Rotameters are simple industrial flow meters that measure liquid or gas flow in a closed pipe. Rotameters are widely used because they have linear scales, a relatively large measuring range, low pressure drop, and are simple to install and maintain.
Rotameters belong to a group of meters called variable area flowmeters, which measure flow by allowing the fluid to move through a conical tube where the cross-sectional area of the tube becomes gradually larger as the flow rate increases. This gradually becomes larger as the fluid travels through the tube.
Flow within the rotameter is measured using a float that is lifted by the fluid based on the buoyancy and velocity of the fluid opposed to gravity pressing down on the float. In the case of gases, the float responds only to velocity.
The float moves up and down inside the conical tube of the rotameter proportionally to the velocity of the fluid flow. It reaches a constant position once the fluid and gravitational forces equalize. Changes in flow cause the spinner float to change position within the tube. Since the float position is based on gravity, it is important that all rotameters are mounted vertically and oriented with the wider end of the cone at the top. It is also important to remember that if there is no flow, the float will go to the bottom of the rotameter due to its own weight.
Rotameters can be calibrated for other fluids by understanding the basic principles of operation. The accuracy of the rotameter is determined by the accuracy of the pressure, temperature and flow control during the initial calibration. Any change in density and float weight will have an impact on the flow reading of the spinner. In addition, any changes that affect the fluid, such as pressure or temperature, will also affect the accuracy of the rotameter. Given this, rotameters should be calibrated annually to correct for any changes in the system that may have occurred.
A manometer is an item that measures pressure, which is used to identify the physical pressure contained in liquids and gases. Generally, it measures relative pressure, which is relative to atmospheric pressure. In addition, pressure gauges can measure differential pressure, absolute pressure and vacuum.
All gauge components should be selected based on knowledge of pressure, temperature and medium to avoid incorrect application. Improper installation may damage the meter and/or cause failures resulting in personal injury or property damage.
The operating conditions of a pressure gauge should always be considered. Pressure gauges should be protected against sudden pressure changes, temperature changes, pulsation and/or mechanical vibration. Proper application of accessories will solve most problems.
Gauges should not be exposed to pressures in excess of the maximum dial reading. It is recommended that the maximum working pressure be in the middle one-third of the scale range when the pressure being measured is constant pressure.
For fluctuating pressures, the maximum working pressure should be no more than one-third of the full scale range. Composite ranges are recommended when the pressure to be measured varies between vacuum and higher atmospheric pressures.
Since the gauge’s measuring element may be directly exposed to the measuring medium, complete information on the exposure of the gauge’s medium should be obtained in order to select suitable materials for the gauge. If the medium is corrosive or would solidify on the gauge, a diaphragm seal protector should be used.
The ambient atmosphere in which the gauge will be installed will have a direct effect on the use, life and accuracy of the instrument. The atmospheric condition may attack the internal components of the gauge or allow dirt to impair the operation of the gauge.