Flow curve analysis

Valve manufacturers usually provide multiple flow curves under different inlet pressures and the same outlet pressure for the same series of pressure reducing valves to illustrate the working range of the pressure reducing valve. As shown in Figure 2, the horizontal axis represents the medium flow, the vertical axis represents the outlet pressure value, and the inlet pressure is represented by curves of different colors, such as 3000psig (206.8bar), 2000psig (137.9bar) and 1000psig (68.9bar). When the medium flow is 0, the outlet pressure shown in the ordinate is the set pressure at the outlet of the pressure reducing valve.

The change of flow curve shows a "attenuation" trend, that is, under a specific inlet pressure and outlet set pressure, the outlet pressure gradually decreases with the gradual increase of medium flow. Due to the limitation of the internal structure and components of the pressure reducing valve, the pressure reducing valve cannot provide a perfect horizontal flow curve under a specific pressure regulation state. With the increase of medium flow, when the pressure reducing valve responds to the change of medium flow, there will be a certain degree of pressure loss at the outlet pressure.

In the practical application of pressure reducing valve, it is usually required to maintain a relatively constant outlet pressure when the system flow changes greatly. Therefore, the smaller the attenuation of the flow curve of the pressure reducing valve, the better the pressure regulating performance of the pressure reducing valve.

Usage of flow curve

For a certain type of pressure reducing valve, first determine the flow curve corresponding to the model, and then select the corresponding single curve under the pressure working condition according to the actual inlet pressure and outlet set pressure value; Then find out the corresponding point on the curve according to the abscissa flow scale. Combined with the ordinate scale of this point, the corresponding actual outlet pressure under the actual inlet pressure and medium flow can be read out. If the flow curve under the required pressure condition cannot be found in the flow curve of the pressure reducing valve provided, a new curve can be deduced between two adjacent existing curves.

In addition, the flow curve provided by the manufacturer is usually measured when the test medium is nitrogen and the test temperature is 70 ° f (20 ℃). When the actual system uses other media and working temperature, the flow scale of the abscissa in the flow curve needs to be corrected according to equation (2), and the curve trend remains unchanged.

Q₂ = Q₁ X F_G X F_T 式 (2)

Where: Q1 is the initial flow scale, Q2 is the corrected flow scale, FG is the specific gravity correction coefficient and FT is the temperature correction coefficient; The values of FG and FT can be referred to table 1 and table 2 respectively.

surface 1

表 2