Hard Suction Hose - Characteristics and Construction

Characteristics and Construction

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

1. It is rigid and generally scalloped. Often, such hose is manufactured using molded synthetic material (such as PVC) shaped into a series of rings. This shape allows the hose to be somewhat flexible, without allowing it to collapse in 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. Large diameter (4-inch (10 cm) or greater) hard suction hose will typically use Storz fittings, which are genderless. 3-inch (7.6 cm) 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, hard suction hose comes in 10 feet (3.0 m) lengths, while fire hose comes in 50 and 100 feet (15 and 30 m) lengths. Since a fire engine's pump only produces a partial vacuum, it is only recommended for lifting water 3 metres (9.8 ft) 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. 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, hard 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".