Keywords: Water supply pipe network, Valve selection
The water supply pipe network is composed of various pipeline accessories and fittings such as pipes and valves. According to various needs (the water volume of the pipe network, the scheduling and allocation of water pressure, the need for water outage during maintenance and emergency repair, the connection of new and old pipelines, the flushing of pipelines, etc.), valves need to be opened and closed every day. The service life and quality of the valves determine the normal operation of the pipe network and play a crucial role in the pipe network, which must be highly valued.
Since the pipe network is a bridge connecting water supply enterprises and the majority of users, it can be said that the quality of a water supply enterprise's management work is reflected in the normal operation of the pipe network; and the normal operation of the water supply pipe network is closely related to the life and quality of the valves. The following are some opinions on the selection of valves for the water supply pipe network.
Safety of water supply
Not affecting water quality is an important indicator for valve selection. The parts of the valve that directly contact with water are mainly the inner side of the valve body, the sealing part, the valve plate, etc. At present, the sealing parts of many valves produced by manufacturers are made of rubber materials. Commonly used rubber materials are nitrile rubber (NBR), neoprene rubber (CR), or ethylene propylene rubber (EPDM). These rubbers are all synthetic rubbers. During the synthesis process, more than ten kinds of raw materials and anti-aging agents and other additives need to be added to the natural rubber. Whether the final synthetic rubber can be used for the sealing of water supply valves must depend on whether this rubber is non-toxic and complies with drinking water hygiene standards. As for the inner side of the valve and the valve plate and other parts, many manufacturers used the method of painting in the past, only considering the problem of rust prevention, but not considering whether it is toxic. In practice, we have found that in the water supply pipe network, the problem of anti-corrosion of the inner lining of the pipeline has been solved, but the pipe network valves have no inner lining. Due to the sedimentation of water and the erosion and deposition of iron bacteria in the water on the inner cavity and valve plate of the valve, some valve inner walls show a hilly accumulation phenomenon. This not only affects the water supply quality but also is one of the main reasons for some valves not closing tightly. Therefore, we require that these parts directly contacting with water should be sprayed with non-toxic coatings, and it is best to spray non-toxic epoxy powder by the electrostatic spraying method. When we select valves, we should first check whether there are non-toxic certificates and inspection certificates for rubber and coatings. Only valves with the above conditions can ensure that the water quality is not polluted and the safety of water supply is guaranteed.
Technological advancement
The production technology of valves is constantly developing, from the old-fashioned gate valves to soft-sealed gate valves, from the initial butterfly valves to wafer-type butterfly valves, single eccentric, double eccentric flange butterfly valves, hard-sealed butterfly valves, from the traditional single-head exhaust valves to high-speed double-port exhaust valves, etc. Therefore, when choosing valves, the advancement of the selected valves should also be considered. However, in the application of new technologies, we oppose the approach of blindly following the trend without distinction and without understanding the actual needs of users. Instead, new technologies and new processes should be combined with the needs of users. Good valves should come from the direct needs of users in actual production applications. For example, although the method of resin extrusion sealing has been proved to have advantages in design ideas and factory tests. However, in actual use, due to resin materials, extrusion resin tools, etc., the problem of how users use it has not been solved. When users use this type of valve, they cannot appreciate the advancement, characteristics and advantages of this valve and use it as an ordinary butterfly valve. Therefore, valve production should not only pay attention to its advancement but also its practicality. And pay attention to solving problems in actual applications, such as the research on the float material and float shape (spherical or cylindrical) of the exhaust valve and its effect on exhaust and service life. How to prevent the operation control (excessive closing) problem of the worm gear and worm butterfly valve, the top crushing problem of the gearbox housing, the marking problem of the switch indication, etc. Therefore, when choosing valves, attention must be paid to their technological advancement and practicality.
Sealing of water flow
Whether the valve plays a sealing role is a basic requirement for the valve. In practical applications, there are many types of seals, such as soft seal, hard seal, valve plate seal, valve body seal, surface seal, line seal, etc. No matter what kind of sealing form is adopted, the sealing effect cannot be affected. In the past, we have used some butterfly valves with valve plate seals. Theoretically, the biggest advantage of this type of butterfly valve is that once the sealing rubber ring fails, the valve does not need to be disassembled and can be replaced online. However, in the actual application of water supply enterprises, the advantages of this type of butterfly valve are difficult to be reflected. Therefore, if the rubber ring is replaced online, not only the pipelines at both ends of the valve need to be disassembled and the water in the pipeline needs to be emptied. At the same time, the replaced rubber ring cannot undergo a sealing test, and the replacement effect cannot be determined. Therefore, when choosing a valve, attention must be paid to the sealing form of the valve and combined with the actual application situation of each to check the sealing effect of the valve.
Authenticity of inspection
The valve production enterprise must be required to provide true and accurate inspection reports. These inspection reports include:
①Inspection of raw materials - The content of components such as C, Si, Mn, P, S in raw iron and the quality of coke, etc.;
②Inspection of castings - Metallographic test, elongation test, strength test, etc.;
③Sealing test - Double-sided pump pressure test and multiple switch tests, etc.;
④Hygiene quarantine reports of rubber and hygiene quarantine reports of coatings, etc. The products produced by enterprises that provide untrue inspection reports cannot be used.
Reliability of quality
The quality of valves is reflected in the entire manufacturing process of valves.
①Selection of raw iron; ②Manufacturing of sand molds; ③Casting of molten iron for castings; ④Machining accuracy, etc.
There should be a relatively complete quality assurance system. The indicator of the number of valve switchings is not very meaningful, and it is not necessary to meet the test of more than 5,000 switchings. Because the valves in the pipe network are not switched frequently. Sometimes, some valves are switched only once every ten or eight years. In our actual work, we have found that the positioning screws on the butterfly valve are loose during installation, and some even have no bolt threads.
Flexibility of operation
Whether the valve operation is flexible is very important. Flexibility of operation is not only reflected in the choice of which transmission method, but also in the processing accuracy of the components related to the transmission mechanism. For example, in the transmission method of butterfly valves. Generally, there are two transmission methods - screw nut type and worm gear and worm type. Generally, the characteristic of the screw nut type is that it is slow at both ends and fast in the middle during switching, which is relatively easy to operate. However, due to the small power moment of the screw, the operator is not easy to grasp the opening and closing degree of the valve plate during operation, and it is easy for the screw to be distorted and broken when the valve has been closed but is still in operation. The worm gear and worm type is generally prone to excessive closing. At the same time, problems such as the sealing of the valve stem of the gate valve and the matching of the rotational speed and rotational torque of the transmission part of the butterfly valve are difficult problems in valve operation. Therefore, when choosing which transmission method, according to the situation of each water supply enterprise, after listening to the opinions of the operators, closely cooperate with the manufacturer to ensure that the selected valve can be operated flexibly and meet the usage and working needs.
Rationality of price
The valve should have a reasonable price, and a reasonable price is not necessarily the lowest price. If only the lowest price is emphasized, it is easy to mislead manufacturers to compete to lower the price in order to promote their products, and even sell them at a price lower than the cost price of the product. In order not to lose money, the manufacturer will inevitably cut corners in the process and materials, and the produced valves will have quality risks. If used in the water supply pipe network, the users themselves will ultimately suffer. Therefore, it must be noted that when choosing valves, manufacturers are encouraged to apply the principle of value engineering, strengthen the main functions, remove redundant functions, and optimize the system functions. Work hard in management and cost accounting. It should be pointed out that a reasonable price can be the lowest price, but the lowest price is not necessarily a reasonable price.
Guarantee of after-sales service
Problems will occur when valves are used in the water supply pipe network. Some are related to the valves themselves, and some are from external factors such as interference and damage, rough construction, illegal operation, poor management and usage, etc. But no matter what the reason is, once the valve has problems, it will affect the operation of the pipe network and require the cooperation of the manufacturer. Therefore, when choosing valves, it is necessary for valve production enterprises to have a good guarantee of after-sales service. Once the valve has problems, they can arrive at the site in the shortest time and solve the problems as soon as possible.
Consistency of ordering and supply
The consistency mentioned here refers to the consistency of all aspects of the valve products produced by the valve production enterprise and the products required by the water supply enterprise. This requires the joint efforts of both the ordering party and the supplying party (the water supply enterprise and the valve production enterprise), not just the efforts of one of them. First of all, as the ordering party, the water supply enterprise, when placing an order with the valve production enterprise, must put forward clear technical requirements to the valve production enterprise in writing. The content should include the type of valve, the technical and quality standards that each part of the valve should implement, the main technical parameters, the materials of each part, the model of the valve, the sealing form, the requirements of the sealing material, the form of the structure, the connection method and the transmission method, the technical standards for pressure testing and strength inspection, the requirements for anti-corrosion and lining, the maximum torque and rotation speed, the assembly and appearance requirements, as well as the delivery time, place, quantity, etc. The valve production enterprise should organize production reasonably according to the order contract and technical conditions, and ensure that the produced products can meet the usage requirements of the ordering unit (water supply enterprise) and ensure the consistency of ordering and supply.
Establish a complete inspection and re-inspection system
When a water supply enterprise, after many investigations, researches and a certain range of tests, finally selects one or several valve production enterprises and issues a pass allowing their products to enter the local water supply market, it means that a supply and demand relationship is established between the water supply enterprise and the valve production enterprise. At the same time, the valve production enterprise also correspondingly assumes joint responsibility for ensuring the safe and reliable water supply of the water supply enterprise. On the one hand, it requires the valve production enterprise to always provide high-quality products in accordance with the requirements of the water supply enterprise. On the other hand, in order to ensure quality, it also requires the water supply enterprise to establish necessary and relatively complete regular inspection and re-inspection systems for the designated manufacturers, generally within 2 to 5 years. The five major elements of personnel, machinery, materials, methods and environment of the designated manufacturers are inspected and evaluated regularly. While inspecting the manufacturers, the water supply enterprise should also make necessary revisions and supplements to the original technical conditions according to the usage situation of the valves of the unit.