SAQCC Gas LPG Commercial/Industrial flashcards

31 cards. Read the term and the definition here. The deck at the top of this page is optional.

LPG vapour density relative to air

LPG vapour is about 1.5 to 2 times denser than air, so leaks sink and accumulate at low points, drains and pits. Ventilation and gas detection must therefore be at low level.

Maximum LPG cylinder fill

Cylinders are filled to roughly 80 to 85 percent of liquid volume, leaving a vapour space. This allows for thermal expansion of liquid LPG, which expands about 0.3 percent per degree Celsius.

Propane versus butane cold performance

Commercial propane remains usable to about minus 40 degrees Celsius, while commercial butane stops vapourising near 0 degrees Celsius. Winter blends are propane-enriched for cold conditions.

LPG lower explosive limit

LPG has a lower explosive limit near 2 percent by volume and an upper limit near 10 percent. Odourisation allows detection at roughly one-fifth of the LEL.

Two-stage LPG regulator pressures

A first-stage regulator reduces cylinder pressure to about 1 to 2 bar. A second-stage regulator then delivers about 28 to 37 mbar to commercial appliances.

LPG cylinder relief valve function

Cylinder relief valves protect against overpressure from fire exposure and are typically set around 15 to 17 bar for propane. They discharge vapour, not liquid.

LPG mass to gas volume

One kilogram of liquid propane yields roughly 0.5 cubic metres of vapour at standard conditions. A 48 kg cylinder therefore holds about 24 cubic metres of gas.

LPG leak detection placement

Because LPG vapour is heavier than air, fixed detectors are mounted near floor level, and low-level ventilation openings are required in cylinder rooms and plant areas.

Natural gas main constituent

Natural gas is typically 85 to 95 percent methane, giving it a relative density near 0.6. Being lighter than air, it rises and disperses, so detectors are mounted high.

Methane explosive range

Methane has a lower explosive limit of about 5 percent and an upper limit of about 15 percent by volume. Combustion is only possible within this band in air.

Methane stoichiometric air ratio

Complete combustion of methane needs about 9.5 volumes of air per volume of gas, roughly 10:1. Insufficient primary air produces carbon monoxide and sooting.

Natural gas calorific value

Typical natural gas gross calorific value is about 38 to 42 megajoules per cubic metre. This figure is used for appliance rating and gas billing calculations.

Natural gas odourisation level

Natural gas is odourised with mercaptan or tetrahydrothiophene so it is smellable at about 1 percent by volume, well below the 5 percent lower explosive limit.

Low-pressure gas pipe pressure drop

Low-pressure natural gas pipework is sized so pressure drop does not exceed about 1 millibar on domestic and commercial runs, with gas velocity kept below roughly 20 to 25 metres per second.

Gas installation leak test

New pipework is strength and leak tested with air or inert gas at about 1.5 times working pressure, held for a defined period. Testing with gas or oxygen is prohibited.

Carbon monoxide from gas appliances

Incomplete combustion produces carbon monoxide. Yellow lazy flames, sooting and flue CO above roughly 20 to 30 parts per million indicate inadequate primary air or a blocked flue.

Natural gas detector mounting height

Methane is lighter than air, so fixed gas detectors and high-level ventilation openings are positioned near the ceiling or roof of the plant room.

R410A composition and pressure

R410A is a 50/50 blend of R32 and R125 and operates at roughly 1.6 times the pressure of R22. Only R410A-rated gauges and hoses may be used.

Refrigerant safety group codes

ASHRAE groups refrigerants by toxicity and flammability: A1 low toxicity and no flame propagation, A2L mildly flammable, A3 highly flammable such as propane, B2L toxic and flammable such as ammonia.

Superheat diagnostic meaning

Superheat is evaporator outlet temperature minus saturation temperature, typically 5 to 8 kelvin. Low superheat suggests overcharge; high superheat suggests undercharge or a restriction.

Subcooling diagnostic meaning

Subcooling is saturation temperature minus liquid line temperature, typically 5 to 10 kelvin. Excessive subcooling indicates overcharge; low subcooling indicates undercharge or flash gas.

Zeotropic blend glide

Blends such as R407C have a temperature glide, so bubble and dew points differ. Charging and leak checking must reference the correct point on the pressure-temperature chart.

Flammable refrigerant charge limit

R290 propane systems are restricted to small charges, typically under 150 grams per circuit for domestic units, and require no ignition sources in the occupied space.

Refrigerant ODP and GWP values

R12 has an ozone depletion potential of 1.0, R22 about 0.055, and HFCs such as R410A zero. Global warming potential: R410A about 2088, R32 about 675, R290 about 3.

Recovery cylinder filling limit

Recovered refrigerant goes into dedicated recovery cylinders, never disposable or unmarked vessels, and cylinders must not be filled above 80 percent liquid volume.

Evacuation micron level

Systems are evacuated to below about 500 microns before charging. Moisture left in the circuit forms acid and ice at the metering device, so a filter-drier is fitted.

Oxygen cylinder identification

In South African and ISO practice, industrial oxygen cylinders are black with a white shoulder, while medical oxygen cylinders are white. Valve thread and shoulder stamping remain the authoritative identifiers.

Acetylene withdrawal rate limit

Acetylene cylinders contain a porous mass and acetone. Maximum safe withdrawal is about one-seventh of cylinder contents per hour, and outlet pressure must never exceed 1.5 bar gauge.

Oxygen handling hazard

Oxygen is an oxidiser, not a fuel, but it greatly accelerates combustion. Oil or grease on oxygen fittings can ignite, so only oxygen-clean equipment may be used.

Cylinder hydrostatic test interval

Compressed gas cylinders undergo periodic hydrostatic testing, commonly every 5 to 10 years depending on gas and standard, and are stamped with the next test date.

Cylinder gas content calculation

Free gas content equals water capacity multiplied by fill pressure. A 50 litre cylinder at 200 bar holds roughly 10,000 litres of gas at atmospheric pressure.