Flow Testing Terminology
Apparatus — A vehicle designed to assist in fighting fires. Also known as fire trucks, fire engines, water tenders and water tankers.
Authority Having Jurisdiction (AHJ) — An organization, office or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation or a procedure.
Bernoulli’s Principle — States that a rise (fall) in pressure in a flowing fluid must always be accompanied by a decrease (increase) in the speed of the fluid. Also see Venturi Effect.
Chlorine — An oxidizer used to kill bacteria in drinking water and pools.
Coefficient — Coefficient of discharge or roughness coefficient. A number multiplied with a variable or an unknown quantity.
Conventional Flushing — The practice of opening one or more fire hydrants and allowing water to run until discharge water appears clean. This method does not guarantee removal of sediment or scouring of pipe. Unidirectional flushing is a more deliberate process used for a higher level of cleaning.
Dechlorination — Process of neutralizing the chlorine in discharge water. The standard for dechlorination is AWWA C655-09 Field Dechlorination.
Extrapolate — To infer or estimate by extending or projecting known information. With flow testing, the known information is static pressure and residual pressure at a known test flow-rate. The inference or estimation is flow-rate available at a specified residual pressure psi.
FM Approved — An approval by Factory Mutual, an internationally recognized testing facility that certifies fire-prevention products meet the highest standards.
Fire Flow Testing — A test performed to gather information needed to predict fire flow-rates at specific residual pressures. It measures the water supply at a given location.
Flow Device — Equipment used for measuring flow-rate in flow testing, main flushing or pump testing.
Flow Hydrant — In a fire flow test, the hydrant that flows water and measures the test flow-rate.
Flushing — The procedure of cleaning the inside of a water main by moving large amounts of water through a hydrant or fire pump.
Flushing Velocity — The speed at which water travels through a main while flushing.
Friction Loss — The resulting resistance as water moves along the inside wall of hose, mains, pipe or hose fittings. Friction loss increases exponentially as the flow-rate of water through the hose increases. Friction loss is also influenced by the diameter of hose, hose length and the inside jacket material.
Gauge Cap — A hydrant cap with a threaded opening for attaching a gauge and drain-cock at the end for relieving air pressure. The gauge cap measures static pressure and residual pressure during a fire flow test.
GPM — Gallons per minute. Describes the rate at which water flows.
Hazen-Williams Formula — Formula which relates the flow of water in a pipe with the physical properties of the pipe and the pressure drop caused by friction. It is used in the design of water pipe systems, such as fire sprinkler systems, water supply networks and irrigation systems. It is named after Allen Hazen and Gardner Stewart Williams.
Hydrant Nozzle — A hydrant nozzle is any of the openings to which the fire department would attach hose. The exterior thread connection is a specific thread spec, such as NH, NST or Storz.
Hydrant Capacity Test — A single-hydrant fire flow test procedure that evaluates the water supply available from the hydrant. In this test, the residual hydrant is the same as the flow hydrant.
Main — Refers to a water-distribution main, an underground piping network.
Main Capacity Test — A flow test involving two or more hydrants to evaluate the water supply available at the fire main at the point of the residual hydrant.
Main Flushing — The procedure of cleaning the inside of a water main by moving large amounts of water through a hydrant or fire pump.
NH — National Hose thread, the most common thread type found on fire hydrants, test headers and standpipes in the United States. (Also called NST — National Standard Thread.)
Nozzle Pressure — Internal pressure measured from the Pitotless NozzleTM.
Playpipe — A nozzle with 21⁄2″ inlet diameter x 30″-long pipe with a 13⁄4″ or 11⁄8″ outlet. Commonly called Underwriter’s Playpipe. It is UL® Listed for flow-rate measurement when used with the 11⁄8″ tip and a hand-held pitot. It is not known to be approved by any independent testing laboratory in the 13⁄4″ size. A hand-held pitot and gauge are used to measure the velocity pressure.
Pitot — Regionally pronounced pee-toe or pit-tot. A pressure- measuring instrument used to measure fluid flow velocity. It is as an integral component of the 21⁄2″ Hose Monster®, with or without FM Nozzle Inserts. A hand-held pitot is also used with a pressure gauge to determine flow-rates through hydrant nozzles or other flow devices.
The pitot was invented by Italian-born French engineer Henri Pitot in the early 1700s and modified to its modern form in the mid- 1800s by French scientist Henry Darcy. It is also used in aviation to determine air speed.
Pitot Formula — Theoretical discharge through circular orifices: Q = 29.84 x QP x D2 x C
Where Q = flow-rate in GPM P = pitot pressure in psi D = orifice diameter in inches C = coefficient of flow device
Pitot Pressure — The pressure measured at the pitot in a fire flow or fire pump test. Pitot pressure and velocity pressure can sometimes be used interchangeably.
Pitotless Nozzle™— A specialty nozzle that is FM Approved for flow-rate measurements. No pitot is used. The pressure of the internal nozzle diameter is measured and corresponds to exact water flow-rates. Used in testing fire pumps and for hydrant flow testing.
Predicted Flow — The flow-rate predicted at a given residual pressure, usually 20 psi since most firefighters will bring the system pressure to this threshold when fighting a fire. A fire flow test measures static pressure, residual pressure and test flow-rate. These measurements are used to extrapolate predicted flow. The formula for determining predicted flow can be found in NFPA 291, 184.108.40.206, 2010:
Q = Q x h 0.54 / h 0.54 RFrf
QR = flow predicted at desired residual pressure QF = total flow measured during test hr = pressure drop to desired residual pressure hf = pressure drop measured during test psi — Pounds per square inch. A unit of pressure. Pumper Port — Also known as steamer port. It is the 4″ or 41⁄2″
port on a hydrant.
Rated Capacity — In fire flow testing, it is the water supply available at a specified residual pressure (usually 20 psi). In fire pump testing, it describes the rated output of the fire pump in terms of a flow-rate such as GPM.
Residual Hydrant — Also known as Test Hydrant. In a fire flow test, this hydrant measures static and residual pressures. Test results apply to this hydrant.
Residual Pressure — The pressure residing in the water-distribution system when flowing in a fire flow test or any other actual flowing condition.
Rooftop Standpipe Testing — The procedure for testing the water supply of a standpipe at the roof level of a building.
Standpipe — Standpipe is a fire-protection system in high-rise buildings that provides water to fire hose stations.
Static Pressure — Water-distribution system pressure at zero test flow.
Steamer Port — Also known as the pumper port, the 4″ or 41⁄2″ outlet of a hydrant.
Test Flow-Rate — The flow-rate of water that is discharged in a fire flow or fire pump test.
Test Hydrant — Also known as Residual Hydrant. In a fire flow test, this hydrant measures static and residual pressures. Test results apply to this hydrant.
Unidirectional Flushing — The procedure for moving water at high velocity one direction through a single segment of pipe. Closing specified valves in the water distribution system increases the velocity of water. When the pipe diameter and the discharge flow-rate are known, the flushing velocity can be determined.
UL® — Underwriters Laboratory, an internationally recognized testing laboratory.
Valve Exercising — The process of closing and opening a valve until it is determined to be mechanically sound.
Velocity Pressure — The pressure measured at the pitot or nozzle in a fire flow or fire pump test. Pitot pressure and velocity pressure can sometimes be used interchangeably.
Venturi Effect — The reduction in fluid pressure that results when a fluid flows through a constricted section of pipe. The effect holds true for the Pitotless Nozzle. As water flows through the Pitotless Nozzle, water speed increases and pressure decreases.