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Fire-water spray nozzle selection sometimes becomes very challenging thus it mandates a little study. As the study prevails, specifically coverage area and water density requirement selection are vital for effective fire protection. Most of the cases open water spray nozzles are very effective to use. We can also select automatic nozzles as per system demand. But it should provide satisfactory performance with respect to activation time and distribution. Water spray nozzles are classified into 3 types as Low, Medium, and High Velocity.
Nozzle type selection
You should select Nozzle type and spray size with proper considerations like design density, discharge characteristics, ambient conditions, the physical characteristics of the hazard, material likely to be burning, and finally the design objectives of the system. The most manufacturer permits to place Water spray nozzles in any position and area. It may include hazardous locations with conforming their listing which is indeed necessary to obtain proper coverage of the protected area.
NOzzles Technicals Parameters
- The design density varies between 0.15 and 0.5 GPM/ft2 (6.1 to 20.4 L/min/m2) of the protected surface.
- Operating Pressure can vary from 1.4 bar to 7 bar based on types of Nozzle for effective application.
- With the change of design density, the Nozzle K factor changes consequently. Normally 22 (1.54 US) to 42 (2.94 US) is mostly used.
- Nozzle spray angle can be 75 deg to 120 deg.
Nozzle Positioning
The positioning of water spray nozzles depend on all the following factors:
- The shape and size of the protected area
- The nozzle design and characteristics of the water spray pattern
- The effect of wind and fire draft on very small drop sizes or on large drop sizes with a little initial velocity
- The potential to miss the target surface and increase water wastage
- The effects of nozzle orientation on coverage characteristics
- The potential for mechanical damage
electrical clearances from nozzle
All system components shall be located so as to maintain minimum electrical clearances from live parts. The electrical clearances in the following Table 6.1.2.2 (NFPA 15) shall apply to altitudes of 1000 m (3300 ft) or less. On the other hand, we should increase the electrical clearance at the rate of 1 percent for each 100 m (330 ft) increase in altitude above 1000 m (3300 ft). In case of unavailability of design information, we can use the highest minimum clearance listed for this group.
Information needed to select a Nozzle
- Maximum working pressure
- Effective working pressure
- End connection
- Material
- Spray angle
- K factor
- Finish type
- Certification
K factor and Spray angle are indeed the most important factors for selecting a fire water spray nozzle. For example, if you can share information like ‘K 26, 100 deg, 3/4 BSPT, brass finish’ with the supplier, you can hope to get the exact nozzle you need.
