Knowledge of structural design for slow closing of

2022-07-23
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Structural design knowledge of slow closing check valve

Abstract: Aiming at the problem of water hammer pressure rise in the use of common structure check valve, the design scheme of adding slow closing auxiliary valve is put forward; The improved product has the function of stable opening and closing and reducing water hammer pressure

as a valve that opens when the pipeline system flows downstream and closes when the pipeline system flows upstream, the check valve is mainly used to prevent the backflow of the medium, the reverse rotation of the pump and drive motor, and the release of the medium in the container; At present, the most commonly used are the swing check valve with the valve disc rotating around the pin axis of the valve body and the lift check valve with the valve disc moving along the vertical centerline of the valve body. However, the medium backflow speed of the above two types of valves drops rapidly from the maximum to zero when they are closed, resulting in a rapid increase in the internal pressure at one side of the water inlet pipe of the pipeline, resulting in a water hammer phenomenon that has a destructive effect on the pipeline system, Therefore, the production diameter of general check valve is 50 ~ 500 mm [1]. In order to reduce the water hammer effect of the check valve and expand the application range of the check valve, the author designed to add a slow closing auxiliary valve on the basis of the original product to solve the problem of pipeline water hammer pressure rise

1. Structural improvement of swing check valve

add slow closing auxiliary valve on the original swing check valve disc. The auxiliary valve is installed at the lower side or both sides of the main valve disc and connected with threads. When the valve with normal medium flow is opened, the medium pressure will open the auxiliary valve, and the medium will flow into the outlet end of the main valve through the small hole of the auxiliary valve, so that the pressure at the water inlet end of the main valve is relieved, the main valve disc is opened, and the front and rear pressures of the main valve tend to be balanced; When the medium is countercurrent, the main valve disc is quickly closed under the action of the countercurrent medium, while the upper part of the auxiliary valve body is a buffer cylinder, the auxiliary valve cover is screwed into the upper part of the valve body, there is a small hole on the cover, there is a certain gap between the auxiliary valve disc and the empty sleeve of the piston rod, the piston and the buffer cylinder are sealed with O-shaped rubber rings, and the lower part of the piston and the valve disc are plane sealed; When the auxiliary valve disc closes with the main valve disc, the medium gradually flows into the upper cavity of the auxiliary valve buffer cylinder through the small hole due to the small hole in the auxiliary valve cover, and part of the medium flows back through the gap between the auxiliary valve disc and the piston rod, so the auxiliary valve piston is closed slowly. The closing of the main valve of the structure is equivalent to the fast closing stage, and the slow closing of the auxiliary valve is equivalent to the slow closing stage. According to the hydraulic and mechanical transition mechanism of the pump station unit, the structure design can effectively prevent the pressure rise of water hammer

2. Structural improvement of lift check valve; The structural improvement of the valve is characterized by adding a slow closing valve between the main valve disc and the valve body support for comparative analysis. The auxiliary valve is shown in Figure 2

a backing ring is added between the valve body and the bottom to supplement the rising height of the valve disc; The buffer piston and the buffer cylinder are sealed with rubber, the valve disc shaft is rigidly connected with the piston, and the clearance between the buffer cylinder and the valve disc shaft is small. When the medium flows downstream, the pressure medium pushes the valve disc into the main valve body cavity, and at the same time pushes the buffer piston upward; When the medium flows back, because the buffer cylinder is filled with medium when it is opened, and the gap between the buffer cylinder and the valve disc shaft is small, as the medium in the buffer cylinder is gradually discharged through the gap, the closing of the main valve disc acts as a buffer, so that the pressure rise of the water hammer in the pipe can be controlled (Fig. 2)

3. Test results before and after the improvement of the slow closing structure of the check valve

the calibrated pressure gauge is used, and the differential pressure transmitter sends the pressure signal to the oscilloscope for recording, and the water hammer pressure change value at each time is read on the oscillogram with the calibrated ratio R. Fig. 4 shows the comparison of test results of common structure check valve (a) and common structure check valve with slow closing auxiliary valve (b)

the diameter of the test valve is 100 mm, the system pressure is 0.5 MPa, and the flow is 5 l/s. When the pump stops suddenly on May 6, it indicates that the pressure time curve at the inlet side of the check valve after the power is cut off [4]

Fig. 4 (a) results of main valve without slow closing auxiliary valve, maximum water hammer pressure rise 0.53 MPa; Fig. 2 (b) results when the main valve is equipped with slow closing auxiliary valve, the maximum water hammer pressure rise is 0.04 MPa

4. Conclusion

(1) the main valve disc opens and closes smoothly, and the slow closing auxiliary valve has compact structure and reliable performance. (2 tensile failure becomes an important phenomenon worthy of discussion) the main valve disc is closed quickly and then slowly, which can effectively prevent destructive water hammer and expand the application range of check valve. (3) The improved structure is simple and convenient for production and exchange. (4) The slow closing auxiliary valve can be overhauled. At the same time, the funds they raised in China or replaced will not hinder the use of the check valve

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