Capacity is the quantity of fluid discharged per unit time. In the fps system, this is expressed in gallons per minute (gpm) for liquids.

Static Head Static head for a liquid being pumped is the difference in elevation, in feet, between the datum line and the liquid surface or the point of free delivery. For the horizontal centrifugal pumps, the datum line is the pump centerline. For the vertical pumps the datum line is taken at the eye of the first-stage impeller.

In Fig. 2-10, Z ₁ and Z ₂ are the static heads. Note that Z ₂ is measured up to the end of the discharge pipe because the pipe end is the point of free delivery. If the pipe were connected at the bottom, Z ₂ would be measured up to the liquid surface.

Pressure Head This is given in feet and defined as follows:

Velocity Head This is given in feet and defined as follows:

where u is the velocity, ft/s, and g _c is Newton's law proportionality factor = 32.17 ft lb/lbf s ²

Static Suction Head This is the difference in elevation, in feet, between the centerline (or impeller eye) of the pump and the liquid surface in the suction vessel. The liquid surface is above the pump centerline. In...