NIULPE 4th Class cheat sheet

Boiler definition: a closed vessel in which water or other liquid is heated under pressure by direct application of heat from combustion or other energy source.

Safety valve setting must not exceed the maximum allowable working pressure (MAWP) of the boiler; the valve is set at or below MAWP and is the final overpressure protection.

A safety valve on a steam boiler must have a relieving capacity sufficient to discharge all steam the boiler can generate without pressure rising more than 6% above the set pressure (ASME Section I rule).

Try cocks are used on low-pressure and small steam boilers to verify water level; they are not a substitute for a gauge glass.

Gauge glass (water column) shows the water level; the lowest visible reading must remain above the lowest permissible water level specified on the boiler nameplate.

Blowdown of the gauge glass and water column verifies that connections are clear; the procedure is open drain, close drain, and confirm water returns to the glass.

Boiler fittings include: safety valve, steam gauge, gauge glass, water column, fusible plug, blowoff valve, feed check valve, and low-water cutout.

Fusible plugs are installed in firebox crowns of some firetube boilers; the plug's alloy melts at a set temperature to warn of low water and overheating.

A steam gauge is protected by a siphon (pigtail) that condenses steam so the Bourdon tube sees water, not live steam.

Combustion requires fuel, oxygen, heat, and an ignition source (the fire tetrahedron adds uninhibited chemical chain reaction).

The three T's of combustion: temperature, turbulence, and time - all must be adequate for complete combustion.

Theoretical (stoichiometric) air is the minimum air needed for complete combustion; excess air is supplied to ensure complete burning and is expressed as a percentage of theoretical.

Typical excess air: about 15% for gas, about 15-20% for oil, and 20-40% for coal or solid fuels; too little excess air produces CO and smoke.

Flue gas CO2 or O2 analyzers indicate excess air; high CO2 (low O2) means little excess air, low CO2 (high O2) means excessive air and stack loss.

Low-water fuel cutoff (LWCO) must be tested and the burner locked out on low water; it is a required safety control on steam and hot water boilers.

Flame safeguard (flame scanner) proves flame during the trial-for-ignition period; loss of flame signal must shut off the fuel within the safety shutoff time.

Pre-purge and post-purge: the furnace must be purged with air before ignition to prevent explosion from accumulated fuel; typical pre-purge is a set time at a set airflow.

A modulating burner varies firing rate with load; a high-low-low-off burner fires at fixed rates and cycles on load demand.

Boiler efficiency losses include dry flue gas loss, moisture loss, incomplete combustion loss, and radiation/convection loss; dry flue gas loss is usually largest.

ASME Section VIII governs unfired pressure vessels; Section I governs power boilers; Section IV governs heating boilers.

MAWP is the maximum allowable working pressure at which a vessel may operate at a given temperature; it is stamped on the vessel nameplate.

Hydrostatic test pressure for a new vessel is typically 1.5 times the MAWP (adjusted for temperature per the code), used to prove strength and tightness.

Safety relief valves protect pressure vessels; a relief valve is for liquid service, a safety valve for gas/vapor, and a safety relief valve serves both.

A rupture disc is a non-reclosing pressure relief device; it may be used alone or upstream of a relief valve.

Gate valves are for on-off isolation, globe valves for throttling, and check valves allow flow in one direction only.

Piping expansion must be accommodated by loops, offsets, or expansion joints; anchors and guides direct movement to the designed locations.

Steam traps remove condensate and air while holding back steam; common types are thermostatic, float-and-thermostatic, inverted bucket, and thermodynamic.

Relief valve discharge must be piped to a safe location and must not be blocked; drain lines on relief valve discharge are left open.

Centrifugal pumps are variable-flow, constant-head machines; the pump curve plots head versus capacity and the operating point is where it intersects the system curve.

Positive displacement pumps deliver a nearly constant flow regardless of pressure; a relief valve is required on their discharge.

Cavitation occurs when the absolute pressure at the pump suction falls below the liquid vapor pressure; symptoms are noise, vibration, and flow loss.

NPSH available must exceed NPSH required to avoid cavitation; NPSH is expressed in feet or meters of liquid head.

A centrifugal pump should be started with the discharge valve closed on a liquid system to reduce starting power, then the valve is opened.

Reciprocating compressors use valves and pistons; rotary screw compressors are common for plant air; centrifugal compressors are used for large flows.

Compressor intercoolers and aftercoolers reduce gas temperature and condense water; receivers store air and dampen pulsation.

Pump shaft seals include packing (with lantern ring for lubrication) and mechanical seals; packing must leak slightly to cool and lubricate.

Amp draw on a motor-driven pump indicates load; operating far to the right of the curve can overload the motor.

A one-pipe steam system feeds steam and returns condensate in the same pipe; a two-pipe system uses separate supply and return mains.

Steam mains slope in the direction of flow (typically 1/4 inch per 10 feet) so condensate drains to traps or returns.

Radiators in steam systems are vented by air vents; a stuck-open vent causes steam to escape and the radiator to overheat.

A Hartford loop prevents water from leaving the boiler through the return when the boiler water level drops, protecting the boiler from low water.

A condensate return pump or boiler feed pump returns condensate to the boiler; a feedwater regulator maintains the water level.

Hot water systems are forced circulation (circulator pump) or gravity; the circulator is placed on the supply or return per design, with expansion tank connection at the point of no pressure change.

An expansion tank absorbs the volume change of heated water; a diaphragm tank separates air from water to prevent waterlogging.

Air in a hot water system causes noise and poor circulation; air vents, air separators, and proper fill pressure remove it.

Outdoor reset controls lower the supply water temperature as outdoor temperature rises, improving efficiency and comfort.

The vapor-compression cycle: compression, condensation, expansion, and evaporation; the refrigerant absorbs heat in the evaporator and rejects heat in the condenser.

Refrigerant pressure-temperature relationship: for a given refrigerant, saturation pressure corresponds to saturation temperature; superheat is temperature above saturation at the same pressure.

Superheat is measured at the evaporator outlet; subcooling is measured at the condenser outlet.

The metering device (TXV, orifice, or capillary tube) drops refrigerant pressure from condensing to evaporating pressure.

A TXV maintains constant superheat at the evaporator outlet; a restricted or failed valve causes low suction pressure and high superheat.

Refrigerant safety groups (ASHRAE 34): A1 low toxicity/no flame propagation, B1 higher toxicity, A2/A3 flammable; ammonia is B2.

Ammonia (R-717) is toxic and flammable at high concentrations; it is detected by its pungent odor and by electronic detectors.

Refrigerant recovery is required before opening a system; venting refrigerant to the atmosphere is prohibited under EPA Section 608 rules.

Psychrometrics: dry-bulb is the air temperature, wet-bulb reflects evaporative cooling, and dew point is the temperature at which condensation begins.

Relative humidity is the ratio of actual water vapor to the maximum the air can hold at that temperature; cooling below dew point causes condensation.

Ohm's law: V = I x R; power: P = V x I (watts), and for three-phase, P = 1.732 x V x I x power factor.

A series circuit has one current path; a parallel circuit has multiple paths and the same voltage across each branch.

Motor overload protection protects the motor from sustained overcurrent; short-circuit protection (fuses or breakers) clears faults.

A magnetic starter uses a contactor and overload relay; a holding contact keeps the coil energized after the start button is released.

Lockout/tagout isolates energy before maintenance; verify de-energization with a meter and test the meter on a known source first.

A ground fault circuit interrupter (GFCI) trips at a small current imbalance (typically 5 mA) to protect people.

Control voltage is commonly 120 V or 24 V; low-voltage thermostats switch a relay or contactor coil.

A flame scanner uses ultraviolet or infrared detection; a photoelectric cell or lead sulfide cell may be used for oil or gas flames.

Electrical schematics show ladder logic with the hot leg on one side and neutral on the other; the load is drawn on the right side of the rung.

Scale forms when dissolved minerals (calcium and magnesium) precipitate on hot surfaces; it insulates and causes overheating and tube failure.

Hardness is measured in grains per gallon (gpg) or ppm as CaCO3; 1 gpg = 17.1 ppm.

Water softeners exchange calcium and magnesium for sodium using ion exchange resin and are regenerated with brine.

pH measures acidity/alkalinity on a 0-14 scale; boiler water is typically maintained alkaline (about pH 10-11) to limit corrosion.

Corrosion in boilers is often caused by dissolved oxygen; oxygen scavengers such as sodium sulfite or hydrazine remove it.

Blowdown controls dissolved solids (TDS); continuous surface blowdown removes dissolved solids, bottom blowdown removes sludge.

The chloride or conductivity test indicates TDS; blowdown rate is adjusted to keep TDS within limits.

Caustic embrittlement (stress corrosion cracking) occurs in highly stressed areas with concentrated caustic; controlled alkalinity and phosphate treatment reduce risk.

Carryover of boiler water into steam causes priming and foaming; causes include high TDS, high alkalinity, and oil contamination.

Natural gas is mostly methane (CH4); its heating value is about 1,000 Btu per cubic foot.

Fuel oil grades: No. 2 (light heating oil), No. 4, No. 5, and No. 6 (heavy residual); heavier oils require preheating for atomization.

Atomization breaks oil into fine droplets so it can mix with air and burn; methods include pressure, air, and steam atomizing.

Flash point is the lowest temperature at which a fuel gives off enough vapor to ignite momentarily; it is a fire-safety property.

Stoichiometric combustion of methane: CH4 + 2 O2 -> CO2 + 2 H2O; each volume of methane needs two volumes of oxygen.

Smoke density (Bacharach) measures unburned carbon in flue gas; high smoke means poor atomization or insufficient air.

NOx formation is reduced by low excess air, flue gas recirculation, low-NOx burners, and staged combustion.

Stack draft is produced by the difference between hot flue gas and cooler outside air; a taller stack increases natural draft.

Sulfur in fuel forms SO2 and SO3; SO3 combines with moisture to form sulfuric acid, causing cold-end corrosion and acid smut.

ASME Boiler and Pressure Vessel Code: Section I (power boilers), Section II (materials), Section IV (heating boilers), Section VIII (pressure vessels), Section IX (welding).

NBIC (National Board Inspection Code) covers repairs, alterations, and inservice inspection; the National Board stamp (R) is used for repairs.

A boiler must have a nameplate showing MAWP, heating surface, capacity, and manufacturer; operating above MAWP is prohibited.

Periodic boiler inspections are required by jurisdiction; internal inspection requires the boiler to be cooled, drained, and isolated with lockout/tagout.

Confined space entry requires testing for oxygen (19.5-23.5%), flammable gas, and toxic gas before entry, plus an attendant and permit.

Hot work permits are required for welding, cutting, and grinding outside a designated area; a fire watch is posted during and after hot work.

The employer must provide training and PPE; the operator must know emergency shutdown procedures and the location of fuel shutoffs.

Safety valves must be tested and are sealed or locked; only authorized personnel may change the setting, and the seal must be replaced after testing.

An accident or near miss must be reported and investigated; documentation supports code compliance and insurance requirements.