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Glossary of Terms

Below is a helpful list of common pump and liquid handling words and terms with their definitions.

AOD stands for Air Operated Diaphragm (pump). These types of pumps are powered by compressed air or gas, making them ideal for hazardous applications such as petroleum based products and other flammable materials. With certain materials of construction, such as steel or conductive plastics, they are easily converted into fully explosion proof (Ex-Proof) pumps. Additionally, they can pull a suction lift and are submersible when installed properly. AOD's can also handle slurries with solids concentrations up to 30% and can be run against a closed suction or "dead head" situation.

AODD stands for Air Operated Double Diaphragm (pump). These types of pumps are powered by compressed air or gas, making them ideal for hazardous applications such as petroleum based products and other flammable materials. With certain materials of construction, such as steel or conductive plastics, they are easily converted into fully explosion proof (Ex-Proof) pumps. Additionally, they can pull a suction lift and are submersible when installed properly. AOD's can also handle slurries with solids concentrations up to 30% and can be run against a closed suction or "dead head" situation.

Best Efficiency Point (B.E.P.)
The point on a pump's performance curve that corresponds to the highest efficiency.
The BHP is the actual amount of horsepower being consumed by the pump as measured on a pony brake or dynamometer.

The body of the pump which encloses the impeller. Primarily used in reference to centrifugal pumps.

The sudden collapse of gas bubbles due to the pressure increase.
Process in which cavities or bubbles form in the fluid low-pressure area and collapse in a higher pressure area of the pump - causing noise, damage to the pump, and loss of efficiency because it distorts the flow pattern. Occurs in centrifugal pumps when NPSHa < NPSH. A properly designed system and a properly sized pump will prevent cavitation.

Centrifugal Force
A force associated with a rotating body. In the case of a pump, the rotating impeller pushes fluid on the back of the impeller blade, imparting motion. Since the motion is circular there is a centrifugal force associated with it. The force pushes the fluid against a fixed pump casing thereby pressurizing the fluid and forcing it through the outlet.

Centrifugal Pump
Centrifugal pumps are the most common type of pump in use today throughout the world. A centrifugal pump is a rotodynamic pump that uses a rotating impeller to increase the velocity of a fluid. Centrifugal pumps are commonly used to move liquids through a piping system. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber, from there it exits into the downstream piping system. A centrifugal pump works by the conversion of the rotational kinetic energy, typically from an electric motor or engine, to an increased static fluid pressure. This action is described by Bernoulli's principle. The rotation of the pump impeller imparts kinetic energy to the fluid as it is drawn in from the impeller eye (center) and is forced outward through the impeller vanes to the periphery. As the fluid exits the impeller, the fluid kinetic energy (velocity) is then converted to (static) pressure due to the change in area the fluid experiences in the volute section. Typically, the volute shape of the pump casing (increasing in volume), or the diffuser vanes (which serve to slow the fluid, converting to kinetic energy in to flow) are responsible for the energy conversion. The energy conversion results in an increased pressure on the downstream side of the pump, causing flow.

Chopper Pump
A chopper pump is a centrifugal pump, which is equipped with a cutting system to facilitate chopping/maceration of solids that are present in the pumped liquid. The main advantage of this type of pump is that it prevents clogging of the pump itself and of the adjacent piping, as all the solids and stringy materials are macerated by the chopping system. Chopper pumps exist in various configurations, including submersible and dry-installed design and they are typically equipped with an electric motor to run the impeller and to provide torque for the chopping system. Due to its high solids handling capabilities, the chopper pump is often used for pumping sewage, sludge, manure slurries, and other liquids that contain large or tough solids.

Control Volume
Limits imposed for the theoretical study of a system. The limits are usually set to intersect the system at locations where conditions are known.

Datum Plane
A reference plane. A conveniently accessible known surface from which all vertical measurements are taken or referred to.

Dewatering Pump
Any pump capable of removing water from an unwanted area. They are usually small, portable pumps that run on single phase power, compressed air or a small engine, but can be large permanently installed units as well.

Discharge Static Head
The difference in elevation between the liquid level of the discharge tank and the centerline of the pump. This head also includes any additional head that may be present at the discharge tank fluid surface.

Dredge Pump
A dredge pump is a submersible, centrifugal pump capable of handling high solids concentrations and is typically used for clearing out and/or deepening harbors and waterways. The material being moved (i.e.) sand, dirt, soil, etc.) is carried away along with the water it is suspended in.

A ratio of total power output to the total power input, expressed as a percent.

A thermodynamic property of a fluid. The enthalpy of a fluid consist of the energy associated with the fluid at a microscopic level (related to the temperature of the fluid) plus the energy present in the form of pressure at the inlet and outlet of a system.

EODD stands for Electrically Operated Double Diaphragm (pumps). These are diaphragm pumps driven either directly or indirectly with an electric motor. Offering many of the same advantages as AOD/AODD pumps with less noise and no compressed air/gas requirements. They cannot run against a closed discharge, which air operated models can, except Graco's e-Series models.

Refers to any device in the system other than pipes, pipe fittings and isolation valves.

Equipment Head Difference
The difference in head between the outlet and inlet of a piece of equipment.

Flooded Suction
In a flooded suction system, the liquid flows to the pump inlet from an elevated source by means of gravity. This is generally recommended for centrifugal pumps.

A measure of the liquid volume capacity of a pump. Given in gallons per minute/hour (gpm, gph), liters per minute/hour (L/min, L/hour), milliliters per minute (mL/min), cubic meters per hour (m3/h) and other rarely used measurements.

The force produced as a reaction to movement. All fluids produce friction when they are in motion. The higher the fluid viscosity, the higher the friction force for the same flow rate. Friction is produced internally as one layer of fluid moves with respect to another and also at the fluid/surface interface.

Friction Head
The pressure expressed in pounds per square inch or feet of liquid needed to overcome the resistance to the flow in pipes and fittings.

Friction Head Difference
The difference in head required to move a mass of fluid from one position to another at a certain flow rate.

Grinder Pump
A grinder pump is a waste management device. Waste from water-using household appliances (toilets, bathtubs, washing machines, etc.) flows through the home's pipes into the grinder pump's holding tank. Once the waste inside the tank reaches a certain level, the pump will turn on, grind the waste into fine slurry, and pump it to the central sewer system.

Refers to the pressure produced by a vertical column of fluid.
A measure of pressure, expressed in feet of head for pumps. Water is used as the default where 10 meters (33.9 ft.) of water equals one atmosphere (14.7 psi. or 1 bar).

Heat Loss
The heat lost by a system (i.e. the heat lost due to friction).

Heat Transfer
The heat lost or gained by a system, this can happen from a variety of factors including, but not limited to: uninsulated pipes, jacketed or non-jacketed pumps, storage vessels/tanks, etc.

The rotating element of a centrifugal pump which imparts movement and pressure to a fluid.

Internal Energy
A thermodynamic property. The energy associated with a substance at a molecular level.

A method of solving an equation by trial and error. An iteration technique is used to solve equations where the unknown variable cannot be explicitly isolated. A frequently used technique is the Newton-Raphson method.

Kinetic Energy
A thermodynamic property. The energy associated with the mass and velocity of a body.

A distinct flow regime that occurs at low Reynolds number (Re < 2000). It is characterized by particles in successive layers moving past one another in a well behaved manner (little to no turbulence).

Magnetic Drive
Also referred to as a Mag-drive. This is a method of connecting the motive force to the pump which uses a series of magnets coupled together, with a containment chamber separating them. Magnetic Drives keep the fluid sealed from atmosphere and other environmental factors and eliminate the need for seals and seal maintenance. Special considerations must be taken into account when specifying a Mag-Drive pump or mixer. Ask Springer Pumps for more information.

Metering Pump
Pumps used for precise introductions of chemicals into a tank, existing fluid stream or some other liquid handling equipment. Types of pumps for these include Diaphragm Pumps (AOD or EOD), Peristaltic Pumps, Hose Pumps, Gear Pumps, Bellows Pumps, Piston Pumps and other less commonly used pump types.

Mercury (Hg)
A metal which remains liquid at room temperature. This property makes it useful when used in a thin vertical glass tube since small changes in pressure can be measured as changes in the mercury column height. The inch of mercury is often used as a unit for negative pressure.

Mixer, Submersible
A submersible mixer is a mechanical device that is used to mix sludge tanks and other liquid volumes. Submersible mixers are often used in sewage treatment plants to keep solids in suspension in the various process tanks and/or sludge holding tanks. The submersible mixer is operated by an electric motor, which is coupled to the mixer's propeller, either direct-coupled or via a planetary gear-reducer. The propeller rotates and creates liquid flow in the tank, which in turn keeps the solids in suspension. The submersible mixer is typically installed on a guide rail system, which enables the mixer to be retrieved for periodic inspection and preventive maintenance.

Mixer, Vertical
This style of mixer uses an extended shaft between the motor and mixing blade such that the motor is above and out of the liquid. These also incorporate a gear reducer to slow the speed of the mixing blades to achieve the desired mixing/tank turnover rate. Vertical mixers are often used in reactor vessels to ensure thorough chemical reactions or to mix different ingredients together in food/beverage applications.

Mixer, Horizontal
This style of mixer uses an extended shaft between the motor and mixing blade such that the motor is to the side and out of the liquid, usually incorporating a seal in the side of the vessel. These also incorporate a gear reducer to slow the speed of the mixing blades to achieve the desired mixing/tank turnover rate. Vertical mixers are often used in reactor vessels to ensure thorough chemical reactions or to mix different ingredients together in food/beverage applications.

Multi-Stage Pump
The multi-stage pump is used for clean, clear liquids requiring significant discharge pressure. A multi-stage pump is nothing more than a standard centrifugal pump with the discharge of the initial volute discharging directly into the suction of the next volute. The numerous "volutes" are all internal to the pump and many times the volutes are hard to spot individually. The number of stages is dependent on the desired Total Discharge Head required by the application. These types of pump can be either horizontal or vertical configuration. Commonly used for boiler feed.

Negative Pressure
Pressure that is less than the pressure in the external environment.

Net Positive Suction Head (N.P.S.H.)
The head in feet of water absolute as measured or calculated at the pump suction flange, less the vapor pressure (converted to feet of water absolute) of the fluid.

Net Positive Suction Head Available (NPSHa)
The NPSHa available to prevent cavitation of the pump. To calculate the NPSHa, take the (Static Suction Head) plus (Suction Vessel Surface Pressure Head) minus (vapor pressure of fluid) minus (friction losses in the suction).

Net Positive Suction Head Required (NPSHr)
The NPSHr to stop a pump from cavitating. The NPSHr is generally supplied to you by the pump manufacturer.

Newtonian Fluid
A fluid where the relation between shear stress and shear rate is linear, related to viscosity.
A fluid whose viscosity does not change with the amount of strain it is subjected to.

Non-Newtonian Fluid
A fluid with properties that is different in any way from those of Newtonian Fluids. This is usually found in the relation of viscosity and shear or shear/time.

Operating Point
The point on the system curve corresponding to the flow and head required to meet the process requirements.

Performance Curve
A curve of flow vs. Total Head for a specific pump model and impeller diameter.
A diagram provided by the pump manufacturer to explain the relationship between the head and the flow rate of a pump using various size impellers, inlets/outlets, motive power, speed and other factors depending on the pump type. The curve also includes efficiency, NPSH required, and horse power consumption as a function of flow.

Pipe Friction Loss
The positive head loss from the friction resistance between the pipe walls and the moving liquid.

Pipe Roughness
A measurement of the average height of peaks producing roughness on the internal surface of pipes. Roughness is measured in many locations, and is usually defined in micro-inches RMS (root mean square).

Piston Pump

The piston pump is a positive displacement type of pump. As the piston is pulled back it draws in the fluid, and then as it's pushed forward it pushes the liquid out. A piston pump can have up to four pistons depending on the application. They should only be used for clear liquids as any solids and/or abrasives in the fluid can damage the pump. Piston pumps are for low flow, high head applications. Frequently used for high-accuracy metering applications.

Potential Energy

A thermodynamic property. The energy associated with the mass and height of a body above a reference plane.

Powder Pump
Powder pumps are normally of the Air Operated Diaphragm type and really can pump just powder and powder like materials such as flour and other fine grained, low bulk, dry-density powders in a dust free operation.

The application of external or internal forces to a body producing tension or compression within the body. This tension divided by a surface is called pressure.

The force exerted on the walls of a surface by a liquid. Normally measured in pounds per square inch (psi).

Pressure Drop
Referring to the loss of pressure between two points in a pipeline system. Generally, this occurs because of pipe friction loss or differences in elevation between the two points.

Progressive Cavity Pump
A pump that uses a stator and rotor in a screw shape. The rotor turning inside the stator causes cavities to move in the direction of flow. Progressive Cavity Pumps cannot run dry for any amount of time.

The pumping mechanism consists of a rotor that looks like a corkscrew inside a stator with a corkscrew shape cut out of it, but they are purposely off center from each other. As the rotor turns, cavities in the stator are created and eliminated by the rotor/stator off center relationship. These pumps are ideal for thick slurries such as food waste, sludge, or any thick fluids. PC pumps have been used to pump ice, fish waste and even cookie dough. PC pumps typically operate at lower speeds, usually below 1000 rpm, and consist of the pump end, motor and reducing gear box.

Propeller Pump
Propeller pumps are similar to other centrifugal impeller pumps, but the fluid being pumped is not sent in a circular path. Rather, it proceeds more or less in a straight direction up to the discharge. The motor sits above the discharge shaft. The propeller can be placed below the surface of the liquid, where it will always be primed. Propeller pumps are generally low-speed but low heads. They can be quite large, measuring over a dozen feet in diameter and moving over 50,000 gallons per minute. Some have adjustable-pitch blades.

Pump Impeller
The moving element in a centrifugal pump that drives the fluid.

Rotary Gear Pump
A Gear pump uses the meshing of gears to pump fluid by displacement. They are one of the most common types of pumps for hydraulic fluid power applications. Gear pumps are also widely used in chemical installations to pump fluid with a certain viscosity. There are two main variations; external gear pumps which use two external spur gears and internal gear pumps which use an external and an internal spur gear. Gear pumps are fixed displacement, meaning they pump a constant amount of fluid for each revolution. Some gear pumps are designed to function as either a motor or pump.

Sanitary Pump
Sanitary pumps describe the materials used for construction of how a pump is built and if they meet specific criteria set forth by certifying agencies. Typical describing words are "FDA Compliant", "Food Grade" and "CIP (Clean in Place)" and EHEDG. Sanitary pumps are normally built from stainless steel, PTFE, EPDM and other "clean" materials.

Screw Centrifugal Pump
A pump which uses an open channel impeller with a screw shape. These pumps are ideal for sludges, large/stringy solids laden fluids, shear sensitive fluids and delicate or highly abrasive materials. Offering true non-clog performance and a steep head curve make these pumps ideal for waste water and other sludge applications. They also handle solids more gently than other pumps. They are specifically used for transporting live fish without harm and delicate foodstuffs without bruising.

Self-Priming Pump
Self-priming pumps are centrifugal pumps with an abnormally large and specially shaped volute. The purpose of the large volute is to allow the pump to pull or "lift" liquid up to the impeller. Initially the pump volute (casing), must be filled with liquid manually to "pre-prime" the pump. As the pump starts it pumps out the liquid that was manually put into it while also drawing up the air in the suction pipe along with pulling up the liquid to be pumped. As the lifted liquid enters the volute the final volume of air is pumped out of the discharge and through an air release valve. Once the liquid hits the air valve, it closes and the pump now operates as a standard centrifugal pump.

Shut-off Head
The Total Head corresponding to zero flow on the pump performance curve.

Slurry is defined as a suspension of solids in a liquid. Typically, the liquid is water and the solids can be anything from soft materials such as sewage and food processing waste (potato skins, fish parts) to abrasive solids like sand, fly ash and coal. Keep in mind a typical centrifugal pump really can't handle more than 3% solids by weight.

Solids Handling Pump
Many types of pumps can be used for solids handling. The size and concentration of solids in the fluid will determine the best type of pump for the application. For sewage applications such as lift stations where the solids concentration does not exceed 3%, but the solids size can reach 3" or 4" a centrifugal pump is usually the best choice. For solids concentration above 3%, Air Operated Diaphragm, Progressive Cavity or even specialty centrifugal pumps, like Hydrostal Pumps, can be used.

Specific Gravity
The ratio of the density of a fluid to that of water at standard conditions
The ratio of the weight of a given volume of liquid to pure water. Pumping heavy liquids (specific gravity greater than 1.0) will require more horsepower.

Specific Speed
A formula that describes the shape of a pump impeller. The higher the specific speed the less N.P.S.H. required.

Split Case Pump
The split case is almost synonymous with multi-stage and can be either horizontal or vertical. Used where high pressures are needed such as boiler feed.

The ratio between the absolute displacements of a reference point within a body to a characteristic length of the body.

In this case refers to tangential stress or the force between the layers of fluid divided by the surface area between the layers.

Submersible Pump
Just like it sounds, these guys operate within the fluid they are pumping. Submersible pumps can be either centrifugal or AOD type pumps. The centrifugal versions are common used in sewage lift stations, while the AODs are used in chemical transfers.

Suction Head
Condition that occurs when the liquid source is above the centerline of the pump.

Suction Static Head
The difference in elevation between the liquid level of the source of supply and the centerline of the pump. This head also includes any additional head that may be present at the suction tank fluid surface.

Suction Lift
Condition that occurs when the liquid source is below the centerline of the pump.

Suction Static Lift
The same definition as the Suction Static head. This term is only used when the pump centerline is above the suction tank fluid surface.

Is a system of piping or tubing where the exit point is lower than the entry point.

Systems, as far as pumps are concerned, include all the piping with or without a pump, starting at the inlet point (often the fluid surface of the suction tank) and ending at the outlet point (often the fluid surface of the discharge tank).

System Curve
Is a plot of flow vs. Total Head that satisfies the system requirements.

System Equation
The equation for Total Head vs. flow for a specific system.

System Requirements
Friction and system inlet and outlet conditions (i.e. velocity, elevation and pressure).
The parameters that determine Total Head.

Total Head / Total Dynamic Head
The amount of head produced by the pump. Calculated by summing the static head, friction head, pressure head, and velocity head.

Total Static Head
The difference between the discharge and suction static head including the difference between the surface pressure of the discharge and suction tanks.

A type of flow regime characterized by the rapid movement of fluid particles in many directions as well as the general direction of the overall fluid flow.

UV Disinfection (UVGI)
Ultraviolet germicidal irradiation (UVGI) is a disinfection method that uses ultraviolet (UV) light at sufficiently short wavelength to kill microorganisms. It is used in a variety of applications, such as food, air and water purification. UVGI utilizes short-wavelength ultraviolet radiation (UV-C) that is harmful to microorganisms. It is effective in destroying the nucleic acids in these organisms so that their DNA is disrupted by the UV radiation, leaving them unable to perform vital cellular functions.

The wavelength of UV that causes this effect is rare on Earth as the atmosphere blocks it. Using a UVGI device in certain environments like circulating air or water systems creates a deadly effect on micro-organisms such as pathogens, viruses and molds that are in these environments. Coupled with a filtration system, UVGI can remove harmful micro-organisms from these environments.

The application of UVGI to disinfection has been an accepted practice since the mid-20th century. It has been used primarily in medical sanitation and sterile work facilities. Increasingly it was employed to sterilize drinking and wastewater, as the holding facilities were enclosed and could be circulated to ensure a higher exposure to the UV. In recent years UVGI has found renewed application in air sanitization.

Vapor Pressure
The pressure at which a liquid boils at a specified temperature.

Variable Frequency Drive
A variable-frequency drive (VFD) is a system for controlling the rotational speed of an alternating current (AC) electric motor by controlling the frequency of the electrical power supplied to the motor. A variable frequency drive is a specific type of adjustable-speed drive. Variable-frequency drives are also known as adjustable-frequency drives (AFD), variable-speed drives (VSD), AC drives, micro drives or inverter drives. Since the voltage is varied along with frequency, these are sometimes also called VVVF (variable voltage variable frequency) drives. Variable-frequency drives are widely used. For example, in water booster stations, pump speed is controlled by the VFD based on system demand.

Velocity Head Difference
The difference in velocity head between the outlet and inlet of the system.

Vertical Turbine Pump
A vertical turbine pump is a centrifugal type pump, often with multiple stages, where the motor is set at ground level and connect via shaft to the pump below. Used as well pumps for irrigation, they can also pump from rivers, lakes and other bodies of water.

A property, which measures a fluid's resistance to movement. The resistance is caused by friction between the fluid and the boundary wall and internally by the fluid layers moving at different velocities.

The energy required to drive the fluid through the system.

A measure of a liquid's resistance to flow. Essentially it's a how thick the liquid is. The viscosity determines the type of pump used, the speed it can run at, and with gear pumps, the internal clearances required.

Well Pump
Well pumps are a centrifugal, submersible type of pump used for bringing underground water up to the surface for domestic use. They can consist of one or several "stages" depending on the well depth and desired discharge pressure. Electrically powered the motor is typically on the bottom of the pump with the suction in the middle and the water is pumped upwards through the impeller(s) and upwards toward the surface.