Hard suction hose
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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 A fire hose (or firehose) is a high-pressure hose that carries water or other fire retardant (such as foam) to a fire to extinguish it. Outdoors, it attaches either to a fire engine, fire hydrant, or a portable fire pump. Indoors, it can perma ...
used in drafting operations, when a
fire engine A fire engine (also known in some places as a fire truck or fire lorry) is a road vehicle (usually a truck) that functions as a firefighting apparatus. The primary purposes of a fire engine include transporting firefighters and water to an i ...
uses a vacuum to draw water from a
portable water tank A portable water tank is a temporary collapsible tank designed for the reserve storage of water in firefighting, emergency relief, and military applications. These tanks can be either supported or unsupported. The supported tanks have a steel or a ...
, pool, or other static water source. It is built to withstand vacuum, rather than pressure, abrasion, and heat. Conversely, hard suction is capable of withstanding up to 200 PSIG, as well as vacuum. In the United States, it is standard equipment according to the
National Fire Protection Association The National Fire Protection Association (NFPA) is an international nonprofit organization devoted to eliminating death, injury, property and economic loss due to fire, electrical and related hazards. As of 2018, the NFPA claims to have 50,000 mem ...
standards for fire engines. It is used in both structural and wildland firefighting throughout the world, and is made in various diameters and connection types.


Usage

Flexible suction hose, also known as a suction hose, is a specific type of rigid
fire hose A fire hose (or firehose) is a high-pressure hose that carries water or other fire retardant (such as foam) to a fire to extinguish it. Outdoors, it attaches either to a fire engine, fire hydrant, or a portable fire pump. Indoors, it can perma ...
used in drafting operations. When using this technique, the
fire engine A fire engine (also known in some places as a fire truck or fire lorry) is a road vehicle (usually a truck) that functions as a firefighting apparatus. The primary purposes of a fire engine include transporting firefighters and water to an i ...
draws water for fire fighting from an unpressurized supply, such as a
portable water tank A portable water tank is a temporary collapsible tank designed for the reserve storage of water in firefighting, emergency relief, and military applications. These tanks can be either supported or unsupported. The supported tanks have a steel or a ...
, pool, or other static water source, instead of drawing water from a pressurized water supply, such as a
fire 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 ...
. Under complete vacuum conditions, a pump would lift water , however pumps on fire apparatus are not capable of producing a perfect/ total vacuum. Due to this limitation and
friction loss The term friction loss (or frictional loss) has a number of different meanings, depending on its context. * In fluid flow it is the head loss that occurs in a containment such as a pipe or duct due to the effect of the fluid's viscosity near the ...
, fire services do not recommend attempting to lift water more than . Hard suction hose may also be used to connect a fire engine to a hydrant, due to its ability to handle both vacuum and pressure. This practice is common in Australia, but woven jacket fire hose is normally used for this purpose in the United States. Using hard suction hose in this manner requires that the fire engine be positioned carefully for the limited flexibility of the hose, and may require multiple firefighters due to the weight and bulk of the hose section. The use of flexible suction in this capacity is both ineffective and hazardous, as the hose and couplings may experience catastrophic failure. In certain circumstances, it may be possible to use hard suction hose to draft from a hydrant with adequate water supply but a low flow rate. Flexible suctions are built to withstand
vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often dis ...
, rather than water pressure, abrasion, and heat. They are, therefore, constructed differently from the standard fire hose and have different end fittings. In the United States, they are standard equipment according to the
National Fire Protection Association The National Fire Protection Association (NFPA) is an international nonprofit organization devoted to eliminating death, injury, property and economic loss due to fire, electrical and related hazards. As of 2018, the NFPA claims to have 50,000 mem ...
standards for fire engines. Since neither hard suction nor flexible suction hose can be folded, it is typically mounted on the side of a fire engine, often opposite ground ladders. Such hose is used in both structural and wildland firefighting throughout the world. Hard suction hose can also be used to extend the range of a
water tender A water tender is a type of firefighting apparatus that specialises in the transport of water from a water source to a fire scene.fire hose A fire hose (or firehose) is a high-pressure hose that carries water or other fire retardant (such as foam) to a fire to extinguish it. Outdoors, it attaches either to a fire engine, fire hydrant, or a portable fire pump. Indoors, it can perma ...
in both its construction and usage: #Hard suction generally has a black opaque wrapped or laminated outer jacket surrounding a flat stock coil spring core. The inner and outer linings provide maximum rigidity, allowing it to be used up to 200 PSIG pressure as well as under vacuum. Flex suction is less rigid and generally corrugated in profile. Often, such hose is manufactured using molded clear or translucent synthetic material (such as PVC) shaped into a series of rings. Construction methods include heat shrinking the material over round stock coil spring core. This shape allows the hose to be somewhat flexible, without allowing it to collapse on itself under
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 ...
, as a normal, woven-jacket fire hose would. #It uses suction gaskets. Gaskets in standard fire hose ("pressure gaskets") are designed to minimize the water leaking out between couplings. The gaskets connecting hard suction hose sections, pump, and strainer must instead prevent air from entering at the coupling, since that would spoil the vacuum and allow air into the pump intake. Large diameter ( or greater) hard suctions most often employ National Standard threaded brass connections while flex suction hose will typically use
Storz Storz is a type of hose coupling invented by Carl August Guido Storz in 1882 and patented in Switzerland in 1890, and patented in the U.S. in 1893 that connects using interlocking hooks and flanges. It was first specified in standard FEN 301-31 ...
fittings, which are
genderless Genderless may refer to: *Agender, an identity for people who do not identify with any gender *Gender-neutral pronoun, a pronoun not associated with a particular gender *Genderless fashion in Japan, a Japanese fashion subculture *Genderless langua ...
. or smaller hard suction hose will typically use threaded fittings. In each case, the hard suction hose connection will match the fittings of the pump intake and supply hose, so that hard suction hose can be used in place of supply hose as appropriate. #It is short. Typically, suction hose comes in lengths, while fire hose comes in lengths. Since a fire engine's pump only produces a
partial vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often dis ...
, it is only recommended for lifting water or less. For this reason, and because each junction is an opportunity for a crack or imperfect seal to spoil the vacuum, it is rare to see many sections of hard suction hose connected together. #It is not designed for use in fire streams. The airtight nature of hard suction hose, necessary for drafting, renders the hose unsuitable for the high pressure water flow needed to spray a pressurized stream of water on a fire. Thus, suction hose is tested for the ability to "prevent collapse under vacuum conditions" rather than its ability to function as an attack hoseline. Hard suction hose predates steam or gas powered fire engines and has been available since at least 1888, sometimes referred to as "spiral suction hose". Modern apparatus are commonly equipped with flexible suction as opposed to hard suction, due to the relative ease of use associated with flexibility, as well as the increasing rarity of employing suction hoses to pressurized water sources.


Diameter

Suction hose comes in multiple sizes, from in diameter. Large diameter hose are carried on full-size fire engines, but smaller diameters of hard suction hose can be carried on apparatus with smaller fire pump ratings, such as
wildland fire engine A wildland fire engine is a fire engine specifically designed to assist in fighting wildfires by transporting firefighters to the scene and providing them with access to the fire, along with water or other equipment. Most commonly used by the Unit ...
s. In the United States,
NFPA 1901 NFPA 1901, the ''Standard for Automotive Fire Apparatus'', is published by the National Fire Protection Association The National Fire Protection Association (NFPA) is an international nonprofit organization devoted to eliminating death, injury, p ...
requires engines to have suction hose that matches the engine's pump rating. For example, an engine with a per minute pump is required to carry or larger hose, while a wildland fire engine will typically carry hard suction hose. The United Kingdom, has a standardised range of metric hose diameters: 7, 9, 12.5 and 15 cm (2.8, 3.5, 4.9 and 5.9 in), with the two smallest diameters sometimes used twinned to provide adequate flow rates.HM Fire Service Inspectorate (2001). Chapter 7: "Pre-Planning" in: ''Fire Service Manual, Volume 1, Fire Service Technology, Equipment and Media: Hydraulics, Pump and Water Supplies''. London: the Stationery Office. . Within this range, the hoses are fitted with "Instantaneous Couplings"; the hoses have
Storz Storz is a type of hose coupling invented by Carl August Guido Storz in 1882 and patented in Switzerland in 1890, and patented in the U.S. in 1893 that connects using interlocking hooks and flanges. It was first specified in standard FEN 301-31 ...
couplings; and the hose comes in two types, one with "Instantaneous Couplings" and one with Storz fittings. Fire Service Manuals provide tables of maximum volumetric flow rates for a given pump pressure, hose diameter and total hose length. The use of these tables, is to facilitate the selection of suitable hoses, taking into account the frictional losses caused by transporting water through the strainer, hoses, pump and fire fighting nozzles, to draft water from source to the fireground.


Strainers

When being used in a drafting operation from a pool, portable water tank, or other uncovered water source, the length of suction hose farthest from the pump is usually attached to a strainer, to keep foreign objects in the water from being pulled into and damaging the pump. If used in a pond, stream, or other body of water, an appropriate flotation device must be used to keep the strainer below the surface and above the bottom, so that neither mud nor air are sucked into the fire engine's pump. Industry accepted standard is to maintain two feet of distance from the water's surface, bottom, or any other obstruction. The United Kingdom official guidance is to:HM Fire Service Inspectorate (2001). Chapter 6: "Pump Operation and the Distribution of Water on the Fireground" in: ''Fire Service Manual, Volume 1, Fire Service Technology, Equipment and Media: Hydraulics, Pump and Water Supplies''. London: the Stationery Office. . * use ropes to take to the weight of the hose and the strainer, in order to avoid putting sideways loadings on the couplings; * ensure that the strainer is a minimum of three strainer-diameters below the water surface to prevent air
cavitation Cavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, cal ...
; * to support the hose with packing, where necessary, when it crosses a wall or other obstruction to prevent an air pocket being formed.


References


External links


Strainer pressure drop calculator
Calculate pressure drop across a strainer. Firefighting equipment Hoses de:Feuerwehrschlauch#Saugschläuche {{good article