Face-to-face - When referring to impellers, a face-to-face arrangement is when two adjacent impellers, in multistage pump, are arranged so that the inlet of the impellers are facing toward each other.
When referring to ball bearings, face-to-face arrangement is when two adjacent bearings are arranged so that the face, or low shoulder of the of the outer rings, are next to each other. The bearing contact angles converge inward to the shaft. See definition of back-to back.
False brinelling - In ball bearing, it refers to the removal of material from bearing elements by the fidgeting action between the balls and races due to mechanical vibration when the bearing is not rotating, such as the occurrence of dents during handling or transportation. False brinelling can cause a bearing to become noisy.
Fire pump - A pump specifically designed and built for fire protection service and meets the specifications set forth in a governing code, or standard. In North America the code is published by the National Fire Protection Association in NFPA 20, and the fire pumps are tested or listed by a third-party agency such as Underwriters Laboratories, Inc. or FM Global. The use of third-party listed or approved fire pumps are usually required not only by building codes, or local regulations, but also by property insurance companies as well.
A fire pump is the main pump unit connected in parallel with a jockey pump in a fire sprinkler system. When a sprinkler opens in the event of a fire the pressure drop in the sprinkler system is detected by the automatic controller and the fire pump is activated. See jockey pump.
First critical speed - ISO Standard 13709 and API Standard 610 define critical speed as the "shaft rotational speed at which the rotor-bearing-support system is in a state of resonance." The lowest resonant frequency that produces the first mode shape is called the first critical speed; the next higher frequency is called the second critical speed, and so on. The second, or third, critical speed is not a multiple of the first critical speed - the numbers have no correlation..
Flexible-coupled pump - a pump directly coupled to its driver through a flexible coupling. The pump and driver each has its own shaft. See close-coupled pump.
Flexible rotor - a rotor which operate near, or above, its critical speed, and when balanced at speed below its critical may lose its balance when it operates above its critical speed.
Flexible shaft - see flexible rotor.
Floating throat bushing - A tight clearance bushing that can move radially to compensate for shaft deflection or shaft whip. The bushing is a plain circular ring, usually made of carbon and is lightly pressed by a spring against the bottom wall of the stuffing box. Because the bushing can slide radially against the wall to adjust to the shaft deflection, it can have a tighter clearance than a fixed throat bushing. A typical range is 0.002" to 0.004" clearance.
Floating throttle bushing - same definition as floating throat bushing. The term throat bushing usually refers to the bushing on the low pressure stuffing box, and the term throttle bushing usually refers to the bushing on the high pressure stuffing box. Also, a throttle bushing usually has a tighter clearance than a throat bushing because it is subjected to a higher differential pressure.
Fluting - a minor form of electrolysis resulting from leakage of small electrical current that passes through a bearing that, over a period of time, is accelerated by the combined effect of vibration and lubricant degeneration due to vibration. Fluting causes a bearing to become noisy.