Mechanical flow meters are the most commonly used flow measurement devices. They have advantages and disadvantages depending on the application they are used for. In general terms the advantages are they are inexpensive to manufacture, can be used for nearly all applications (some oft the other type flow meters cannot be used with flammable liquids for instance) and they are readily available. The primary disadvantages of the mechanical flow meters is that most of them employ moving parts making them susceptible to wear and they often constrict the flow of liquids or gasses through them.

There are a number of different types of mechanical flow meters that are appropriate to specific uses. For instance one type uses an inline chamber with an impeller. The chamber has a fixed volume and calculations based on each rotation of the impeller can be used to determine a flow rate. These are the most susceptible to wear. This type of flow meter also restricts the flow of substance through it to some extent. These can be entirely mechanical or they can use some type of electronics to count and display the flow rate, relay flow rate to other equipment or work with flow control devices.

Other mechanical flow meters include venturi meters, orifice plates and vortex meters and all of these can cause a drop in the flow rate of the liquid or gas being measured. These work on Bernoulli's principle that states that the increase in velocity will result in a decrease of pressure. One example of this type of flow meter is the Venturi flow meter that measures pressure changes and these changes can be used to calculate flow rate. Another type is the orifice plate that works on the same principle of the venturi flow meters.

Vortex flow meters are similar to the orifice plate type and they measure the pressure changes of vortexes created as a liquid passes an object in the stream. Vortex flow meters have less impact on the flow rate of the substance who's rate of flow is being measured.

There are other variations of these basic mechanical flow meters that go beyond the scope of this introductory article. These will be discussed in other articles that we will produce at a later date. The primary differences between the applications for the various types mechanical flow meters is how much they restrict or cause flow rate drop and accuracy.

Other types of flow meters are discussed in part three Magnetic, Ultrasound and Coriolis flow meters.