In power plants, it is required to measure the flow of fluids like cooling water, feedwater, steam, air, etc. Various types of flow meters are used for this. Some of the common types are given below:

1. Mechanical flow meter
2. Differential flow meter
3. Electromagnetic flow meter
4. Ultrasonic flow meter
5. Rotameter

Flowmeters may be classified by the general method in which flow information is extracted from the fluid system.

Inferential flowmeters

• Inferential flowmeters are, by far, the most widely used form of the flowmeter.
• Common types of this flowmeter include the orifice plate, venturi, sonic nozzle, and pitot/pitot-static tube, which all infer flow rate from a differential pressure measurement imparted by an inertial change in flow velocity. Laminar flow elements also measure flow velocity from an inferential, frictionally generated differential pressure basis.
• The variable-area flowmeters, including the rotameter and spring-loaded variable aperture, as well as the drag body or target flowmeter, vortex shedding flowmeter, and fluidic (or Coanda) flow- meter, also use an inferential basis to measure flow.

Types of flow meters are divided into two functional groups:

1. One measures quantity (Positive Displacement)

2. The other measures rate of flow (Inferential)

??Some of the more common positive displacement meters are:

1. Weighers

2. Reciprocating Piston

3. Rotating Piston

Inferential type flow meter (Rate Meter):

1. Orifice Plate

2. Flow Nozzles & Venturi Tubes

3. Swirl meters, Vortex Shedding Meters, Rotameters, Mass Flow Meters.