How to select a Centrifugal Pump

A centrifugal pump is a machine that uses centrifugal force generated by an impeller spinning at high speed to convert mechanical energy into kinetic and pressure energy, moving low-viscosity fluids such as water, solvents, and light chemicals.

Fluid enters through the center of the impeller (the impeller eye) and is accelerated radially by the vanes. The high velocity at the impeller outlet is converted into pressure by the volute (spiral casing). The pressure difference between suction and discharge drives the fluid through the system.

The characteristic curve relates flow and head for a defined model, impeller diameter and speed. Efficiency, power and required NPSH curves complete the selection data. BEP is the point of maximum efficiency on the efficiency curve. The operating point results from the intersection of the pump and system Q×H curves.

Centrifugal pumps serve process and cooling water, solvents and chemicals compatible with the model materials and seals. Selection requires fluid composition, solids, temperature and viscosity. For viscous liquids, assess corrected curves and power at the duty point; 100 cP is not a universal cutoff.

It is a pump that follows standardized requirements within a declared scope. The FBCN manual describes mechanical construction to ASME B73.1 and back pull-out construction. For replacement, compare drawings, connections and operating conditions; the term standardized does not guarantee pump equivalence or spare-parts interchangeability.

ASME B73.1 covers horizontal, end-suction, single-stage centrifugal pumps for chemical processes. It includes dimensional and design requirements within its scope. The FBCN manual declares mechanical construction to this standard; confirm the edition, configuration and drawing before specifying a replacement.

B73.1 covers horizontal end-suction construction; B73.2 covers vertical in-line construction. This distinction changes the pump arrangement and interfaces. The FBCN presented in this guide is horizontal; a B73.2 requirement must not be met by a nominal substitution without assessing the required construction.

Selection between gear and centrifugal pumps depends on flow, pressure or head, viscosity at operating temperature, suction conditions and materials. FBE and FBEI serve viscous fluids; FBCN serves centrifugal applications and FBOT thermal oil circuits. There is no universal 100 cP threshold: compare corrected curves, internal losses and power at the same duty point with engineering.

FBCN can be assessed as a replacement. Send the current pump's nameplate, dimensional drawing and operating conditions. Engineering compares the curve, suction, materials, sealing, connections, baseplate and power, identifying any modifications in the proposal. Equal rated flow or nozzle diameter does not establish equivalence.

Single-phase and three-phase describe the electric motor supply, not the pump's hydraulic principle. Provide the available voltage, frequency and number of phases, together with the duty point. Select the motor and starting arrangement for required power, duty and installation conditions; there is no universal power cutoff between these supplies.

The main components are the impeller, casing, shaft, bearing support and sealing system. Wear rings and other parts depend on the configuration. To identify FBCN parts, use the manual's sectional drawing and parts list, checking the pump's full model code and serial number.

It is a centrifugal pump with a horizontally arranged shaft. FBCN uses this configuration and back pull-out construction. Select the application from liquid conditions, curve, materials, sealing and installation. For fire protection, also confirm the configuration, tests and documents required by the design.

The impeller is the rotating component that transfers energy to the liquid in a centrifugal pump. Its geometry and diameter affect flow, head, efficiency and power curves. For the FBCN, the manual describes a pressure-side wear ring, except on models 25-150, 32-125 and 32-125.1. Consult the model drawing and parts list to identify the assembly; construction is not identical throughout the series.

A stainless steel centrifugal pump is indicated when the fluid is corrosive or requires purity. Manual MTEC-03/00 lists the FBCN in chemical, petrochemical and pharmaceutical industries, among others (p.1), and provides A743 CF8M stainless steel, in addition to cast iron, ductile iron and A216 WCB carbon steel, each with its own limits; for another material, consult FB.

Motor power alone does not determine flow. To select 5 cv, 10 cv, 15 cv or another rating, establish flow, total head, fluid density and viscosity and consult the model input-power curve. The drive must cover the intended operating range under the motor manufacturer’s criteria. Table 2 of the FBCN manual uses metric horsepower (cv); cv and HP are not identical units, and each power rating does not correspond to a fixed flow.

Manometric head (H) is the total energy the pump delivers to the fluid, expressed in meters of liquid column. It includes: elevation difference between suction and discharge, friction losses in the piping, and required pressure at the delivery point. The FBCN series from FB Bombas achieves up to 135 meters of manometric head, with Q×H curves published for 53 of the 54 models (43 standard DN25-150 and 10 large capacity, from 150-500 to 300-340); the 100-500 curve is supplied on request.

Calculate available NPSH under the most adverse process conditions: absolute reservoir pressure, minimum level, suction losses and vapor pressure at pumping temperature. Compare it with pump required NPSH throughout the operating range and use an application-appropriate margin agreed with engineering. A fixed 0.5 m margin is not a universal rule. Also check air ingress, obstructions, temperature and operation outside the manufacturer’s allowable region.

Self-priming centrifugal designs exist, but this feature should not be assumed for FBCN. Check how the pump and suction line will be filled and how air will be removed before starting. Priming does not replace available-NPSH verification or permit dry running.