The Theory and Practice of Variable Orifice in Automatic Sprinklers VOS

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The Theory and Practice of Variable Orifice in
Automatic Sprinklers VOS

• Fire Protection Engineering Ltd
• Ralph R Mehr D.Sc. PE

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QKP½

• Q The Flow gpm
• P The Pressure psi
• K A constant Coefficient gpm/psi½

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QVP½

• 5.6 gpm/psi½ V 28gpm/psi½
• 7 psi P 175 psi

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VaPb

• V2.12P1/2
• Q2.12P

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The size of V as a function of the Pressure P
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V performance compare to K
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Add-on Device stand-by position
maximum pressure
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Special Sprinklerstand-by position
maximum pressure
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Insert to a Large SprinklerThe Insert
stand-by maximum
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Droplet Size Description Droplet Size Description Sprinkler Type
Low Pressure High Pressure Sprinkler Type
The ESFR barely had drops at this pressure. It was closer to a continuous drip of water at the center of the spray pattern with a small canopy at which the droplets were large, but with no thrust. The ESFR sprinkler had large drops but there was also a fair amount of mist that was created by the sprinkler as well. ESFR
The VOS had large drops that were also mixed with a little mist. There was quite obviously a better developed spray pattern, but the water in the center of the spray pattern was noticeably reduced. The VOS had smaller drops than the ESFR sprinkler, but the same amount of mist was created. VOS
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Spray Pattern Radius m (ft) Spray Pattern Radius m (ft) Sprinkler Type
Low Pressure High Pressure Sprinkler Type
1.30 (4.25) 4.04 (13.3) ESFR
2.19 (7.17) 4.36 (14.3) VOS
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Spray Pattern Spray Pattern Sprinkler Type
Low Pressure High Pressure Sprinkler Type
ESFR
VOS
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Final Conclusions

• The Variable Orifice Sprinkler can operate within
  a wide range of pressures.
• The Variable Orifice Sprinkler demonstrates a
  high degree of flexibility, and can operate at
  all kinds of hazard occupancies from light hazard
  to extra hazard and special hazard, including
  storage etc.
• As the first sprinklers deliver much more water,
  it is expected that fewer sprinklers will be
  needed to control or even to suppress the fire,
  as a result, less water might be needed and less
  water damage is expected.

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Recommendations for additional research

• Determination of the optimal function of V in the
  basic equation (QVP½) so that the first
  sprinklers will deliver the maximum possible
  water, while all sprinklers calculated will
  deliver a total amount of water, as required by
  the standard.
• As the insert type device seems to be the most
  cost effective, the insert should be designed to
  best comply with the optimal function of V.
• A full scale research to re-determine the minimum
  number of sprinklers needed for each occupancy
  hazard should be performed.
• Investigation to determine if the VOS fulfils the
  criteria of Quick Response Early Suppression
  sprinklers (QRES) as defined by the standard
  (Budnick Fleming) which may improve the Fire
  Protection Level with much less water.

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Thank you Fire Protection
Engineering Ltd
For more information or a copy
of the research please send
an e-mail to mehr_at_fpe.co.il