Water spray systems are operationally identical to a deluge system, but the piping and discharge nozzle spray patterns are designed to protect a uniquely configured hazard, usually being three dimensional components or equipment. The nozzles used may not be listed fire sprinklers, and are usually selected for a specific spray pattern to conform to the three dimensional nature of the hazard (e.g., typical spray patterns being oval, fan, full circle, narrow jet). The Two types of water spray system are :
High Velocity (HV) Waterspray
As the name implies, High Velocity nozzles discharge a jet of water at a high velocity and momentum.The internal design of this nozzle is such that the jet takes the form of a cone of coarse spray of uniform density.The coarse spray issued from this nozzle is desirable when used on fires involving heavy and medium oils, and similar products in order to penetrate the flame zone and so reach the surface of the burning oil or the rupture area of the equipment.The principal contributor of extinguishment on hazards of this type is the oil-in-water emulsion formed on the surface of the oil. Secondary assistance to extinguishment is given by the effects of vapour dilution, cooling and smothering.To provide adequately for the wide range of application requirements of water spray systems various types of nozzles have been developed, each differing in flow rates and discharge characteristics.
Medium Velocity Waterspray (MV)
Medium Velocity sprayers discharge water in the form of a spray of finely divided droplets at medium velocity. These sprayers utilise an external deflector to achieve the desired discharge angle and spray characteristics.Due to the discharge characteristics given by the medium velocity sprayer, the spray issued has a high heat absorption rate, making it ideal for the protection of hazards involving light oils where emulsification is not possible although unless applied as part of a foam system, it is generally not possible to extinguish flammable liquid fires with medium velocity (MV) waterspray systems.These same discharge characteristics are also desirable where controlled burning and/or exposure rotection is required.A number of types of medium velocity sprayers are available with various orifice sizes, each being available with varying discharge patterns.