The irreplaceability of water and the necessity of people’s survival determine the importance of the safe operation of the water supply network.
But due to various reasons, it’s hard to avoid the water shutdown of the local section. It is necessary to install the control valve properly in the pipe network in order to reduce the water cut-off area. Therefore, in a city’s water supply network, there are tens of thousands of valves and all of them are randomly distributed under the city streets.
Valves in the supply line are not frequently operated and are on standby for a long period of time. Once needed, the valve should be able to close quickly and reliably shut off the flow; It requires the valve can open in place to reduce the loss of head pipeline section; Valve integrity rate is related to valve selection, valve manufacturing, pipeline design, valve assembly, valve opening and closing, and valve management. Of course, the most important reason is valve quality. The number of valves in the water supply network is large and the valves are widely distributed with a big function.
Therefore, there are many problems in valve selection, inspection, performance and management that are worthy to discuss.
Selection of Valve
There are several types of valves, such as butterfly valves, gate valves, ball valves, and plug valves etc. Different valves have different application ranges in the water supply network.
In order to reduce the soil depth of the pipeline, butterfly valves are usually equipped with larger diameter pipes. For those with little effect on the depth of overburden, try to choose the gate valve. Ball valve and plug valve are difficult to cast and process, and the price is more expensive so it is generally suitable for small and medium diameter pipes. In recent years, because of the improvement of casting technology, mechanical processing can be avoided or reduced thus reducing the costs. Therefore, the feasibility of using ball valves on large-caliber pipes is worth exploring. As for the boundary of the size of the caliber, it should be divided according to specific circumstances.
The main disadvantage of butterfly valves is that the butterfly plate occupies a certain water cross-section and 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 soil coverage of the pipeline, and the length of the large-diameter horizontal gate valve increases transverse area occupied by the pipe and affects the arrangement of other pipelines; The ball valve and the plug valve maintain the advantages of a single gate valve, low water flow resistance, reliable sealing, flexible action, and convenient operation and maintenance.
In recent years, many China valve manufacturers have developed soft-sealed gate valves. This type of gate valve has the following characteristics compared to the traditional chock or parallel double-gate gate valve:
- The valve body and valve bonnet of the soft-sealed gate valve are cast by precision casting method, once formed, no more mechanical processing, no sealing copper ring was used,this means non-ferrous metals are saved.
- Soft-sealed gate valve has no pits at the bottom, no slag deposits, and low failure rate of gate valve opening and closing.
- Soft seal rubber lined valve plate has strong interchangeability because of the uniform size.
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-sealed gate valve, do not close it too much as long as it achieves water-stopping effect, otherwise it is not easy to open or it would cause cause liner stripping.
Most of the butterfly valves used in the water supply industry are soft-sealed butterfly valves. In order to prevent the rubber ring from being damaged during the installation of the butterfly valve, many manufacturers have pushed out metal-sealed butterfly valves instead of rubber-sealed butterfly valves. Due to the small elasticity of the seal, the metal seal butterfly valve generally adopts an eccentric structure, especially a three-dimensional eccentric structure is more reasonable.
Valve performance and testing
The special characteristics of the valve require its reliable quality and excellent performance. When evaluating the valve performance and performance of testing, the following points should be noted:
1. The valve is flexible and light to open and close under working pressure,and detect opening torque under working water pressure by a torque wrench.
2. The valve is tightly closed, and no leakage or leakage meets the standard requirements (metal-sealed butterfly valve) at 1.1 times of the working water pressure. This requires that the two sides of the valve are alternately bear the pressure and tested separately, and the same effect is achieved by opening and closing multiple times. It is required that valves of various diameters and different types should be tested for life with the load opening and closing at the manufacturer and a unit with test qualification. This test also includes an evaluation of the sealing effect of the valve shaft.
3. The valve’s flow capacity must be strong, especially for butterfly valves, the flow resistance of the butterfly plate should be small, and the effective area of flow should be large. This requires that various diameters and different types of valves should be tested for flow resistance.
4. The capacity of the valve body to withstand water pressure should be same with that of the pipeline, that is, the valve can withstand the test pressure requirements of the pipeline when the valve is open.
Lining and outer corrosion protection of 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 resistance to water flow is as small as possible.
If the materials of pressure plate, bolt and butterfly plate of the valve are different, it is easy to occur electrochemical corrosion, corrosion generated rust extends to the sealing surface and affects the sealing effect of the valve,In addition, the valve is installed in the valve well, soaked in water, so it is very important to prevent corrosion.
Therefore, the lining should be completely covered to prevent secondary pollution of the water supply caused by rust. The valve’s external anti-corrosion can be polished and sanded, and then electrostatic sprayed non-toxic epoxy resin anti-corrosion, or you can first brush 1-2 times red varnish, and then two times anti-rust paint.
Valve operation management
Whether a valve can be opened and closed well requires not only proper valve selection, good product quality, careful construction and installation, but also careful management. Good operation management is reflected in the following three aspects:
1. All Technical Data are available
The valve’s technical information includes the valve’s factory manual, the inspection qualification certificate after the valve is purchased, the valve’s assembly and position card, and the valve’s maintenance record. For street changes, the valve card should be updated in a timely manner, and strive to establish a GIS management system.
2. Thoughtful Valve operation and management
The quality requirements of valve operation management include that the valve should be closed tightly, there is no leakage at the valve shaft sealing packing, the valve is easy to open and close, and the instructions are intact. The valve operation management includes the approval record and operation record of the opening and closing operation orders of each time of the valve, and the opening and closing records of the regular inspection of the valve.
For valves that have not been operated for a long time, it is necessary to establish different detection cycles according to the size of the caliber. A maintenance plan should be proposed for the faults found, and dealt with it in a timely manner, especially the valves that cannot be opened after closing should be urgently handled.
3. Valve well in good condition
The condition of the valve well includes that valve well masonry in accordance with industry standards and design specifications, the well cover is well connected with the road surface, the position of the valve is accurate, there is no debris and sewage in the well, and there is noin a timely manner rust spot on the valve surface. When conditions permit, large-diameter valve wells should consider technical measures for long-term convection of air in the wells. Valve wells should be inspected regularly, and the loss and damage of well covers should be handled .