The schematic diagram of the turbine flowmeter is shown in Figure 3-1. A turbine is placed in the center of the pipeline, both ends of which are supported by bearings. When the fluid passes through the pipeline, it impacts the turbine blades and generates a driving torque for the turbine, so that the turbine can overcome the friction torque and the fluid resistance torque and rotate. In a certain flow range, the rotational angular velocity of the turbine is directly proportional to the fluid flow rate for a certain viscosity. The fluid velocity can be obtained by the rotational angular velocity of the turbine, so that the fluid flow through the pipeline can be calculated.

The rotational speed of the turbine is detected by the sensor coil installed outside the casing. When the turbine blades cut the magnetic lines generated by the permanent magnetic steel in the casing, the magnetic flux in the sensor coil will change. The sensor coil sends the detected magnetic flux periodic change signal to the preamplifier, amplifies and shapes the signal, generates a pulse signal proportional to the flow rate, and sends it to the unit conversion and flow integration circuit to obtain and display the accumulated flow value. At the same time, the pulse signal is also sent to the frequency-current conversion circuit, which converts the pulse signal into analog current, and then indicates the instantaneous flow value.

2. The structure of the turbine flowmeter

Fluid flows in from the inlet of the casing. A pair of sleeve bearings are fixed on the central axis of the pipe through brackets, and the turbine is installed on bearings. The brackets at the upstream and downstream of the turbine are equipped with radial rectifying plates to guide the fluid. In order to prevent the fluid from spinning and changing the angle of action on the turbine blades, a sensing coil is installed outside the casing above the turbine to receive the signal of flux change.

The main components are introduced below.

(1) The turbine is made of magnetically permeable stainless steel material and equipped with spiral blades. The number of blades varies according to the diameter change, ranging from 2 to 24. In order to make the turbine have a good response to the flow rate, the mass is required to be as small as possible. < p Leaf overlap p is 1-1.2; The clearance between the blade and the inner shell is .5-1 mm.

(2) Bearings

Generally, the bearings of turbines adopt sliding cemented carbide bearings, which require good wear resistance.

As the fluid passes through the turbine, it will generate an axial thrust on the turbine, which will increase the friction torque of the uranium bearing and accelerate the wear of the uranium bearing. In order to eliminate the axial force, it is necessary to adopt hydraulic balance measures in the structure. The principle of this method is shown in Figure 3-3. Because the diameter DH at the turbine is slightly smaller than the diameter Ds and www.okeycar.com at the front and rear supports, the flow section in the turbine section is enlarged, the flow velocity is reduced, and the hydrostatic pressure is increased by P, and the static pressure of this P will play a role in offsetting part of the axial thrust.