Rotating Equipment Masterclass : Pumps & Compressors

Explore centrifugal pumps from fundamentals to diagnostics, including net positive section head, cavitation, affinity laws, and system curves, with focus on preventing failures and maintaining bearings and seals.

Explore centrifugal pumps and how they move liquids from low to high pressure, including 30 psi drum transfers, and learn about impeller, shaft, mechanical seal, bearings, and head concepts.

Explore atmospheric, absolute, and gauge pressure, plus vacuum, and how pressure transmits in liquids; clarify vacuum as absence of atmospheric pressure, not a negative value.

Learn how section piping, the eye of the impeller, and system head determine the energy entering the pump, enabling pressure and flow while avoiding inadequate energy.

NPSHr is the energy the liquid needs to overcome suction losses and prevent vaporization. It appears on the pump curve and varies with design, size, and operating conditions.

Calculate the net positive suction head available, compare it to the net positive suction head required, and apply design adjustments to prevent cavitation.

Explain how system pressure and inadequate net positive suction head drive cavitation in a centrifugal pump by vapor pressure exceeding eye of impeller, with temperature and altitude altering boiling.

Explore how vapor pressure and cavitation impact pump performance in the rotating equipment masterclass: pumps & compressors, including causes, effects, and five cavitation types.

Vaporization cavitation, or classic cavitation, happens when the impeller eye pressure drops and water boils. Maintain the net positive head available higher than the pump's requirement, with a three-foot margin.

Understand vane passing syndrome, a cavitation caused by blade tips dipping near the cut water; keep at least 4% clearance, about 0.5 inches on a 13-inch impeller.

Prevent air aspiration-induced cavitation by sealing all entrance points. Tighten gaskets and consider dual mechanical seals to control air entry through valves, joints, O-rings, and fittings.

Turbulence cavitation results from vortex formation and flow restrictions, such as sharp elbows, connections, filters, strainers, and submergence violations, observed when the pump is disassembled and cavitation resembles vaporization.

learn to prevent cavitation by maintaining a three-foot safety margin between net positive section head available and required, and reduce friction, optimize piping, valves, and vessel levels.

Explore factors affecting pump efficiency, including impeller velocity, diameter, blade count, surface finish, wear tolerances, and specific speed, plus how to compute efficiency from water horsepower, head, and brake horsepower.

Identify the two principal pump families—kinetic energy pumps and positive displacement pumps—and how each adds energy to a liquid to move it through pipelines and increase pressure.

Positive displacement pumps, such as gear pumps, expand a cavity to draw in liquid and compress it to the discharge, with flow set by driver speed and tolerances.

Explore centrifugal pumps: pressure from accelerating fluid converts velocity to head, noting the net positive suction head and eye of the impeller, suction head, and the head-capacity curve.

Compare centrifugal and positive displacement pumps by showing how their pump curves intersect the system curve, and note that about 90% of industry pumps are centrifugal.

Explore how centrifugal volute pumps convert fluid velocity into pressure and head using an impeller, volute channel, and discharge nozzle, guiding flow from entry to outlet.

Explore the diverse family of centrifugal pumps, from overhung and motor-driven units to single- and multi-stage types, vertical turbine and non-metallic variants.

An impeller in a pump receives liquid at the eye and imparts velocity, with head by speed and diameter and flow by blade height, single or dual section designs.

Explore suction specific speed, calculated from speed, flow, and net positive section head, and how it defines the pump’s operating window via performance curves and best efficiency point.

Explore centrifugal pump impeller classifications including totally open, semi-open, and totally enclosed, with emphasis on axial flow impellers, tolerances, solids handling, and factors affecting efficiency and wear.

Learn how replaceable wear bands on the impeller outside diameter and on the housing bore control tolerance and restore about 2% efficiency per 0.001 inch wear, with material compatibility considerations.

Explore specific speed Ns as a dimensionless index describing impeller geometry and guiding pump design, casing choices, and operation near the best efficiency point for radial, mixed, and axial impellers.

Explore pump performance curves - head-flow, efficiency, energy, and the net positive section heads required curve - and learn how these interconnected curves indicate discharge, head, and horsepower for operators.

Understand the head-capacity (H-Q) curve and the pump curve linking flow (gpm) to head. A pump operates along its curve from shut-off head to maximum flow.

Explore pump efficiency by comparing it to a water stream from a garden hose, and identify the best efficiency point, BP, on the pump curve.

Explore the energy curve of pumps, showing how brake horsepower rises from shut-off head as flow increases, with the BHP curve often appearing as a straight line.

Examine the pump performance curve and the minimum requirements curve (NPSHr) for net positive suction head; flow stays flat to rising until the bp zone, then NPSHr grows exponentially.