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Analysis on the selection and operation of water supply pipe network valves

The irreplaceability of water and the necessity of people's survival determine the importance of safe operation of the water supply network. However, due to the subjective and objective reasons, the pipeline often has some failures. The pipe network is always updated and rebuilt. The water users often have to increase or decrease. Therefore, the water stoppage of the local pipe sections is difficult to avoid. In order to reduce the water stop range, it is necessary to properly install the control valve in the pipe network. Therefore, in a city's water supply network, the number of valves is tens of thousands, and it is irregularly distributed under the city streets.
The valve operation on the water supply network is not frequent, and it is long-awaited. Once needed, the valve should be able to close quickly and the interception is reliable. Usually, the valve should be opened to reduce the head loss of the pipe section, so the valve is a kind of "fighting soldiers for a thousand days. "Control equipment; valve integrity rate, related to valve selection, valve manufacturing, pipeline design, valve assembly, valve opening and closing and valve management, of course, the main reason is the quality of the valve. The valve has a large number, wide distribution and great effect in the water supply pipe network. Therefore, there are many problems in valve selection, inspection, performance and management that are worth discussing.
First, the selection of valves
Valves have butterfly valves, gate valves, ball valves and plug valves, and the range used in the water supply network is different. In order to reduce the depth of soil cover, the larger diameter of the pipeline is matched with the butterfly valve; for the depth of the soil, the gate valve is selected. The ball valve and the plug valve are difficult to cast and process, and the price is relatively expensive. It is generally suitable for small and medium-sized pipes. In recent years, due to the improvement of casting technology, the resin sand casting method can avoid or reduce the machining, thereby reducing the cost. Therefore, the feasibility of the ball valve for the large diameter pipe is worth exploring. As for the dividing line of the size of the caliber, it should be divided according to the specific circumstances.
The main disadvantage of the butterfly valve is that the butterfly plate occupies a certain cross-section of the water and increases the loss of the head; although the gate valve does not have this problem, the height of the large-diameter vertical gate valve affects the depth of the soil, and the length of the large-diameter horizontal gate valve increases. Pipes occupy a horizontal area, affecting the arrangement of other pipelines; ball valves and plug valves maintain the advantages of single valve gate, small water flow resistance, reliable sealing, flexible operation, and convenient operation and maintenance. Plug valves also have similar advantages, except that the cross section of the water is not a perfect circle.
In recent years, many domestic valve manufacturers have developed soft-sealed gate valves. Compared with traditional squat or parallel double-gate gate valves, this gate valve has the following characteristics:
1. The valve body and valve cover of the soft sealing gate valve are cast by precision casting method. Once formed, it is no longer machined at all, and no sealed copper ring is used to save non-ferrous metals.
2. There is no pit at the bottom of the soft seal gate valve, no slag is accumulated, and the failure rate of the gate valve opening and closing is low;
3. The soft seal rubber-lined valve plate is uniform in size and interchangeable.
Therefore, the soft seal 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 much, as long as the water stop effect is achieved, otherwise it will not be easy to open or the rubber stripping.
Most of the butterfly valves used in the water supply industry are soft-sealed butterfly valves. For the butterfly valve during the installation process, the rubber ring is easily damaged, which affects the sealing. Many manufacturers have introduced metal sealing butterfly valves instead of rubber ring sealing butterfly valves. Due to the small elasticity of the seal, the metal sealing butterfly valve generally adopts an eccentric structure, and it is more reasonable to use a three-dimensional eccentric structure.
Second, the performance and testing of the valve
The particularity of the valve requires reliable quality and excellent performance. When evaluating the performance and performance testing of valves, the following points should be noted:
1. The valve is flexible and light to open and close under working water pressure, and the opening torque is detected by a torque wrench under working water pressure.
2. The valve is tightly closed, and it does not leak or leak under 1.1 times working water pressure to meet the standard requirements (metal-sealed butterfly valve). This requires the two sides of the valve to be under pressure and separately tested, and the multiple opening and closing achieve the same effect. . It is required that all kinds of valves with different calibers and different types should be tested for life with load opening and closing in the manufacturer and the qualified units. This test also includes an evaluation of the valve shaft sealing effect.
3. The valve has a strong overcurrent capability, especially for butterfly valves. The overcurrent resistance of the butterfly plate is small, and the effective area of the overcurrent is large. This requires the determination of the flow resistance coefficient for all types of valves of different calibers and types.
4. The ability of the valve body to withstand water pressure should be consistent with the pipeline, that is, the valve can withstand the test pressure of the pipeline when the valve is open.
Third, the valve lining and external anti-corrosion
The valve is a device for conveying drinking water. The valve body lining 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 disc of the valve are made of different materials, electrochemical corrosion is easy 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 immersed in water to prevent corrosion. 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 sand-cleaned, and then electrostatically sprayed with non-toxic epoxy resin to prevent corrosion. It can also be brushed 1-2 times with red dan paint, and then brushed twice with anti-rust paint.
Fourth, the operation management of the valve
Whether the valve can be opened and closed well, not only the valve selection is appropriate, the product quality is good, the construction is carefully installed, but also the management must be thoughtful, in order to achieve the effect of "fostering a thousand days, using soldiers for a while". Good operational management is reflected in the following three aspects:
1. Complete technical information
The technical data of the valve includes the valve manufacturer's manual, the inspection certificate after the valve is purchased, the valve assembly and position card, and the valve maintenance record. For the change of the street, the valve card should be updated in time to strive to establish a GIS management system.
2. Valve operation management and thoughtful
The quality requirements of valve operation management include that the valve should be closed tightly, the valve shaft seal packing is not leaking, the valve is light and easy to open and close. The daily operation of valve operation management includes the approval record of the 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 determine different detection cycles depending on the size of the caliber. For the faults found, a maintenance plan should be proposed and dealt with in a timely manner. In particular, valves that cannot be opened after closing should be treated urgently like a bursting pipe.
3. Well valve is in good condition
The valve well condition includes the valve well masonry in line with industry standards and design specifications, the well cover and the road surface are well connected, the hole position of the operating valve is accurate, there is no debris and sewage in the well, and the valve surface has no rust spots. Large-calibre valve wells should take into account technical measures for long-term convection of the air in the well, where conditions permit. The valve well should be inspected regularly, and the loss and damage of the manhole cover should be dealt with in a timely manner.

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