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. Q=K*P ½. Q = The Flow [gpm] P = The Pressure [psi] K = A constant Coefficient [gpm/psi ½ ]. Q= V* P ½. 5.6 gpm/psi½ ≤ V ≤ 28gpm/psi½

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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

The Theory and Practice of Variable Orifice in Automatic Sprinklers VOS

Fire Protection Engineering Ltd

Ralph R Mehr D.Sc. PE


Q k p

Q=K*P½

Q = The Flow [gpm]

P = The Pressure [psi]

K = A constant Coefficient [gpm/psi½]


Q v p

Q=V*P½

5.6 gpm/psi½ ≤V≤ 28gpm/psi½

7 psi ≤P≤ 175 psi


V a p b

V=a*Pb

V=2.12*P1/2

Q=2.12*P


The size of v as a function of the pressure p

The size of V as a function of the Pressure P


V performance compare to k

V performance compare to K


Add on device stand by position maximum pressure

Add-on Devicestand-by position maximum pressure


Special sprinkler stand by position maximum pressure

Special Sprinklerstand-by position maximum pressure


Insert to a large sprinkler the insert stand by maximum

Insert to a Large SprinklerThe Insert stand-by maximum


Final conclusions

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.


Recommendations for additional research

Recommendations for additional research

Determination of the optimal function of V in the basic equation (Q=V*P½) 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.


Thank you fire protection engineering ltd

Thank you Fire Protection Engineering Ltd

For more information or a copy of the research

please send an e-mail to [email protected]


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