Power Eng 4th Class 4B key terms

A spring-loaded pressure relief device that opens automatically to discharge steam or water when boiler pressure exceeds the set point, protecting the vessel from overpressure and reseating when pressure drops.

A small manually operated valve on the boiler drum or water column used to confirm that water is present at a specific level, commonly checked at low and high gauge glass limits.

A transparent tube or flat glass assembly connected to the boiler drum that shows the actual water level, allowing the operator to verify level and detect a blocked or falsely reading level control.

A safety control that senses boiler water level and shuts off the burner when the level falls below a safe minimum, preventing overheating and possible furnace explosion or vessel damage.

A test performed on a boiler safety valve to confirm that the valve can discharge all steam the boiler can generate without pressure rising more than a permitted percentage above the maximum allowable working pressure.

The air supplied to a burner beyond the theoretical amount needed for complete combustion, expressed as a percentage; enough is required to burn all fuel, but too much lowers efficiency by carrying heat up the stack.

Measurement of oxygen, carbon dioxide, carbon monoxide, and temperature in the exhaust gas, used to calculate combustion efficiency and to adjust burner air and fuel settings for safe, economical operation.

The exact quantity of air theoretically required to burn a given amount of fuel completely, with no oxygen or combustible left over; actual burners operate above this value to ensure complete combustion.

A fan located after the boiler that pulls combustion gases through the furnace and heat-transfer sections, maintaining a negative furnace pressure and exhausting products to the stack.

The slight negative pressure maintained inside a boiler furnace, measured in inches of water, which keeps hot gases from escaping and pulls combustion air in through the burner.

A sensor, such as an ultraviolet or infrared detector, that proves a burner flame is present; loss of its signal triggers a fuel trip to prevent unburned fuel from accumulating and exploding.

A measure of a water sample's ability to carry electric current, used to estimate dissolved solids in boiler water and to control blowdown so that concentration stays within limits.

The controlled removal of boiler water, either from the bottom to clear sludge or from the surface to reduce dissolved solids, keeping water chemistry within limits and preventing carryover.

A vessel that heats feedwater with steam to drive off dissolved oxygen and other gases, reducing corrosion in the boiler and downstream piping; it often also serves as the feedwater storage tank.

Oxygen gas present in feedwater, which causes pitting corrosion in boiler metal; it is removed by deaeration and chemical scavengers such as sodium sulfite or hydrazine.

A pump that uses a rotating impeller to impart kinetic energy to liquid, converting it to pressure in the casing; it is the most common type for boiler feedwater and general plant service.

The formation and collapse of vapor bubbles in a pump when local pressure drops below the liquid's vapor pressure, causing noise, vibration, reduced flow, and eventual damage to the impeller.

The absolute pressure at a pump suction, above the liquid vapor pressure, that is available or required to keep liquid from vaporizing; insufficient margin leads to cavitation.

A device that automatically discharges condensate and non-condensable gases from steam lines while retaining live steam, maintaining heat transfer and preventing water hammer.

A pressure surge caused by sudden stopping or reversing of liquid flow, or by slugs of condensate driven through piping, producing loud bangs and possible pipe or fitting failure.

A valve that allows flow in one direction only and closes automatically when flow reverses, protecting pumps, compressors, and piping from backflow and reverse rotation.

A graph relating dry-bulb temperature, wet-bulb temperature, humidity ratio, relative humidity, and enthalpy of moist air, used to analyze heating, cooling, humidifying, and dehumidifying processes.

The ratio of the water vapor actually present in air to the maximum amount the air could hold at the same temperature, expressed as a percentage and indicating how close the air is to saturation.

A heat exchanger in an air-handling unit through which refrigerant or chilled water flows to remove sensible and latent heat from air passing over its fins, cooling and often dehumidifying it.

A fluid that absorbs heat as it evaporates at low pressure and releases heat as it condenses at high pressure, circulating in a refrigeration system to move heat from a cold space to a warmer one.

The amount by which a refrigerant's temperature exceeds its saturation temperature at a given pressure; measured at the evaporator outlet, it confirms that liquid has fully boiled off before reaching the compressor.

A machine that raises the pressure of a gas or vapor by reducing its volume, used in refrigeration to compress refrigerant vapor and in plants to supply instrument or service air.

A procedure for isolating energy sources and attaching locks and tags before maintenance, ensuring equipment cannot be started or energized while personnel are working on it.

A protective device that quickly interrupts a circuit when it detects current leaking to ground, reducing the risk of electric shock to personnel using portable or wet-location equipment.

An instrument that applies a high direct voltage to measure insulation resistance of motors, cables, and windings in megohms, revealing moisture, dirt, or deterioration before failure occurs.

The range of controlled variable over which a controller's output changes from fully open to fully closed; a narrow band gives more sensitive but potentially cycling response, while a wide band gives smoother, slower control.

A field device that senses a variable such as pressure, temperature, or flow and converts it into a standard electrical or pneumatic signal for transmission to a controller or indicator.

A valve fitted with an actuator that positions its plug in response to a controller signal, regulating flow of steam, water, or fuel to maintain a process variable at set point.

An internal combustion engine in which fuel is injected into high-temperature compressed air and ignites without a spark; often used for standby generator drive in plants.

A device that senses engine or turbine speed and adjusts fuel or steam admission to hold speed nearly constant as load changes, enabling stable generator frequency.

The controlled procedure for entering a tank, vessel, or pit with limited openings and poor ventilation, requiring atmospheric testing, a permit, an attendant, and rescue provisions before entry.

The highest pressure at which a boiler or pressure vessel may legally operate, established by its design, materials, and thickness, and marked on the nameplate and safety valve setting.

The ratio of a burner's or compressor's maximum output to its minimum stable output, indicating how far it can be throttled while still operating safely and efficiently.

A value expressing how readily heat passes between a fluid and a surface per unit area and temperature difference; fouling or poor flow lowers it and reduces boiler or exchanger performance.