- Hydraulic calculation
- A method of proving a sprinkler system can deliver the required density over its design area, adding friction and elevation losses along the pipe. The result is compared with a flow test of the water supply to see whether the supply is enough.
- Light hazard
- A sprinkler design class for spaces with little burnable material, such as offices and guest rooms. It carries the lowest design density and the widest allowed coverage per sprinkler, which affects both pipe size and the number of heads.
- Quick-response sprinkler
- A sprinkler with a small, fast-reacting heat element that opens sooner than a standard unit. Some settings, such as clean rooms and light hazard areas, call for it, so the head type is part of both design and parts selection.
- K-factor
- A constant describing how much water a sprinkler discharges relative to the square root of the pressure behind it. A larger K delivers more water at the same pressure, which is why hydraulic calculations start with it.
- Preaction system
- A system whose piping is dry until a detection device signals a fire, after which water enters the pipe and discharges only where sprinklers open. It is chosen for water-sensitive spaces such as data rooms and archives.
- Double interlock
- A preaction arrangement that needs both a detection signal and a sprinkler opening, shown by air pressure loss, before water enters the pipe. It adds protection against accidental discharge.
- Deluge system
- A system whose sprinklers or nozzles are open, on dry pipe, so a detection signal opens the deluge valve and water flows from all of them at once. It suits fast-spreading hazards like fuel handling or aircraft hangars.
- Dry-pipe valve
- A valve that holds water back with compressed air in the pipe. When a sprinkler opens, air pressure falls and the valve trips, so the system works in unheated spaces where wet pipe would freeze.
- Fire department connection
- The inlet on a building's exterior where fire apparatus can pump extra water into sprinkler or standpipe piping. It must be visible, unobstructed, facing the street side and tied into the system in the correct place.
- Standpipe
- A vertical pipe with hose connections at each floor that gives firefighters, and sometimes occupants, a water source inside the building. Classes differ by who uses the hose and how it is connected.
- Churn pressure
- The pressure a fire pump develops when its discharge is closed and no water flows. It is the first point on the pump's performance curve and is checked during acceptance and routine testing.
- Tamper switch
- A supervisory switch on a control valve that signals when the valve is moved away from fully open. It prevents a closed valve from being forgotten, which would leave a sprinkler system unable to deliver water.
- Main drain test
- Opening the main drain valve at a riser and watching how much the static pressure drops. Comparing results over time can reveal a partly closed valve or a blocked supply before a fire exposes the problem.
- Inspector's test connection
- A valve and orifice at the far end of a wet system that imitate the flow of one open sprinkler. Opening it confirms that the waterflow alarm sounds and that the signal reaches the monitoring panel.
- Hose stream allowance
- Extra water demand added to the sprinkler demand to account for firefighters using hoses. A building's water supply must cover the total, so the allowance affects the size of mains, pumps and tanks.
- Required fire flow
- The rate of water, at a stated residual pressure, that a supply must provide to fight a fire in a given building. It rises with building area and combustible construction, and sprinklers can reduce the figure.
- Wet chemical system
- A kitchen hood suppression system that sprays a liquid agent which turns grease into a soapy layer and cools the appliance. It also shuts off fuel and power to the cooking equipment as it discharges.
- Hydraulic design information sign
- A permanent placard at the control valve of a hydraulically designed system listing its design density, area, flow, pressure and hose allowance. The installing contractor attaches it so later users can see what the system was built to do.
- Sway bracing
- Bracing that keeps sprinkler pipe from swinging during an earthquake. Fasteners, brace pipe and attachment points are specified, and some quick fastening methods are prohibited in higher seismic design categories.
- Thrust block
- Concrete poured against solid ground behind a bend, tee or hydrant branch in an underground main. It carries the force of the water into the soil, and it must be in place, and cured, before the main is pressure tested.
