Rotary flow meter

You mean a glass rotameter, right? It consists of a vertically installed conical glass tube that is narrower at the bottom and wider at the top, along with a float that can move up and down inside it. When fluid flows upward through the conical glass tube, a pressure difference is created between the upper and lower parts of the float; driven by this pressure difference, the float rises, and the flow rate can be determined from the scale corresponding to the position of the float. The advantage of this type of flow meter is its low cost, while the disadvantage is its relatively low accuracy; it is only suitable for situations where the flow rate is relatively stable

A rotameter relies on the flow of liquid to drive the rotor, so in most cases, fluid enters from below and exits from above.

This belongs to the variable-area flow meter type, and it is necessary to lower it

The flow sensing element of a rotameter consists of a vertically conical tube that widens from bottom to top, and a rotor assembly that moves up and down along the axis of the conical tube. As the fluid under test flows from bottom to top through the annular gap 3 formed by cone tube 1 and rotor 2, a pressure difference is created between the upper and lower ends of the rotor, generating a force that pushes the rotor upward. When this upward force exceeds the weight of the rotor submerged in the fluid, the rotor rises; as a result, the area of the annular gap increases, the flow velocity of the fluid in that gap drops immediately, the pressure difference between the upper and lower ends of the rotor decreases, and the upward force acting on the rotor also decreases. Eventually, when this upward force equals the weight of the rotor submerged in the fluid, the rotor stabilizes at a certain height. There is a relationship between the height of the rotor in the conical tube and the flow rate passing through it.