Hard suction hose

Hard suction hose (alternatively, suction hose) is a specific type of fire hose used in drafting operations, when a fire engine draws water from a portable water tank, pool, or other static water source. Hard suction hose differs from standard fire hose in several ways:

5" hard suction hose with Storz fittings, mounted on an engine It is rigid and often scalloped. Often, this is done by using some type of molded material, such as plastic, shaped into a series of rings. This shape allows the hose to be flexible, without causing it to collapse in on itself under suction, as a normal, woven-jacket fire hose would.

It is short. Typically, hard suction hose comes in 10 foot lengths, while fire hose comes in 50-100' lengths. Since a fire engine's pump only produces a partial vacuum, it can only lift water a few feet, rendering long lays of hard suction hose problematic.

It uses suction gaskets. Gaskets in normal fire hose ("pressure gaskets") are designed to minimize the water leaking out between hose couplings. The gaskets connecting hard suction hose sections, pump, and strainer must also prevent air from entering, since that would spoil the vacuum and allow air into the pump intake. "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."

It is not designed for use in fire streams. The airtight nature of hard suction hose, necessary for drafting, precludes the hose being able to endure high pressure water flow. Thus, hard suction hose is tested for the ability to "prevent collapse under vacuum conditions" rather than its ability to function as an attack hose line.

Hard suction hose comes in multiple sizes, from 2 1/2 to 6 inches 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 hard suction hose that matches the engine's pump rating. For example, an engine with a 1000 gallon per minute pump is required to carry 5" or larger hose.

When being used in a drafting operation, the length of hard suction hose farthest from the pump is usually attached to a strainer, to keep foreign objects from being pulled into and damaging the pump. If used in a pond, stream, or other body of water, an appropriate means, such as a flotation device, must be used to keep the strainer below the surface and above the bottom.

Дата добавления: 2014-12-27