BC Gas Fitter ARD flashcards
BC Gas Fitter ARD · Build recall with a focused review session.
31 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Water column pressure unit
- Gas appliance pressures are measured in inches of water column; one psi equals about 27.7 in. w.c., so natural gas manifold pressure near 3.5 in. w.c. is a small fraction of line pressure.
- Clock meter formula
- Input BTU per hour equals 3600 divided by seconds per revolution, multiplied by cubic feet per revolution and by the gas heating value; used to verify actual appliance input.
- Sediment trap purpose
- A drip leg at the appliance connection traps scale and debris before it reaches the gas valve; built as a tee with a capped nipple extending downward below the inlet.
- Propane orifice sizing
- Propane delivers roughly 2,500 BTU per cubic foot versus about 1,000 for natural gas, so propane orifices are smaller because less volume is needed for the same heat output.
- Combustion air rule
- A confined space needs 50 cubic feet per 1,000 BTU/h input and two openings sized 1 square inch per 1,000 BTU/h to an unconfined space, or 1 per 2,000 direct to outdoors.
- Yellow sooting flame
- A yellow, sooting flame tip signals insufficient primary air, a blocked orifice, or excessive gas pressure; a properly adjusted natural gas flame is blue with a slight yellow tip.
- Gas leak test pressure
- Piping is tested at the greater of 10 in. w.c. or 1.5 times working pressure for a duration long enough to show no drop; soap solution or electronic detectors are used, never flame.
- Ohm's law and power
- Voltage equals current times resistance, and power equals voltage times current; these forms let you solve for current draw, resistance, or wattage in a control circuit.
- Bonding gas piping
- Gas piping must be bonded to the electrical grounding system so it cannot become a difference in potential, but it may never serve as a grounding electrode or neutral conductor.
- Flame rectification principle
- A flame conducts current in one direction between sensor and burner, producing a microamp DC signal; the control module reads that signal to prove flame is present.
- 24 volt control transformer
- A transformer steps line voltage down to 24 volts for thermostats and gas valves; a shorted low-voltage circuit usually opens the transformer's integral fuse or board fuse.
- Run capacitor function
- A run capacitor shifts phase in a permanent split capacitor motor; a failed capacitor causes the motor to hum, draw high current, and overheat instead of reaching speed.
- Wire size and breaker
- Copper conductors must have ampacity at least equal to the overcurrent device: 14 AWG for 15 amps, 12 AWG for 20 amps, and 10 AWG for 30 amps.
- Class 2 separation
- Low-voltage thermostat and control conductors must be kept separate from line-voltage conductors unless the insulation rating and physical separation rules are satisfied.
- Neutral versus ground bar
- The white grounded conductor terminates on the neutral bar and the green or bare equipment grounding conductor on the ground bar; reversing polarity can energize an appliance chassis.
- T and P relief setting
- A water heater temperature and pressure relief valve opens at 150 psi or 210 degrees Fahrenheit; its discharge must terminate within 6 inches of the floor or outside, untrapped.
- Thermal expansion tank
- A closed water system with a check valve or pressure reducing valve needs an expansion tank; without it, heated water expands and the relief valve weeps.
- Air gap backflow protection
- An air gap provides the highest protection against backflow because it physically separates the potable supply from the fixture; an RPZ assembly is next, then a double check.
- Drain slope rule
- Drain pipe 2 inches and smaller is installed at 1/4 inch per foot, while 3 inch and larger may use 1/8 inch per foot; a vent must rise 6 inches before offsetting.
- Fixture unit conversion
- A private water closet counts 2.5 fixture units, a public one 3, and a lavatory 1; total fixture units are converted to pipe size using the demand tables.
- Water hammer arrestor
- A water hammer arrestor absorbs the pressure surge from quick-closing valves; an air chamber must be sized to the system and located near the fixture group it protects.
- Water heater vent connector
- A gas water heater needs a draft hood and a vent connector pitched at least 1/4 inch per foot toward the chimney, with clearance to combustibles per the listing.
- Boiler backflow protection
- A cross connection between potable water and a heating boiler is prevented by a backflow preventer or a double-wall heat exchanger, keeping boiler water out of the supply.
- Saturated steam temperature
- Saturated steam at 0 psig is 212 degrees Fahrenheit; at 15 psig it is about 250 degrees, following the saturation curve rather than the superheat tables.
- Steam trap function
- A steam trap discharges condensate and noncondensable gas while holding back steam; thermostatic, float-and-thermostatic, and inverted bucket types respond to different conditions.
- Steam main pitch
- Steam mains pitch in the direction of flow at 1/8 inch per foot for low pressure and 1/4 inch per foot for high pressure, with drip pockets at low points and before risers.
- Hartford loop purpose
- A Hartford loop ties the equalizer and return together near the boiler waterline to keep the boiler water level from dropping to an unsafe point.
- Steam safety valve
- A steam boiler safety valve is set at or below the maximum allowable working pressure and discharges to atmosphere with no valve or restriction downstream.
- Steam quality meaning
- Steam quality is the mass fraction of vapor in a steam-water mixture; wet steam carries entrained droplets that cause water hammer and erosion, so separators and traps dry it.
- Thermal expansion formula
- Change in length equals original length times the expansion coefficient times temperature change; carbon steel at about 6.5 times ten to the minus six per degree Fahrenheit grows 1.6 inches per 100 feet over 200 degrees.
- Water hammer cause
- Water hammer in steam systems comes from slug flow of condensate moving at high velocity; it is corrected with proper pitch, working traps, and slow-opening valves, not higher pressure.