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

Hard face
A seal face either rotating or stationary. The most common materials are silicone carbide, ceramic, tungsten carbide, Stellite, Ni-resist. The hard face must be the wider seal face.

Harmonic vibration
Vibtrating in harmony with something near by. This can be a big problem for bearings in stationary or non running equipment.

Grease seal
A spring loaded elastomer seal commonly used to seal bearings. Sometimes called a 'lip seal'. Not a good choice for sealing the bearing casing of a pump. A labyrinth or face seal would be a better choice.

Halogen
Elements that attack carbon. Fluorine, bromine, chlorine, astatine and iodine.

Gasket
Used between two static surfaces to provide a seal. Made from a variety of deformable materials.

Gland
The part that holds one half of the mechanical seal and attaches to the stuffing box.

Galvanic series
A list of metals with those on the top of the list being attacked by those lower down in the list. The father apart on the list, the faster the attack.

Fugitive emission
The government has designated certain chemicals as hazardous to the environment. If any of these chemicals is released to the atmosphere they are called fugitive emissions.

Frett or fretting
Damage or grooving caused by the removal of the protective oxide that is formed on most corrosion resistant metals. It happens when a softer material (rubber) rubs against a hard shaft or sleeve. A common problem with low cost O.E.M. mechanical seals and bearing grease or lip seals.

Francis vane impeller
The most popular impeller shape with a specific speed between 1500 and 4000.

Free length
The uncompressed axial length of a seal.

Foot
Supports the wet and power end of the pump and attaches it to the base plate.

Force
Created whenever pressure works on an area. The units are pounds. (F = P x A)

Formed metal bellows
Manufactured by stretching and compressing the metal bellows material. Not usually used in mechanical seals because of its high spring rate.

Flush
Putting an outside liquid into the stuffing box of the pump at a pressure higher than stuffing box pressure. All of this liquid mixes with and dilutes the pumped fluid.

Flurocarbon
Genetic term for the elastomer called Viton®. Viton is a Dupont Dow elastomer product.

Fluid
The material assumes the shape of its container. It could be either a liquid or a gas.

Flexible shaft
A shaft with an operating speed higher than its first critical speed

Flexible member
The portion of the seal containing the springs or bellows.

Flashing
A rapid change in liquid state from a liquid to a gas.

Flatness
Measured by Helium light bands (0.0000116' or 0,3 microns) as opposed to surface finish that is measured by R.M.S. or C.L.A.

Flexibility factor
Same as L³/D⁴ Used to predict shaft bending problems.

Finite element analysis
A computer generated method of predicting seal face distortion.

Filled carbon
Contains organic or inorganic materials that might be sensitive to temperature, or be attacked by the fluid you are sealing. Usually a low cost carbon.

Filter
A devise used to remove solid particles from liquid. It removes smaller paricles than a strainer.

Face lubrication
The fluid or vapor that sometimes exists between lapped mechanical seal faces.

Face pressure
The sum of all the loads on the seal face including the spring load, hydraulic load and shaft axial thrust, divided by the area of the seal face. This face load is reduced by friction between the sliding elastomer and the shaft or sleeve.

Face flatness
Measured by an optical flat and a monochromatic light. The measurement is read in helium light bands (.0000116 inches or 0,3 microns).

Face combination
The materials chosen for the lapped seal faces. Usually a grade of carbon graphite running on a hard face material.

Face to face seals
Two seals running against a common seal face. The barrier fluid pressure is always lower than stuffing box pressure.

Endurance limit.
Beyond this point the metal will fatigue without increasing the stress.

Extrusion
Permanent displacement of a portion of the O-ring into a gap, under the action of fluid pressure.

Eye of the impeller
The center of the impeller, where the fluid enters.

Elastomer
A rubber like material that, when compressed and then released will return to 90% of its original shape in less than five seconds.

Electrolysis
A process involving chemical change caused by the passage of an electric current through a liquid.

Efficiency
Power out of the equipment divided by power in.

Elastic range
The stressed part retains its memory and returns to its original shape.

Dynamic head (system head)
The pump head created by friction in the piping system.

Effective diameter
In metal bellows terminology it is the calculated diameter where the pressure penetrates between the metal plates. This number is used to determine the hydraulic balance diameter of the seal face.

Dynamic elastomer
The rubber part that has to move to move or flex to compensate for seal face wear or shaft movement.

Dry running
Running without fluid at the seal face.

Dual Seal
Two seals running in various configurations: back to back, tandem, face to face, or concentric.

Ductility
The property of a metal that lets you give it a great deal of mechanical deformation without cracking.

Drive lugs
These lugs or pins transmit the torque from the set screws to the seal face.

Double suction pump
The rotor is suspended between two bearings with the fluid entering on either side of the impeller. Used at higher capacities.

Double volute
A centrifugal pump design that incorporates two cut waters to prevent shaft deflection when the pump is operating off of the B.E.P. Lowers the efficiency of the pump and therefore seldom used on smaller size impellers.

DN factor
Do not use precision bearings if the bearing bore (millimeters) x rpm. is 300,000 or greater

Double balanced seal
Hydraulically balanced in both directions. A desirable feature, but seldom provided by seal manufacturers.

Double seal
An out dated term describing two seals in a pump. The latest terminology is 'dual seals'. In the past the term was used to describe a higher pressure barrier fluid between dual seals.

Discharge recirculation
Connecting a line from the discharge side of the pump to the stuffing box. Should be used with a close fitting bushing in the end of the stuffing box to increase the stuffing box pressure. A common application when pumping a fluid close to its vapor point.

Disaster bushing
Used in A.P.I. glands to support the shaft in the event of a bearing failure, or to prevent product from rushing to atmosphere after a seal failure. The close clearance (0.025 inch or 0.5 mm.) directs most of the leakage through a drain connection in the seal gland to an appropriate container.

Dial indicator
A tool used to measure concentricity or displacement of a shaft.

Dilatant
A liquid that thickens (increases its viscosity) with agitation.

Deflection
Movement or displacement of the shaft in a radial direction.

Density
Measured in gm/cm² or lb/in ² A measure of the weight of the fluid. A better term than specific gravity.

Cyclone separator
A device used in some seal applications to separate solids from liquid by utilizing centrifugal force. Not very reliable.

Damping
The physical touching of a component to arrest vibration.

Dead ending
Isolating the stuffing box. No recirculation or flushing lines in or out.

Cryogenic
Very cold temperatures.

Cutwater
Directs the pumped liquid to the discharge piping.

Coupling
Used to connect the pump to the driver. It transmits torque and compensates for axial growth, but not for radial misalignment.

Critical speed
Any object made of an elastic material has a natural period of vibration. When a pump rotor or shaft rotates at any speed corresponding to its natural frequency, minor unbalances will be magnified. These speeds are called the critical speeds.

Corrosion resistant
Corrodes at a rate of less than 0.002 inches (0.05 mm) per year.

Cooling jacket
Surrounds the stuffing box of the pump to control the temperature of the fluid in the stuffing box. Usually molded into the back plate.

Convolution
Two metal bellows plates welded or formed together. To count the number of convolutions in a metal bellows you count the spaces between the bellows plates.

Convection tank
Used to contain fluid between two mechanical seals. An enclosed heater or cooler can be used to control the barrier or buffer fluid temperature. Pressure or level gages can indicate which seal has failed.

Concentricity
When the parts share the same center line they are concentric to each other.

Condensate
Condensed steam.

Convection
A natural circulation of fluid. The hot fluid (lighter) rises and the cool fluid (heavier) sinks.

Concentric dual seal
One seal is located inside the other, with a common hard face shared by both of them. Because of its large radial space requirement the seal is usually limited to mixer type applications.

Compression set
The elastomer changes shape when it has been exposed to too much heat. Round O-rings come out square.

Coke
A hard black substance that forms when petroleum products are over heated. It interferes with seal movement and will open the lapped faces.

Composite
When used in the content of mechanical seal faces, it refers to either a non metallic material or a combination of non metallic face inserted into a metal holder.

Close coupled
The pump impeller is mounted directly on the motor shaft. There is no separate bearing case.

Coated Face
A hard coating is plated or welded to a softer base material. Presents problems with different thermal expansion rates, the hard coating can 'heat check' or crack. Not recommended as a seal face material.

Circular casing
Used with centrifugal pumps that circulate fluid rather than build head or pressure.

Clam Shell
Used to set the pitch (distance between convolutions) while heat treating a metal bellows core.

Chrome Oxide
The passivated layer that forms on the 300 series of stainless steel.

Chrome carbide
Forms when chrome forms with carbon in the heat affected zone during the welding of stainless steel. The use of low carbon stainless steel is recommended in these applications.

Chemraz
An 'elastomer like' material manufactured by Green Tweed of England. Used to seal most solvents and other aggressive fluids.

Chloride stress corrosion
Occurs in the 300 series of stainless steel. Caused by a combination of tensile stress, chlorides and heat. No one knows the threshold values.

Change of state
When a liquid flashes into a vapor, solidifies, crystallizes, cokes etc.

Ceramic
A hard, chemically inert seal face material that includes products refereed to as silicone carbide.

Centrifugal separator
Sometimes called a cyclone separator. Uses centrifugal force to throw solids out of the fluid. Does not work very well in slurry seal applications.

Centipoise
The metric system unit of viscosity.

Centistoke
The kinematic unit of viscosity. Viscosity in centipoises divided by the liquid density at the same temperature, gives kinematic viscosity in centistokes.

Centrifugal pump
Moves liquid with centrifugal force. Available in circular and volute configurations.

Cavitate
Cavities or bubbles form in the fluid low pressure area and collapse in a higher pressure area of the pump, causing noise, damage and a loss of capacity.

Center line design
The pump is suspended on feet attached to the sides of the volute instead of the bottom. Used in higher temperature (> 100°C) pumping applications.

Catalyst
A chemical additive that decreases the time of a chemical reaction with out being affected by the reaction.

Cartridge seal
A self contained assembly containing the seal, gland, sleeve, and both stationary and rotating seal faces. Usually needs no installation measurement. Must be used if impeller adjustments are made. Cartridge seals are the standard for A.P.I. seal applications.

Carbonizing
A reduction of hydrocarbons resulting in the formation of carbonaceous residue that will interfere with the movement of a mechanical seal. Often called 'coking'.

Carcinogen
A cancer producing substance.

Carbon/ graphite
A common mechanical seal face material chemically inert to most fluids with the exception of oxidizers, bleaches, halogens and a few other fluids.

Carbon bushing
Used as a restrictive bushing in flushing applications, a thermal barrier in high temperature applications, a disaster bushing in an A.P.I. gland and to support a deflecting shaft in many mechanical seal applications.

Capacity
Fluid flow measured in gpm, liters/min, M³/hr. etc.

Carbide
The compound formed when carbon combines with an element. The carbides of metal are very hard and are often used as a mechanical seal face.

Atmospheric pressure
At sea level, atmospheric pressure is 14.7 psi.

AVS Standard
An old, obsolete standard that has been replaced by the A.N.S.I. standard.

Canned pump
A non seal pump with the shaft, bearings and rotor contained in a can to prevent product leakage. Limited to pumping clean lubricating liquids.