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# Differential Pressure measurement

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As per Bernoulli’s equation, The pressure gauges mounted perpendicular to the flow of the fluid measures only the static pressure, Increase in CFM or volume flow rate (Velocity) will not impact the static pressure, it only impacts on the dynamic pressure. I wanted to know the impact of variation in CFM or volume flow rate on the differential pressure that we measure across the filters because I have various dust collectors of different capacity, if the CFM impacts then I may not standardize my acceptable or alerting limits.

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I may no t be understanding you r question properly, but it looks like you may be misunderstanding what the "static pressure" actually is....

When the flow increases through an enclose space - be it pipe or venturi - the presure reduces proportionally to the velocity of the flow. Basically, the faster the flow rate, the lower the pressure is.

This flow rate presure (was historically....there are now sensors that can....)/(is) difficult to measure directly, so there's a "trick" that can be used to infer - with  a very high degree of accuracy - the velocity of the fluid - be it gas or liquid - in the pipe....that is the measurement of the static pressure. Effectively, the static pressure is the pressure to which the internal flow presure drops.

This is from memory, so I may get it upside down, but it still works anyway as it is a ratio of proportionality....it's:
rho1/v1 = rho2/v2

The static presure measurement is the measurement of the rho(1 or 2).

It's basically the mass flow calculation at two different speeds for the same mass...rho = m/v

This then becomes

rho1/v1 = m and rho2/v2 = m

and, as m is the same,

rho1/v1 = rho2/v2

Therefore, if the flow velocity increases, the pressure drops - this is measured by a static tube measuring hte drop in the static pressure as a result of the change in velocity - so therefore any change in velocity DOES affect the static pressure.

Hope this helps