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As can be seen in the figure above, a certain head, h, is required to overcome surface tension and form a water droplet. The graph above indicates this relationship between the height required to form the water droplet and the diameter of an orifice subject to the water head. Any value beneath of the line indicates that there is not sufficient head to form a water droplet, and no flow will occur. If the head subject to a set orifice size is above the line, there is adequate water height to cause flow.
The relationship shown in the graph above is represented by the formula:

{latex}$$
\Delta h = {{2\sigma } \over {\rho g{d \over 2}}} - {{2{d \over 2}} \over 3}
$${latex}

where:

{latex}$$\Delta h$${latex}

{latex}$$\sigma $${latex}

{latex}$$\rho $${latex}

$$d$$

{latex}$$d$${latex}

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