Discussion on Valve Problem in Water Supply

1 Valve in the water supply pipe network function

Water supply pipe network will be sent to the tap water supply and distribution to thousands of households, so water distribution network in every corner of the city, water supply pipe network pipe length as few as hundreds of kilometers, up to thousands of kilometers.

The irreplaceable of water and the necessity of people's existence determine the importance of safe operation of water supply network. However, due to various aspects of subjective and objective reasons, the pipeline is often to some failures, the pipe network is always constantly updated transformation, water users often have to increase or decrease so the local pipe section of the water phenomenon is difficult to avoid. In order to reduce the scope of water, in the pipe network to properly install the control valve is very necessary. Therefore, in a city's water supply pipe network, the number of thousands of valves, and irregularly distributed in the city streets below.

Valve is a "maintenance for thousands of days, for the moment," the control equipmen t, usually require the valve to open in place to reduce the water loss of the pipe section. Once required, the valve should be able to close quickly and reliably.

Valve intact, related to the valve selection, valve manufacturing, piping design, valve assembly, valve opening and closing operations and valve management, of course, the most important reason is the quality of the valve.

2 Problem research

Valve in the water supply network in the role of large, number, wide distribution, there are many problems. Water supply pipe in the valve operation is not frequent, long-term standby, once the call, it is difficult to work. Therefore, the valve selection, valve manufacturing, valve inspection, valve assembly, valve management, there are many e lements worth discussing.

2.1 water supply pipe valve selection

(1) gate valve and butterfly valve.

In the water supply pipe network in order to reduce the depth of pipe casing, the general diameter larger pipe matching butterfly valve, little effect on the casing depth, and strive to matching valve, caused by the diameter of the dividing line should be around the specific circumstances. From the use of the past decade, the butterfly valve failure than the high valve, so the conditions permit, to expand the use of gate valve range is noteworthy.

(2) gate valve

In recent years, many Chinese valve manufacturers, development, imitation soft seal gate valve, the gate valve than the traditional wedge-type or parallel double-gate valve has the following characteristics:

A.Soft sealing valve body, valve cover using precision casting method of casting, a molding, the basic non-mechanical processing, do not use sealed copper ring, saving non-ferrous metals.

B. Soft sealing gate valve bottom without pits, no accumulation of residue, the gate valve opening and closing of the failure rate is low.

C. Soft sealing rubber valve plate uniform size, interchangeable.

3) Butterfly valve.

Several Issues Concerned in Selection of Current Butterfly Valves:

A. Center line butterfly valve.

Butterfly valve in the small-diameter butterfly valve in the use of large, the effect is better.

B. Comparison of vertical and horizontal butterfly valves.

In the large butterfly valve, the valve shaft there is vertical and horizontal difference, usually vertical butterfly valve casing soil deep, the water debris easy to wrap around the shaft, the impact of opening and closing; horizontal butterfly valve in the side of the transmission box, Valve wells on the road occupies a wide position in the plane, affecting the arrangement of other pipelines. Therefore, in the medium-sized vertical butterfly valve with more, large-diameter butterfly valve in the plane position permission under the conditions of horizontal. Regardless of vertical or horizontal, valve opening and closing indicators should take measures to be observed from the ground.

C. Eccentric butterfly valve.

Center line butterfly valve closed seal, in essence, a rubber lining of the extrusion seal, especially around the valve shaft is squeezed larger, so that the service life of the valve is affected, the valve opening and closing torque is too large. In order to alleviate the shortcomings in this area, the design of one-dimensional, two-dimensional and three-dimensional eccentric butterfly valve. Eccentric butterfly valve in bearing water pressure is directional, especially the three-dimensional butterfly valve revers e bearing capacity is weak. As the pipe network is ring-shaped, requiring two-way valve to withstand the pressure requirements are the same, so the order should be stressed that the requirements.

D. Soft sealing and metal sealing

Water supply industry, most of the butterfly valve is a soft seal butterfly valve, this seal in the use of the following problems arise:

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

② valve in the manufacturing process, it is difficult to ensure that the valve disc cavity in the center line of the body, often over-squeeze the way to solve the sealing problem, thus affecting the valve life;

③ vertical butterfly valve shaft and sleeve processing accuracy and thrust imbalance, resulting in disc slippage and droop, forming a leak;

④ Butterfly valve in the installation process of the rubber ring damaged, affecting the sealing.

Metal seal butterfly valve seal as the elasticity of the smaller, generally used eccentric structure, especially with three-dimensional eccentric structure is ideal. Metal sealing butterfly valve was originally used for high-pressure steam pipe, the price is more expensive, it is not easy to damage the sealing surface in operation, but its manufacturing accuracy is higher, once the leakage is difficult to repair.

4) Ball Valves and Plug Valves.

The main disadvantage of the butterfly valve is that the disc occupies a certain water cross section, increasing the loss of a certain head; Although the gate valve without this problem, but the large diameter vertical gate height of the pipe casing depth, large diameter horizontal gate valve length, Large pipelines occupy the horizontal area, affecting the arrangement of other pipelines; ball valves and plug valves to maintain the gate valve over the water cross section, but also to overcome its shortcomings. Ball valve has the advantages of simple structure, small flow resistance, reliable sealing, flexible movement, easy maintenance and operation. Plug valve also has a similar advantage, only the water area is not parked. .

Ball valves and plug valves are heavier than the butterfly valve, casting and machining difficult, more expensive, generally applicable to small and medium-diameter pipe. In the past ten years, due to the improvement of casting technology, the lost-die method or resin sand casting can avoid or reduce machining, thus reducing the cost, so the feasibility of ball valve for large diameter pipe is worth exploring.