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1. Structural improvement of swing check valve
A slow closing auxiliary valve is added on the flap of the original swing check valve. The auxiliary valve is installed on the lower side or both sides of the main valve

flap and is connected by threads. When the medium flow valve is opened, the medium pressure opens the auxiliary valve, and the medium flows into the main valve outlet through the small valve orifice, so that the main valve inlet end When the pressure is relieved, the valve flap of the main valve opens, and the pressure before and after the main valve tends to balance; when the medium reverses flow, the valve flap of the main valve closes quickly under the action of the reverse flow medium, and the upper part of the auxiliary valve body is a buffer cylinder, and the auxiliary valve cover is screwed into the valve.

There is a small hole on the cover of the upper part of the body. There is a certain gap between the valve flap of the auxiliary valve and the piston rod. The O-ring rubber seal is used between the piston and the buffer cylinder. The flat seal between the lower part of the piston and the valve flap; When the flap is closed with the main valve flap closed, the medium gradually flows into the upper chamber of the auxiliary valve buffer cylinder through the small hole due to the small hole of the auxiliary valve cover, and part of the medium flows back through the gap between the auxiliary valve flap and the piston rod Therefore, the auxiliary valve piston is closed slowly. In this structure, the closing of the main valve 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 water hammer from boosting.

2. Improvement of lift check valve structure
The lifting check valve, also known as the bottom valve, can maintain the water column required for pumping when the pump is stopped; the feature of the valve structure improvement is that a slow closing auxiliary valve is added between the main valve flap and the valve body bracket as shown.

A gasket ring is added between the valve body and the bottom net to increase the height of the valve flap. The buffer piston and the buffer cylinder are sealed with rubber. The valve flap shaft and the piston are rigidly connected, and the gap between the buffer cylinder and the valve flap shaft is small. When the medium flows downstream, the pressure medium pushes the valve flap into the main valve body cavity, and at the same time pushes the buffer piston upward; when the medium flows backward, the buffer cylinder is fully filled with the medium when it is opened, and the gap between the buffer cylinder and the valve disc shaft is relatively large. It is small, so as the medium in the buffer cylinder is gradually discharged through the gap, the main valve flap closes to play a buffering role, so that the water hammer boost in the pipe network can be controlled.

3. Test results before and after the improvement of the check valve slow closing structure
A calibrated pressure gauge is used, and the pressure signal is sent to the oscilloscope for recording by the differential pressure transmitter, and the water hammer pressure change value at each moment is read on the oscillogram with the calibrated ratio R.
The test valve has a diameter of 100mm, a system pressure of 0.5MPa, and a flow rate of 5L/s. When the pump stops suddenly, it shows the pressure-time curve of the inlet side of the check valve after the power is cut off
(1) The main valve flap opens and closes smoothly, the slow-closing auxiliary valve has a compact structure and reliable performance.
(2) The valve flap of the main valve closes first and then closes slowly, which can effectively prevent destructive water hammer and expand the use range of the check valve.
(3) The improved structure is simple and easy to produce and interchange.
(4) The slow-closing auxiliary valve can be repaired or replaced without hindering the use of the check valve.

The check valve is a valve that opens when the pipeline system is downstream and closes when it is upstream. It is mainly used to prevent backflow of the medium, prevent the pump and drive motor from reversing, and release the medium in the container. The rotary check valve with the shaft rotating and the lift check valve moving along the vertical center line of the valve body, but the valves of the above two structures both have the medium backflow speed rapidly reduced from the maximum to zero when the valve is closed, causing the pipeline The internal pressure on the side of the water inlet pipe rises rapidly, resulting in a water hammer phenomenon that has a destructive effect on the pipeline system, so the general check valve production caliber is 50 to 500 mm. In order to reduce the water hammer effect of the check valve and expand the range of use of the check valve, on the basis of the original product, a slow closing auxiliary valve was added to solve the problem of pipeline water hammer boosting.

Tianjin Tanghai Valve Manufacturing Co., Ltd. is one of the largest butterfly valve, check valve manufacturers in China. After 14+ years of continuous development and innovation, the company now has a group of high-tech engineers, technicians and skilled production workers, advanced production technology, sophisticated manufacturing equipment, complete testing methods, in strict accordance with international standards and quality management system, formed A comprehensive quality control network.

Related news/knowledges: Working principle diagram of lift check valve; Introduction of cast steel lift swing check valve