Gas installations: the path of gas
A building can use city gas (natural gas, piped, mainly methane, lighter than air) or LPG (liquid petroleum gas in cylinders or a tank, heavier than air). Piped gas follows a path:
- Main: street pipe at higher pressure.
- Service pipe into the building.
- Regulator: lowers pressure to a safe, steady value.
- Meter: counts the gas used.
- Indoor pipe and valves: carry gas to appliances such as stove, geyser and heater.
Pipes are made of steel, copper or approved flexible hose. Joints must be gas-tight.
Gas safety
Gas can burn or explode, and burning in a closed room can make poisonous carbon monoxide. So we need:
- Gas-leak alarm: placed high for natural gas (it rises) and low for LPG (it sinks).
- Automatic shut-off valve: closes when the alarm senses gas.
- Ventilation: fresh air in the kitchen.
- Flame-failure device: stops the gas if the flame goes out.
If you smell gas: do not touch switches or flames, open windows, close the valve and leave.
Communication installations
A building needs links for telephone, internet, TV, intercom and alarms. The path of data is:
- Outside cable: often optical fibre. Light pulses travel in a glass thread. It is fast and not hurt by electrical noise.
- Entry box (converter) where the cable enters.
- Router or switch: sends data to the right device.
- Inside cabling: twisted-pair LAN cable (Cat 6) or Wi-Fi to rooms.
Planners also add a TV antenna or cable, an intercom and PA (public address) speakers in big buildings. Communication cables are kept away from power cables to avoid noise.
Speed and capacity
Speed is measured in bits per second. 8 bits make 1 byte. Time to send a file = file size in bits ÷ speed. Gas capacity is measured in cubic metres per hour; a stove burner uses far less than a water heater, so the pipe size and the regulator are chosen from the total of all appliances.
Try it: trace the lines
At home, find where the gas pipe or LPG cylinder is and where the internet wire enters. Draw each path on paper. Predict: where is the gas valve? Then check. Look for the leak alarm and the router.
Key formulas and definitions
- Gas path: Main → Regulator → Meter → Appliance
- Energy from gas (MJ) = volume (m³) × calorific value (MJ/m³)
- Data time (s) = file size (bits) ÷ speed (bits/s); 1 byte = 8 bits
- Natural gas alarm: high on the wall; LPG alarm: low near floor
- Data path: Fibre → Entry box → Router → Rooms
Worked examples
1. Name the part that lowers gas pressure.
The regulator.
2. A stove burns 0.5 m³ of natural gas (40 MJ/m³). How much energy?
0.5 × 40 = 20 MJ.
3. Where do you fix a leak alarm for LPG?
Low, near the floor, because LPG is heavier than air and sinks.
4. A file of 800 MB goes at 100 Mbit/s. How long?
800 MB = 800 × 8 = 6,400 Mbit. 6,400 ÷ 100 = 64 s.
5. Why is optical fibre better than a copper wire for long distance?
Light pulses lose little energy, carry a lot of data and are not affected by electrical noise.
6. A kitchen has a 4 MJ/h burner and a 24 MJ/h water heater. Total demand per hour?
4 + 24 = 28 MJ/h. The regulator and pipe must handle this.
Common mistakes
- Putting an LPG alarm high on the wall. LPG sinks.
- Checking a leak with a flame. Use soap water.
- Running communication cables right next to power cables.
- Mixing up Mbit (bits) and MB (bytes): 1 MB = 8 Mbit.