation. Even with adequate pressure, however, it can cause unbalanced forces on the seals and bearings. Either one can lead to shortened pump life.

Keep in mind also some of those pre-made panels with package boilers are tight. So tight I can't imagine ever making a plumbing repair.
So try for the right dimension if you can get it.
I can tell you on my own house, there just wasn't enough room with 6 zones/circs.

Solid_Fuel_Man said:

It's interesting to note that in pretty much all wet rotor circulators (choose your color) the inlet (suction) is a 90 degree bend right into the impeller.



We all know this isnt true on base mounted pumps of any real horsepower. The inlet is a straight line to the center of the impeller.

True. But in your wet rotor circulators it isn't just a simple elbow -- some poor soul spent hours on a model table (or computation fluid dynamics program) getting the geometry of the bend right to get an even pressure distribution at the flow rate of best efficiency. It's amazing what small tweaks to the geometry of the flow can do...