Copy of `McNally - pump and seal terms`

The wordlist doesn't exist anymore, or, the website doesn't exist anymore. On this page you can find a copy of the original information. The information may have been taken offline because it is outdated.

McNally - pump and seal terms Category: General technical and industrial > Pump and Seal terms Date & country: 24/09/2008, USA Words: 312

Run out
Twice the distance that the center of the shaft is displaced from the axis of rotation.

Seal faces
The lapped faces that that provide the primary sealing in a mechanical seal.

Rockwell "C"
The scale most often used to measure hardness of the hard seal face.

Reverse balance
A common type of hydraulic balance used on outside mounted mechanical seals.

Rigid shaft
A shaft with a rotating speed lower than its first critical speed.

RMS
Root mean square. A measure of surface finish or smoothness. Metric uses C.L.A. or centerline average for the same purpose.

Renkin scale
Used to measure low temperatures in the Fahrenheit scale. Similar to Kelvin which is used to measure low temperatures in the Centigrade system.

Repeller
A second impeller used to lower the stuffing box pressure.

Reaction bonded
A method of manufacturing silicone carbide mechanical seal faces. These materials are sensitive to caustic and some other high pH liquids.

Radial
90 degrees to the centerline of the shaft.

Radial bearing
In an end suction centrifugal pump it is the bearing located closest to the stuffing box. This bearing handles most of the radial loads put on the impeller.

Quench
The introduction of a fluid outside the seal to cool the product, or dilute any leakage across the seal faces.

Quill shaft
A hollow shaft with another shaft inside it.

Pusher seal
A design that has a spring loaded dynamic elastomer or rubber like part. A very poor design that should be avoided.

Pump out vane
Located behind the impeller shroud in some impeller designs to lower stuffing box pressure. Should no be used in hot well condensate pumps or any pump running with a negative stuffing box pressure.

Pumping ring
Used with a convection system to get circulation between two mechanical seals. Absolutely necessary if oil is used as a barrier fluid because of oil's poor specific heat..

Pump curve
A diagram supplied by the pump manufacture to describe the relationship between the head and the capacity of a particular pump using various size impellers. The curve also include information about efficiency, horse power consumption, N.P.S.H. required, etc.

Press fit
The best way to insert a carbon/graphite face into a metal holder. The carbon will shear to conform to the holder's irregular shape. Usually done with an arbor press.

Pressure head
The pump head exerted by atmospheric pressure or any additional pressure that might be in the vessel.

Power factor
A measure of how the voltage leads or lags the amperage.

Precision bearing
Ball or roller bearing as opposed to a sleeve or babbitt bearing.

Pressure drop
Referring to the loss of pressure from the outside to the inside of the mechanical seal faces or across the individual rings of packing.

Power end
The end of the pump that attaches to the power source and does not get wet from the pumpage. The bearings are in this part.

Plastic range
The metal has been stressed beyond its yield point and will not return to its original shape.

Positive displacement pump
Called a PD pump. Gear, sliding vane, progressive cavity, lobe etc. the capacity determined by the pump speed. The maximum head is determined by the horsepower available and the casing strength.

Pitting
Surface voids caused by corrosion, erosion or cavitation.

Plasma spray
A method of putting a hard coating on a base material. Not recommended for mechanical seal faces.

Plastic range
If you stress metal enough, it stretches through the elastic range, its yield point and ends up in the plastic range where it loses its memory.

Physicals
Same as the specifications.

Pipe strain
The strain on the pump volute caused by the piping. It will cause excessive mechanical seal movement and can cause contact between rotating and stationary pump and seal components.

Pascal
A metric unit for pressure. 100 kPa = one atmosphere.

Passivated
The protective oxide layer (ceramic) has formed on the metal surface.

pH
A measure of the acidity or the alkalinity of a fluid. The scale ranges from 0 (acid) to 14 (alkali) with 7 considered neutral.

Parallel operation
The pumps are discharging to a common header. It is important that the impeller speed and outside diameters be the same or one of the pumps will throttle the other.

Packing
The soft rings that mechanical seal replace to stop leakage. Packing must leak because it works on the theory of a series of pressure drops to reduce the stuffing box pressure to the point where the leakage is acceptable. A minimum of five rings of packing is required to do this.

Ozone
Created by oxygen atoms combining with oxygen molecules in a high energy atmosphere .Will prematurely age Buna rubber. Ozone forms in the shop as a result of the sparking of electric motor brushes.

Oxidizer
Combines with carbon to form carbon monoxide or carbon dioxide. The oxidizers attack all forms of carbon including the seal face and any black O-rings in the system.

Over hung impeller
Not supported with bearings on either side of the impeller.

Optical flat
A high quality glass lapped flat on one side and used with a monochromatic light to read seal face flatness.

OSHA
Occupational and Safety Health Act. Government regulations that affec the sealing business. OSHA 1910 is one of the more important that impacts the training of seal mechanics and operators.

Oil mist
A lubrication system where oil and air are mixed and sent into the pump bearing case. Not friendly to the environment.

Operating length
Measured after the seal has been compressed the proper amount. The measurement is usually made from the face of the stuffing box.

Oil analysis
A sensible preventative maintenance technique to check the oil for solids, water etc.

Oil life
Lubricating oil has a useful life of about thirty years at thirty degrees centigrade if it is not contaminated.

Non lubricant
The fluid that will not maintain a film thickness of at least one micron at its operating temperature and load. A concern with mechanical sealing.

Monochromatic light
A single color light used with an optical flat to read seal face flatness.

Negative pressure
Less than atmospheric pressure.

Newton
A metric unit of force. Kilogram x gravity.

Newtonian fluid
A fluid that does not change viscosity as it is agitated.

Moment of inertia
Referring to rotation about an axis. In the pump business it refers to a formula that describes the shape of the shaft. A solid shaft would have a different moment of inertia than a hollow shaft.

Modulus of elasticity
Refers to the stiffness of the material. The higher the modulus the stiffer the shaft. Most pump shafts have similar modules numbers. Also called Young's modulus. The relationship of stress to strain. If seal faces have a high modulus they are less likely to distort under pressure.

Minimum flow
A condition that can cause excessive heat inside the pump volute. A temperature rise of 10°C (18°F) across the operating pump is considered excessive. Normally caused by throttling a pump discharge valve.

Miscible
When one liquid mixes or blend with another liquid. Same as soluble.

Micro Organisms
Used in a variety of chemical processes. Can cause corrosion of stainless steel if they penetrate the passivated layer and attack the carbon content of the stainless steel.

Metal bellows
Used in mechanical seal designs to eliminate the need for a dynamic elastomer.

Metal fatigue
A breakage of the metal caused by the bending and flexing of a metal part beyond its endurance limit.

Mean Diameter
The middle diameter. Usually refers to the center of the seal face. The term is commonly used with metal belows seals to describe the middle diameter of the bellows plate.

Mechanical seal
A positive sealing device used to seal all fluids (liquids and gases). The primary seal is a set of lapped seal faces that are installed perpendicular to the shaft.

Mating ring
Another name for the hard face in a mechanical seal. It can be either rotating or stationary.

Magnetic seal
Uses magnetic materials rather than springs to keep the lapped seal faces together. Limited to non corrosive fluids because of the magnets.

Magnetite
Iron oxide ( Fe₃O₄). A protective coating the forms on iron pipe to prevent further rapid corrosion. Usually black or maroon in color. Can be very destructive to mechanical seal components until the oxide stabalizes. We often find these iron pipes in new hot water systems

Lubricant
Any fluid that will maintain a film thickness of one micron or more at its operating temperature and load.

Mach number
The relationship between a moving body and the speed of sound in that locality which can vary with temperature, altitude and there fore pressure.

Magnetic drive
A type of seal less pump that is pretty much limited to pumping clean lubricating liquids. Similar in concept to a canned pump.

Lip Seal
See grease seal.

Low flow
A condition that can cause excessive heat inside the pump volute. A temperature rise of 10°C (18°F) across the operating pump is considered excessive. Usually caused by throttling a pump discharge valve.

Line bearings
Position the rotor or shaft radially. Normally of the sleeve type.

Line bored
When the drilling or boring is done on a jig that insures every component is in a straight line.

Labyrinth seal
A non contacting seal utilizing a tortured path for the escape of the fluid. Utilizes a series of pressure drops to reduce the leakage.

Linear pressure drop
A straight line pressure drop across the lapped seal faces. Seldom happens.

kPa
A metric unit for pressure. 100 kPa = one atmosphere.

Kalrez
An 'elastomer like' material manufactured by E.I. Dupont that is used to seal most solvents and other aggressive fluids. It is available in several different grades.

Kilowatt
One thousand watts. The normal unit for work in the metric system

Iteration
A technique used in impeller design. You repeat the action until you get to the final result. Very difficult to do until the new computer programs became available.

Joule
A metric unit for the measurement of heat. Defined as the energy required to move one Newton over one meter.

Inline pump
Mounted in the piping. No base plate or alignment required.

Internal recirculation
A loss of efficiency caused by liquid flowing through wear rings or the impeller to volute clearances.

Intergranular corrosion
A corrosion of the grain boundaries in the body of the material.

Inducer
A small axial flow vane that attaches to the impeller of a centrifugal pump to increase the N.P.S.H. available.

Induction motor
The most common type used in industry. Has a slippage of 2 to 5 percent compared to synchronous motors.

Implode
The opposite of explode. Bubbles implode in the higher pressure areas of the pump making noise and causing damage to the metal parts. This is normally called cavitation

Inclusion
A non metallic slug of material which has become entangled in the metal during its manufacture. A severe problem in thin cross section metal bellows manufacture.

Impeller shroud
the plates located on one or both sides of the impeller vanes. Prevents solids from penetrating behind the vanes.

Impeller vane
Located between the eye and the discharge side of the impeller. Directs the flow of the liquid to the outside diameter of the impeller.

Impeller setting
Open impellers require a clearance between the volute or the pump back plate depending upon design. This clearance must be set when the pump is at operating temperature and must be reset to compensate for wear. (0.015' to 0.020' or 0,04 mm to 0,05 mm is typical)

Hysteresis
The delay or lag that causes seal faces to open.

Impeller
Attaches to the end of the shaft to impart energy to the fluid being pumped. Available in open, semi- open and closed designs.

Impeller eye
The center of the impeller or the point where fluid enters the impeller.

Hydronium ion
An ion formed by the transfer of a proton from one molecule of water to another. Used to determine the pH of a substance. Each step increases by a factor of ten.

Hydrostatic seal
Maintains a controlled gap between the seal faces by balancing the open and closing forces. There is a small amount of leakage across the faces when the shaft is rotating. Used in some compressor applications, but not very practical for the chemicals found in the process industry.

Hydrogen embrittlement
A premature fatigue of metal caused by the presence of free hydrogen. This is a major cause of ceramic breakage in hot water seal applications, and bearing fatigue if moisture penetrates into the bearing case.

Hydrocarbon
A petroleum product consisting of hydrogen and carbon.

Hydrodynamic force
Generated at the seal faces because, for all practical purposes, liquid is not compressible.

Hydrodynamic seal
Special geometric features on the seal face that provide lift by taking advantage of the rotation of one seal face upon the other.

Hydraulic force
Occurs any time pressure acts on a seal face area. Force times distance divided by time is a measurement of work done.

Horse power
33,000 foot pounds per minute. A common method of measuring work.

Hydraulic balance
A method of reducing mechanical seal face loading by reducing the seal face closing area.

Head
The equivalent height of the liquid. 20° C. water is used as the standard where 10 meters (33.9 ft.) of water equals one atmosphere (14.7 psi. or 1 bar). The term head is used instead of pressure in the centrifugal pump business.

Helium Light Band
A method of measuring seal face flatness. One helium light band equals 0.0000116 inches or 0.3 microns. Seal faces are normally lapped to within three helium light bands of flatness.

Hastelloy "C"
A nickel rich, corrosion resistant metal used for mechanical seal springs and metal bellows because it is not sensitive to chloride stress corrosion.