Those values are typical values that I've seen when dealing with fluids close to their boiling point. Basically, low velocity = low suction line losses that serve to minimize NPSHA issues.
On fluids where the temperature, pressure or elevation are such that NPSHA isn't as much of an issue, I've seen much higher velocities used. I did some work on a tank farm and was surprised at the suction velocities the inline pumps operated at (diesel, kerosene) coming off atmospheric storage tanks. If you are interested I can dig up the data but if memory serves me right, they were in the area of 10 ft/sec. The reliability of the pumps was very good I remember.
For example, if you are dealing with a cooling water booster pump where the suction pressure is say 30 psig, you have close to 100 feet NPHSA. In that case, I wouldn't use those values.
Gasoline at summer exposed tank and pipe temperatures is close to vapor pressure and can present problems at a velocity of 10 fps. Its also better to keep velocities at 5 or less to avoid possible water hammer troubles too. If you want to use high velocities, they are much more compatible in discharge lines. Use lower velocities on suction lines whenever possible. A few dollars for larger diameter pipe easily pays for itself with much reduced pump maintenance costs. At least go to as wide a diameter as possible when you get to 10-20 diameters of the pump suction flange.
The application I’m dealing with is boiler feed water from a deaerator, so it is near boiling.
I'm participating in a 3rd-party review of another engineer’s design. The pump suction velocities in some cases are higher than the limits in the linked document. I want to suggest these velocity limits, but they will carry much more weight if they are from a recognized industry organization rather than something I found on a website.
Can anyone cite a source for these limits?
BTW engineeringtoolbox.com does not respond to my enquiry.
There were a couple publications by EPRI in the mid-1980's regarding optimal line sizing for the application you identified. The 'optimal' solution is not solely based on velocity considerations.
I think velocity has little to do with adequate suction, other than as a measure to keep friction loss low, as velocity actually adds head provided it does not also cause additional turbulence.
With BFW, it is much more important to guarantee NPSHR is definately equalled or exceeded.
