Piping Design

How much liquid do you need to pump?

How often?

"Dosing" implies small amounts but 5 HP can move lots.

Liquid type, SG, temperature and much more detail is needed.

If this is all the information you have a 4" pipe will be overkill, unless you're pumping molasses.

There are web site for this you know, that will do the calculations for you, with the information I asked for.

And a pump curve, and viscosity, and what is the fluid?

As has beeing said you need to provide more data, but actually by the time you figured which data it is you will be able to find the answer yourself.

If in doubt make it big!

And if you make it big, dont worry about the money!

It depends on how quickly you want to pump it, Mildred! And you can only work that out using the pump's performance curve. Once you have the flowrate, divide by, say, 2 metres per second to get the pipe area, use pi, the number 4 and the square root function to get a diameter, then select the next size up.

If you don't have a pump curve, and a phone call to the manufacturer will usually produce one, then make the discharge pipe the same diameter as the discharge connection, as a first stab at it.

Voilà!