The History and Advantages of the Classical Venturi Flow meter

The Herschel long and short form classical venturi meter is one of the first commercially applied examples of accurate and reliable flow metering technology. Introduced in the early 1900’s, it is still widely specified worldwide particularly on applications that require ASME or ISO code compliance.

Over the years, modifications to the initial design have been made that enhance the performance of this particular meter design. One example is the use of external pressure averaging rings as noted in photo number 1A.

(Photo # 1A)

Another example of the external averaging manifold can be seen in photo number 1B and, in this example, PFS provided a fusion bonded interior and exterior coating to allow for the use of carbon steel base metal but with the corrosion protection afforded by using the special coating process.

(Photo # 1B)

While the early 1900’s design for cast classical meters called for an “averaging annulus” which was cast into the body of the meter at the high and low pressure sensing points, over some years of service, the annular chamber succumbed to rust, scale and corrosion. Since the purpose of the annular chamber was to provide an averaged high and low pressure signal which improved the installed accuracy of the meter, interior degradation of the annular chamber would result in impaired accuracy.

Today, we do not use an internal annular chamber design. Instead, an external high and low pressure “manifold” is used to inter-connect multiple high and low pressure taps that are installed around the circumference of the meter. The external tubing can be easily and quickly removed should any plugging occur and all of the performance benefits of the annular chamber design apply.

Another enhancement of the early classical venturi meter design is the use of a wide variety of interior and exterior coatings that allow the use of less expensive metals. Photo number 2 is an example of a specially applied coating to the exterior of a 44.0” PFS-CVF

that is installed on a jet engine testing stand in SE Asia.

(Photo# 2)

Another benefit of experienced design engineering which leads to cost savings is the use of external gussets and/or supports which allow the use of thinner materials without any service related risks. This is particularly beneficial when using stainless steel, Hastelloy, Monel or other corrosion resistant materials. Photo number 3 is shown with a pair of throat stiffening rings which reduced the wall thickness of the machined throat significantly.

(Photo# 3)

Please contact Primary Flow Signal for your flow measurement requirements.