The domestic blowtorch, shown here, utilizes disposable bottled-gas cartridges. For use, the gas cartridge is first fitted into the cartridge holder. The valve unit is then screwed into the cartridge holder, the pin it contains piercing the gas cartridge. When the needle valve is opened by turning the control knob, gas is allowed to pass through the filter to the burner head. As the gas flows through the burner head, air is drawn through the holes provided, allowing a hot flame to be ignited outside the mouth of the burner head.
Often a variety of burner-head attachments are supplied, producing different flame configurations suitable for specific jobs.