Application Of Valves In Water Supply System

Oct 25,2019

The irreplaceability of water and the necessity of people's survival determine the importance of safe operation of water supply network. However, due to the subjective and objective reasons, the pipeline often appears some faults, the pipeline network is always to be updated, water users often have to increase or decrease, so the local pipe section of the water cut-off phenomenon is difficult to avoid. In order to reduce the scope of water cut-off, it is necessary to install the control valve properly in the pipe network. So in a city's water supply network, there are thousands of valves, which are distributed irregularly under the city streets.
The valve operation on the water supply network is not frequent, long-term standby, once needed, the valve should be able to close quickly, closure reliable; usually required to be in place to open the valve, reduce the head loss of the pipe section, therefore, the valve is a kind of control equipment which can be used for a long time, and the intact 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 main reason is the quality of the valve.
Valves in the water supply network in the number of large, widely distributed, large role. Therefore, in the valve selection, inspection, performance and management have many issues worthy of study.

1. Selection of Valves

There are several kinds of valves, such as butterfly valve, gate valve, ball valve and cock valve, etc. In order to reduce the depth of the earth covering of the pipeline, the butterfly valve should be selected for the large diameter pipeline, the gate valve should be selected for the small-diameter pipeline, the ball valve and the cock valve are difficult to cast and processed, and the price is more expensive. In recent years, due to the improvement of casting technology, resin sand casting can avoid or reduce mechanical processing, thus reducing the cost, so the feasibility of using ball valve in large diameter pipeline is worth exploring. As for the size of the demarcation line should be divided according to the specific circumstances of each place.

The main disadvantage of the butterfly valve is that the butterfly plate occupies a certain cross-section of water flow and increases a certain loss of water head. The length of large diameter horizontal gate valve increases the transverse area of pipeline and affects the arrangement of other pipelines ball valve and cock valve is to maintain a single gate valve, water resistance, reliable sealing, flexible action, easy operation and maintenance and other advantages. Plug valves have similar advantages, except that the cross-section is not perfectly circular.

In recent years, many domestic valve manufacturers developed soft-seal gate valve, this gate valve and the traditional wedge or parallel double gate valve has the following characteristics:
(1). The body and cover of the soft sealing gate valve are cast by precision casting method, once forming, no machining at all, no sealing copper ring, saving Non-ferrous metal.
(2). There is no pit in the bottom of the soft seal gate valve, there is no residue, the failure rate of the gate valve opening and closing is low.
(3). Soft sealing rubber valve plate with uniform size and strong interchangeability.

Therefore, the soft seal gate valve will be the development direction of gate valve, but also the water supply industry is willing to use a valve. Open and close soft seal gate valve, do not close too dead, as long as the effect of water can not easily open or lining rubber stripping.
Most of the butterfly valves used in water supply industry are soft sealing butterfly valves. In view of the vulnerability of rubber ring in the installation process of butterfly valves, many manufacturers introduce metal sealing butterfly valves instead of rubber ring sealing butterfly valves. Metal seal butterfly valve because of the small elastic seal, generally eccentric structure, especially with a three-dimensional eccentric structure is more reasonable.

2. Performance And Testing Of Valves

The particularity of the valve requires its reliable quality and excellent performance. When evaluating valve performance and performance testing, the following points should be noted:
(1). The valve is flexible and portable to open and close under working water pressure, and the torque wrench is used to detect the opening torque under working water pressure.
(2). The valve is tightly closed and does not leak or leak under 1.1 times working water pressure to meet the standard requirements (metal-sealed butterfly valve) , which requires the two sides of the valve to take turns to bear pressure, test separately, and repeatedly open and close to achieve the same effect. Require all kinds of calibers, different types of valves should be in the manufacturers and qualified units to test the life of the load opening and closing. This test also includes an evaluation of the sealing effectiveness of the valve shaft.
(3). Valve flow capacity to be strong, especially the butterfly valve, butterfly plate flow resistance to be small, the effective area of flow to be large. This request each kind of caliber, the different type valve should carry on the flow resistance coefficient the determination.
(4). The ability of the valve body to bear the water pressure shall be the same as that of the pipeline, that is, the valve can bear the requirement of the pipeline test pressure when the valve is open.

3. Inner Lining And Outer Anti-corrosion Of Valve

Valve is the equipment to transport drinking water, the valve body lining must be non-toxic, corrosion-resistant, wear-resistant, smooth, so that the flow resistance as small as possible. Such as the valve pressure plate, bolt and butterfly plate material is different, it is easy to have electrochemical corrosion, corrosion generated rust extends to the sealing surface, affect the sealing effect of the valve, in addition to the valve installed in the well, immersed in water, it is important to prevent corrosion, so the lining should be well covered to prevent the secondary pollution of water supply caused by corrosion.
The external anti-corrosion valve can be polished sand, then for electrostatic spray non-toxic Epoxy anti-corrosion, can also brush 1-2 times red paint, then brush twice anti-rust paint.

4. Operation And Management Of Valve

Whether the valve can open and close well, not only the valve type selection is appropriate, product quality is good, careful construction and installation, but also thoughtful management, in order to play the "a thousand days, a time" effect. Good operational management is achieved in the following three areas:
(1). Technical Information Is Available
Valve technical information including the valve factory manual, valve after the purchase of the inspection certificate, valve assembly and location card, valve repair record. For the changes in the street, the valve card should be updated in time, and strive to establish gis management system.
(2). Valve Operation Is Well Managed
The quality requirements of valve operation management include that the valve should be closed tightly, the valve shaft seal packing does not leak, the valve open and close portable, indicating good. The daily work of valve operation management includes valve opening and closing operation record and operation record, valve opening and closing record and so on. For valves that have not been operated for a long time, it is necessary to determine a different test cycle based on the size of the caliper. For the failure to be found should be put forward maintenance program, timely treatment, especially after closing the valve can not be opened should be like emergency treatment of burst pipe.
(3). Valve Well In Good Condition
Valve well status includes valve well masonry in line with industry standards and design specifications, well cover and road interface is intact, the operation of the valve hole position accurate, well without debris and sewage, valve surface without rust spots. The technical measures for long-term convection of air in large-bore valve wells should be taken into account when conditions permit. Inspect the valve well regularly and deal with the loss and damage of the cover in time.