Inlet and outlet to a condenser water pump

[ssn61]

I see some condenser (cooling tower) water pumps have inlet pipe size larger than the outlet. What is the reason for that?

 

[trashcanman]

To reduce pressure drop in the pump suction, so as to avoid cavitation.

 

[walz]

I see the same on the chilled water pumps as well

 

[Artisi]

Nothing unusual in having the inlet size larger than the outlet, for me it would be more unusual to have the inlet and outlet the same.
As already pointed out, it is desireable to reduce the inlet losses to a minimum, therefore having an increased diameter for the inlet pipework is one way of reducing inlet losses.
When you look at many pump ranges you will see that inlet /outlet configurations are usually something like

1.5" x 1"
2" x 1.5"
3" x 2"
4" x 3"
6" X 4"
8" X 6"
10" x 8"
12" x 10"
^
^
24" x 20" etc