Mod 1 - Centrifugal Pumps

Module from the Rotating Equipment Training Curriculum curriculum.

CENTRIFUGAL PUMP FUNDAMENTALS · Learning Objectives · 1. Apply affinity laws for speed and impeller diameter changes 2. Calculate NPSHa and compare to NPSHr with proper margin per API 610 3. Construct system curves and determine pump operating point 4. Select pump type and configuration for given service conditions 5. Interpret pump performance curves (H-Q, efficiency, power, NPSHr) · Affinity Laws

Parameter	Law	Speed Change	Impeller Trim	Units	Application
Flow (Q)	Q₂ = Q₁ × (N₂/N₁)	Linear with speed	Q₂ = Q₁ × (D₂/D₁)	GPM	Predict flow at new speed or diameter
Head (H)	H₂ = H₁ × (N₂/N₁)²	Square of speed ratio	H₂ = H₁ × (D₂/D₁)²	ft	Predict head at new conditions
Power (P)	P₂ = P₁ × (N₂/N₁)³	Cube of speed ratio	P₂ = P₁ × (D₂/D₁)³	HP	Power changes dramatically with speed
NPSHr	NPSHr₂ ≈ NPSHr₁ × (N₂/N₁)²	Approximate square relationship	Not typically trimmed for NPSHr	ft	Estimate only — verify with vendor curve
NPSH Analysis
Parameter	Formula	Typical Values	Units	Source	Notes
NPSHa		8-40 ft	ft	System design calc	Must exceed NPSHr by margin
NPSHr	From pump vendor curve at operating flow	3-25 ft	ft	Pump performance curve	Increases with flow rate
API 610 Margin	NPSHa ≥ NPSHr + 3 ft (or NPSHr × 1.25, whichever greater)	3 ft min or 25% min	ft	API 610 12th Ed	Conservative approach for reliability
Suction Specific Speed	Nss = N × √Q / (NPSHr)^0.75	8,000-11,000 typical	dimensionless	Calculated	Nss >11,000 indicates recirculation risk
Vapor Pressure	Pvp at pumping temperature	Varies with fluid/temp	psia	Fluid properties data	Critical for hot liquids and LPG/NGL service
Pump Types per API 610
API Type	Configuration	Max Flow (GPM)	Max Head (ft)	Max Temp (°F)	Typical Service
OH1	Overhung, foot-mounted	3,000	700	500	General refinery service
OH2	Overhung, centerline-mounted	5,000	900	800	Hot service (>300°F), high-pressure
BB1	Between-bearings, axially split	10,000	600	500	Large-flow, low-head
BB2	Between-bearings, radially split	8,000	6,000	800	High-pressure, multi-stage BFW
BB5	Between-bearings, barrel type	3,000	12,000	800	High-pressure boiler feed, hydrocracker charge
VS1	Vertical, single-casing	15,000	500	400	Sump, wet pit, cooling water
VS6	Vertical, double-casing	5,000	3,000	500	Vertical can, deepwell, condensate
Source: API 610 12th Ed, FOS Chief Files — Centrifugal Pumps.pdf, Pump_Sizing_NPSH_Calculator_v1.xlsx, IPE-EP-6-1-1

Source: Rotating_Equipment_Training_Curriculum_v1.xlsx · Sheet: Mod 1 - Centrifugal Pumps

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