FIGURE 1
6.1 Introduction
• One eighth revolution later the measured liquid is now moving out of the meter. • A second measurement chamber is being created between vanes B and C • Vane A has begun to retract, and vane C is beginning to extend
FIGURE 4
• Unmeasured liquid (shaded area) enters meter. • Rotor and vanes turn clockwise • Vanes A and D are fully extended forming chamber
There are many different types of meters on the market today; however, historically, custody transfer measurements have typically been made with two types of meter, which are the displacement meter and the turbine meter. 6.2 Displacement Meter Displacement meters are one of the oldest of the mechanical devices used to measure liquids and have proven to be reliable, in spite of certain limitations. A lower section houses a rotor and blades, the middle section houses gears connecting the rotor to the register, and the upper section houses the meter register. Liquid flows through the lower section and turns the rotor and blades. As the rotor turns, the blades, or sliding vanes, and the housing form a seal. When the seal is formed, the liquid between the blades is isolated from the rest of the stream in a measuring chamber. In other words, the meter separates the flowing stream into separate volumetric portions. The number of these portions is transmitted through the gears in the middle section to the register above, which indicates the amount of liquid flowing through the meter.
• Vanes C and D are retracted
• This cycle will repeat as long as liquid flows The operation of a displacement meter is similar to that of a revolving door. As people stream through a revolving door, they fill the chambers between each dividing section of the door (the equivalent of the meter’s blades). The door displaces the stream of people into separate groups. Each group rotates around the center of the door and exits the other side. If you had a counter connected to the door, you could count the number of people going through the door by counting the revolutions. For example, if the revolving door had 5 sections and 1 person fit into each section, then 1 revolution of the door would mean 5 people had gone through the door, 60 revolutions would indicate 300 people, and so on. Suppose, continuing the door analogy, that a number of people avoided the revolving door by going through the side doors instead of waiting to fill one of the sections. These people would not be
FIGURE 2
• Rotor and vanes have made a one-eighth revolution
• Vane A is fully extended
• Vane B is partially extended
• Vane C is fully retracted
• Vane D is partially retracted
FIGURE 3
• A quarter revolution has been made
• Vane A is still extended
• Vane B is now fully extended
• An exact and known volume of new liquid is now in the measurement chamber
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