Keywords: waterworks; valves; selection 1, the role of the valve in the urban and rural water supply pipe network In the distribution of water resources, indispensable, it plays a role in the transport agency, the use of urban and rural water supply network is very Wide range of construction projects are also very large, different types of urban and rural water supply network to meet the different needs of people. Valves are not always used in normal management, but in an emergency, a qualified valve must provide flexible control over the flow of water. Valve in the choice, the main concern type, material, manufacturer, production technology, etc., from all aspects to determine the quality of the valve in line with standards.
2, conventional water system valve distribution 2.1 Raw water intake valve process The head of the water valve is characterized by its larger valve diameter, without frequent operation, most of them belong to a year or even years before they need to operate once, the valve is long in the Normally open or normally closed state. Therefore, from the control method, more than 95% of the manual valve is selected from the valve type are gate valve or butterfly valve , the valve head loss than the butterfly valve, head valve gate valve slightly more than the butterfly valve. Caliber focus on 1200 ~ 1600mm, in the head of the water pipe there are also caliber 3000mm or more valves.
2.2 Sedimentation tank valve Sedimentation tank valve is the main valve, outlet valve and isolation valve. The valve is normally open, the valve is normally closed and operates once a year. Therefore, the two types of valves use manual gate valves with specifications ranging from 2200 Ã— 1800 to 1200 Ã— 840. The sedimentation tank water valve to undertake the important responsibility of the water distribution, requiring frequent adjustment, reliable performance, and distributed in various sedimentation tanks, the distribution of more scattered, are used with intelligent control system of electric control valve . It determines the sedimentation tank water and system balance a key part of the water line is based on the dynamic adjustment of water output system is particularly important, and also need to adjust the dynamic tracking of PID, then the full travel time of the valve, Allowed starting and stopping frequencies will have the corresponding requirements.
2.3 filter valve The most common filter for the four valve filter, which is the most basic filter configuration. That no matter what kind of filter are at least four inlet valve, drain valve, flush valve and water valve. Of course, there are many five-valve, six-valve (V-type filter) or even seven-valve filter, but also equipped with a gas valve, the first filter valve or more with a water inlet valve and so on. From the structure of the valve to distinguish between the water valve and flushing valve is usually selected butterfly valve, the main reason is that the water valve and flushing valve are installed in the pipe in the pipe gallery, and the need for frequent adjustment of the water valve, and flushing valve will have to adjust the intensity The demand. The water and drainage usually through the channel, so the inlet valve and drain valve are basically selected gate valve. Filter flushing valve diameter is slightly larger than the diameter of the water valve, flushing valve according to the filter area, flushing intensity and flushing time requirements basically in DN600 ~ DN800, and the water valve according to the flow, filtration and other requirements in the DN400 ~ DN600. Inlet valve and drain valve size and sedimentation tank design flow, channel size related.
2.4 pump room pump valve room pump is mainly on the water inlet valve, outlet valve, check valve and check valve . The first three basic selection of butterfly valve, the difference lies in the control mode. Inlet valves and service valves require only manual valves as they are normally open. Pump outlet valve selection, the first need to meet the pump to start and stop the valve can be closed, taking into account the outlet valve to adjust the water, the pump has different conditions to meet the demand factors, the outlet valve also needs to be controlled intelligent device control; Followed by the need to be equipped with non-return valve, the pump unit can be shut down quickly in case of accidental shutdown of the valve to prevent long-term reversal of the pump, but also to stop the pump water hammer phenomenon.
2.5 Waterworks dosing system valves Waterworks dosing system determines the characteristics of the valve used in the above small caliber, small flow, but the flow regulation requirements, high precision, fast regulation, it is usually the choice of flow control valve , This valve makes the medium flow capacity depends only on the structure of the valve itself, so to do a complete flow control. Waterworks dosing system The main medium of the pipeline is aluminum sulfate, ammonium sulfate, sodium hypochlorite and other solutions, which requires the valve also has anti-corrosion ability. Ammonium sulfate has a corrosive effect on copper. Valves made of copper can not be used. Generally, stainless steel ball valves or UPVC ball valves are used . Sodium hypochlorite has a corrosive effect on steel and iron. Valves made of steel or iron can not be used. Generally, UPVC ball valves or PTFE-lined Hastelloy valves are used.
In addition dosing system will use stainless steel ball valve, UPVC ball valve or butterfly valve as the switching valve, switching valves.
3, the choice of valve based on the first step, the use of the selected valve, the use of conditions and control conditions.
The second step, the installation size and dimensions, and pipe connections.
The third step, the characteristics of the valve fluid requirements: head loss, flow characteristics, sealing and so on.
The fourth step, the nature of the working medium: working pressure, working temperature, corrosion performance, contains solid particles.
The fifth step, if the valve is to be used for control, must determine the following additional parameters: control mode, maximum and minimum flow requirements, normal flow pressure drop, pressure drop when closed, the valve maximum and minimum inlet pressure.
4, the valve selection steps The first step, the valve sealing performance to meet the requirements of the media.
The second step, to determine the process requirements, that is, to determine the pressure inside the pipeline, flow and back pressure, and then determine the nominal diameter of the pipe and the diameter of the valve seat hole to determine the type and type of valve.
The third step, according to the pipe diameter, the scene conditions, select the type of valve, combined with the second step of the process parameters, select the valve, at the same time according to the valve installation location, to determine the structure of the selected valve length, flange connection and Size, opening and closing the valve height direction of the size of the bolt holes connected to the number and size of the entire valve dimensions.
The fourth step, according to pipeline transportation of media, working pressure, working temperature to determine the selected valve shell and inner parts of the material.
The fifth step, select the transmission mechanism according to the transmission form, the butterfly valve of the water plant is mainly multi-turn rotary mechanism, while the gate valve is the transmission mechanism of the straight stroke.
The sixth step, to determine the control mode, for the pneumatic control system is the cylinder and the matching drive selection, for the electric control system is the electric actuator selection. For the choice of electric actuator that is based on the valve required full travel time, the valve torque and other parameters to determine the transmission speed ratio and output torque, interface type, determine the motor speed, power and so on.
The seventh step, consider the implementing agencies of the protection level, communication methods, whether to use SCR and other configurations.
The eighth step, the use of existing information: valve product catalog, valve product samples, select the appropriate valve products.
Conclusion In summary, with the improvement of the automation level, the requirements of the water treatment plant are also getting higher and higher, more and more, however, anyway, the conventional selection is generally within the scope of this article. The main valve mentioned in this article, of course, there are also used water plants exhaust valve , solenoid valve , back pressure valve, here is no longer described in detail.
 Ma Zhicheng. Waterworks water purification model of the production and use of [J]. Experimental Teaching and Instruments .2015 (01)
 Liu Yingcheng. Speed â€‹â€‹governing fluid coupling in the water plant with water pump application and energy saving [J]. General Machinery .2016 (03)
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