Hard suction hose explained

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, 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 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

See main article: Drafting water. Flexible suction hose, also known as a suction hose, is a specific type of rigid fire hose used in drafting operations. When using this technique, the fire engine draws water for fire fighting from an unpressurized supply, such as a portable water tank, pool, or other static water source, instead of drawing water from a pressurized water supply, such as a fire hydrant. Under complete vacuum conditions, a pump would lift water 33.9feet, however pumps on fire apparatus are not capable of producing a perfect/ total vacuum. Due to this limitation and friction loss, fire services do not recommend attempting to lift water more than 3m (10feet).

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.[1] [2] 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.[3] 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.[4]

Flexible suctions are built to withstand vacuum, 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 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.[5] Such hose is used in both structural and wildland firefighting throughout the world.[6] [7]

Hard suction hose can also be used to extend the range of a water tender's dumping capability, if the fittings of the hard suction hose match those of the tender dumping water. This could be used to fill a portable dump tank not immediately adjacent to the water tender, from which another fire engine can draft. Since water movement during dumping relies on gravity, rather than mechanical pressurization, hard suction hose is useful for this task.[8]

Characteristics and construction

Suction hose differs from standard fire hose in both its construction and usage:

  1. 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.[9] 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, as a normal, woven-jacket fire hose would.
  2. 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.[10] Large diameter (4inches or greater) hard suctions most often employ National Standard threaded brass connections while flex suction hose will typically use Storz fittings, which are genderless. 3inches 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.
  3. It is short. Typically, suction hose comes in 10feet lengths, while fire hose comes in 50feetand100feetft (andft) lengths. Since a fire engine's pump only produces a partial vacuum, it is only recommended for lifting water 3m (10feet) 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.
  4. It is not designed for use in fire streams.[11] 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.[12] 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".[13] 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 2inchesto6inchesin (toin) 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 engines. In the United States, NFPA 1901 requires engines to have suction hose that matches the engine's pump rating.[14] For example, an engine with a 1000USgal per minute pump is required to carry 5inches or larger hose,[15] while a wildland fire engine will typically carry 2to hard suction hose.[16]

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.[17] Within this range, the 7cm (03inches) hoses are fitted with "Instantaneous Couplings"; the 12.5and hoses have Storz couplings; and the 9cm (04inches) hose comes in two types, one with "Instantaneous Couplings" and one with Storz fittings.[17] 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.[17]

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:[18]

External links

Notes and References

  1. Web site: GL 08 Hard Suction (Storz) connections. 2008. 2009-08-19. Fire & Emergency Services Authority of Western Australia.
  2. Web site: Fornell: Hydrant Hook-ups, Chicago Style . Fornell . Dave . 2013-01-14 . Firehouse . 2023-05-20.
  3. Book: Industrial Fire Brigade: Principles and Practice. International Association of Fire Chiefs. 492. 2007. Jones & Bartlett. 978-0-7637-3502-9. 2009-08-19.
  4. Web site: Lamm. Willis. Drafting From Low Pressure Hydrants. 2001. 2009-08-19. firehydrant.org.
  5. Book: Shapiro, Larry. Pumpers: Workhorse Fire Engines. 1999. MBI Publishing. 0-7603-0672-9. 2009-08-30. 25.
  6. Web site: Vehicle Mounted Pump - Godiva World Series WT2010 and WT4010. 2009-08-19. Hampshire Fire and Rescue Service. dead. https://web.archive.org/web/20110720231825/http://www.hantsfire.gov.uk/theservice/operations/equipmentdatasheets.htm?id=13238. 2011-07-20.
  7. Web site: Draft Number: DZ 4509, New Zealand Fire Service Firefighting Water Supplies Code of Practice . 2008-02-05 . 2009-08-19 . dead . https://web.archive.org/web/20100526022617/http://shop.standards.co.nz/drafts/DZ4509-DZ4509Publiccommentdraft.PDF . May 26, 2010 .
  8. Book: Eckman, William F.. The Fire Department Water Supply Handbook. 1994. PennWell Books. 0-912212-35-7. 285. 2008-08-10.
  9. Book: The Firefighter's Handbook: Essentials of Firefighting and Emergency Response. Delmar Publishers. 0-7668-0581-6. 2000. 209. registration. hard suction hose.. 2008-08-10.
  10. Web site: FAQ's. Jerome Fire Equipment Co., Inc.. 2008-08-06. dead. https://web.archive.org/web/20080513184114/http://www.jeromefire.com/faqs.htm. 2008-05-13. "Suction gaskets have a flap on the outer rim, facing the outside. The coupling torque to assemble mating suction couplings is higher so that these flaps on mating couplings are pressed together initially, sealing out the outside air, so that the draft can be started."
  11. Web site: Manual: LDH Hard Suction Hose. 2007-03-21. Task Force Tips. 2008-08-06.
  12. Web site: Report of the Committee on Fire Hose. 2001. Stacey. John W.. National Fire Protection Association. 2009-08-19. dead. https://web.archive.org/web/20110609072301/http://www.nfpa.org/assets/files/pdf/rop/1961-f2001-rop.pdf. 2011-06-09. "Positivepressure requirements for hard suction hose were deleted as using hard suction hose for positive pressures is not a practical application."
  13. Book: 177. The Goulds M'f'g. Co's. illustrated ...: catalogue and price list, of pumps, engines .... The Goulds Mfg. Co.. 1888. 2009-08-30.
  14. Book: Sturtevant, Thomas B.. Introduction to Fire Pump Operations. Thomas Delmar Learning. 2004. 0-7668-5452-3. 2008-08-10.
  15. Book: Mahoney, Gene . Introduction to Fire Apparatus and Equipment . PennWell Books . 1986 . 0-912212-12-8 . 2008-08-10.
  16. Web site: Glossary of Wildland Fire Terminology. National Wildfire Coordinating Group (NWCG). 2009-08-19.
  17. 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. .
  18. 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. .

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