Face combination: The material(s) that is used on the seal faces of mechanical seals. Critical to choose correct material for your application to prevent premature seal failure.
Face flatness: A measure of how flat a seal face is. As the seal faces are lapped, they must be flat to form a seal and prevent leakage. In this case, flat means less than 300 mm in variation across the seal face. Measured by an optical technique involving an optical flat, a monochromatic light source and interference.
Face lubrication:The lubricant used between lapped seal faces of mechanical seals.
Face pressure: Pressure at the mechanical seal face. This is calculated by summing all the loads on the seal face, including the spring load, hydraulic load and shaft axial thrust and then dividing by the area of the seal face.
Face to faceseals: Two seals in a face to face configuration, where there is a common seal face. In this type of seal, the barrier fluid pressure will always be lower than the stuffing box pressure.
False brinelling: Refers to the removal of material from a ball bearing. In contrast to brinelling, in which the removal happens in one load event, false brinelling happens over time, through corrosion or fretting.
Filled carbon: A carbon that is composed of carbon plus organic or inorganic materials. These extras may not be as robust as the carbon itself, and provide a lower grade carbon, costing less to manufacture and purchase.
Filter: A device that separates liquid from solid. Characterized by the size of particles it can remove from the liquid.
Finite element analysis: A mathematical technique to find approximate solutions to boundary value problems. Used in hydraulics to calculate seal face distortion.
Fire pump: A pump designed specifically to protect from fires. They must meet certain specifications as set out in a code published by a fire regulatory agency. These pumps are then tested/approved by third party agencies. Alternatively,a fire pump may refer to the main pump of a fire sprinkler system.
First critical speed: When increasing in velocity, it is the first speed at which the rotor bearing support system is in a state of resonance. The lowest speed that produces this resonance is the first critical speed. Subsequent increased speeds where this happens are known as the second, third, etc. critical speeds.
Flashing: A rapid change in the state of matter from liquid to gas.
Flatness: When two metal surfaces must seal, the flatness of the surface is important. It is measured by placing an optical flat on the surface, shining a Helium Neon laser through the flat and reflecting it off the surface, and then looking at the resulting interference patterns to identify how flat the surface is.
Flexible-coupled pump: In contrast to the situation in a “close-coupled pump”, in a flexible coupled pump, the pump and driver each have separate shafts that are coupled through a flexible coupling.
Flexible member: The flexible component of a mechanical seal, contains the spring or bellows.
Flexible rotor: A rotor is flexible if it operates at or near its critical speed. In this case, if a rotor operates at >70% of its critical speed it is flexible.
Flexible shaft: A shaft that operates normally at a speed that is higher than its first critical speed.
Flexibility factor: Ratio of the length of a shaft cubed divided by the diameter to the fourth power. Used to predict whether the shaft will have bending problems.
Floating throat bushing: A bushing that has some radial movement to compensate for shafts that are not true. The bushing is a plain circular ring,usually made of carbon. Because the bushing can move radially it can have less clearance than a fixed throat bushing.
Floating throttle bushing: This is the same as the “floating throat bushing”. In general, the term “throat” bushing is used in low-pressure stuffing boxes and “throttle” bushing refers to the bushing in a high-pressure stuffing box.
Flooded suction: If the pump is below the liquid source, and the suction is fed by gravity. This is a preferred method for centrifugal pumps.
Fluid: A state of material that continually deforms under an applied shear stress. Gas, liquid and plasma are examples.
Fluorocarbon: A term for a compound that contains only carbon and fluorine, bonded together with carbon-fluorine bonds.
Flush: Padding an extraneous source of fluid to the pump’s stuffing box at a higher pressure than the operating pressure of the stuffing box. Mixes with and dilutes the process fluid.
Fluting: a term for bearing degeneration caused by electrolysis due to small amount of current that pass through the bearing. When this happens over an extended period of time, and is accompanied by lubricant breakdown, it can cause the bearing to become noisy.
Foot valve: A valve that prevents loss of priming in centrifugal pumps when the source of process fluid is lower than the pump.
Formed metal bellows: Manufactured by compressing and stretching the metal bellows material. Contrast this with welded bellows.
FPM (fpm): Feet per minute. Used as a measure of speed, or velocity.
Francis vane impeller: An impeller design that is most popular in fans/pumps that operate between 1500 and 4000 rpm.
Free length: The axial length of a mechanical seal before it is compressed.
Fret or fretting: Damage to the inside of the pump or fitting caused by removal of the protective oxide layer from a corrosion resistant material. The rubbing of a softer material against a hard shaft or sleeve causes this. Happens more frequently in low cost seals.
Friction head: The force (pressure) required to overcome the friction that is solely due to the inside of the pipes / fittings / pumps in a system.
Friction factor f (pipe): The friction factor of piping is a measure of how much frictional force is produced per length of pipe. This will be specific for each type of pipe and will depend also on whether the flow is laminar or turbulent. This factor is required to calculate the friction loss in a run of pipe.
Friction loss (pump): Friction between the pump and the process fluid results in loss of pressure. Different parts of the pump are more or less susceptible to this force.
Friction (pipe): The force produced as the process fluid flows through the pipes of a system. Caused by movement of the fluid internally as one fluid layer moves against another. Also caused by movement of the fluid against the pipe wall. Rougher pipes will lead to higher friction.
Fugitive emission: Regulatory agencies have declared that some chemicals are harmful to your health. If any of these escape into the atmosphere, it’s known as a fugitive emission.