NIULPE 4th Class flashcards
NIULPE 4th Class · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- MAWP
- Maximum allowable working pressure: the highest pressure at which a boiler or pressure vessel may legally operate at a stated temperature, stamped on the nameplate.
- Fusible plug
- A fitting with a low-melting alloy core installed in the crown sheet of some firetube boilers; it melts when water level is low and the metal overheats, warning of danger.
- Try cocks
- Small valves on a boiler water column used to check water level by opening them; they supplement but do not replace the gauge glass.
- Three T's of combustion
- Temperature, turbulence, and time: the three conditions that must be adequate for complete combustion of fuel in a boiler furnace.
- Excess air
- Air supplied above the theoretical amount needed for complete combustion, expressed as a percentage; it ensures complete burning but raises stack loss if excessive.
- Low-water fuel cutoff
- A safety control that shuts off the burner when boiler water falls below a safe level, preventing overheating and explosion; it must be tested regularly.
- Flame safeguard
- A control system that proves flame presence during ignition and operation and shuts off fuel within a set time if the flame signal is lost.
- Pre-purge
- A timed period of forced airflow through the furnace before ignition that removes accumulated combustible gases and prevents explosion on light-off.
- Safety relief valve
- An automatic pressure relief device that opens at a set pressure to protect a vessel; a safety valve serves gas or vapor, a relief valve serves liquid.
- Hydrostatic test
- A pressure test using water, typically at 1.5 times the MAWP, to prove the strength and tightness of a boiler or pressure vessel.
- Steam trap
- A device that removes condensate and air from steam lines while preventing the escape of live steam, maintaining steam quality and efficiency.
- Gate valve
- A valve with a wedge-shaped disc that moves perpendicular to flow; used for full-open or full-closed isolation, not for throttling.
- NPSH
- Net positive suction head: the absolute pressure energy at a pump suction above the liquid vapor pressure; available NPSH must exceed required NPSH to avoid cavitation.
- Cavitation
- Formation and collapse of vapor bubbles in a pump when suction pressure falls below vapor pressure; causes noise, vibration, erosion, and loss of capacity.
- Pump curve
- A graph of head versus capacity for a centrifugal pump; the operating point is where the pump curve intersects the system curve.
- Positive displacement pump
- A pump that traps a fixed volume of liquid per cycle and delivers nearly constant flow regardless of discharge pressure; requires a relief valve.
- Hartford loop
- A piping arrangement that keeps the boiler water level above the return connection, preventing water from draining out of the boiler through the condensate return.
- Expansion tank
- A tank that absorbs the volume increase of heated water in a hot water system, preventing excessive pressure; a diaphragm tank separates air from water.
- One-pipe steam system
- A steam heating system in which steam supply and condensate return travel in the same pipe, with air vents on each radiator.
- Vapor-compression cycle
- The refrigeration cycle of compression, condensation, expansion, and evaporation in which refrigerant absorbs heat in the evaporator and rejects it in the condenser.
- Superheat
- The temperature of refrigerant vapor above its saturation temperature at the same pressure; measured at the evaporator outlet to check metering device performance.
- Dew point
- The temperature to which air must be cooled at constant pressure for water vapor to begin condensing; cooling below dew point produces condensate.
- Thermostatic expansion valve
- A metering device that regulates refrigerant flow into the evaporator to maintain a constant superheat at the evaporator outlet under varying loads.
- Ohm's law
- The relationship V = I x R, where voltage equals current times resistance; used to calculate current, voltage, or resistance in a circuit.
- Motor overload relay
- A protective device that trips on sustained overcurrent to protect a motor winding from overheating; it does not clear short circuits.
- Lockout/tagout
- A safety procedure that isolates and locks energy sources before maintenance, with tags identifying the work; verify de-energization before starting.
- Scale
- A hard deposit of calcium and magnesium compounds on heated surfaces; it insulates the metal, reduces heat transfer, and can cause tube overheating.
- Oxygen scavenger
- A chemical such as sodium sulfite added to boiler water to remove dissolved oxygen and prevent pitting corrosion of boiler metal.
- Blowdown
- Removal of boiler water to control dissolved solids and sludge; surface blowdown removes dissolved solids and bottom blowdown removes sludge.
- Flash point
- The lowest temperature at which a fuel releases enough vapor to ignite momentarily when exposed to a flame; a key fire-safety property of liquid fuels.
- Stoichiometric combustion
- Complete combustion with exactly the theoretical amount of air, producing only carbon dioxide, water, and nitrogen with no excess oxygen or unburned fuel.
- ASME Section I
- The section of the ASME Boiler and Pressure Vessel Code that sets rules for construction of power boilers, including safety valve capacity requirements.