A flow system can be easily introduced with the use of an orifice plate, one of the simplest devices. The flow meter is the most commonly used flow meter. In addition to measuring flow rate, it also acts as a primary flowmeter. As with venturi meters, this device uses the same principle. Comparatively to venturi, orifice meters cause substantial pressure drops. Thus, restriction plates are often made of Orifice plates.
Working principle of differential pressure flow meters
A Venturi Meter’s applications, advantages, and disadvantages
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Orifice plate construction and design
For orifices, it is essential that the sharp edges and surface do not corrode or erode. A thin, circular plate attached to two pipe flanges has a circular hole concentric with the pipe center. Bidirectional flow can be measured using a square edged (90°) orifice. Fluid flows more smoothly across thicker orifice plates when they are tapered 45° at the downstream edge. There is only one direction for the beveled orifice. When plates meet pipes, there is always a hole for draining or venting. This is done to prevent gas or air bubbles from accumulating within the tube. At both the upstream and downstream ends of the flow, a differential manometer is connected.
Types of orifice plates
A typical orifice plate looks like the following
- An orifice plate with a concentric hole
- Eccentric orifice plate
- Segmental orifice plate
- Quadrant edge orifice plate
Concentric orifice plate
The Simplest and least expensive of all head meters is a concentric sharp-edged orifice plate. Stainless steel is usually used. Materials like nickel, Monel, are used for corrosive resistance when they need to be strong and durable. These types of orifices are extremely accurate.
Eccentric orifice plate
The offset hole is bored tangential to the circle, unlike the concentric orifice plate. Its location makes it possible to measure fluids containing suspended solid particles because it prevents solids or foreign particles from accumulating. If compared with the concentric orifice plate, the eccentric orifice is less accurate and has a higher degree of uncertainty. Gas dissolved in a liquid is called a gaseous liquid.
An orifice plate segmented into segments
In the same way as eccentric orifice plates, this device is used for the same purposes. An arc segment is a hole in the middle. Solid particles are present in fluids that use this device. The eccentric orifice is more expensive.
A four-sided orifice plate
For dense fluids, such as crude oil, slurries, and viscous flows, this type is used. Quarter circles are formed by rounding the edges. They are useful when the pipe has a small diameter (2 inches or less). Drain holes are provided in order to allow condensate to pass and to prevent its build-up at the orifice plate when gases are measured. In the same way, gases can pass through the top of the container when measuring liquids, avoiding a gas pocket.
What the orifice plate has going for it and what its limitations are
Advantages
- Construction and calibration standards are readily available and simple in construction.
- There is no dramatic increase in price with size, so they are cheap.
- Installation and uninstallation are both easy.
- Many years of efficiency and reliability can be attributed to them.
- Various materials are available.
- A pressure drop across the orifice makes it easy to measure the flow rate.
- Various sizes can be used with them.
- They exhibit predictable characteristics.
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