Industrial Pump Dictionary

There are two NPSH values: NPSH available (NPSHa), calculated by the installation designer from suction height, friction losses and fluid vapor pressure; and NPSH required (NPSHr), provided by the pump manufacturer on the characteristic curve. The rule of thumb is NPSHa > NPSHr + safety margin (typically 0.5 to 1.5 m), otherwise cavitation occurs and damages the impeller. Hot, volatile or near-vaporization fluids require special attention in sizing.

Classic cavitation symptoms are characteristic noise ("gravel inside the pump"), excessive vibration, flow and efficiency drop, and premature erosive wear on the impeller suction side. Prevention is achieved by correct NPSHa sizing, keeping the pump near the suction level, avoiding restrictions on the suction line, and selecting resistant materials for critical applications. External gear pumps (FBE) are less sensitive to cavitation than standardized centrifugals (FBCN) due to the positive displacement principle.

In centrifugal pumps (like the FBCN), flow depends directly on the installation head — the higher the head, the lower the flow. In positive displacement pumps (like FBE and FBEI), flow is nearly constant and proportional to speed, regardless of discharge pressure, making them ideal for precise dosing. The FBCN covers flow up to 2,200 m³/h; the FBE, from 0.5 to 6,550 L/min; and FB Bombas fire systems go up to 10,000 L/min.

Unlike gauge pressure in bar or kgf/cm², total head in meters is independent of fluid density — which simplifies comparison between pumps for different liquids. Conversion is direct: H(m) = P(bar) × 10.2 / specific gravity. The FBCN line delivers up to 135 m of head in standard configurations; for greater heights, series or multistage pumps are used.

Operating far from the BEP (for example, with the discharge valve partially closed) causes internal recirculation, vibration, accelerated bearing and seal wear, and unnecessary energy consumption. Best practice is to select a pump whose BEP falls between 80% and 110% of the expected operating flow. FBCN technical manuals include characteristic curves with the BEP clearly marked for each of the 43 standard models.

The curve is the central technical document for pump selection: the operating point is determined by the intersection of the pump curve and the installation friction curve. For correct selection, the designer must overlay both curves and verify that the crossing point is near the BEP of the chosen pump. FBE (12 sizes) and FBCN (43 models) technical manuals include curves for 1750 and 3500 rpm at 60 Hz.

The maximum allowable pressure depends on casing material and fluid temperature — the FBCN manual includes charts (Figures 1-4) showing how maximum pressure drops with temperature for cast iron, A216 WCB carbon steel and A743 CF8M stainless steel. For cast iron, the typical limit is 20 bar at -50 to 120°C, dropping to 10 bar at 260°C. Operating above these limits compromises the pump's mechanical integrity.

Reference values: water (1 cSt ≈ 31 SSU), diesel oil (3 cSt ≈ 37 SSU), SAE 30 oil at 40°C (150 cSt ≈ 700 SSU), honey (10,000 cSt ≈ 46,500 SSU), hot asphalt (50,000 cSt ≈ 230,000 SSU). The FBE line supports up to 100,000 SSU — above this, FB Bombas engineering recommends the FBEI with specific configuration. Standardized centrifugals (FBCN) lose efficiency dramatically above 500 SSU.

It is the most common type of industrial pump for low-viscosity liquids at medium to high flow. Ideal for water, aqueous solutions, light solvents, thin fuels and process fluids. FB Bombas' FBCN line follows the ASME B73.1 (mechanical) standard, with back pull-out construction allowing impeller maintenance without disconnecting piping. Variations exist: end-suction (FBCN), double suction, multistage and vertical.

It is the ideal type for viscous fluids — lubricating oils, heavy fuels, asphalt, resins, biodiesel, molasses, chocolate and viscous chemicals. FB Bombas is the original Brazilian manufacturer of this type of pump at industrial scale, continuously operating since 1944. The FBE line has 12 standard sizes from 1/8" to 6", covering flow from 0.5 to 6,550 L/min, pressure up to 22 kgf/cm² and viscosity up to 100,000 SSU with heat-treated alloy steel helical gears.

The main advantage over external gear is practically continuous pulseless flow, making this type ideal for precise dosing, hot-melt applications, polymers, latex and very viscous fluids. The FBEI by FB Bombas is available in 8 sizes (1.1/2" to 8") including the FBEI-LS (Large Size) version with integrated gear reducer for very high-torque applications. Standard integrated relief valve and optional heating jacket (steam up to 185°C, thermal fluid up to 232°C).

The most important characteristic is that flow depends almost exclusively on rotation — allowing precise dosing. In contrast, centrifugal pumps deliver variable flow with system pressure. Positive displacement pumps must never be operated with closed discharge without a relief valve, under penalty of reaching destructive pressure. The FBE and FBEI lines include an integrated relief valve as optional (FBE) or standard (FBEI).

The big advantage is maintenance time: impeller replacement, mechanical seal inspection and sleeve adjustment are done in hours, not days. It is a requirement of the ASME B73.1 standard for process standardized centrifugals. The FB Bombas FBCN line meets this standard and maintains coupling alignment even after rotating assembly intervention.

It is the preferred option over packing when zero visible leakage, operation with toxic/flammable/high-value fluids, and extended maintenance intervals are required. Configurations include single, double (with barrier fluid), cartridge, balanced and unbalanced. Typical face materials: silicon carbide, tungsten carbide, ceramic. The FBCN line includes 6 sealing chamber configurations (ST, S1, S2, S3, S4 and S) described in the technical manual to serve different fluid/temperature/solids-in-suspension combinations.

Unlike a mechanical seal, packing operates with intentional controlled drip — this small flow is needed to lubricate and cool the rings. It is the economical choice for water, non-aggressive fluids and applications where small leakage is acceptable. FB Bombas technical manuals include the required sealing liquid flow table for each pump size, typically 1 to 5 L/min. Packing requires periodic retightening and replacement every 6-12 months depending on service.

There are three basic centrifugal impeller types by exit angle: radial (blade perpendicular to shaft, high pressure, low flow), mixed-flow (intermediate) and axial (blade parallel to shaft, high flow, low pressure). The FBCN line uses a radial impeller with single suction — suitable for most industrial process applications. For wear resistance in fluids with light solids, there is a pressure-side wear ring (except in smaller models 25-150, 32-125 and 32-125.1).

The volute spiral profile is designed so that fluid velocity drops continuously as the cross-section increases toward discharge — minimizing turbulence losses. The FBCN has a single-piece cast volute in cast iron, A216 WCB carbon steel or A743 CF8M stainless steel, with a suction-side wear ring to maintain ideal clearance even after hours of operation.

The FBCN line uses pairs of 6306 C3, 6308 C3, 6310 C3, 6314 C3 or 6315 C3 bearings by size range, with oil lubrication via sight gauge or optional automatic refill cup. The FBE line uses self-lubricating TM23 bronze sliding bushings — robust, silent and requiring no external lubrication in normal conditions. Bearing MTBF is one of the main reliability indicators of an industrial pump.

ASME B73.1 focuses on the internal mechanics of normalized horizontal centrifugals: mandatory back pull-out construction, minimum 3 mm corrosion allowance, hydrostatic test at 1.5× maximum operating pressure, and minimum clearance between impeller and volute. The FBCN fully meets this standard and all models undergo hydrostatic testing per ANSI B73.1 before shipping.

The standard requires robust construction for continuous 24/7 operation in severe conditions, corrosion and high-temperature resistant materials, redundant sealing for hazardous fluids, and detailed acceptance tests. API 610 pumps are classified by types (OH, BB, VS) according to shaft orientation and construction configuration. FB Bombas has pumps meeting API 610 requirements and is a registered supplier in the CRCC (Supplier Registry) of Petrobras.

The standard requires redundant configuration (main pump + reserve pump + jockey pump for pressurization), independent power source (diesel motor in addition to electric to ensure operation during power loss), certified automatic control panel, and performance curve testing per NFPA. In Brazil, it is complemented by ABNT standards NBR 10897 (sprinklers), NBR 13714 (hydrants) and NBR 16704 (fire pumps). FB Bombas fire-fighting systems fully meet this standard.

The FAT generates a formal signed report documenting results and serving as basis for equipment acceptance. It is mandatory in large projects, Petrobras contracts (CRCC) and critical applications in refineries and petrochemical plants. FB Bombas has its own test bench in Cabreúva-SP with capacity to test all standard models of the FBE, FBEI, FBCN and FBOT lines with calibrated instrumentation and complete documentation.

The main components limiting MTBF in industrial pumps are: mechanical seal (3,000 to 25,000 h), bearings (8,000 to 40,000 h), impeller (depending on erosion and cavitation) and coupling. Best practices to maximize MTBF include operating near BEP, avoiding cavitation, maintaining correct alignment, using adequate lubrication and following the preventive maintenance plan. Robust construction and FB Bombas' design tradition contribute to high MTBF even in severe environments.

The ASME B73.1 standard requires a minimum corrosion allowance of 3 mm for chemical process pumps. FB Bombas' FBCN comes with 3.3 mm corrosion allowance, providing margin above the normative minimum. This margin is critical in moderately corrosive fluids and high-temperature environments that accelerate corrosion rate. For highly corrosive service, more noble materials (316 stainless, duplex) should be used instead of increasing the allowance.