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Water system valve selection reference

hits:626   times:2015/8/22

In the water supply network in order to reduce the depth of the pipe casing, generally larger diameter piping matching butterfly, little effect on the overburden depth, and strive to matching valve, caused in diameter around the dividing line should be considered according to the specific circumstances. From the last decade in terms of usage, failure butterfly appeared higher than the gate, so when conditions permit, to expand the use of gate valve is noteworthy.

(1) gate

In recent years, many domestic valve manufacturer, development, imitation soft seal valve, this valve than traditional wedge or parallel double plate valve has the following characteristics:

a. soft sealing gate valve body, valve cover using precision casting casting, forming a basic non-mechanical processing, without use of sealed copper ring, saving non-ferrous metals.

b. the bottom of the soft sealing gate no pits, no accumulation of slag material, valve opening and closing low failure rate.

c. soft sealing rubber lined valve plate size uniform and interchangeable.

So soft sealing valve would be willing to use a form of the water supply industry. Currently the domestic manufacture of soft sealing valve diameter up to 1500mm, but most manufacturers manufacture caliber in between 80-300mm, the domestic manufacturing process there are still many problems, from the investigation of the case, the Shanghai valve body of a valve manufacturing company was commissioned domestic foundry casting resin sand molding turn, the soft sealing valve plate is imported from a foreign company. The company believes that key components are rubber lined soft sealing gate valve plate, and high technical requirements of rubber lined valve plate, not all foreign manufacturers can achieve, often purchased from a reliable quality factory assembly.

Domestic soft sealing gate valve brass nut blocks are embedded in a rubber lined valve plate hanging side, similar to the gate structure, since the movable friction nut block valve plate rubber lining is easy to peel. Foreign companys soft seal valve, brass nut blocks are embedded in the rubber lined gate, integrally formed to overcome these shortcomings, but the higher the valve cover and valve combination of concentricity requirements.

When closing the soft seal valve, do not close off dead, as long as you can to achieve sealing effect, otherwise difficult to peel open or rubber lining. Shandong, a valve manufacturing company, when the valve pressure test inspection, use torque wrench to control the degree of closure, as the water company operator of such valves open and close methods should effect.

(2) Butterfly

Several Issues butterfly Selection of concern:

a. butterfly valve

Butterfly valve in the use of a large amount of small-caliber valve, the effect is better. There are two major differences in manufacturing methods: After a body with rubber layer support bracket (in Tanggu product represented); without the support frame after a valve rubber lining layer (in Zhengzhou product represented). The former amount Chenjiao fewer, larger flow area latter. Some people suspect the latter valve life is short, but not so, according to the survey.

b compared vertical and horizontal butterfly

In large butterfly, there is the difference between vertical and horizontal valve shaft, usually vertical butterfly valve casing deeper, debris in the water is easy winding shaft, affect the opening and closing; horizontal shift gearbox butterfly next to the side, plane position of the valve shaft on the road accounted for wider impact arrange other pipelines. Therefore, as with vertical, large diameter butterfly valve strive horizontal plane of the license under the conditions in the medium-diameter butterfly valve. Whether vertical or horizontal, valve opening and closing index shall take measures in order to observe from the ground.

c. butterfly valve

Butterfly valve closure seal, essentially squeezing a rubber liner seal, especially by the large crowd near the valve shaft, which affected the life of the valve, the valve opening and closing torque is too large. To alleviate the shortcomings in this area, designed one-, two- and three-dimensional eccentric butterfly valve, which developed the three-dimensional eccentric butterfly valve, sealed state theory is a contact seal state, many manufacturers have been developed in this area, on Haichuan Shanghai products using computer-controlled machining of products close to the technical requirements in this regard.

Eccentric butterfly valve in the hydraulic pressure on the carrier is directional, particularly three-dimensional partial butterfly reverse pressure capability is weak. As the pipe network is cyclic, requires valve to withstand the pressure of the two requirements are the same, therefore the order should emphasize this requirement.

d. soft seal and metal seal

Most butterfly water industry uses a soft seal butterfly valve, this sealing method the following problems arise in the use of:

① poor rubber quality, easy to aging, long-term compressive deformation, extrusion cracking;

② valve in the manufacturing process, it is difficult to ensure concentricity of the disc in the body cavity, often excessive compression seal way to solve the problem, which affected the life of the valve;

③ vertical butterfly valve shaft and sleeve machining accuracy and thrust mode imbalance, resulting disc shaking and sagging, forming a leakage;

④ valve in the installation and construction process Aprons damaged, affecting the seal.

To solve these problems, some manufacturers made the following improvements:

① apron sentinel outsourcing production, strengthen quality control, commonly used for water supply industry valve, use eye EPDM rubber and natural rubber and butyl rubber is not much, is prohibited blending recycled plastic;

Shanghai Haichuan on ② valve plate gasket to block the butterfly plate into short blocks assembled dovetail connection to adjust the degree of pressing various parts of the plate to balance the butterfly life, but this adjustment technique is difficult to master ʱ??

③ Haichuan Shanghai launched the DB valve and flange butterfly, their sealing gasket mounted on the dovetail slot, there is a certain margin of activity, you can adjust itself when the valve closed Aprons extrusion conditions;

④ Haichuan Shanghai to launch a "fluoroplastic" ring replacement rubber seals, seals improve wear resistance and resistance to aging;

⑤ many manufacturers have introduced metal sealing butterfly valve replacement O-ring seal.

Because of the elastic metal sealing butterfly valve seals small, generally eccentric structure, especially the use of three-dimensional asymmetric structure is preferable. Metal sealing butterfly valves for high pressure steam piping original, more expensive, it is easy to damage the sealing surface in operation, but its high manufacturing precision, once difficult to repair leaks.

(4) Ball and plug valves

The main disadvantage is that the butterfly valve plate occupy a certain cross section, increased by a certain head loss; gate although no problem, but the length of casing depth large diameter vertical pipe valve of high-impact, large-diameter horizontal gate valves, increasing occupy a large pipeline lateral area, affecting other pipelines arrangements; ball and plug valves remained the gate of cross section, but also overcome its shortcomings. Ball has a simple structure, small flow resistance, reliable seal, flexible movement, easy maintenance and operation. Plug valves also have similar advantages over the water area is not the only positive circular.

Butterfly valve and plug than heavy, casting and machining difficult, expensive, generally applies to small and medium diameter pipe. Nearly a decade due to improvements in casting technology, using EPC method or resin sand casting method, can avoid or reduce machining, thereby reducing the cost, and therefore the feasibility of large-diameter pipe for the ball on the worth exploring.

In recent years, Shanghai Haichuan modeled on US products, developed a fan-shaped eccentric plug valves, fan-shaped valve plate lined with rubber, sealing, small opening and closing torque, flow area, and by the Department of Mechanical valve testing center made a valve opening and closing durability testing and flow resistance testing to fill the gaps of such valve type. The current sector eccentric bottom plug has a recess, easy slag accumulation, open and close easily lead to failure, should be improved.

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