The water supply pipe network distributes the tap water sent from the water plant to thousands of households. Therefore, the water supply pipe network is distributed in every corner of the city, and its length ranges from hundreds of kilometers to thousands of kilometers.
The irreplaceability of water and the necessity of people’s survival determine the importance of the safe operation of the water supply network. However, due to various subjective and objective reasons, pipelines often have some failures, the pipeline network is always updated and reconstructed, and water users often have to increase or decrease. Therefore, it is difficult to avoid the phenomenon of water cuts in local pipeline sections. In order to reduce the scope of water cut, it is very necessary to install control valves properly in the pipe network. Therefore, in the water supply pipe network of a city, there are thousands of valves, which are randomly distributed under the city streets.
The valves on the water supply pipe network are not operated frequently and have a long life expectancy. Once needed, the valve should be able to close quickly and shut off reliably; it is usually required that the valve be opened in place to reduce the head loss of the pipe section. Therefore, the valve is a kind of “reliance for thousands of days, for a short time.” “The control equipment; the integrity rate of the valve is related to the selection of the valve, the manufacture of the valve, the design of the pipeline, the assembly of the valve, the opening and closing of the valve, and the management of the valve. Of course, the most important reason is the quality of the valve.
Valves have a large number, wide distribution and great effect in the water supply pipe network. Therefore, there are many issues worthy of discussion in valve selection, inspection, performance and management.
First, the selection of the valve
There are several types of valves, such as butterfly valves, gate valves, ball valves, and plug valves, and they are used in different ranges in water supply pipe networks. In order to reduce the depth of pipe coverings, butterfly valves are generally used for larger diameter pipes; for those that have little effect on the covering depth, try to select gate valves; ball valves and plug valves are difficult to cast and process, and the price is more expensive. Generally, they are suitable for small and medium diameter pipes. In recent years, due to the improvement of casting technology, the use of resin sand casting can avoid or reduce mechanical processing, thereby reducing costs, so the feasibility of ball valves for large-diameter pipelines is worth exploring. As for the demarcation line of the size of the caliber, it should be divided according to the specific conditions of each region.
The main disadvantage of the butterfly valve is that the butterfly plate occupies a certain cross-section of the water, which increases a certain head loss; although the gate valve does not have this problem, the height of the large-diameter vertical gate valve affects the depth of the pipeline, and the length of the large-diameter horizontal gate valve increases The pipeline occupies the horizontal area, which affects the arrangement of other pipelines; the ball valve and the plug valve maintain the advantages of single gate valve, small water flow resistance, reliable sealing, flexible action, convenient operation and maintenance. The plug valve also has similar advantages, but the cross-section of the water is not a perfect circle.
In recent years, many domestic valve manufacturers have developed soft-seal gate valves. Compared with the traditional wedge or parallel double gate valve, this gate valve has the following characteristics:
- 1. The valve body and bonnet of the soft-sealed gate valve are cast by precision casting, which is formed at one time, no mechanical processing is required at all, and the sealing copper ring is not used, which saves non-ferrous metals;
- 2. There is no pit at the bottom of the soft seal gate valve, no slag accumulation, and the failure rate of the gate valve opening and closing is low;
- 3. The size of the soft-seal rubber-lined valve plate is uniform and highly interchangeable.
Therefore, the soft-sealed gate valve will be the development direction of the gate valve, and it is also a kind of valve that the water supply industry is willing to adopt. When opening and closing the soft-seal gate valve, do not close it too tightly, as long as it achieves the water-stop effect, otherwise it will not be easy to open or the rubber lining will peel off.
Most of the butterfly valves used in the water supply industry are soft-sealed butterfly valves. In view of the easy damage of the rubber ring during the installation process of the butterfly valve, which affects the sealing performance, many manufacturers have introduced metal-sealed butterfly valves instead of rubber-sealed butterfly valves. The metal-sealed butterfly valve generally adopts an eccentric structure due to the small elasticity of the sealing element, and it is more reasonable to use a three-dimensional eccentric structure in particular.
Second, the performance and testing of the valve
The particularity of the valve requires reliable quality and excellent performance. When evaluating valve performance and performance testing, the following points should be noted:
- 1. The valve opens and closes flexibly and lightly under the working water pressure. Under the working water pressure, a torque wrench is used to detect the opening torque.
- 2. The valve is closed tightly and does not leak under 1.1 times the working water pressure or meets the standard requirements (metal-sealed butterfly valve). This requires that both sides of the valve are under pressure in turn, tested separately, and opened and closed multiple times to achieve the same effect . It is required that valves of various calibers and different types should be tested by the manufacturer and qualified units for the life test of the load opening and closing. This test also includes the evaluation of the valve shaft sealing effect.
- 3. The flow capacity of the valve should be strong, especially the butterfly valve, the flow resistance of the butterfly plate should be small, and the effective area of the flow should be large. This requires valves of various calibers and different types to be measured for flow resistance coefficient.
- 4. The ability of the valve body to withstand water pressure should be consistent with that of the pipeline, that is, the valve can withstand the requirements of the pipeline test pressure when the valve is open.
Third, the inner lining and external corrosion protection of the valve
The valve is a device for transporting drinking water. The inner lining of the valve must be non-toxic, corrosion-resistant, wear-resistant, and smooth, so that the water flow resistance is as small as possible. If the pressure plate, bolt and butterfly plate of the valve are of different materials, electrochemical corrosion is prone to occur. The rust generated by corrosion extends to the sealing surface and affects the sealing effect of the valve. In addition, the valve is installed in the valve well and soaked in water to prevent rust. Therefore, the lining should be well covered to prevent secondary pollution of the water supply caused by rust.
The external anti-corrosion of the valve can be polished and sanded, then electrostatically sprayed with non-toxic epoxy resin for anti-corrosion, or it can be brushed with red lead paint 1-2 times, and then the anti-rust paint twice.
Fourth, the operation and management of the valve
Whether the valve can open and close well, not only requires proper valve selection, good product quality, meticulous construction and installation, but also thoughtful management, in order to achieve the effect of “raising soldiers for a thousand days and using them for a while”. Good operation management is reflected in the following three aspects:
1. Complete technical information
The technical data of the valve includes the factory manual of the valve, the inspection certificate after the valve is purchased, the assembly and position card of the valve, and the maintenance record of the valve. For changes in the streets, the valve card should be updated in time, and strive to establish a GIS management system.
2. Thoughtful valve operation management
The quality requirements of valve operation management include that the valve should be closed tightly, there should be no leakage at the valve shaft seal packing, the valve can be opened and closed easily, and the instructions are intact. The daily work of valve operation management includes the approval record of the previous valve opening and closing operation orders and the improvement of the operation record, and the opening and closing records of the valve periodic inspection. For valves that have not been operated for a long time, it is necessary to set different inspection cycles according to the size of the caliber. For the faults found, a repair plan should be proposed and dealt with in a timely manner. In particular, the valves that cannot be opened after being closed should be dealt with as emergency treatment as a burst pipe.
3. Valve well is in good condition
The valve well condition includes the valve well masonry complies with industry standards and design specifications, the well cover is well connected to the road surface, the valve hole position is accurate, there is no debris and sewage in the well, and the valve surface has no rust spots. Where conditions permit, technical measures for long-term convection of air in the well should be considered for large-diameter valve wells. The valve well should be inspected regularly, and the loss and damage of the manhole cover should be dealt with in time.
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