Pumps, Fans & Turbomachinery — Engineering Reference

See also (Tier 3 family index): Pumps Taxonomy

1. At a glance

A turbomachine is any device that exchanges energy between a fluid and a rotating shaft. Pumps, fans, blowers, and compressors add energy to a fluid (electrical or mechanical work in, pressure / kinetic / potential energy out); turbines extract it (fluid energy in, mechanical work out). The same fundamental physics — angular-momentum transfer through bladed wheels — covers everything from a 5 W aquarium pump to a 500 MW hydraulic turbine, and from a desk fan to the multi-stage axial compressor inside a jet engine.

Family branches by working fluid (liquid versus gas), pressure ratio, and impeller geometry:

• Liquid pumps — incompressible flow (Δρ/ρ < 1 %); rated in head H (m or ft) and flow Q (m³/h or gpm). Centrifugal dominates installed base; positive-displacement (PD) handles viscous, metering, and high-pressure duty.
• Fans — gas, ΔP ≤ 6 kPa (~0.06 bar), density change negligible (< 3 %); rated in static pressure (Pa or in WG) and volumetric flow (m³/s or cfm).
• Blowers — gas, 6 ≤ ΔP ≤ 200 kPa; transition between fan and compressor; rated similarly to fans but with attention to compression heating.
• Compressors — gas, ΔP > 200 kPa, density change significant; rated in pressure ratio π and mass flow (kg/s or lb/min); thermodynamic state at inlet and outlet matters.
• Turbines — fluid energy → shaft work; hydraulic (water), steam, gas (combustion products or process gas), wind, tidal.

Pumping accounts for roughly 20 % of global electrical energy consumption (US DOE, IEA). Mis-selection of pumps — typically gross over-sizing — is the single largest source of energy waste in industrial fluid systems, commonly 30–50 % above optimal. A correctly selected pump runs near its best efficiency point (BEP), has adequate net positive suction head (NPSH) margin, and is matched to the system curve rather than throttled.

Where it sits in the design stack: pumps and turbomachines live at the intersection of fluid mechanics (Euler turbomachine equation, Bernoulli, system head loss), thermodynamics (compressor and turbine work, isentropic efficiency, refrigeration cycles), heat-transfer (cavitation as a thermodynamic event, compressor intercooling), electric-motors (the driver — nearly all industrial pumps are induction or PMSM-driven), bearings (rotor support, axial thrust management), gears-power-transmission (speed-increase gearboxes for centrifugal compressors, speed-reduction for hydro turbines), vibration-dynamics (rotor dynamics, ISO 10816 condition monitoring), and manufacturing (impeller casting, balancing, surface finish).

2. First principles

2.1 Energy equation across a pump

For incompressible steady flow between inlet station 1 and discharge station 2, the specific work added by the pump is:

w_pump  =  (P₂ − P₁)/ρ  +  (V₂² − V₁²)/2  +  g·(z₂ − z₁)  +  h_loss·g       [J/kg]

Dividing by g gives head, the quantity actually plotted on pump curves:

H  =  w_pump / g  =  (P₂ − P₁)/(ρg)  +  (V₂² − V₁²)/(2g)  +  (z₂ − z₁)  +  h_loss       [m]

Head is independent of fluid density — the same centrifugal pump produces the same head (m) in water, kerosene, or brine, but the pressure rise ΔP = ρgH scales with density, and the shaft power scales with both flow and density.

Hydraulic power (the useful work delivered to the fluid):

P_hyd  =  ρ · g · Q · H       [W]   (Q in m³/s, H in m, ρ in kg/m³)

Shaft power (mechanical input at the coupling):

P_shaft  =  P_hyd / η_pump       η_pump = η_hydraulic · η_volumetric · η_mechanical

with η_pump typically 0.45–0.85 for centrifugal water pumps near BEP, 0.30–0.60 for small pumps, and up to 0.90 for very large multi-stage units. The remainder is dissipated as heat in the fluid and bearings.

2.2 Euler turbomachine equation

The fundamental energy equation for any bladed wheel — pump, compressor, turbine — relates shaft work to the change in fluid angular momentum:

w_turbomachine  =  U₂ · V_θ₂  −  U₁ · V_θ₁       [J/kg]

where U = blade speed = ω·r at the inlet (1) and outlet (2) edges of the impeller, and V_θ is the tangential (whirl) component of absolute fluid velocity. For a pump, w > 0; for a turbine, w < 0. This single equation is the kinematic core of all turbomachinery design. The blade angles and meridional shape of the impeller are chosen to produce the desired V_θ₂ at the design flow.

2.3 Specific speed and impeller geometry

The specific speed N_s is a dimensional similarity parameter that selects which impeller shape is appropriate for a given duty (H, Q, N):

N_s  =  N · √Q / H^(3/4)

with N in rpm, Q in m³/s (metric) or gpm (US), H in m or ft. The US-units N_s is ≈ 51.6× the metric SI value. Roughly:

N_s (US units)	N_s (metric, SI)	Geometry	H/Q character
500 – 3 000	10 – 60	Radial-flow (centrifugal)	High H, low Q
3 000 – 7 000	60 – 140	Mixed-flow (Francis-type)	Moderate H, moderate Q
7 000 – 15 000	140 – 300	Axial-flow (propeller)	Low H, high Q
15 000+	300+	Axial / propeller	Very high Q

The chart drives the first design decision: a duty at 50 m head and 100 m³/h calls for a radial impeller; 5 m head and 5 000 m³/h calls for an axial pump (e.g. a cooling-water circulator).

2.4 Affinity laws

For a centrifugal pump at fixed geometry, scaling speed N:

Q ∝ N           H ∝ N²          P ∝ N³          NPSH_R ∝ N²

For a fixed speed, scaling impeller diameter D (within a family, by trimming):

Q ∝ D           H ∝ D²          P ∝ D³

The cubic relationship between speed and power is the reason variable-frequency drives (VFDs) save energy: throttling a pump from 100 % to 70 % flow with a discharge valve dissipates the difference as heat; reducing speed to deliver the same 70 % flow cuts shaft power by a factor of (0.7)³ = 0.34 — a 66 % power reduction. This is the single largest energy-efficiency opportunity in industrial fluid systems.

2.5 System curve and operating point

The piping system imposes a system head curve:

H_sys  =  H_static  +  K_sys · Q²

where H_static = elevation lift + back-pressure (independent of flow), and K_sys lumps all friction losses (which scale with Q² in fully turbulent flow per Darcy–Weisbach). The operating point is the intersection of the pump H–Q curve with the system curve. Anything that moves this intersection — a partially closed valve, a fouled exchanger, a different tank level — moves the operating flow.

Parallel pumps at common H sum their flows: Q_total = Q_A + Q_B. Series pumps at common Q sum their heads: H_total = H_A + H_B. Both relationships hold only at the operating point — the combined curve must be re-intersected with the system curve, and pumps in parallel on a steep system curve often deliver substantially less than 2× a single pump’s flow (see worked example B).

3. Practical math / design equations

3.1 NPSH — net positive suction head

NPSH is the absolute pressure (in head units) available at the pump suction above the fluid’s vapour pressure. If NPSH_available falls below NPSH_required, the fluid flashes to vapour inside the impeller eye — cavitation — collapsing back to liquid as it crosses the pressure rise and pitting metal.

NPSH_A  =  P_atm/(ρg)  −  h_lift  −  h_friction  −  P_vap/(ρg)  +  V_suction²/(2g)       [m]

with h_lift = vertical distance from free surface to pump centreline (positive for lift, negative for flooded suction), h_friction = friction loss in suction piping, P_vap = fluid vapour pressure at operating temperature, V_suction = suction-line velocity. NPSH_R is read off the pump curve as a function of Q.

Margin requirements by standard:

Standard	NPSH margin requirement
ANSI/HI 9.6.1 (Hydraulic Institute)	NPSH_A ≥ NPSH_R + 0.6 m, or NPSH_A ≥ 1.25 · NPSH_R (whichever larger)
API 610 12th ed. (petrochemical)	NPSH_A ≥ NPSH_R + 1.0 m (3 ft) on hydrocarbons; ≥ 1.5 m on water
ISO 13709	Same as API 610 (harmonised)
Boiler-feed practice (multi-stage)	NPSH_A ≥ 2 × NPSH_R minimum
Cryogenic / LNG	Margin computed from fluid-specific thermodynamic depression

The NPSH_R quoted on a pump curve is the 3 %-head-drop NPSH — measured at the point where head has fallen 3 % from the cavitation-free value. Onset of cavitation damage begins at higher NPSH than this (incipient cavitation); at the 3 % point, damage is already occurring at industrial rates.

3.2 Cavitation classes

Class	Trigger	Damage rate	Notes
Incipient	NPSH_A just above NPSH_R	Low	First audible noise; pitting begins
3 % head-drop	NPSH_A = NPSH_R (catalogue)	Moderate–high	Manufacturer’s stated point
Suction recirculation	Q << Q_BEP, low flow	High at suction	Vortices in eye; damages impeller back side. Onset at S_n > 11 000 (metric) or 8 500 (US)
Discharge recirculation	Q << Q_BEP	High at discharge	Damages volute and impeller vane trailing edges
FAFC (full air-filled cavitation)	NPSH_A << NPSH_R	Terminal	Head collapses; pump runs dry

S_n (suction specific speed) = N·√Q_BEP / NPSH_R^0.75. High S_n means the impeller is optimised for low NPSH_R but is more susceptible to recirculation. API 610 limits S_n to 11 000 metric (≈ 8 500 US) on new-pump specifications, and the Hydraulic Institute recommends operating window 70 %–120 % of Q_BEP to avoid recirculation damage.

3.3 Compressor work (compressible flow)

For a gas compressor, density changes substantially and pump-style head loses meaning. Instead, the specific work is computed from thermodynamic states:

w_isentropic  =  c_p · T₁ · [ π^((γ−1)/γ) − 1 ]       [J/kg]      π = P₂/P₁
w_actual      =  w_isentropic / η_isentropic
P_shaft       =  ṁ · w_actual                          [W]

with c_p = specific heat at constant pressure (1005 J/kg·K for air at 300 K), γ = c_p/c_v (1.40 for air, 1.30 for natural gas, ≈ 1.10 for refrigerants), T₁ = inlet absolute temperature, ṁ = mass flow. η_isentropic typically 0.72–0.85 for industrial centrifugal compressors, 0.85–0.92 for high-efficiency axial.

Outlet temperature follows:

T₂ / T₁  =  1  +  (1/η) · [ π^((γ−1)/γ) − 1 ]

A single-stage air compressor at π = 4 (atmosphere to 4 bar abs) with η = 0.80 raises 20 °C inlet air to about 175 °C — which is why intercooling between stages is universal in any compressor with π > ~3.

3.4 Worked example A — centrifugal pump selection for water supply

Given: Municipal water-supply duty. Q = 200 m³/h (880 gpm), H = 60 m (197 ft), water at 20 °C (ρ = 998 kg/m³, P_vap = 2.34 kPa). Suction lift 4 m below pump centreline through 8 m of DN150 pipe.

Step 1 — specific speed. Try 50 Hz at 2 900 rpm. Q in m³/s = 0.0556.

N_s (metric)  =  2900 · √0.0556 / 60^0.75
              =  2900 · 0.2358 / 21.6
              =  31.7

This is solidly in the radial-flow band (10–60 metric) — single-stage end-suction centrifugal is appropriate.

Step 2 — pump family and series. Single-stage end-suction water pumps for this duty: Grundfos NB / NBE 65-200, KSB Etanorm 80-200, Goulds 3196 ST 1×1.5-10, Sulzer A21-100, Xylem Lowara FH 65-200, Pentair Aurora 341A. From the Grundfos NB 65-200 50 Hz family curve, trim the impeller to a full diameter near 200 mm; at 200 m³/h the curve passes through approximately H = 62 m at D = 219 mm full impeller.

Step 3 — impeller trim. Apply affinity law in D: target 60 m at 200 m³/h. From full curve at 200 m³/h, full diameter 219 mm gives 62 m. Trim ratio = √(60/62) = 0.984, so D_trim ≈ 215 mm. (Manufacturer’s published trim curves should be used in practice — H scales slightly less than D² for trimmed impellers because the volute–impeller match degrades.)

Step 4 — efficiency and shaft power. From the curve at 200 m³/h, trim 215 mm: η ≈ 78 %. NPSH_R ≈ 3.5 m at this flow.

P_hyd    =  ρ · g · Q · H  =  998 · 9.81 · 0.0556 · 60  =  32 700 W  =  32.7 kW
P_shaft  =  32.7 / 0.78  =  41.9 kW       →  specify 45 kW (60 hp) IE3 4-pole motor

Motor selection per NEMA / IEC: 45 kW IE3 4-pole induction = approx WEG W22 IE3 200L 4P or ABB M3BP 200 MLA 4 or Siemens 1LE10. NEMA 326T frame.

Step 5 — NPSH check.

P_atm/(ρg)       =  101.3 kPa / (998 · 9.81)  =  10.35 m
h_lift           =  4 m
h_friction       =  estimate for 8 m of DN150 at V ≈ 3.1 m/s; f = 0.018, K_fittings = 3
                 =  (0.018 · 8/0.15 + 3) · 3.1² / (2·9.81) ≈ 2.0 m
P_vap/(ρg)       =  2.34 kPa / (998 · 9.81)  =  0.24 m
V²/(2g)          ≈ 0.49 m

NPSH_A  =  10.35  −  4.0  −  2.0  −  0.24  +  0.49  =  4.6 m

NPSH_A = 4.6 m versus NPSH_R = 3.5 m → margin 1.1 m or 31 %. Meets HI 14.6 (≥ 0.6 m and ≥ 25 %). For API 610 service the margin would need to be ≥ 1.5 m on water — borderline; widen the suction pipe to DN200 to reduce friction.

Step 6 — material. Clean potable water at ambient T → cast-iron casing (EN-GJL-250 / ASTM A48 CL30), cast-bronze impeller (CuSn10 / C90700) or 304 stainless. Sulzer A21-100 cast-iron / bronze trim or Grundfos NB 65-200 cast-iron would be specified. Mechanical seal: API plan 11 (recirculation from discharge to seal chamber) with carbon-vs-SiC faces, EPDM elastomers for potable water.

3.5 Worked example B — parallel pumps on a steep system curve

Given: The pump from Example A is installed and we need to expand capacity to 300 m³/h on the same piping system. System curve: H_static = 30 m, K = 7.5 × 10⁻⁴ m·(h/m³)² → H_sys = 30 + 7.5×10⁻⁴ · Q². Verify by plugging the existing operating point: H_sys(200) = 30 + 7.5×10⁻⁴ · 200² = 30 + 30 = 60 m. ✓

Question: Will two pumps in parallel deliver 300 m³/h?

Single-pump curve (from manufacturer, simplified): H_pump = 65 − 5×10⁻⁵ · Q² (gives 65 m shutoff, ≈ 60 m at 200 m³/h, ≈ 45 m at 600 m³/h).

Two pumps in parallel: Each delivers Q/2 at common H. Equivalent curve H = 65 − 5×10⁻⁵ · (Q/2)² = 65 − 1.25×10⁻⁵ · Q².

Find new operating point — equate to system curve:

65 − 1.25×10⁻⁵ · Q²  =  30 + 7.5×10⁻⁴ · Q²
35  =  7.625×10⁻⁴ · Q²
Q²  =  45 900
Q   =  214 m³/h        H = 30 + 7.5×10⁻⁴ · 214² = 64.4 m

Wait — that gives only 214 m³/h total across two pumps, not 300. Each pump runs at 107 m³/h, well left of its BEP at 200 m³/h. Efficiency drops (probably to 65 % from 78 %), each pump approaches its minimum continuous flow, and recirculation cavitation is likely.

Lesson: When the system curve is steep (friction-dominated, K_sys large), adding a parallel pump moves the operating point up the H–Q curves more than it adds flow. Parallel pumping pays off only on flat (static-dominated) system curves — pipelines, tank-to-tank transfers with small friction. For a friction-dominated system, the right answer is a larger pump or a bigger pipe (cutting K_sys), not parallel pumps.

For 300 m³/h on this system, the system head at 300 m³/h is 30 + 7.5×10⁻⁴ · 300² = 97.5 m. A single Grundfos CR 90 multi-stage or a larger end-suction (Grundfos NB 80-250) at higher speed would land 300 m³/h at ≈ 100 m head with one pump.

3.6 Worked example C — refrigeration compressor power

Given: R-134a refrigeration cycle. ṁ = 0.5 kg/s. Evaporator at P_evap = 0.30 MPa (saturation T ≈ −10 °C), condenser at P_cond = 1.00 MPa (saturation T ≈ 40 °C). Isentropic compressor efficiency η_c = 0.78.

State 1 — compressor inlet (saturated vapour at 0.30 MPa):

• h₁ = 244.5 kJ/kg, s₁ = 0.9374 kJ/kg·K (NIST REFPROP / ASHRAE Handbook tables)

State 2s — isentropic compressor outlet (1.00 MPa, s₂s = s₁):

• Interpolate on superheat table at 1.00 MPa: h_2s ≈ 282.0 kJ/kg, T_2s ≈ 49 °C

State 2 — actual compressor outlet:

h₂  =  h₁ + (h_2s − h₁)/η_c  =  244.5 + (282.0 − 244.5)/0.78  =  244.5 + 48.1  =  292.6 kJ/kg

State 3 — condenser outlet (saturated liquid at 1.00 MPa):

• h₃ = 107.3 kJ/kg

State 4 — evaporator inlet (after isenthalpic throttle):

• h₄ = h₃ = 107.3 kJ/kg

Energy balances:

W_compressor  =  ṁ · (h₂ − h₁)  =  0.5 · 48.1  =  24.1 kW
Q_evaporator  =  ṁ · (h₁ − h₄)  =  0.5 · (244.5 − 107.3)  =  68.6 kW
Q_condenser   =  ṁ · (h₂ − h₃)  =  0.5 · (292.6 − 107.3)  =  92.7 kW
COP_cooling   =  Q_evap / W_comp  =  68.6 / 24.1  =  2.85

Power balance check: Q_cond = W_comp + Q_evap = 24.1 + 68.6 = 92.7 kW ✓

A 24 kW R-134a duty fits a Bitzer 4FES-5 / 6FE-44Y semi-hermetic reciprocating or a Bitzer CSH7561 semi-hermetic screw; for chiller integration, Trane CenTraVac (centrifugal), Carrier 19XR (centrifugal), or York YK at this size; for smaller packaged applications, Copeland ZR / ZP scroll compressors are the standard.

4. Reference data

4.1 Pump family selection chart (by Q, H, N_s)

Family	Typical Q range (m³/h)	Typical H range (m)	Notes
Single-stage end-suction centrifugal (ANSI B73.1, ISO 5199)	5 – 2 000	5 – 150	The default; 80 % of process pumping
Horizontal split-case (HSC)	100 – 20 000	20 – 250	Double-suction reduces axial thrust and halves NPSH_R
Multi-stage horizontal (API BB3)	50 – 1 500	100 – 2 000	Boiler-feed, high-P process; KSB CHTC, Sulzer MC
Multi-stage vertical inline	5 – 800	50 – 600	Grundfos CR/CRN, KSB Movitec; compact footprint
Vertical turbine (deep well)	5 – 2 500	10 – 800	Submerged bowls; bowl-stack scales to needed H
Submersible (well/sump)	1 – 5 000	5 – 600	Motor sealed, runs in fluid; Grundfos SP / Flygt N
Axial-flow propeller	1 000 – 100 000	1 – 12	Flood pumping, cooling-water circulation
Mixed-flow (volute or bowl)	200 – 50 000	5 – 50	Storm-water, condenser-cooling intermediates
API 610 BB5 barrel	50 – 2 000	500 – 4 000	High-P refinery, hydrocrackers; Flowserve HPX, Sulzer GSG
Mag-drive sealless	0.5 – 500	5 – 200	Hazardous / expensive fluids; no shaft seal
Canned-motor pump	0.5 – 1 500	5 – 350	Same idea, motor canned in fluid; HERMETIC, Teikoku
Self-priming centrifugal	5 – 500	5 – 60	Tank trucks, sumps, intermittent service
Positive-displacement
Reciprocating piston/plunger	0.5 – 200	100 – 2 500 bar	Mud pumps, water-jet, hydraulic, well-service
Diaphragm (AODD or motor-driven)	0.05 – 100	1 – 100 bar	Chemicals, slurries, dosing; Wilden, ARO, Grundfos
External gear	0.1 – 100	5 – 250 bar	Lube oil, hydraulic, fuel; Viking, Bosch Rexroth
Internal gear / gerotor	0.1 – 200	5 – 200 bar	Viscous, asphalt, polymers; Viking, Maag
Lobe (twin)	1 – 500	5 – 30 bar	Hygienic dairy, food, sewage; Alfa Laval, GEA, Waukesha
Vane (sliding-vane)	0.5 – 200	5 – 25 bar	LPG, light hydrocarbons; Blackmer
Progressive cavity (PC)	0.05 – 200	5 – 240 bar	Slurries, sludges, polymers; Moyno, Mono, Seepex, NETZSCH
Twin / triple screw	1 – 1 500	5 – 250 bar	Multiphase, viscous, lube oil; Leistritz, Bornemann
Peristaltic (hose)	0.01 – 80	1 – 16 bar	Abrasives, shear-sensitive, dosing; Watson-Marlow, Verderflex

4.2 Mechanical seal flush plans (API 682, current 4th ed. 2014)

Plan	Description	Application
Plan 01	Internal recirculation from discharge to seal	Older designs; rarely specified new
Plan 02	Dead-ended seal chamber, no flush	Clean cool fluid only
Plan 11	External recirculation from discharge through orifice to seal	Standard for clean fluids; “the default”
Plan 13	Recirculation from seal chamber back to suction through orifice	Vertical pumps; venting at seal chamber
Plan 14	Combines 11 + 13: discharge → seal → suction	Higher cooling than 11 alone
Plan 21	Discharge → cooler → seal	Hot fluids; cools to seal-tolerable T
Plan 23	Closed-loop with pumping ring + cooler	Boiler-feed water (high-T high-P)
Plan 32	Clean external flush (fresh fluid) injected into seal chamber	Dirty / abrasive process fluids
Plan 41	Discharge → cyclone separator → seal	Solids in service fluid
Plan 52	Unpressurised buffer fluid between dual seals	Toxic/hazardous; outboard seal acts as backup
Plan 53A/B/C	Pressurised barrier fluid between dual seals	Lethal / valuable / VOC-controlled; positive isolation
Plan 54	Externally pressurised barrier from clean source	Same as 53 with external supply
Plan 62	Quench (steam/water/nitrogen) to outboard side of single seal	Crystallising / freezing fluids
Plan 65A/B	Leakage detection (collection chamber with level switch)	Required for hazardous services
Plan 75/76	Vapour leakage collection for gas seals	LNG, light hydrocarbons

4.3 Fan types vs ΔP class (AMCA 210)

Type	ΔP range (Pa)	Efficiency	Application
Centrifugal — forward-curved (sirocco)	100 – 1 250	55 – 70 %	HVAC supply, low-pressure low-noise
Centrifugal — backward-inclined	250 – 2 500	75 – 85 %	Industrial supply/exhaust
Centrifugal — backward-curved airfoil	500 – 5 000	80 – 90 %	High-efficiency HVAC, clean air
Centrifugal — radial-tip (radial bladed)	1 000 – 7 500	60 – 75 %	Material handling, dirty / abrasive
Axial — propeller	0 – 100	40 – 60 %	Wall fans, low-resistance exhaust
Axial — tubeaxial	100 – 750	60 – 75 %	Duct boosters, drying
Axial — vaneaxial	500 – 2 500	75 – 85 %	High flow at moderate ΔP; tunnel ventilation
Mixed-flow inline	200 – 1 500	65 – 80 %	Compact duct applications
Cross-flow (tangential)	50 – 250	30 – 50 %	Fan-coil units, air curtains

4.4 Compressor selection (P_disc, Q range)

Type	P_disc range (bar)	Q range	Efficiency	Notes
Reciprocating — single-stage	1 – 10	0.5 – 100 m³/min	60 – 75 %	Small workshop air
Reciprocating — multi-stage	10 – 350	1 – 600 m³/min	70 – 85 %	Process, breathing air, CNG, hyperbaric
Rotary screw — oil-injected	5 – 13	1 – 600 m³/min	70 – 80 %	Plant air, the industry workhorse
Rotary screw — oil-free	5 – 13	5 – 1 500 m³/min	65 – 75 %	Food, pharma, electronics
Scroll (oil-less)	5 – 13	0.3 – 25 m³/min	70 – 80 %	Small clean-air, dental, medical
Centrifugal — single-stage	1.5 – 15	1 000 – 200 000 m³/h	75 – 85 %	HVAC chillers, plant air
Centrifugal — multi-stage (intercooled)	10 – 700	500 – 500 000 m³/h	75 – 88 %	Process, refinery, gas pipeline
Centrifugal — geared (integrally geared)	5 – 200	5 000 – 200 000 m³/h	80 – 88 %	Air separation, syngas
Axial — multi-stage	1.5 – 40	100 000 – 3 000 000 m³/h	85 – 92 %	Blast-furnace blowers, gas-turbine compressor sections
Roots blower (PD)	< 1.0 ΔP	50 – 50 000 m³/h	60 – 75 %	Wastewater aeration, pneumatic conveying
Liquid-ring vacuum	33 mbar abs minimum	25 – 30 000 m³/h	—	Wet vacuum, condensable vapours

4.5 Vibration severity zones (ISO 10816-3 / ISO 20816-3)

For Class II machines (medium-sized, 15–300 kW, rigid foundation), broadband RMS velocity 10–1 000 Hz:

Zone	RMS velocity (mm/s)	Action
A	≤ 1.4	Newly commissioned; acceptable for long-term operation
B	1.4 – 2.8	Acceptable for unrestricted long-term operation
C	2.8 – 4.5	Unsatisfactory for long-term; corrective action within reasonable interval
D	> 4.5	Severe; vibration causing damage; shutdown advised

Class IV (large rigid foundation, > 300 kW): A ≤ 2.8, B 2.8–4.5, C 4.5–11.2, D > 11.2 mm/s.

Vibration spectral signatures used in pump/fan diagnosis:

Frequency component	Likely cause
1× shaft speed	Unbalance
2× shaft speed	Misalignment (parallel or angular)
Vane-pass frequency (Z_vane · N)	Recirculation, vane-volute interaction, cavitation onset
0.4–0.5× shaft speed	Oil whirl in journal bearings
Bearing defect frequencies (BPFI, BPFO, BSF, FTF)	Rolling-bearing surface damage
Broadband > 5 kHz	Cavitation, bearing late-stage
Sub-synchronous (< 1×)	Rotor-stator rub, structural resonance

4.6 Materials by service

Service	Casing	Impeller	Shaft / sleeve
Clean cold water	Cast iron (ASTM A48 CL30)	Bronze (C90700) or 304 SS	410 SS / 416 SS
Hot water / boiler feed	Carbon steel / 1.0619 / WCB	12-Cr steel (CA6NM)	13-Cr SS
Sea water / chloride brine	Duplex 2205 / super-duplex 2507	Same	Same
Sulphuric / strong acid	Alloy 20 / CN7M / Hastelloy C-276	Same	Same
Caustic	Cast iron (concentrated, cold) or Ni-Resist	Same	316 SS
Hydrocarbons (API 610)	A216 WCB (carbon steel)	12-Cr or duplex	13-Cr or duplex
High-T hydrocarbons (>200 °C)	A217 WC6 / WC9 (Cr-Mo)	12-Cr / Inconel 718	Inconel / 17-4PH
Slurries (abrasive, mining)	High-chrome white iron (ASTM A532)	Same	4140 / 17-4PH
Food / pharma (hygienic)	316L SS electro-polished	316L SS	316L SS
Cryogenic LNG / LIN / LOX	Austenitic SS (304L / 316L)	Same	Same
HF acid, fuming HNO₃	Hastelloy C-276 / Inconel 625	Same	Same

5. Variants & topologies (component-specific section 5c)

5c.1 Centrifugal pumps — by configuration

• End-suction (overhung impeller, ANSI B73.1 / ISO 2858 / ISO 5199) — single impeller cantilevered on shaft beyond the bearings; suction axial, discharge radial. Most common configuration; covers most process duties below 250 kW.
• Close-coupled (motor-mounted) — impeller direct on motor shaft. Compact; common in HVAC and small water duty.
• Long-coupled (frame-mounted) — pump and motor on separate bearings, coupled with a flexible coupling and spacer. Permits seal replacement without motor removal.
• Horizontal split-case (HSC) — casing split on horizontal centreline; double-suction impeller. Inherent axial-thrust balance; halved NPSH_R (each half-impeller sees half the flow). Standard for high-flow water supply (Goulds 3409, Sulzer ZE, Flowserve LR).
• Vertical inline — discharge axial, suction axial, pump mounts directly in the pipeline like a valve. No separate baseplate. Grundfos TPE / Wilo IL / Bell & Gossett VSC.
• Vertical multi-stage — stacked stages on a single shaft (Grundfos CR/CRN, KSB Movitec, Lowara SV). Compact for high-H low-Q duty. Common 5–100 kW.
• API 610 BB1 / BB2 / BB3 / BB5 — two-bearing between-bearings designs; BB5 (barrel / double-casing) for very high pressure / high temperature refinery service.
• OH1 / OH2 / OH3 — overhung designs in API 610 nomenclature; OH2 (foot-mounted process pump) is the petrochem equivalent of ANSI B73.1.
• Submersible — sealed motor-pump in single unit, runs submerged. Grundfos SP (deep well), Flygt N (sewage), KSB Amarex.
• Vertical turbine (line shaft) — surface motor drives long line shaft down to submerged bowl assembly. Goulds VIT, Layne, Peerless, National Pump.
• Mag-drive (sealless) — outer driver magnet on motor shaft, inner driven magnet on pump shaft, separated by a non-magnetic containment shell. No shaft seal. Iwaki, Magnatex, Sundyne LMV, KSB MegaCPK-M.
• Canned-motor — motor stator outside a thin pressure can, rotor inside in the process fluid. No shaft penetration at all. HERMETIC, Teikoku, Nikkiso.
• Self-priming — designed to re-establish suction after losing prime (suction chamber retains fluid; air evacuated through impeller on restart). Gorman-Rupp T-series, Pioneer.

5c.2 Positive-displacement pumps — by mechanism

• Reciprocating piston (single- / double-acting) — high P, modest Q; mud pumps (drilling), water-jet cutting (Flow, KMT), well-service.
• Reciprocating plunger — plunger sliding through packing (no return stroke as piston); highest pressures, 1 000–3 000 bar achievable. Wheatley, Gardner Denver, NOV.
• Diaphragm — air-operated double-diaphragm (AODD) — pneumatic actuation, no electrical, intrinsically explosion-safe. Wilden, ARO, Yamada, Versa-Matic.
• Diaphragm — motor / hydraulic-driven (metering) — precise dosing, ±0.5 % repeatability. ProMinent, Milton Roy, LEWA, Grundfos DDA/DDE.
• External gear — two meshing spur gears in close-fit housing; trapped volume carries fluid around gear OD from suction to discharge. Lube oil, hydraulic. Bosch Rexroth, Parker, Viking, Marzocchi.
• Internal gear / gerotor — internal gear pair with one-tooth-difference; high efficiency at low to medium pressures. Viking, Maag, Eaton.
• Lobe — two non-contacting rotating lobes (timed by external gears); large entrapment volume, gentle flow. Dairy, beverage, hygienic. Alfa Laval, GEA, Waukesha, Boerger.
• Vane (sliding-vane) — slotted rotor with sliding vanes that follow eccentric casing. LPG, light hydrocarbons. Blackmer, Corken.
• Progressive cavity (PC) — single helical rotor in double-helical stator; fluid carried in progressing closed cavities. Slurries, sludges, polymers. Moyno, Mono, Seepex, NETZSCH, Allweiler.
• Twin / triple screw — intermeshing helical screws; high flow at high pressure, very low pulsation. Lube-oil transfer in marine, multiphase well-service. Leistritz, Bornemann (Itt), Colfax (Allweiler/Imo).
• Peristaltic (hose) — flexible hose squeezed by rotating shoes/rollers; only the hose contacts the fluid. Abrasive slurries, shear-sensitive biological. Watson-Marlow, Verderflex, ProMinent DULCO·flex.

5c.3 Fans, blowers, compressors

Coverage already in §4.3 (fans) and §4.4 (compressors); families branch on impeller geometry (centrifugal / axial / mixed-flow / scroll / lobed / screw / reciprocating) and on whether the working fluid is treated as incompressible (fan) or compressible (compressor). Industrial vacuum pumps form a related family using the same mechanisms in reverse — Edwards (oil-sealed rotary vane, dry screw), Leybold (turbomolecular, claw), Busch (claw, screw), Pfeiffer Vacuum.

5c.4 Turbines — by working fluid and head/pressure

• Hydraulic — Pelton (impulse): high head (50–1 800 m), low flow; multiple buckets on a wheel struck by jets. Andritz Hydro, Voith, GE Renewable.
• Hydraulic — Francis (reaction, mixed-flow): medium head (10–700 m), medium-to-high flow; the world’s most common hydro turbine. Same suppliers.
• Hydraulic — Kaplan / propeller (reaction, axial): low head (1.5–60 m), very high flow; adjustable-pitch runner (Kaplan) or fixed (propeller). Bulb turbines for very low head tidal / run-of-river.
• Steam — impulse (Curtis, De Laval, Rateau): high-pressure HP-stages of utility plants; entire pressure drop happens in fixed nozzles, blades absorb only kinetic energy. GE, Siemens Energy, MHI, Toshiba, Doosan Škoda.
• Steam — reaction (Parsons): pressure drops across both fixed and rotating rows; LP-stages of utility plants. Last-stage blades are some of the largest precision-manufactured rotating components ever built (1.4 m+).
• Gas — axial multi-stage: jet engine cores (Pratt & Whitney, Rolls-Royce, GE Aviation, CFM, Safran), ground-based power generation (GE 7HA/9HA, Siemens SGT, MHI M501J), large compressor drivers in LNG / refineries.
• Gas — radial inflow: turbochargers (Garrett/Honeywell, BorgWarner, Mitsubishi, IHI), small APUs, cryogenic expanders.
• Wind — horizontal-axis (HAWT): dominant utility design. Vestas, Siemens Gamesa, GE Renewable Energy, Goldwind, Mingyang, Nordex.
• Wind — vertical-axis (VAWT): Darrieus, H-rotor, Savonius — niche urban / low-Re applications.
• Tidal stream / wave: emerging; MeyGen (Andritz HAMMERFEST), Orbital Marine O2, Wave Swell Energy King Island.

6c. Selection criteria

A disciplined pump-selection process — applicable with minor modifications to fans and compressors — follows ten ordered steps.

Step 1 — Define the process duty completely. Q (range, not just rated), H (system curve, not just rated), fluid (composition, T, viscosity, vapour pressure, abrasiveness, hazard class), and required NPSH_A. Many selection failures originate here, in incomplete data.

Step 2 — Compute specific speed. N_s tells you whether to look at radial, mixed, or axial impellers. With N undetermined, compute for the candidate speeds (1450, 1750, 2900, 3550 rpm at 50/60 Hz).

Step 3 — Choose pump family. Centrifugal versus PD based on Q/H ratio, viscosity, shear-sensitivity, dosing accuracy. Viscosity > 100 cSt favours PD. Slurries with solids > 10 % favour PC, lobe, or specialised slurry centrifugal (Warman, Metso).

Step 4 — Pick manufacturer and series. Major suppliers’ catalogues are organised so each series covers a specific Q/H envelope. Use selection software (Grundfos GO Replace, KSB SelectPump, Goulds Hydraulic Selector, Sulzer SelectionTool, Xylem ResiBoost, Wilo Select) to land the right series.

Step 5 — Pick speed. Higher speed = smaller, cheaper, lower-η, higher-noise, higher-NPSH_R pump. Pumping low-NPSH service (boiler condensate, hot oil) usually forces a low-speed (1 450/1 750 rpm) pump despite the size penalty.

Step 6 — Pick impeller diameter on family curve. Land near BEP at the design duty. Operate within 80 %–110 % of BEP for long bearing/seal life (HI 9.6.3 preferred-operating range). Below 70 % BEP, suction recirculation damage accumulates; above 120 %, discharge recirculation and motor overload.

Step 7 — Verify NPSH margin. Per §3.1, NPSH_A ≥ NPSH_R + appropriate margin for the standard. If margin is inadequate, options: lower the pump (reduce h_lift), enlarge the suction line (reduce h_friction), cool the fluid (lower P_vap), pressurise the source vessel, or pick a different pump with lower NPSH_R (often a slower-speed or double-suction design).

Step 8 — Material selection. Per §4.6 by service. Don’t downgrade for cost without metallurgical justification — pump-component corrosion is a leading cause of unplanned shutdowns.

Step 9 — Driver sizing. Specify motor at the end-of-curve (maximum continuous power) at the trimmed impeller, plus 10–15 % service margin. For variable-speed (VFD) drives, the motor and VFD must be matched and inverter-duty insulation specified per NEMA MG 1 Part 31 / IEC 60034-25 (and bearing-current protection per [[Engineering/bearings]] §10c.5).

Step 10 — Mechanical seal selection. Per §4.2 plan number; faces (carbon / SiC / TC / WC / Al₂O₃), elastomers (NBR / EPDM / FKM / FFKM / Kalrez), single vs dual, pressurised vs unpressurised barrier. Manufacturer support: John Crane, Flowserve / Durametallic, AESSEAL, EagleBurgmann, Chesterton, Garlock.

7c. Datasheet decoding

Pump curves and datasheets contain consistent fields that translate across manufacturers once you know the conventions.

• H–Q curve at rated speed: family curves usually show 3–6 impeller-diameter trims. Select the trim that places the duty point at the operating flow on the curve interpolated for that diameter. The curve at maximum trim and minimum trim brackets the envelope the casing can accommodate; intermediate trims are linear-ish interpolations.
• Efficiency curve (η-Q): iso-efficiency islands (“eye” patterns) overlaid on H-Q curves identify BEP. Specify a duty at η ≥ (BEP − 3 %). Below η = BEP − 5 %, you’re effectively buying capacity you can’t use efficiently.
• NPSH_R curve: rises steeply at high Q; values quoted on the curve are at 3 % head drop. For applications with low NPSH_A (boiler condensate, hot liquids), specify NPSH_R curve at zero head drop where the manufacturer publishes it — the catalogue 3 % value already implies some cavitation.
• Power curve (P-Q): for radial impellers, P rises monotonically with Q — sizing the motor at end-of-curve means it cannot overload at any flow. For mixed-flow, P is roughly flat. For axial, P falls then rises — motor sizing must check both ends of the curve.
• Service factor (SF): a 1.15 SF motor can deliver 15 % more power continuously. Used as the “design margin” in HVAC pump motors; rarely needed for inverter-fed motors that have explicit overload protection.
• API 610 datasheet: standardised 4-page format (rating, materials, mechanical seal, instrumentation, driver). Mandatory for refinery / petrochem; ANSI / ISO 5199 use shorter manufacturer-specific datasheets.
• What’s marketing: “maximum efficiency 92 %” (only at one point on the curve at one trim); “low NPSH” (compared to what?); “smart” / “intelligent” (means it has a VFD); “premium efficient” (the motor is IE3, which is now legally required in most jurisdictions, not premium).

8c. Drive / interface electronics

Pumps and fans are driven by motors (see [[Engineering/electric-motors]] for selection of the motor itself). The drive side of the system involves several layers:

• Direct-on-line (DOL) start — induction motor connected straight to the line through a contactor. Cheap; draws 6–8× full-load current at start. Acceptable for small motors (≤ 7.5 kW typical) on robust supplies. Pump life suffers from the water-hammer of step starts.
• Soft-starter — phase-angle control on a thyristor bank ramps voltage; current limited to 2–3× FLC. Common on 7.5–250 kW pumps where speed control isn’t required.
• Variable-frequency drive (VFD) — full inverter; controls speed continuously by varying frequency and voltage together (V/f or vector control). The standard for any new industrial pump installation > 7.5 kW. ABB ACS580 / ACS880, Siemens SINAMICS G120 / S120, Schneider Altivar 630, Yaskawa GA800 / U1000, Danfoss VLT AQUA / FC202, Rockwell PowerFlex 753 / 755.
• Permanent-magnet motor + dedicated drive — emerging for high-efficiency duty (Grundfos MGE / TPE3, Wilo Stratos, Xylem ecocirc — built-in PMSM with integrated drive). 85–92 % wire-to-water efficiency versus 70–78 % for standard induction + VFD + standard pump.
• VFD interface to plant: 4–20 mA (the universal analog standard) or 0–10 V analog speed reference; Modbus RTU over RS-485 for digital; Profinet / EtherNet/IP / EtherCAT for industrial Ethernet; HART for legacy. Pump VFDs increasingly support MQTT / OPC UA for cloud telemetry.
• Pressure / flow sensing: feedback for closed-loop control. Pressure transmitters (Rosemount 3051, Endress+Hauser Cerabar, WIKA UPT-20), magnetic flowmeters (Rosemount 8700, Endress+Hauser Promag), Coriolis mass meters (Emerson Micro Motion, Endress+Hauser Promass) for high-accuracy / multi-fluid.

9c. Real parts & sourcing

Centrifugal industrial process (ANSI B73.1 / ISO 5199 / ISO 2858):

• Grundfos NB / NK / NBE / NKE
• KSB Etanorm / Etabloc / Movitec / Multitec
• Goulds (ITT) 3196 / ICS / NM3196
• Sulzer OHH / OHHL / OHC / AHLSTAR
• Flowserve Durco Mark 3 / HPX / ETN
• Pentair Aurora / Fairbanks
• Xylem Lowara e-NSC / Goulds (now Xylem) ICS
• Wilo IL / Norm

API 610 / ISO 13709 process (refinery / petrochem):

• Sulzer OHH (OH2), MBN (BB1), MC (BB3), GSG (BB5)
• Flowserve HPX (OH2), HDX, DMX (BB3), BB5
• Goulds 3700 (OH2), 3600 (BB3), 3640 (BB5)
• Ruhrpumpen RON (OH2), HSR (BB2), MD (BB5)
• IDP Pacific / Worthington / WSP
• KSB CHTC (boiler feed), HGM (BB3)

Multi-stage vertical (HVAC, water supply, RO booster):

• Grundfos CR / CRN / CRNE
• KSB Movitec / Multitec V
• Lowara (Xylem) SV / e-SV
• Wilo Helix / Multivert
• Pentair Aurora 800 series

Submersible:

• Grundfos SP (well), SE/SL (sewage), SEG (grinder)
• Flygt (Xylem) N / NP (sewage), C (drainage)
• KSB Amarex / Amacan / Sewatec
• Tsurumi (Japan) C / KTZ
• ABS (now Sulzer) AFP / XFP

Hygienic / process (dairy, beverage, pharma):

• Alfa Laval LKH (centrifugal), SRU / SX (lobe)
• GEA Hilge (centrifugal), VARIPUMP (lobe)
• SPX FLOW APV / Waukesha (lobe), Universal (rotary lobe)
• Fristam FP / FPR

Slurry / mining:

• Weir Warman AH / AHP / WBH
• Metso HM / MD / MR
• KSB GIW LSA / LCC / LCV
• Schurco

Industrial air compressors:

• Atlas Copco GA (oil-injected screw), ZR / ZT (oil-free screw)
• Ingersoll Rand Sierra (oil-free), R-Series (screw)
• Kaeser AS / CSD / DSD (screw)
• Sullair LS (screw)
• Gardner Denver L-Series, ESM (screw)
• Quincy QGV (variable-speed screw), QR (recip)

Refrigeration compressors:

• Bitzer 4F-6F (semi-hermetic recip), CSH / CSW (screw), Octagon
• Copeland (Emerson) ZR / ZP (scroll), Discus (recip), Stream (digital scroll)
• Danfoss Maneurop / Performer (scroll)
• Carlyle (Carrier) 5H / 6D (recip), 06D (screw)
• Frascold (recip, scroll)

HVAC chillers (centrifugal/screw):

• Trane CenTraVac (centrifugal), CGAM / RTAC (screw)
• Carrier 19DV / 19XR (centrifugal), 23XRV / 30XW (screw)
• York / Johnson Controls YK / YMC² (centrifugal mag-bearing)
• Daikin Magnitude (centrifugal mag-bearing), Pathfinder (screw)
• Smardt mag-bearing oil-free chillers

Industrial fans:

• Greenheck (HVAC, kitchen exhaust)
• Loren Cook, Twin City Fan, Hartzell, New York Blower
• Howden (heavy industrial, mining ventilation)
• ebm-papst (EC fans, axials, centrifugals for HVAC and electronics)
• Ziehl-Abegg (EC fans)

Vacuum:

• Edwards (oil-sealed rotary vane, dry screw, turbomolecular)
• Leybold, Pfeiffer Vacuum, Busch, Atlas Copco (acquired Edwards)

Hydraulic / steam / gas turbines:

• Andritz Hydro, Voith Hydro, GE Renewable Energy (hydro)
• GE Vernova (formerly GE Power), Siemens Energy, Mitsubishi Power, Toshiba, Doosan (steam, gas)
• Pratt & Whitney, Rolls-Royce, GE Aviation, Safran, CFM, MTU (aero gas turbines)

Wind turbines:

• Vestas, Siemens Gamesa, GE Renewable Energy, Goldwind, Mingyang, Nordex, Suzlon, Envision

10c. Failure modes & derating

10c.1 Mechanical seal failure

By a wide margin the dominant pump-failure cost in industrial fleets: HI / API data attribute 40–60 % of unplanned pump shutdowns to seal failure. Root causes (in declining order of frequency):

• Dry running — seal faces require a fluid film for lubrication and heat removal. Loss of suction, pump stoppage with closed discharge, gas entrainment from vortexing — all kill seals in seconds.
• Abrasive solids in the seal chamber — grit ingress through wear of impeller / casing clearances. Mitigation: API plan 32 (external clean flush) or plan 41 (cyclone separator).
• Thermal excursion — hot fluid causes face thermal cracking, elastomer extrusion. Mitigation: plan 21 / 23 cooler.
• Vibration beyond seal tolerance (typically 0.1–0.2 mm peak-peak at the seal chamber) — alignment errors, cavitation, recirculation.
• Wrong seal selection — face material incompatible with fluid (carbon dissolves in caustic; alumina ceramic shocks on thermal cycling), elastomer incompatible (NBR fails on aromatics; EPDM fails on mineral oils; only FFKM / Kalrez tolerates strong oxidisers).

10c.2 Bearing failure

Pump bearings see thrust loads (axial residual from imbalance, radial from hydraulic forces) plus vibration. Failure modes per [[Engineering/bearings]] §10c:

• Misalignment between motor and pump — laser alignment per ANSI/ASA S2.75 to ≤ 0.05 mm parallel and 0.05 mm/100 mm angular at the coupling.
• Lubrication starvation / overgreasing — both kill bearings; OEM relubrication interval and quantity should be followed.
• Contamination ingress through housing seals — labyrinth seals (Inpro/Seal, Garlock Bearing Isolator) outperform lip seals on long-life pumps.
• Electrical erosion (VFD-fed motors) — manage per [[Engineering/bearings]] §10c.5: insulated NDE bearing + shaft grounding ring on motors ≥ 22 kW.

10c.3 Cavitation damage

Impeller eye and vane leading edges show characteristic pitting (irregular cratered surface, sharp-edged). Erosion rate scales steeply with NPSH deficit; sustained operation below NPSH_R can perforate an impeller in months. Mitigation per §3.1–3.2.

10c.4 Erosion / corrosion

Distinct from cavitation: high-velocity regions (impeller tips, volute cutwater) on aggressive fluids show smooth flow-line wear (erosion) or pitting/intergranular attack (corrosion). Mitigation: material upgrade (duplex, super-duplex, Hastelloy), coating (tungsten carbide HVOF, ceramic), or design flow reduction.

10c.5 Shaft cracking

Cyclic loading at speeds near rotor critical speeds, alignment errors causing reverse-bending, or stress raisers at shaft step changes. Crack initiates at the shaft surface and propagates radially; terminal fracture at the seal area or coupling end. Mitigation: keep operating speed away from rotor critical by ≥ 20 %, generous fillet radii at steps, magnetic-particle inspection at every overhaul.

10c.6 Coupling failure

Misalignment exceeding manufacturer limits (typically 0.05–0.1 mm parallel, 0.1–0.2° angular) causes flexible-element fatigue (disc-pack, elastomeric jaw) or wear (gear couplings). Most couplings are designed to fail before the shafts — a failed coupling is a feature, not a defect, if the shafts are intact.

10c.7 Hydraulic-induced failures

• Water hammer in pumps — abrupt valve closure or pump trip generates a pressure surge (ΔP = ρ·a·ΔV, Joukowsky equation, with a = wave speed ≈ 1 200 m/s in steel pipes). Can burst pipes and crack casings. Mitigation: surge tanks, slow-closing valves, surge anticipator valves.
• Surge in centrifugal compressors — flow reversal when compressor pressure ratio exceeds the unstable limit at the operating flow; violent oscillation that destroys bearings, seals, and blades in minutes. Mitigation: anti-surge control valve (recycle), API 670 surge protection system.
• Choke in compressors — at high flow, mach number at impeller / inlet vane reaches 1; flow saturates and head collapses. Less damaging than surge but inefficient.

10c.8 Vibration diagnostics (ISO 20816 / ISO 10816)

Vibration spectra (see §4.5) tell the story. Engineering judgement points:

• 1× shaft speed dominant — first check is balance, second is bent shaft, third is loose impeller on shaft.
• 2× shaft speed dominant — laser-realign the coupling before doing anything else.
• Vane-pass peak (Z × N) elevated — pump is operating away from BEP (recirculation), suction is gas-bound, or cutwater clearance is wrong.
• Broadband > 5 kHz rising — cavitation, bearing damage, or seal-face contact. Demodulate (envelope detection) to identify bearing defect frequencies.
• 0.4–0.5× shaft speed peak — oil whirl in journal bearings; clean / change oil, check bearing clearance.

10c.9 Engineering judgement on derating

• Operate within the preferred operating region 80–110 % BEP. The HI POR is the most important reliability metric, more so than the bearing L₁₀. Pumps run continuously below 50 % BEP fail seals and bearings 5–10× faster than those at BEP.
• Always specify NPSH_A with margin, not just to spec. A 1.5 m margin allows for fouled strainer, dropped tank level, and process temperature creep.
• Size motors for end-of-curve, not duty point. Pump curves drift right as wear opens internal clearances; a motor sized exactly at duty trips on overload after 6–12 months.
• Specify VFD bypass for critical service. VFDs fail more often than motors do; a bypass contactor lets the motor run at line frequency (full speed) while the VFD is repaired.
• For compressor service, anti-surge control is not optional. API 670 surge protection (rapid recycle valve + dedicated controller, not relying on the DCS) is mandatory for any centrifugal compressor.
• Do not parallel dissimilar pumps. Two pumps with different H-Q curves operating in parallel will have one pump running at low flow (and at risk of cavitation / recirculation) while the other carries most of the duty.

11. Cross-references

• thermodynamics — compressor work, refrigeration cycles, turbine isentropic / polytropic efficiency, Brayton / Rankine
• heat-transfer — intercooling between compressor stages, condenser / evaporator design, fluid-temperature management
• electric-motors — driver selection, VFD-induced bearing currents, NEMA / IEC frame sizing, inverter-duty insulation
• bearings — pump and compressor rotor bearings, thrust bearings, electrical erosion mitigation, ISO 10816 diagnosis
• gears-power-transmission — speed-increase gearboxes (integrally geared compressors), speed-reducers (hydro turbine to generator)
• vibration-dynamics — rotor dynamics, critical speeds, ISO 10816 / 20816 vibration severity, condition monitoring
• mechanics-of-materials — impeller stress at design speed, casing hoop stress, shaft fatigue
• materials-steel — pump materials by service: cast iron, carbon steel, 12-Cr, duplex 2205, super-duplex 2507, Hastelloy
• bearings — bearing and gear lubrication, mineral vs synthetic, viscosity selection for pump bearings
• seals-taxonomy — mechanical seal selection, API 682 plans, face materials, elastomers, dual-seal configurations
• fluid-mechanics (planned) — Bernoulli, Darcy–Weisbach friction, system head curves, transient analysis
• hvac-fundamentals (planned) — fan-coil units, air-handling units, chilled-water and condenser-water pumping
• aerodynamics (planned) — axial compressor / fan blade design, cascade theory, Mach-number effects
• propulsion (planned) — gas-turbine cycles, jet engines, propeller and ducted-fan thrust
• end-effectors (planned) — hydraulic and pneumatic actuators driven by pumps / compressors

12. Citations

1. Karassik, I. J.; Messina, J. P.; Cooper, P.; Heald, C. C. “Pump Handbook,” 5th ed., McGraw-Hill, 2023. The canonical 4-author pump reference — covers theory, selection, materials, drivers, controls, and applications in a single 2 000-page volume.
2. Gülich, J. F. “Centrifugal Pumps,” 4th ed., Springer, 2020. The deepest technical treatment available — hydraulic design, rotor dynamics, cavitation, hydraulic-induced vibration. The textbook OEM impeller designers learn from.
3. Volk, M. W. “Pump Characteristics and Applications,” 3rd ed., CRC Press, 2013. Application-oriented practitioner reference; clear and concise on selection trade-offs.
4. Stepanoff, A. J. “Centrifugal and Axial Flow Pumps: Theory, Design, and Application,” 2nd ed., Wiley, 1957 (reprinted Krieger 1992). The legacy classic; specific-speed and similarity theory still cited from this book.
5. Lobanoff, V. S.; Ross, R. R. “Centrifugal Pumps: Design and Application,” 2nd ed., Gulf Professional Publishing, 1992. Standard OEM design reference.
6. Bloch, H. P.; Budris, A. R. “Pump User’s Handbook: Life Extension,” 4th ed., Fairmont Press, 2014. The operations-and-reliability companion to Karassik — what to do after the pump is installed.
7. Cumpsty, N. A. “Compressor Aerodynamics,” 2nd ed., Krieger, 2004. The standard reference for axial and centrifugal compressor design.
8. Bloch, H. P.; Soares, C. “Turboexpanders and Process Applications,” Gulf Professional Publishing, 2001. Industrial cryogenic / process turboexpanders.
9. Brown, R. N. “Compressors: Selection and Sizing,” 3rd ed., Gulf Professional Publishing, 2005. Practitioner reference for all compressor families.
10. ANSI/HI 14.6-2022 “Rotodynamic Pumps for Hydraulic Performance Acceptance Tests.” The North American pump-test standard.
11. ANSI/HI 9.6.1-2017 “Rotodynamic Pumps Guideline for NPSH Margin.” Margin recommendations between NPSH_A and NPSH_R.
12. ANSI/HI 9.6.3-2022 “Rotodynamic Pumps Guideline for Operating Region.” Defines POR (preferred operating region) and AOR (allowable operating region).
13. ANSI/HI 1.1-1.2, 2.1-2.2, 3.1-3.5, 5.1-5.6, 7.1-7.5 — Hydraulic Institute family-specific standards for end-suction, vertical pump, rotary, mag-drive, controlled-volume, and submersible pumps respectively.
14. API 610 12th ed. (ISO 13709:2022) “Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries.” The petrochemical pump standard.
15. API 674 3rd ed. “Positive Displacement Pumps — Reciprocating.” Petrochemical PD pump standard.
16. API 675 4th ed. “Positive Displacement Pumps — Controlled Volume for Chemical Injection.” Metering / dosing pump standard.
17. API 676 3rd ed. “Positive Displacement Pumps — Rotary.” Rotary PD pump standard.
18. API 617 9th ed. “Axial and Centrifugal Compressors and Expander-Compressors.” Petrochemical compressor standard.
19. API 618 5th ed. “Reciprocating Compressors for Petroleum, Chemical, and Gas Industry Services.”
20. API 619 5th ed. “Rotary-Type Positive-Displacement Compressors for Petroleum, Petrochemical, and Natural Gas Industries.”
21. API 670 5th ed. “Machinery Protection Systems.” Vibration, axial-position, surge protection.
22. API 682 4th ed. “Pumps — Shaft Sealing Systems for Centrifugal and Rotary Pumps.” Mechanical seal selection including the plan numbers.
23. ISO 5199:2002 “Technical specifications for centrifugal pumps — Class II.” International equivalent of ANSI B73.1.
24. ISO 2858:1975 “End-suction centrifugal pumps (rating 16 bar) — Designation, nominal duty point and dimensions.”
25. ISO 13709:2022 “Centrifugal pumps for petroleum, petrochemical and natural gas industries.” Same as API 610 12th ed.
26. AMCA 210-16 (ANSI/AMCA Standard 210) “Laboratory Methods of Testing Fans for Certified Aerodynamic Performance Rating.”
27. AMCA 211 / 311 / 411 — companion fan certification, sound, and energy-rating standards.
28. ASME PTC 8.2-2020 “Centrifugal Pumps — Performance Test Codes.”
29. ASME PTC 10-1997 (R2014) “Performance Test Code on Compressors and Exhausters.”
30. ASME PTC 11-2008 (R2014) “Fans — Performance Test Code.”
31. ASME PTC 6-2004 “Steam Turbines — Performance Test Code”; PTC 22-2014 “Gas Turbines.”
32. IEC 60193:2019 “Hydraulic turbines, storage pumps and pump-turbines — Model acceptance tests.”
33. IEC 60041:1991 “Field acceptance tests to determine the hydraulic performance of hydraulic turbines, storage pumps and pump-turbines.”
34. ISO 10816 / ISO 20816 (parts 1–9) “Mechanical vibration — Evaluation of machine vibration by measurements on non-rotating parts.” The vibration-severity standards used in §4.5.
35. NEMA MG 1-2021 Part 31 “Definite-Purpose Inverter-Fed Polyphase Motors.” Drive-end / non-drive-end insulation and bearing-current requirements.
36. IEC 60034-25:2014 “Rotating electrical machines — Part 25: AC electrical machines used in power drive systems.” International equivalent.
37. Hydraulic Institute — multiple guidelines: HI 9.8 (intake design), HI 9.6.5 (pump piping), HI 9.6.7 (effect of liquid viscosity on rotodynamic pump performance). Free / member documents at pumps.org.
38. Whitney, W. “Pump Engineering Manual,” Hydraulic Institute. Classic compendium of pump applications and selection methodology.