The Pump Operating Point Comes from Two Curves

A requested flow is a duty requirement. The corresponding pump operating point also depends on the system it is connected to.

Find the Shared Condition

KSB defines a centrifugal pump operating point as the intersection of its head/flow curve and the system head/flow curve. Both head and flow must correspond at that point. A pump curve alone does not establish the delivered flow for every connected route.

Ask for the system basis beside the proposed curve. A nominal selection point and an actual operating point should remain distinguishable. This matters when a receiver level, piping option or operating condition changes after the pump was initially shortlisted. KSB primary engineering reference.

Illustrative Intersection

Invented curves are Hpump = 30 − 0.02Q² and Hsys = 6 + 0.04Q², with H in metres and Q in m³/h. Equating them gives 24 = 0.06Q², so Q = 20 and H = 22. This is an educational model, not performance data.

The result uses both curves. Reading the pump curve at an arbitrary Q of 10 would produce another pump-head value but would not satisfy this hypothetical system curve. A desired quantity should therefore be checked against the matching required head.

Review Changes Without Guessing Controls

If the system curve changes, the intersection can move while the pump curve remains the same. If pump speed changes, the pump curve can change as well. Keep the changed input and its reason in the engineering record instead of silently substituting a new result.

Complete the worksheet with the designer and retain the selected operating envelope, not only one intersection. This guide explains the comparison and supplies no start-up procedure, adjustment instruction or assurance that an actual pump is suitable across all batch conditions. Relevant HM context: Processing Tank.