The industry's most authoritative handbook on flow measurement provides a road map to the field of flow measurement. This best-seller discusses strategies for problem solving and puts the whole array of types of flowmeters at the reader's disposal. The text includes laminar flow elements, critical flowmeters, statistics for measurement, laboratory primary standards, and uncertainty in flow measurement. Emphasis is placed on the importance of accuracy in measurements and ways of ensuring accuracy and avoiding equipment damage through correct forecast of operating conditions, flowmeter selection, installation, calibration, and maintenance. Fundamental considerations such as mixed-phase flow, piping effects, and flow conditioning are examined at length. The problem of attaining a meaningful flow signal through linearization, compensation, and totalization is discussed. Join the thousands of engineers, technicians, managers, and salespeople that have found this reference text an invaluable resource.
TABLE OF CONTENTS Chapter 15 - Positive Displacement Flowmeters for Liquid Measurement
Positive displacement liquid flowmeters (commonly called PD meters) have
long been used to measure liquid fluid products. Patents for these devices date
back into the 1800s and are among the earliest type of flowmeters due to their
simplistic nature and mechanical principles of operation.
Through the years, there have been many types of positive displacement flowmeter
concepts developed utilizing varying unique and often times creative techniques.
Many of the designs have similar concepts and principles of operation
used in positive displacement pumps and hydraulic motors.
In many cases, positive displacement meters have changed very little over the
years. Some have remained purely mechanical devices with local display only and
no capability to transmit a signal remotely. Some earlier designs have been reconfigured
or upgraded to add electrical outputs for data transmission to remote
instrumentation. Other positive displacement flowmeter design concepts have
been developed with completely new approaches and signal generation techniques
to further meet the user's needs and the process fluid measurement challenges.
Principles of Operation
In simplistic terms, a positive displacement flowmeter takes a flowing fluid
stream, puts it into "buckets," and then empties those buckets back into the flow
stream. Each full bucket has a known volume and by counting the number of
buckets, the total volume of fluid passed can be determined.
The space within the flowmeter housing where the fluid passes is known as the
| Positive displacement flowmeters continuously divide the flowing fluid stream into known volumetric segments, isolate the segments momentarily, and return them to the flowing stream while counting the number of segments. |
