Definitions and Names of Hydrant Components
Taken from AWWA Manual M17
Base. A part that provides a lateral connection to the hydrant lead and directs the flow vertically upward into the lower barrel. Also called shoe, bottom, boot, elbow, bury
Bonnet. A part that attaches to the top of the nozzle section and encloses the support portions of the operating mechanism. It may be integral with the nozzle section. Also called cap, cover
Breakable barrel coupling. A coupling used to fasten the upper barrel to the lower barrel. It is designed to break if stressed severely, should a vehicle strike the hydrant.
Breakable bolt. Bolts used to fasten the upper barrel to the lower barrel. Breakable bolts are designed to break if stressed severely, should a vehicle strike the hydrant.
Breakable flange. A part that bolts to a mating flange at a joint between the hydrant upper and lower barrels, which is located immediately above the ground line. It is designed to break if stressed severely, should a vehicle strike the hydrant.Also called breakaway flange, traffic flange.
Direction to open. The direction in which the operating nut is rotated to open the hydrant; open left is counterclockwise when viewed from above and open right is clockwise.
Drain outlet. The opening in the base through which water escapes to the ground when the drain valve is open.
Drain valve. A valve located at or adjacent to the valve seat ring. The drain valve opens automatically when the main valve is closed; this allows water to drain from the barrel into the ground. In like fashion, the drain valve closes automatically when the main valve is being opened, the drain valve closes completely after only one to five turns of the operating nut.
Dry top. A compression type hydrant in which the operating mechanism at the top of the hydrant is sealed from the barrel so that water does not come into contact with the mechanism during hydrant use.
Frangible stem coupling. A stem coupling designed to break if it is stressed severely, should a vehicle strike the hydrant. Also called breakable coupling.
Gate. A part that supports the main valve. It is moved, first horizontally and then vertically, to open or close the main valve opening in a slide gate hydrant.
Gland bushing. A part that is used to line a gland.
Hose outlet nozzle. An outlet nozzle that has an opening that is 3 in. or smaller in diameter, and is suitable for attachment of a fire hose.
Lower barrel. A part that extends from the base to the ground line, enclosing the stem. The lower barrel conducts water from the base to the upper portion of the hydrant.
Lower valve plate. A part that is positioned below that main valve and clamps the main valve against the upper valve plate.
Main valve. A part made of rubber or some similar resilient material; the main valve is forced against a seat to form a watertight seal when the hydrant is closed. Also called valve, valve rubber, valve ball rubber, valve seat, valve gasket, valve disc.
Main valve opening. The inside diameter of the valve seat ring.
Nozzle section. A part that extends upward from the barrel and contains the outlet nozzles. It may be integral with the upper barrel.
Operating nut. An external hydrant part that is turned by a hydrant wrench in order to rotate the stem nut or stem; it may be integral with the stem nut or stem.
Outlet nozzle. The outlet nozzle is secured in the nozzle section and has an opening through which water can be discharged. The outlet nozzle is threaded or otherwise formed to permit attachment of a fire hose connection.
Outlet nozzle cap. A cap that is attached to an outlet nozzle and covers the nozzle opening. The cap is furnished with a nut or other means to permit the application of force adequate to firmly attach it to or remove it from the outlet nozzle.
Packing gland. A part that compresses packing rings in a stuffing box.
Packing plate.. A part that partitions the interior of the hydrant and contains or supports a stuffing box or other means of sealing one compartment from another. Also called seal plate, support ring
Pumper outlet nozzle. An outlet nozzle with an opening of at least 3.5 in. in diameter, suitable for attachment of a fire hose. Also called steamer nozzle, steamer connection
Seat-ring insert. A part with internal threads that is secured and sealed to the hydrant base. The internal threads engage with the external threads on the valve seat ring. The seat ring insert may also serve as a part of the drain system. Also called drain ring, retainer ring, insert ring.
Stem. A part of the operating mechanism that extends down to the main valve assembly and moves the main valve to close or open the hydrant. The stem is often in two parts, particularly in a traffic model: the upper stem and the lower stem. Also called upper rod, lower rod.
Stem coupling. A part that joins the portions of a two part stem. Also called a rod coupling.
Stem nut. A part that is internally threaded and engages with threads on the stem so that when the part is rotated, or when the stem is rotated and the stem nut is stationary, the stem is raised or lowered to move the valve. Also called operating nut, operating stem nut, revolving nut.
Stop nut. A part that is permanently threaded or otherwise attached to the stem and limits the vertical travel of the stem. Also called stem stop, travel stop nut.
Stuffing box. A cylindrical cavity that surrounds the stem and contains a number of packing rings used to prevent leakage along the stem. The stuffing box may be an individual component or a portion of another component. Also called packing box
Traffic model. A hydrant designed and constructed so that if it is struck by a vehicle, certain easily replaceable components will break and allow the upper portion (above the ground line) to become detached from the lower portion (below the ground line) . The below ground line section will remain intact and undamaged.
Upper barrel. A part that extends from the lower barrel at the ground line to the nozzle section, enclosing the stem. It may be integral with the nozzle section.
Upper valve plate. A support for the main valve, positioned above the valve. The upper valve plate may also serve as the portion of the drain valve that is moved when the stem rotates. It may also serve as the means to prevent rotation of the valve, stem ad associated parts.
Valve seat ring. A part threaded into and sealed to the hydrant base (or associated part adjacent to the base). The main valve is forced against the valve seat ring to close the hydrant.
Weather shield. A part that forms a skirt above and surrounding the opening in the hydrant top through which the stem, stem nut, or operating nut protrudes. It may be integral with the operating nut. also called the weather cap.
Wet top. A compression type hydrant in which the operating mechanism at the top of the hydrant is not sealed from the water when the hydrant is opened.
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