NIULPE Class 5 flashcards
NIULPE Class 5 · 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.
- Low-water fuel cutoff
- A safety device that stops fuel and combustion air when the boiler water level drops below the safe limit, preventing overheating of surfaces exposed to flame.
- Safety valve set pressure
- The pressure at which the safety valve begins to open, set at or below the boiler maximum allowable working pressure and verified by a pop test.
- Water column function
- A vertical fitting connected to the boiler shell that dampens water level motion and supports the gauge glass and low-water cutoff connections.
- Fusible plug purpose
- A plug with a low-melting alloy core that melts when the crown sheet overheats from low water, releasing steam or water as a warning.
- Pre-purge requirement
- A fan-driven airflow through the furnace and flue before light-off, at the required airflow and duration, to clear any accumulated combustible gases.
- Flame failure response
- On loss of the flame signal, the flame safeguard closes the fuel valve within the code interval, typically 4 seconds, and starts a post-purge.
- Three-element feedwater control
- A drum level control scheme using drum level, steam flow, and feedwater flow signals to correct level before shrink or swell causes false readings.
- Short cycling
- Frequent burner starts and stops caused by a boiler oversized for the load, producing purge losses, pressure swings, and added wear.
- Steam trap failure modes
- A trap failed open passes live steam and wastes energy; a trap failed closed backs up condensate and can cause water hammer or flooding.
- Water hammer cause
- Trapped condensate or sudden valve closure creates a pressure wave in steam piping; prevention requires drainage, trapping, and slow valve operation.
- Gate versus globe valve
- Gate valves isolate flow fully open or closed; globe valves throttle flow and are installed so pressure acts under the seat.
- Expansion tank purpose
- In a hot water system, a tank that absorbs the volume increase of heated water, limiting pressure rise and protecting the relief valve.
- Pump affinity laws
- For a centrifugal pump, flow varies with speed, head with speed squared, and power with speed cubed, allowing prediction of performance at new speeds.
- NPSH available
- The net positive suction head at the pump inlet from system pressure, static head, and friction, minus vapor pressure; it must exceed the pump requirement.
- Cavitation symptoms
- Noise, vibration, and reduced head caused by vapor bubbles collapsing in the pump; prevention requires adequate suction pressure and cool water.
- Deaerator function
- A vessel that heats feedwater with steam to near saturation, driving off dissolved oxygen and other gases before they cause corrosion.
- Stoichiometric air
- The exact air quantity needed to burn a fuel completely, about 10:1 by volume for natural gas and roughly 14.4 lb air per lb of oil.
- Excess air effect
- Air supplied above stoichiometric; too little produces carbon monoxide and smoke, too much lowers efficiency by carrying heat up the stack.
- Balanced draft
- A draft arrangement with forced draft fans before the furnace and induced draft fans after the boiler, holding furnace pressure slightly below atmospheric.
- Acid dew point
- The temperature at which sulfur trioxide and water vapor in flue gas condense as acid, typically above 250 F, limiting how low stack temperature can go.
- Scale formation
- Hardness minerals precipitating on hot tube surfaces, insulating metal, raising metal temperature, and possibly causing tube overheating and failure.
- Oxygen scavenger
- A chemical such as sodium sulfite or carbohydrazide added to feedwater to remove residual dissolved oxygen and prevent pitting corrosion.
- Conductivity blowdown control
- Boiler water conductivity is measured as an indicator of dissolved solids; blowdown rate is adjusted to keep solids within the specified limit.
- Caustic embrittlement
- Cracking of stressed steel from concentrated alkaline boiler water, promoted by high pH and leakage at seams; controlled by pH and water chemistry limits.
- ASME Code Sections I and IV
- Section I covers power boilers and Section IV covers heating boilers; these construction rules are adopted by most jurisdictions as legal requirements.
- NBIC scope
- The National Board Inspection Code sets rules for in-service inspection, repair, and alteration of boilers and pressure vessels, including repair nameplate requirements.
- Lockout/tagout
- A procedure that isolates and locks all energy sources, verifies zero energy, and tags equipment before maintenance to prevent unexpected startup or release.
- Confined space entry
- Entry into a boiler requires atmospheric testing, ventilation, an attendant outside, a permit, and isolation from steam, water, fuel, and electrical energy.
- Hydrostatic test
- A pressure test with water, usually at 1.5 times maximum allowable working pressure for new construction, held to reveal leaks and deformation.
- Ultrasonic thickness testing
- A nondestructive method using sound waves to measure remaining wall thickness and estimate corrosion or erosion loss in tubes and shells.
- 4-20 mA loop
- An analog instrumentation standard where 4 mA is zero, 20 mA is full scale, and a current below 4 mA indicates a broken wire or fault.
- PID control action
- Proportional action responds to error, integral action removes offset, and derivative action responds to rate of change but amplifies signal noise.