- MVWS System Definition: An MVWS system is a fire protection technology that sprays water at a medium velocity to control or extinguish fires in industrial environments.
- Applications: MVWS systems are crucial for safeguarding areas with lighter oils and flammable liquids, as well as various critical plant rooms and galleries.
- Operational Mechanics: The operation of an MVWS system is triggered by fire detection, activating deluge valves to spray water and control the spread of fire.
- Design Specifics: The design of MVWS systems involves a network of nozzles and pipes, configured to spray water effectively over the protected area.
- Comparison with HVWS: Unlike HVWS systems, MVWS systems are designed for lighter oils and are less intensive, avoiding emulsification and focusing on cooling and containment.
An MVWS system (short for a Medium Velocity Water Spray System) is a water-based fire protection system of open sprayers and a deluge valve. It cools surfaces and controls burning on light-oil and conveyor hazards, including Indian thermal power plants.
MVWS sprayers throw a slower cone of medium-size droplets than HVWS projectors. IS 15325 uses that spray on flammable liquids with flash points below 65 C (150 F), where a high-velocity jet cannot form a stable oil-in-water emulsion.
The same sprayers also wet nearby steel and vessels so radiated heat from a fire elsewhere does not heat those surfaces to ignition.
MVWS System Applications
Medium velocity water spray systems are commonly used to protect a lot of equipment within a plant, including:
- Cable gallery and cable spreader room in the main plant area
- ESP control room
- Switchyard room
- Ash handling plant area
- Coal handling plant area
- Water treatment plant area
- Circulating water pump area
- Seawater intake area
- Fuel oil pump house
- Coal conveyor galleries in tunnels, underground and above ground
- Coal transfer points and junction towers
- Crusher house
- Emergency DG Building
- Fuel oil pump house (loading and unloading areas)
- Fuel oil storage tanks
Difference Between High Velocity and Medium Velocity Water Spray System
A High Velocity Water Spray (HVWS) system uses projector nozzles that throw a faster, coarser jet than MVWS sprayers.
Higher nozzle velocity does not make HVWS the right system for every oil fire. IS 15325 picks HVWS or MVWS from flash point and whether an emulsion can form.
HVWS systems protect equipment that holds heavy or medium oils: oil-type circuit breakers and transformers, diesel engines, fuel-oil tanks, turbo-alternator lube-oil skids and oil-fired boilers.
The high-velocity jet forms a coarse cone that can reach the burning oil through the flame. Turbulence then mixes oil into water on the surface, making an emulsion that will not burn. Cooling and steam blanketing add to that emulsification.
IS 15325 flash-point split used on this page:
- Medium-velocity water spray systems control fires in lighter oils, LPG and other flammable liquids with flash points typically below 65 C (150 F) per IS 15325.
- High-velocity water spray systems are installed to extinguish fires involving heavy or medium oils, and other flammable liquids with flash points typically above 65 C (150 F).
MVWS System Design Requirements
Indian insured plants write MVWS to TAC, with IS 15325 as the BIS water-spray code. Open sprayers with deflectors set the cone angle over the protected surface.
Those sprayers discharge a cone of medium-size droplets. A deluge valve, tripped by an electric solenoid when detection releases the priming pressure, floods the open-nozzle pipework.
Cable galleries and coal conveyors are split into zones so one fire does not flood the whole length. Each zone has its own deluge valve.
A fire detection system trips the deluge valve for that zone. This TAC sheet also opens the deluge valves of the zones on either side.
MVWS System for Cable Galleries
Cable galleries have several rows and tiers of trays. Each row has its own distribution header and spray nozzles.
Drop pipes from each header cover all tray tiers. Detection on this sheet is addressable multi-sensor heads plus digital linear heat-sensing cable.
The deluge valve then opens so the sprayers wet the trays. Water cools the cables and limits air at the burning surface; it does not replace electrical isolation or a checked water duration.
This TAC sheet asks 12.2 lpm/m2 on cable-gallery surfaces and at least 2.8 bar at the hydraulically most remote nozzle. IS 15325:2020 instead uses 10.2 lpm/m2 of exposed cable-rack area, at least 2.1 bar at the remote sprayer and not more than 3.5 bar. Use the adopted code, not both figures at once.
MVWS System in Mining
MVWS covers the top and return coal belts plus junction towers, transfer towers and crusher houses. Linear heat-sensing cable and infrared ember detectors trip the deluge valves electrically.
Top-belt sprayers sit on the conveyor centreline. Return-belt sprayers sit on both sides at 4 m spacing on this sheet and are staggered. Route pipe so walkways stay clear. IS 15325 spaces ceiling sprayers at not more than 4 m above each belt.
This TAC sheet and IS 15325 both use 10.2 lpm/m2 on the exposed conveyor surface. Remote-sprayer pressure is at least 1.4 bar; the hydraulically favourable sprayer stays at or below 3.5 bar.
MVWS System for Fuel Oil Pump House and EDG Buildings
The fuel-oil pump house and emergency diesel-generator building are each one MVWS zone on this sheet. Roof-level sprayers feed from a deluge valve.
Quartzoid-bulb detectors trip the deluge valve in the pump house and EDG building. Probe-type heat detectors watch the fuel-oil storage tanks.
This TAC sheet asks 10.2 lpm/m2 on the fuel-oil pump house and EDG building. It names both 1.4 bar and 2.8 bar as remote-nozzle minima; that pair is not one IS 15325 rule. Confirm which occupancy uses which residual pressure on the project calculation.
This TAC sheet uses 3 lpm/m2 on the fuel-oil tank shell. IS 15325 vessel cooling is often 10.2 lpm/m2 of exposed area, so treat that tank figure as this specification, not a universal density.
