1. What is a motor-pump assembly
A motor-pump assembly is the integration of pump and motor on a common baseplate, connected by flexible coupling. It is the most reliable way to install an industrial pump because alignment is done in a controlled factory environment with precision instruments.
Misalignment is the second leading cause of industrial pump failure (after dry running). When the assembly arrives factory-mounted, this risk is virtually eliminated.
2. Motor-pump assembly components
A complete motor-pump assembly consists of five main components:
- Pump — centrifugal (FBCN), external gear (FBE), internal gear (FBEI) or thermal oil (FBOT). Sized for application flow, pressure and fluid.
- Electric motor — typically WEG, with power selected per power reserve (20% up to 2 hp, 15% up to 20 hp, 10% above 20 hp — FBCN manual data). Available in 2 or 4 poles, 220/380/440V.
- Flexible coupling — transmits motor torque to pump with tolerance for minor residual misalignment (angular, parallel and axial). Common types: grid (Falk), jaw (Lovejoy), flexible disc.
- Coupling guard — metal cover preventing access to rotating coupling. Mandatory per safety standard (NR-12).
- Metal baseplate — common structure supporting aligned pump and motor. For FBCN, the baseplate is sized per ASME B73.1. Can be painted carbon steel or stainless depending on environment.
3. Factory assembly advantages
Factory assembly of the motor-pump unit offers significant advantages over field assembly:
- Precision alignment with dial indicator or laser — impossible to replicate at construction site
- Hydraulic bench test before shipping — performance guarantee per curve
- 60-80% reduction in field installation time
- Single manufacturer warranty on entire assembly
- Elimination of incompatibilities between components from different suppliers
4. How to specify a motor-pump assembly
To request a motor-pump assembly from FB Bombas, provide:
- Fluid data — name, viscosity, density, operating temperature and solids presence
- Operating conditions — flow (m³/h or L/min), pressure (bar or kgf/cm²), available NPSH
- Available electrical voltage — 220V, 380V, 440V, frequency (50 or 60 Hz)
- Area classification — explosion risk (classified areas require Ex motor)
- Materials — cast iron, stainless steel or special alloys per chemical compatibility
5. Alignment and tolerances
Alignment between pump and motor shafts is the critical point of the assembly. FB Bombas adopts tolerances tighter than ANSI/HI 9.6.4 — maximum angular misalignment of 0.05 mm/100 mm and maximum parallel misalignment of 0.08 mm — using laser alignment on the assembly bench. These values are up to 30% better than required by standard and translate into proven reduction in startup and continuous-operation vibration.
In the field, the customer must recheck alignment after anchoring the base to the foundation and after piping connections — operating temperatures and pipe stresses may slightly shift the pump. FB Bombas provides a factory alignment report as a reference for periodic checks every 6 months or after any mechanical intervention.
6. NPSH and cavitation in the motor-pump assembly
Available NPSH (NPSHa) at the installation must always be greater than the pump required NPSH (NPSHr) — the minimum margin recommended by API 610 is 1 m. When the pump is supplied as a motor-pump assembly, FB Bombas validates the NPSHr for the operating point provided by the customer and indicates whether the designed suction is viable before manufacturing. If cavitation risk exists, we recommend modifications to the suction line (diameter increase, height reduction, elimination of elbows near the pump).
Cavitation reduces the service life of bearings, mechanical seals and impeller — in severe cases, failure within weeks. The factory-assembled unit does not eliminate cavitation if NPSHa is insufficient; that is why FB Bombas application engineering performs numerical NPSHa sizing using real customer data.
7. Vibration and predictive maintenance
In a well-aligned motor-pump assembly operating close to BEP, total RMS vibration on the casing (bearings) should be below 4.5 mm/s for pumps up to 15 kW and below 7.1 mm/s for larger pumps — ISO 10816-7 zone B limits. FB Bombas measures vibration on the bench before shipping and provides the report as reference.
In the field, periodic monitoring (monthly or continuous via sensor) detects progressive degradation well before failure — misalignment, unbalance, bearing issues and cavitation have distinct spectral signatures.
Predictive maintenance based on vibration and bearing temperature is the modern practice for critical process assemblies. For customers adopting this strategy, we recommend triaxial acceleration sensors at pump and motor bearings + PT100 temperature sensor — typical 3–5% investment of assembly value that pays back in a single prevented failure. FB Bombas provides ready mechanical interface (standardized threaded holes) for non-intrusive sensor installation.
