Differential pressure flow meters and mechanical flow meters. Both of these types of flow meters will affect the flow rate it self as they either force a liquid through a chamber where a shaft with a propeller or some device to constrict the flow is used. By affecting your flow we mean that downstream from the flow meter the stream flow will be less than the upstream.
Differential pressure flow meters work by reading a pressure loss across a constriction across the flow being measured. Usually a portion of the flow is measured rather than the entire flow and the portion that is being measure is returned to the unrestricted flow.
This will have varying effect on the downstream depending on model used and application used. You may need to compensate the upstream flow to achieve the downstream flow you desire but some of the more advanced flow meters may have programmable chips that do calculations to manage that for you.
The advantage to differential pressure flow meters is the low to medium cost to set up, wide range of applications and they have simple and sturdy structures. The disadvantage is they come with a medium to high drop in pressure depending on type use. These are common in industrial applications.
As with the other basic types of flow meters the mechanical flow meters has many different models and sub-types with it. Mechanical flow meters involve moving parts that are somehow affected by the flow of the substance being measured. A common configuration would be a shaft with paddles or cups attached so that a flow passing through it would turn it. Since the quantity of fluid being measure is know the rotations can be counted and a flow rate can be calculated.
Normally a portion of the flow is passed on to the measuring device and then returned to the main flow but there is still a decrease in flow to take into consideration. This siphoning off of the flow works to ensure that you are measuring a known quantity of a fluid or gas. Most mechanical flow meters are of the type positive displacement flow meters and measure volumetric flow of liquids or gasses in a pipe or other sealed conduit.
Mechanical mengdemåler is used in many applications and systems including industrial, automotive, chemical plants and many others. Most of this type of flow meters should be used with liquids free of any gas bubbles or particulates. Any particulates in the flow may cause damage over time due to the abrasive nature.