self priming slurry pump leaking water

What is a centrifugal pump and how does it work?

What is a centrifugal pump and what is its physical principle?

A centrifugal pump is a generating turbomachine designed to transform mechanical energy (usually from an electric motor) into hydraulic energy (pressure and speed) for an incompressible fluid. Unlike positive displacement pumps (such as gear or lobe pumps), which move fluid by trapping fixed volumes, the centrifugal pump is based on hydrodynamics. Its fundamental principle is centrifugal force: a rotating impeller transfers kinetic energy to the fluid, accelerating it radially outwards. Subsequently, the housing or volute is responsible for decelerating this fluid, converting that high speed into pressure energy (manometric head). They are the most used equipment in the industry due to their ability to offer constant flow rates, their mechanical simplicity, and their versatility to handle everything from clean water to products with a certain viscosity.

Key components of a centrifugal pump

To understand its operation and maintenance, it is vital to dissect its critical parts. In InoxMIM equipment, such as the ranges FL and FLUID, these components are designed under industrial and sanitary standards:The impeller

It is the heart of the pump. As it rotates, its blades impart energy to the fluid. Depending on the product to be pumped, we use different geometries:

Open or semi-open impeller: Present in models such as the FL31CI or FL51CI. They are ideal for liquids that may contain small particles in suspension or medium viscosities, facilitating cleaning.

Helical impeller: Used in specific pumps such as the FL–CH, designed for the delicate transfer of solids in suspension (such as in wine pumping over).

Materials: Commonly manufactured in AISI 316L Stainless Steel to guarantee corrosion resistance and hygiene.

The housing or volute

It is the body of the pump that collects the fluid expelled by the impeller and conducts it towards the discharge pipe. Its spiral geometry is crucial for the efficient conversion of speed into pressure. In sanitary models such as the FLUID, the design of the housing follows EHEDG regulations to ensure total cleaning (CIP/SIP) without disassembly.

The shaft

It is the element that transmits power from the motor to the impeller. It must be perfectly aligned and manufactured in robust materials such as AISI 316 to withstand torque and avoid vibrations.

The sealing system (Mechanical Seal)

It is the most critical point to avoid leaks. Replacing the old packing, the mechanical seal consists of a fixed and a rotating part that slide over each other.

• Configurations: They can be simple (internal or external) or double (thermosiphon-cooled for abrasive, sticky, or high-temperature products).
• Materials of the rubbing faces: Silicon Carbide, Tungsten Carbide, or Graphite, selected according to the abrasiveness of the fluid.
• Seals: Manufactured in EPDM, Viton, or Nitrile according to the required chemical and thermal compatibility.

Motorization

Generally, asynchronous electric motors that comply with IEC standards. Depending on the required flow and pressure, they can operate at 2900 rpm (higher pressure/flow) or 1450 rpm (gentler treatment of the product).

How does it really work? The step-by-step process

Although at first glance it seems like an instantaneous process, the internal operation of a centrifugal pump follows a precise hydrodynamic sequence. It is not simply about “pushing” the liquid, but about a transfer of energy in three critical phases:

• Suction and Inlet (The Eye of the Impeller): The process begins when the fluid enters through the suction flange, directed directly towards the center of the impeller, technically known as the “eye of the impeller.”. At this point, the pressure is low, which facilitates the entry of the liquid.
• Radial Acceleration (Kinetic Energy Generation): Once inside, the impeller blades (which rotate together with the motor shaft) trap the fluid and make it rotate. The centrifugal force projects the liquid violently towards the periphery of the impeller. In this short journey, the fluid acquires a great kinetic energy (speed), reaching its maximum acceleration right at the ends of the blades.
• Conversion and Discharge (Pressure Generation): Here occurs the magic of hydraulic engineering. The high-speed fluid leaves the impeller and enters the volute (housing). The geometry of the volute is designed to expand progressively; this decelerates the fluid in a controlled manner. Following Bernoulli’s principle, this reduction in speed transforms the accumulated kinetic energy into pressure energy (manometric head). Finally, the fluid

Key Difference: Pressure vs. Flow

It is vital for any plant manager to understand that, unlike positive displacement pumps (such as piston or lobe pumps), a centrifugal pump does not generate a fixed flow rate. A centrifugal pump generates energy (pressure). The resulting flow rate will depend on the resistance that the installation opposes to that pressure. This relationship is represented in the Characteristic Curve (H-Q) of the equipment. If the backpressure of the system increases (closing a valve or raising the pumping height), the flow rate will decrease, and vice versa. Understanding this curve is essential to select the correct model, whether it is an FL30CI industrial or a FLUID sanitary, and avoid operating outside the point of efficiency.

Types of centrifugal pumps from InoxMIM: solutions for every need

In the InoxMIM catalog, centrifugal pumps are classified not only by their hydraulic capacity, but also by the level of finish and the nature of the application. It is not the same to pump process water as a sensitive cosmetic emulsion or a corrosive fluid. Below, we break down the main categories:

Industrial and simple centrifugal pumps

Designed for robustness and efficiency in general applications where strict hygiene is not the limiting factor, but durability and operating cost are.

FL20C (Simple Centrifugal Pump): This compact model is characterized by its high performance despite its small size. It is capable of providing flow rates of up to 12 m³/h. It is designed for the transfer of low-viscosity fluids such as water, oils, glycols, and wines. Its construction in aISI 316 stainless steel and its semi-open impeller make it versatile and resistant.

FL30CI (Industrial Centrifugal Pump): A step further in capacity. Used in transfer processes in the chemical, food, and oenological industries. Its design stands out for the simplicity of components, which greatly facilitates maintenance. It allows configurations with open or semi-open impeller and different types of mechanical seal (Graphite/Inox, Tungsten/Tungsten) depending on the abrasiveness of the fluid.

Sanitary and high-performance centrifugal pumps

When the process requires CIP/SIP cleaning, absence of dead zones, and materials certified for food or pharmaceutical contact.

FL50CI (Food/Sanitary Pump): Designed specifically for the food, pharmaceutical, and cosmetic industries. It maintains the mechanical simplicity of the industrial series, but with a design and surface finish that guarantees a high degree of sanitation. It has a hygienic seal and standard DIN 11851 connections to ensure sanitary tightness.

FLUID (High Performance Hygienic Pump): The jewel in the crown for critical applications. Its internal design complies with the requirements of theEHEDG, ensuring total cleaning without the need for disassembly. It incorporates a high-efficiency impeller developed through computational design that allows flow rates of up to 100 m³/h with a very low required NPSH, minimizing the risk of cavitation and treating the product with maximum smoothness.

Self-priming pumps: solution for lines with air

Standard centrifugal pumps cannot evacuate air from the suction pipe. To solve this in processes where it is not possible to aspirate under load (the tank is below the pump), we use self-priming models.

FL80CAI and FL90CAI: These self-priming centrifugal pumps are designed for transfer processes where suction is negative. They eliminate the need for foot valves or external vacuum systems thanks to their internal design that allows the fluid to recirculate and expel air. They are ideal for the food, chemical, and oenological industries, maintaining hygienic conditions thanks to their finish and hygienic closure. They can aspirate from depths of up to 3-6 meters depending on the model.

Applications in different industries: Where is a centrifugal pump essential?

The versatility of the centrifugal pump makes it the most ubiquitous transfer equipment in the industry. However, its configuration varies drastically depending on the sector. At InoxMIM, we adapt the design (from the type of mechanical seal to the surface finish) to comply with the specific regulations of each industry.

Food and beverage industry

In this sector, hygiene and CIP (Cleaning In Place) cleaning capacity are non-negotiable. Sanitary centrifugal pumps, such as the models FL50CI or the FLUID range, are essential for the transfer of low-viscosity products.

• Dairy: Transport of raw milk, whey, skim milk, and diluted cleaning solutions. The hygienic design prevents bacterial proliferation in dead zones.
• Oenology and Oil: For the transfer of wines, musts, vinegars, and oils. In applications such as wine pumping over, where solid particles (skins) may exist, specific variants such as the FL–CH with helical impeller are used for delicate handling of the product.
• Beverages: Pumping of water, juices, soft drinks, and diluted syrups, where a constant flow rate and high transfer speed are required.

Pharmaceutical and cosmetic industry

This sector demands the highest safety standards (EHEDG, 3A regulations). The pumps must not only move the fluid, but guarantee that there will be no cross-contamination or particle detachment.

• Process water: Pumping of purified water (PW) and water for injection (WFI) in distribution loops. Here, the pump FLUID stands out for its drainable design and high-quality surface finishes.
• Low-viscosity cosmetics: Transfer of alcohols, perfumes, tonic lotions, and aqueous solutions. For more viscous products such as creams or gels, positive displacement pumps are usually preferred, but the centrifugal pump is still vital for cleaning reactors and moving liquid bases.

Chemical industry and water treatment

Here, the priority shifts to chemical resistance and mechanical durability. Industrial pumps like the FL30CI are designed to withstand aggressive working conditions.

• Chemical transfer: Movement of solvents, light acids, detergents, inks, and fertilizers. The correct choice of seals (Viton, EPDM) and mechanical seal is vital to avoid dangerous leaks.
• Water treatment: Purification, filtering, and recirculation processes. The robustness of the AISI 316 stainless steel used in our equipment guarantees a long service life against corrosion, surpassing cast iron alternatives.

Technical selection criteria: What should I keep in mind?

Selecting a centrifugal pump “by catalog” without analyzing the operating conditions is a recipe for premature failure. For engineers and plant managers, these are the four technical pillars that should define the purchase:

Fluid viscosity: The physical limit

Centrifugal pumps are excellent for low-viscosity fluids (similar to water). As viscosity increases (for example, above 150-300 cP), the pump’s efficiency drops dramatically and power consumption soars. General rule: If your product is viscous (honey, thick cream, paste), a centrifugal pump is not the right choice; you should opt for a lobe pump (FL–PRL) or progressive cavity pump. The centrifugal pump is ideal for water, milk, wine, solvents, and light oils.

The operating point (Q-H Curve)

Do not buy a pump based solely on motor power (kW). You should select it based on its characteristic curve. You need to know two pieces of data:

• Flow rate (Q): How much volume do you need to move per hour?
• Total head (H): What pressure do you need to overcome the geometric height and pressure losses of the pipe? Always select a pump whose best efficiency point (BEP) matches your operational needs to minimize energy consumption and shaft fatigue.

NPSH and the risk of cavitation

As we mentioned in the installation section, cavitation is the silent enemy. You must calculate the available NPSH of your system. If you have to draw from a level below the pump (negative suction), make sure that the NPSH required by the pump is very low, or opt directly for a self-priming pump from the FL–CAI series, capable of evacuating air from the line.

Chemical compatibility and materials

Not all steels or elastomers are suitable for everything.

• Body and Impeller: At InoxMIM, we standardize AISI 316/316L Stainless Steel for its excellent corrosion resistance and food suitability.
• Seals and Closures: It is vital to configure the pump with the correct elastomers. EPDM for water, steam, and mild acids; Viton (FKM) for oils, hydrocarbons, and high temperatures; or Nitrile for general oil and grease applications.

Do you need advice on our centrifugal pump models?

Choosing the right centrifugal pump not only guarantees the operation of your production line but also defines the energy efficiency and safety of your daily operations. Whether for robust industrial applications or delicate sanitary processes, the right technology makes the difference. Do you need advice on selecting the ideal equipment for your plant? Contact the technical team of InoxMIM. We will analyze your product and installation conditions to offer you the most efficient and durable pumping solution.