Electric Pump Types – Working Principle – Selection – Sizing

This article is about What is Industrial Electric Pump, Types, Components and its basic working principle with advantages and disadvantages. More will discussed about technical aspects like Pump selection, pump design, pump operation, Layout and Piping requirement, Pump sizing and Valving and Isolation in plants and oil refineries.

What is an Electric Pump?

An electric pump, also known as an electric pump, is a device that uses electrical power to move fluid or generate pressure. It is a common type of pump used in various applications, including industrial processes, water supply systems, HVAC systems, and more. Electrical pumps are typically driven by an electric motor that converts electrical energy into mechanical energy, which in turn drives the pumping mechanism.

Components of Electric Pumps:

1. Electric Motor: The electric motor is the primary component that converts electrical energy into mechanical energy to drive the pump.
2. Impeller: The impeller is a rotating component that creates the flow and pressure of the fluid. It is usually mounted on the shaft of the electric motor.
3. Casing: The casing or housing surrounds the impeller and provides a passage for the fluid to flow.
4. Inlet and Outlet: The inlet allows the fluid to enter the pump, while the outlet directs the fluid out of the pump.
5. Control Panel: In some cases, electrical pumps may have a control panel that includes switches, gauges, and other controls for monitoring and operating the pump.

Different Pump Types

Pumps can be broadly classified into two main categories based on their operating principle: dynamic pumps and positive displacement pumps.

1. Dynamic Pumps:

Centrifugal Pumps:

Centrifugal pumps are a type of dynamic pump that uses an impeller to create a flow of fluid by converting kinetic energy into pressure. They are commonly used for low-viscosity liquids and high flow rates in applications such as water supply, HVAC systems, and industrial processes.

Centrifugal pumps are widely used and known for their simplicity, efficiency, and robustness. When the pump operates, fluid pressure rises from inlet to outlet, propelling the fluid through the system.

These pumps work by converting mechanical power from the motor into force through a rotating impeller. The fluid enters the impeller’s center and exits through its vanes, increasing its velocity due to centrifugal force, converting kinetic energy into force.

Centrifugal pumps have three subtypes based on the water flow they produce, determined by the impeller shape and pump construction.

1. Axial Flow Pumps: Axial flow pumps are a type of centrifugal pump that moves fluid parallel to the pump axis. They are suitable for large flow rates at low heads and are often used in water and irrigation systems.
2. Mixed Flow Pumps: Mixed flow pumps combine characteristics of both radial and axial flow pumps, moving fluid both radially and axially. They are commonly used for medium flow rates and heads in applications like flood control and wastewater treatment.

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Submersible Pumps

Submersible pumps, also known as stormwater, sewage, and septic pumps, find applications in various areas such as building services, domestic, industrial, commercial, rural, municipal, and stormwater recycling.

These pumps are versatile and can transfer different types of fluids like stormwater, groundwater, sewage, blackwater, greywater, rainwater, trade waste, chemicals, bore water, and food. They come with various impellers such as closed type pumps, convection pumps, vortex pumps, multistage pumps, single channel pumps, cutting pumps, or grinder pumps, each suited for specific plumbing applications.

Submersible pumps offer a wide range of options, including high flow, low flow, low head, or high head, making them suitable for different needs and preferences.

Fire Hydrant Pumps

Fire hydrant systems, also known as fire hydrant boosters or fire pumps, are high-pressure pumps designed to enhance the firefighting capacity of a building. They are utilized when the mains water supply is inadequate for firefighting purposes. These systems are commonly used for irrigation and water distribution in buildings.

2. Positive Displacement Pumps:

1. Reciprocating Pumps: Reciprocating pumps are positive displacement pumps that use a reciprocating motion of a piston or plunger to create pressure and move fluid. They are suitable for high-pressure applications and are commonly used in oil and gas industries.
2. Rotary Pumps: Rotary pumps are positive displacement pumps that use rotating mechanisms, such as gears, lobes, or vanes, to transfer fluid from the inlet to the outlet. They are known for their steady flow and are used in various applications, including hydraulic systems, fuel transfer, and food processing.

Diaphragm Pumps:

Diaphragm pumps, also known as membrane pumps or air-operated double diaphragm (AODD) pumps, are a type of positive displacement pump. They use a flexible diaphragm to transfer fluids by alternating the pressure on either side of the diaphragm. These pumps are widely used in various industries for their versatility, efficiency, and ability to handle a wide range of fluids.

The diaphragm in the pump acts as a barrier between the fluid and the air or gas that drives the pumping action. When the air pressure is applied to one side of the diaphragm, it flexes and pushes the fluid out of the pump. On the other side of the diaphragm, a vacuum is created, causing it to retract and draw more fluid into the pump.

Diaphragm pumps are well-suited for handling abrasive, viscous, and shear-sensitive fluids, as well as fluids containing solids or chemicals. They are commonly used in applications where a gentle pumping action is required to avoid damaging the fluid or where a leak-free pumping solution is essential.

One of the key advantages of diaphragm pumps is their ability to run dry without causing damage to the pump or affecting its performance. This makes them suitable for applications where variable flow rates or intermittent operation is required. Additionally, diaphragm pumps are self-priming, meaning they can start pumping without the need for external priming.

Screw Pumps

Screw pumps are a type of positive displacement pump that use two or more intermeshing screws to move fluid through the pump. These pumps are widely used for various applications, including oil and gas, chemical processing, food and beverage, and wastewater treatment.

The basic design of a screw pump consists of two or more helical screws that rotate inside a cylindrical cavity. As the screws turn, they create cavities that trap and move the fluid along the screw’s threads from the pump’s inlet to its outlet.

One of the main advantages of screw pumps is their ability to handle a wide range of viscosities, from low to high, making them suitable for pumping thick and abrasive fluids. They are known for their smooth and pulsation-free flow, which reduces the risk of damage to the pumped fluid and the system.

Screw pumps are also appreciated for their self-priming capability, meaning they can start pumping without the need for external priming. This feature is particularly beneficial in applications where the pump is located above the fluid level.

There are two main types of screw pumps: single screw (progressive cavity) pumps and twin screw pumps. Single screw pumps consist of a single screw rotating within a stator, while twin screw pumps have two intermeshing screws rotating inside a cylindrical housing.

Rotary Vane Pump

A rotary vane pump is a type of positive displacement pump that uses rotating vanes or blades to move fluid. These pumps are commonly used for various applications, including vacuum creation, gas compression, and fluid transfer.

The basic design of a rotary vane pump consists of an eccentrically mounted rotor with vanes that slide in and out of slots within the rotor. As the rotor spins, the vanes create expanding and contracting chambers. When the chambers expand, they create a vacuum, drawing in fluid or gas through the inlet. As the chambers contract, they compress the fluid or gas and push it out through the outlet.

One of the key advantages of rotary vane pumps is their ability to generate high vacuum levels and achieve a continuous flow of fluid or gas. They are known for their efficiency and reliability, making them suitable for various industrial and scientific applications.

Rotary vane pumps are commonly used in automotive applications, such as in power brake systems and engine vacuum systems. They are also used in vacuum packaging machines, vacuum pumps for laboratory equipment, and in HVAC systems for air conditioning and refrigeration.

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Gear Pumps

Gear pumps are positive displacement pumps that use the meshing of gears to transfer fluids. They are widely used in various industries for their simplicity, reliability, and efficient pumping capabilities. Gear pumps consist of two gears, usually mounted in a close-fitting housing. As the gears rotate, fluid is drawn into the pump and then discharged as the gears separate.

There are two main types of gear pumps: external gear pumps and internal gear pumps. In external gear pumps, the gears are mounted outside the pump casing and rotate on parallel axes. The fluid is trapped between the gear teeth and the pump casing as the gears rotate, creating a continuous flow. External gear pumps are commonly used for higher flow rates and moderate pressures.

Internal gear pumps, on the other hand, have one gear inside another, with the teeth of the gears meshing internally. The fluid is carried in the spaces between the teeth of the larger gear and the smaller gear, and it is then forced out as the gears mesh and rotate. Internal gear pumps are known for their smooth, pulse-free flow and are suitable for low to medium flow rates and higher pressures.

Gear pumps are valued for their ability to handle a wide range of fluids, including both thin and thick liquids, as well as liquids with high viscosity. They can operate at high pressures and are often used in hydraulic systems, lubrication systems, and other industrial applications where precise flow and pressure control are essential.

Peristaltic Pumps:

Peristaltic pumps, also known as hose pumps or tube pumps, are positive displacement pumps that use a flexible tube or hose to move fluids. The pump works by squeezing the tube between rotating rollers or shoes, creating a “peristaltic” action that propels the fluid through the tube. As the rollers move along the tube, they create a series of occlusions, which push the fluid forward.

Peristaltic pumps are commonly used in applications where precise and accurate dosing or pumping of fluids is required. They are known for their gentle pumping action, which is ideal for handling delicate or shear-sensitive fluids. Peristaltic pumps are often used in industries such as pharmaceuticals, biotechnology, food and beverage, and water treatment.

One of the major advantages of peristaltic pumps is that the fluid being pumped only comes into contact with the tube, making them suitable for handling corrosive, abrasive, or sensitive fluids without any contamination risk. Additionally, they are easy to clean and maintain, as the only component that comes into contact with the fluid is the replaceable tube.

Piston Pumps

Piston pumps are mechanical devices that use reciprocating pistons to transfer fluids or gases. These pumps work by creating a pressure difference in the fluid to move it through the system. The piston moves back and forth inside a cylinder, drawing in the fluid during the suction stroke and pushing it out during the discharge stroke.

They are commonly used in various industries for applications such as fuel transfer, hydraulic systems, and high-pressure cleaning. Piston pumps are known for their efficiency, reliability, and ability to handle a wide range of viscosities and pressures.

Lobe pumps

Lobe pumps are positive displacement pumps that use two or more lobes (also called rotors) to transfer fluids. These pumps work by trapping and transporting the fluid between the lobes and the pump casing. As the lobes rotate, the fluid is carried from the inlet to the outlet, creating a continuous flow.

Lobe pumps are commonly used for handling viscous liquids, slurries, and delicate solids in industries such as food and beverage, pharmaceuticals, and wastewater treatment. They are known for their gentle pumping action, low shear, and ability to handle sensitive or shear-sensitive materials. Lobe pumps are also easy to clean and maintain, making them a popular choice for hygienic applications.

Both dynamic and positive displacement pumps have their advantages and are chosen based on factors such as flow rate, pressure requirements, fluid properties, efficiency, and the specific application’s demands.

A. Pump Selection

1. Centrifugal pumps will be the preferred selection.

2. Dosing or injection pumps for acid, caustic or chemical dosing will be of proportioning type where it is possible to control flow by adjusting the stroke while the pump is in operation.

3. Rotary or screw pumps are preferred for high viscosity service.

B. Pump Design

1. Unless otherwise specified elsewhere, the design flow quantity shall be the maximum quantity as shown on process flow diagram plus 20% (min). For circulating cooling, seawater and firewater pumps, no operating margin will be added unless otherwise specified.

2. The pump rated capacity is the design flow quantity as indicated above. Use the table below to determine this flow rate if other guidelines are not provided. Normally, a service will have one (1) pump operating and one 100% spare. For this case, the normal pump capacity will be based upon the material balance number

C. Pump Operation

1. All pumps to have local start/stop switches. Use DCS for remote stop, if required. Do not provide remote start for pumps (except as specially approved by Company*). Provide autostart only if necessary. All auto-start pumps to have warning sign that pump can start automatically.

*DCS Start, requiring action from Field operator and/or DCS operator, philosophy to be proposed by the Contractor.

2. Emergency stop shall be linked to ESD system if the pump is part of a safety loop.

3. Where practical, all major process pumps, Reactor & Furnace feed pumps, Compressor lube oil & seal oil pumps and critical pumps with auto start, shall be provided with an installed spare pump.

D. Layout and Piping requirement

1. Each centrifugal pump will have a suction block valve, discharge check valve, block valves and pressure gauge, all of which will be located as close to the pump nozzle as possible. For clean fluids, suction piping will use an eccentric reducer with the flat side at the top to avoid vapour lock.

For slurries, the eccentric reducer will be flat side at the bottom to avoid pockets for settling. The discharge check valve will be located between the discharge nozzle and the discharge block valve. The pressure gauge connection will normally be supplied on pump discharge lines between the check valve and block valve.

2. Suction block valves and pump inlet nozzles shall be rated for pump discharge pressure.

3. Drains will be installed downstream of the seat in flanged check valves in vertical lines.

4. Check valves are required in the discharge of all pumps.

5. Temporary or start-up strainers will be specified as appropriate for pumps to prevent damage during start-up from loose foreign bodies. The strainer open area will be at least equal to 200% of the pipe cross sectional area. The distance between strainer and pump nozzle will be 5 times pipe diameter.

6. A warm-up and cool down bypass will be provided for pumps that may be idle or on standby during plant operation and which will operate at or above 149 C, or if the process fluid will solidify at ambient temperature. The bypass will be sized for 2% of the normal flow or will have a ¾” line whichever is larger. The bypass will have a globe valve and will be installed around the pump discharge check valve. Drilled check valves can only be used with SABIC permission. Chill down systems for cryogenic pumps are also required. These will be appropriately designed per pump services.

7. For pumps in cryogenic service, the following will be included in the design. These are in addition to the normal pump vent and drain criteria.

a. Pump casing vent with gate isolation valve and globe throttling valve to closed system.

b. Discharge piping highpoint vent to closed system.

c. Discharge check valve to have ¾ inch globe valve bypass for pump cool down.

d. Pump and discharge piping to be protected by a relief valve downstream of the discharge check valve, sized for liquid expansion and two phase flow.

e. Consider a suction line temperature indicator with high alarm.

8. Positive displacement pumps will be provided with a relief valve in the discharge line, in addition to the relief valve furnished as an integral part of the pump. Reciprocating pumps will have pulsation dampeners on the discharge side. If required, pulsation dampeners shall be provided on the suction side of positive displacement pumps.

9. Auxiliary Lube Oil pumps & other critical machinery shall be driven by steam turbine and motor driven shall be Stand-by.

10. Motor of stand-by Auxiliary Lube Oil pumps & other critical machinery shall be able to start-up on Auto-mode in case the turbine of the on-line machinery fails, without affecting the plant load and operation. Emergency power for the auxiliary lube Oil pump motor including auxiliary lube Oil pump motor for all critical compressors, shall be provided with company’s approval.

11. Pump Casing Venting:

Pumps in auto start service shall be self venting. Suitable vacuum systems shall be provided where required to ensure pump casings are always flooded and any vapors generated are removed to a safe place.

E. Pump Sizing

1. The safety margins shall be subtracted from the calculated NPSH available i.e., (NPSHA–NPSHR > Safety Margin) for centrifugal and rotary pumps .No safety margin shall be used for reciprocating pumps other than the friction and acceleration losses.

2. Low capacity pumps (less than 15 m3/hr) may use a continuous minimum flow through a restriction orifice.

3. The pump capacity must be increased by the amount of the minimum flow.

4. Suction valves for all hydrocarbon pumps (C4 and lighter), hydrocarbon pumps at high temperature, and large hydrocarbon inventory pumps (e.g. column bottoms) must be tight shutoff and shall be locally operated at 15 meters minimum distance (upwind) from the pump for isolation in case of seal failure. The valves shall be pneumatically operated and fail in the last position. Remote indication of the valve position shall be provided with interlock with the pump motor.

5. All material used in the lube oil system shall be Stainless Steel.

F. Valving and Isolation

Block valves will be provided at the following locations in pump, turbine and compressor piping:

a) In suction and discharge piping of pumps.

b) At the equipment for auxiliary piping of gland oil, flushing oil and cooling water.

c) In all auxiliary piping, when necessary, to allow removal of the equipment during operation of the unit.

d) A casing vent and drain valve will be provided for pumps.

g. Safeguarding

Minimum flow protection is only required where there is a possibility of the process constraining the flow below the pump manufacturer’s recommendation. Minimum flow provisions for centrifugal pumps will consist of a line from the discharge to the suction vessel, or to the pump suction line through a cooler, if required.

The minimum flow line will be provided with a flow element and control valve (preferred arrangement). Alternatives such as an auto recirculation type valve or a solenoid valve with block valves, actuated from a low flow switch in the pump discharge will only be considered by exception for approval by Company. As the bare minimum, a manual block valve with a restriction orifice will be installed.

Advantages of Electrical Pumps:

1. Efficient and Reliable: Electrical pumps are known for their high efficiency and reliability in delivering consistent flow and pressure.
2. Ease of Operation: They are easy to operate and control, often featuring on/off switches or automated control systems.
3. Versatility: Electrical pumps can handle a wide range of fluids, including water, chemicals, oils, and more, making them suitable for various applications.
4. Compact and Space-saving: Electric pumps are typically compact in size, allowing for installation in tight spaces or limited areas.
5. Low Maintenance: Compared to other types of pumps, electrical pumps generally require minimal maintenance, resulting in cost savings and less downtime.

Disadvantages of Electrical Pumps:

1. Dependence on Power Supply: Electrical pumps rely on a stable power supply to operate effectively. Power outages or electrical failures can disrupt their operation.
2. Initial Cost: The initial cost of electrical pumps, including the electric motor and control system, can be higher than some other pump types.
3. Heat Generation: Electric pumps can generate heat during operation, requiring adequate cooling measures to prevent overheating.
4. Limited Mobility: Electrical pumps are typically stationary and require a fixed power source, limiting their mobility compared to portable or engine-driven pumps.

In summary, electrical pumps are widely used for their efficiency, reliability, and ease of operation. They are suitable for various applications and offer advantages in terms of performance and space-saving design. However, they are dependent on a stable power supply and may have higher initial costs compared to other pump types.

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