Alarm check valve—A clapper valve that opens a system’s water supply when one or more sprinkler heads operate. It also directs water to activate alarm devices.

Illustrations courtesy of the National Fire Sprinkler Association

Figure 1. Single riser with alarm check valveFigure 2. Single riser with water flow alarm

Check valve—A valve in the run of a pipe that allows water flow in only one direction.

Clapper—A swing check valve inside a connection that swings in the direction of system supply. It permits the use of additional inlets after the system is charged.

Downstream—Toward the output side of a protection system.

Draw-down—The reduction of available water flow and pressure for a fixed suppression system when hydrants attached to the same water main are being used.

Fire department connection—A

dry pipe that’s connected to a fixed suppression system at one end and has one or more female swivel couplings at the other end. FDCs are used to augment and in some cases to supply standpipe and sprinkler systems; they’re mandatory on the former and recommended on the latter.

Flow alarm—An electrical or mechanical device that transmits a local or supervised alarm, or both, when water flow in a system reaches a predetermined level.

Frost break—Dry piping inside a protected structure that links a fire department connection to a supply riser. Not less than four feet long, it prevents frost from forming between the fire department connection and the riser.

Open stem and yoke valve—A valve with a protruding stem that indicates at a glance whether the valve is open or closed.

Out of round—(In reference to a male or female coupling) Misshapen in a way that renders the coupling incapable of being connected.

Pipe schedule—A sprinkler system design chart that sets forth a maximum number of heads that can be fed by pipe of a specific size.

Post indicator valve (PIV)—A manual shutoff valve for sprinkler and standpipe systems which is located above the ground and outside of the protected structure.

Riser—The supply piping to floor outlets on standpipe systems or the vertical supply piping to all or a portion of a sprinkler system.

Steamer—The large outlet on a public fire hydrant.

Thrust blocks—Concrete or stone slabs used as underground piping supports to prevent movement of the pipe as water flows through.

Upstream—Toward the supply side of a protection system.

Wall post valve—A post indicator valve located on a wall.

Yard hydrant—A standpipe outlet in an open area which appears as a hydrant and is designed for handline use only. The term also refers to horizontal standpipe systems.

Zone—An area protected by a single sprinkler system.

Figure 3. Single riser with dry pipe valveFigure 4. Multiple riser system




Alloy—A blend of polymers and/ or copolymers.

Blow molding—Forming hot plastic into the desired shape by injecting air into the molten plastic to force it against the interior of a mold.

Cast or casting—Pouring molten or liquid plastic into a mold or onto a moving belt and then solidifying by heat.

Compound—A mixture of resin and the additives necessary to give the resin the properties required of the finished part.

Copolymer—Where two chemically different monomers are polymerized together.

Extrusion—The process whereby a shape is imparted to a plastic material by forcing the molten mass through a die.

Oade of plastic—The same polymer may be made to have significantly different properties by altering the polymerization process and/or additives included during polymerization.

Injection molding—Forming plastic parts by forcing molten plastic into a mold by use of a ram or screw.

Laminate—Two or more layers of materials are bonded together either by use of heat and/or pressure, and sometimes adhesive.

Molecule—The smallest particle of a compound that can still be identified as the compound.

Plasticizer—A material added to a plastic or compound to make it more flexible.

Pyrolysis—Transformation of a compound into one or more other substances by heat alone. It is often the initial step in combustion of solids.

Resin—Usually a pure polymer in powder or pelletized form.

Service temperature—The temperature range in which a plastic part is designed to retain its integrity and strength.