When trying to accelerate media, force is required.
Force (F) = Mass (M) x Acceleration (A) and M = Volume (V) x Density (D)
Thus, we can accelerate fluid by applying a difference in pressure across its length. This pressure will always be in proportion to its density and acceleration. How do we achieve this differential pressure? With a differential pressure flowmeter. However, this can be a complex subject. Differential flowmeters have an interesting history. There have been a variety of models introduced over the years, all with their own sets of pros and cons. Orifice plates, Venturis, wedges and cones are all different styles of flowmeters worth a deeper look.
Orifice plates were one of the first technologies that became prevalent for closed pipe flow measurement. One of its strongest benefits is its ease of installation. Additionally, due to their popularity and acceptance, maintenance has remained inexpensive. From a “con” perspective, they can be inaccurate at times due to its proclivity to attract dirt and wear on the orifice itself.
Venturi is another widely accepted technology utilized as custody transfer meters. However, Venturi maintains a relatively low PPL and boasts a higher accuracy than the orifice plates. The main negative associated with Venturis is their need for a long straight pipe meter, which can be costly.
Pitot tubes can be used to measure flowrate and can be inexpensive to install. However, they only allow for a single point of measurement and can only produce a low differential pressure.
Cone technology can achieve a 10:1 turndown ratio and allow for selectable beta ratios to optimize the D.P. range and/or a low PPL. However, this technology can be costly to install, requiring the removal of a section of pipe and installing mating flanges.
The Accelebar is an averaging Pitot tube through which a 30:1 turndown can be achieved if the flow velocity is high enough. It produces high differential pressure and a low PPL.
Wedge meters were designed for dirty, high suspended-solid flows and slurries. With this technology, the wedge is stalled perpendicular to the flow direction, creating restriction.
This is a very brief outline of the variety of differential flowmeter technologies available today. To see a more detailed description of each, please check out the article I had published in Process Instrumentation last year.
If you’re looking for someone to walk you through the different options and what works best for your process, give us a call at (855) 737-4714 or fill out our online form to reach one of our technical specialists.