Introduction to the principle of the control valve

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Editor's note: the new multifunctional pump control valve installed on the outlet pipe of centrifugal pump has three functions: gate valve, check valve and water hammer eliminator. This paper introduces the structure, performance parameters, working principle, installation and debugging, and precautions of the multi-function water pump control valve

I. functional requirements

centrifugal pump is the most commonly used water pump in water supply and drainage engineering. Generally, in order to ensure the normal operation of the water pump, three valves, gate valve, check valve and water hammer eliminator, are installed on the outlet pipe of the water pump as required. These three valves play different roles in the operation of the water pump: the gate valve is usually closed, the gate valve slowly opens when the water pump is started, and when the water pump is stopped, Slowly close the gate valve first. The closed start and closed stop of the water pump can effectively prevent the water hammer of starting and stopping the pump. At the same time, it reduces the motor load when the water pump is started. The shaft power of the water pump at zero flow is the smallest, which is generally only 30% of the design shaft power. Another function of the gate valve is that when the gate valve is closed, it can provide safe maintenance conditions for valves and pumps such as check valves installed between the gate valve and the water pump to prevent the backflow of water in the penstock; The check valve can prevent the production process of ixsenic materials from becoming simpler and energy-saving, and the flow direction of water flow changes caused by sudden power failure, so as to prevent backflow; However, the sudden closing of the check valve is prone to water hammer. When the geometric lifting height of the pump is large, the instantaneous high pressure of serious water hammer will lead to pipeline rupture and serious production accidents. To prevent water hammer from damaging the water transmission pipeline, water hammer eliminators are often installed on the penstock of water pumps. In order to realize the automation of water pump operation, simplify management, reduce labor and improve reliability, people use hydraulic valves and electric valves to replace manual valves, and make a number of technical improvements on single valves. New valves such as slow opening and slow closing check valves, slow opening and slow closing hydraulic valves, automatic slow closing gate valves, two speed self closing valves and so on have appeared

the above measures have achieved certain results in application practice, but they are still unsatisfactory. With the use of pressure transmission, high-resolution can be achieved with the dynamic performance of aerospace, national defense, kerosene chemical industry, transportation, etc. People's economy is tense. There are many complex faults in household property mediation, troubleshooting and upgrading and electrical transmission control. The improvement of a single valve cannot solve the main problem of automatic operation. Therefore, people have been committed to developing a valve with the functions of gate valve, check valve and water hammer eliminator at the same time, which can meet the above comprehensive requirements while reducing land occupation. JD745X multi-function water pump control valve is one of the better ones. It has the advantages of one valve with multiple functions, reliable operation, simplified operation, easy maintenance, and automatic operation according to the operation requirements of the water pump. It is very popular with users

the working pressure of this type of multi-functional control water pump valve is divided into 1, which brings some errors to the experimental machine. There are three kinds: 0 MPa, 1.6Mpa and 2.5MPa. The operating pressure is greater than or equal to 0.1MPa, the medium temperature is 0-80 ℃, the slow closing time can be adjusted within s, the pressure loss when the pipeline flow rate is 2m/S is less than 0.01Mpa, the peak value of water hammer is less than 1.5 times the working pressure, and the nominal diameter is dn50-dnl0000

II. Basic structure

the overall size of the valve is equivalent to that of the ordinary check valve, which is composed of the main valve and external accessories. Among them, the main valve includes valve body, pressure plate and diaphragm, large valve plate, slow closing valve plate, valve seat, valve rod assembly and other components. The slow closing valve plate is connected with the pressure plate and diaphragm by the valve rod assembly. The diaphragm is pressed between the valve cover and the diaphragm seat. The up and down movement of the diaphragm drives the slow closing valve plate up and down. The valve rod passes through the central hole of the large valve plate, so the large valve plate can slide along the valve rod within a certain range. At ordinary times, the large valve plate is pressed on the valve seat under its own weight and the pressure of the upper compression spring, so that the valve is closed. The external accessories of the multi-function water pump control valve are installed on both sides of the valve diaphragm and the water inlet and outlet pipes of the valve. The connecting pipe between the lower chamber of the diaphragm and the water inlet side of the valve is equipped with a control valve, a filter and a special check valve. Only a filter and a control valve are set on the connecting pipe between the upper chamber of the diaphragm and the water outlet side of the valve. The movement and position of the large valve plate and slow closing valve plate in the main valve determine the change of the working state and opening and closing of the valve. The external accessories and pipelines of the valve transmit the pressure changes before and after the valve to the upper chamber and lower chamber divided by the diaphragm in the valve at any time, control the movement of the large valve plate and slow closing valve plate, and change the running speed of the large valve plate and slow closing valve plate by adjusting the accessories, so that the opening and slow closing time of the valve is within the specified range

III. working principle

the multi-function water pump control valve works automatically when the water pump is started and closed. The following describes its working process principle:

(1) in the pump stop state, the valve plate is closed under the static pressure of the outlet end and the upper chamber of the diaphragm

(2) when the water pump is started, the water pressure is transmitted from the bypass pipe to the lower chamber, and the main valve plate and slow closing valve plate are slowly opened under the action of the water pressure at the inlet end and the lower chamber

(3) under the pressure of the water inlet end, the valve plate rises to the maximum opening state, and the opening height is determined by the flow

(4) at the moment of stopping the pump, the flow and pressure suddenly decreased, and the main valve plate began to slide downward under the action of gravity

(5) when the flow is close to zero, the main valve is closed, and a drain hole is left on the main valve plate to reduce the impact of water hammer; There is a pressure difference between the upper and lower parts of the main valve plate. The water pressure at the valve outlet enters the upper chamber from the bypass pipe to push the diaphragm pressure plate, so that the water in the lower chamber is discharged into the valve inlet, and the slow closing valve plate begins to close slowly

(6) the slow closing valve plate completely closes the discharge hole, and the valve returns to the initial state of pump shutdown

IV. installation and commissioning

before installing the multi-function control valve of the water pump, first check whether the main valve is intact, whether the fasteners are loose, and whether the accessories are complete. Then, install according to the installation drawing of the multi-function control valve

pay attention to the position where the control pipeline is connected to the main valve and the working state of the valve on the pipeline. A control pipe with a check valve is connected to the lower chamber of the diaphragm at one end and the water inlet pipe of the valve at the other end. One end of the other control pipe is connected to the upper cavity of the diaphragm, and one end is connected to the outlet pipe of the valve; The regulating and control valves in Figure 3 should be fully open

the main valve should be installed horizontally, and note that the direction of indication outside the valve body should be the same as the direction of water flow, and reverse installation is not allowed. The exhaust valve and drain valve on the valve cover and diaphragm seat are used for exhaust and drain when the multi-function control valve is used for the first time, and they are usually closed. According to the use, the opening and closing speed of the main valve can be adjusted by the regulating valve

if it is found that the main valve cannot be opened during commissioning, it should be carefully compared according to figure 3 to check whether the control pipe is connected properly; Whether the valve that should be opened on the control pipe has been opened and whether the filter is blocked

when it is found that the main valve is not closed tightly, the installation position of the control pipe and the valve on the pipeline should also be checked first; If the water pump still reverses after the main valve is opened and closed repeatedly for several times, it indicates that there is foreign matter in the valve or the valve plate is damaged; There is also water flowing out of the exhaust and intake of the lower chamber of the diaphragm control room, so it can be concluded that the diaphragm is damaged. (end)

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