A draft is the use of suction to move a liquid such as water from a vessel or body of water below the intake of a

suction Suction is the colloquial term to describe the air pressure differential between areas. Removing air from a space results in a pressure differential. Suction pressure is therefore limited by external air pressure. Even a perfect vacuum cannot ...

pump A pump is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups according to the method they u ...

. A rural

fire department A fire department (American English) or fire brigade (Commonwealth English), also known as a fire authority, fire district, fire and rescue, or fire service in some areas, is an organization that provides fire prevention and fire suppression se ...

or farmer might draft water from a pond as the first step in moving the water elsewhere. A suction pump creates a partial vacuum (a "draft") and the

atmospheric pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, 7 ...

on the water's surface forces the water into the pump, usually via a rigid pipe (sometimes called a

dry hydrant A fire hydrant, waterplug, or firecock (archaic) is a connection point by which firefighters can tap into a water supply. It is a component of active fire protection. Underground fire hydrants have been used in Europe and Asia since at least ...

) or a semi-rigid

hard suction hose Flexible suction hose (Flex suction or suction hose), not to be confused with hard suction hose in U.S., is a specific type of fire hose used in drafting operations, when a fire engine uses a vacuum to draw water from a portable water tank, pool, ...

. Standard atmospheric pressure is 101 kPa (14.7 lbf/in²) and that can only raise water to a theoretical maximum of 10.3 metres (33.9 ft). Depending on application, fire department pumps lift water 6 to 10 metres (20 to 30 ft). To reduce drafting friction and obtain a larger flow or higher lift, a larger cross-section of suction hose is employed. For example, using a five-inch (127 mm) hose, a pump that could lift 500 US gallons per minute (30 L/s) up 23 feet (7 m) would only be able to lift the same amount of water 12.5 feet (4 m) through a 3.5-inch (76 mm) hose. Fire engines are often seen carrying two or three 10-foot (3 m) lengths of suction hose, but the longer the lift, the lower the flow, for a fixed-diameter suction hose and a given pump. Multiple relays could be used if the need arises, with a suction pump drafting up to 10 metres (30 ft) and discharging at great distances. It is also possible to use a gravity

siphon A siphon (from grc, σίφων, síphōn, "pipe, tube", also spelled nonetymologically syphon) is any of a wide variety of devices that involve the flow of liquids through tubes. In a narrower sense, the word refers particularly to a tube in a ...

to draft water for a small lift, and this technique is often used in

forest fire A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of Combustibility and flammability, combustible vegetation. Depending on the type of vegetation present, a wildfire ...

suppression, where portable

reservoirs A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including control ...

of 1,000 to 3,000 US gallons (5 to 10 m³) are filled with water and small hoses are used downhill of the tanks. The nozzle pressure is proportional to its distance below the reservoir surface. 100ft height change yields approximately 43 psi. The tank may itself be gravity-fed through hoses from a nearby water source, or by pumps or helicopters delivering water from further away.

References

{{DEFAULTSORT:Drafting Water Firefighting

See also

References