What is a Medium Velocity Spray System?

An MVWS system (short for a Medium Velocity Water Spray System) is a water-based fire protection system. MVWS systems are used to provide cooling and/or control the burning in many large scale industrial applications, such as in thermal power plants.

As their name suggests, medium velocity water spray nozzles are designed to spray water at a medium velocity (i.e. the strength of the spray is weaker than HVWS systems). MVWS systems are best suited for protecting hazards involving light oils – where emulsification from high-velocity water sprayers (HVWS) is not possible.

When a fire occurs in another area of the plant, medium velocity sprayers are an effective method of protecting nearby structures from heat during a fire by providing a continuous cooling spray over the exposed surfaces.

MVWS System Applications

Medium velocity water spray systems are commonly used to protect a lot of equipment within a plant, including:

  1. Cable gallery and cable spreader room in the main plant area

  2. ESP control room

  3. Switchyard room

  4. Ash handling plant area

  5. Coal handling plant area

  6. Water treatment plant area

  7. Circulating water pump area

  8. Seawater intake area

  9. Fuel oil pump house

  10. All coal conveyor gallery in tunnels/underground and above ground

  11. Coal transfer points and junction towers

  12. Crusher house

  13. Emergency DG Building

  14. Fuel oil pump house (loading and unloading areas)

  15. Fuel oil storage tanks


FAQ's

A High Velocity Water Spray (HVWS) system is a water-based fire protection system that sprays water a high velocity – i.e. at a higher strength than a MVWS system.
You would be forgiven for thinking that a HVWS system is strictly better than a MVWS system since the water pressure is higher. But, this isn’t always the case.
HVWS systems are often used to protect equipment that incorporates heavy or medium oils. Equipment such as oil type circuit breakers and transformers, diesel engines and fuel oil storage tanks, turboalternator lube oil systems, and oil-fired boilers.

The high-velocity discharge water jet forms a cone of coarse spray of uniform density. This coarse spray is able to penetrate the flame zone and reach the surface of the burning oil. The turbulence created by the high velocity spray forms an oil-in-water emulsion on the surface of the oil that will not burn. This “emulsification” is the main way the fire is extinguished – along with the cooling and smothering effect.
So now the we understand what HVWS systems do, let’s summarise the main differences between MVWS vs HVWS systems:
Medium-velocity water spray systems are designed to control fires involving lighter oils, liquefied petroleum gases, and other flammable liquids with flash points typically below 650 C.
High-velocity water spray systems are installed to extinguish fires involving heavy or medium oils, and other flammable liquids with flash points typically above 650 C (1500 F)

Medium velocity water spray system design requirements are designed as per TAC regulations. The MVWS system shall consists of a network of open spray nozzles fitted with a special deflector to give required angle of discharge for the water around the area mentioned above.

The sprayers shall discharge a cone of water spray consisting of medium size droplets of water. The water supply to the MVWS system shall consist of a network of open spray nozzles fitted with a special deflector to give the required angle of discharge for the water around the area to be protected. The water supply to the MVWS system shall be controlled by a deluge valve which shall operate electrically actuated solenoid valve on the release of water pressure.

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