Glossary of Pump Terms: D
D frame adapter:
Used to connect and align the pump and motor (manufactured in metric dimensions). The Imperial version is called a “C” frame adapter.
D.I.N. standard:
The German standard for industrial products.
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.
Dilatant:
A liquid that thickens (increases its viscosity) with agitation.
Differential Pressure:
The difference between the outlet pressure and the inlet pressure. Differential Pressure is sometimes
Called the Pump Total Differential Pressure.
Discharge Head:
The outlet pressure of a pump operation.
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.
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.
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.
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 allows a great deal of mechanical deformation without cracking.
Dynamic elastomer:
The rubber part that has to move to move or flex to compensate for seal face wear or shaft movement.
Dynamic head (system head):
The pump head created by friction in the piping system.
Glossary of Pump Terms: E
Efficiency:
Power out of the equipment divided by power in.
Elastic range:
The stressed part retains its memory and returns to its original shape.
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.
Endurance limit:
Beyond this point the metal will fatigue without increasing the stress.
E.P.R.
Ethylene propylene rubber. The most common elastomer used in the sealing of water based and higher pH materials. Cannot be used in petroleum products.
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.
Glossary of Pump Terms: F
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.
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 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.
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 particles than a strainer.
Finite element analysis:
A computer generated method of predicting seal face distortion.
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.
Flexible member:
The portion of the seal containing the springs or bellows.
Flexible shaft:
A shaft with an operating speed higher than its first critical speed.
Flooded suction:
When the liquid source is higher than the pump, and the liquid flows to the pump by gravity. Preferable
for centrifugal pump installations.
Fluid:
The material assumes the shape of its container. It could be either a liquid or a gas.
Fluorocarbon:
Genetic term for the elastomer called Viton? Viton is a Dupont Dow elastomer product.
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.
Foot Valve:
A type of check valve with a built-in strainer. Used at the point of the liquid intake to retain liquid in the system, preventing the loss of prime when the liquid source is lower than the pump.
Force:
Created whenever pressure works on an area. The units are pounds. (F = P x A)
F.P.M. (fpm.):
Feet per minute. When used in the context of seals it is measured at the center of the seal face.
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.
Fret 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 OEM mechanical seals and bearing grease or lip seals.
Friction Head:
The pressure expressed in lbs./sq. in. or feet of liquid needed to overcome the resistance to the flow in the pipe and fittings.