Characteristics and selection of valves

1. valve: valve is closed parts (RAM) vertical movement of the valve in the pipeline along the channel axis, used primarily as a medium cut that open and close use. In general, the valve can not be used as a regulation flow. The utility model can be applied to low temperature pressure, and can also be applied to high temperature and high pressure, and can be made according to different materials of the valve. But the valve is generally not used to transport mud and other media pipeline.

Advantage：

Fluid resistance is small;

The torque needed for opening and closing is smaller;

May use in the medium to the two direction flow ring network pipeline, namely the medium flow direction is not restricted;

When opening fully, the sealing surface is eroded by the working medium smaller than the cut-off valve;

The structure of the body is relatively simple, and the manufacturing process is better;

The structure of relatively short length.

Shortcoming:

The dimensions and the opening height are large, and the installation space is larger;

In the process of opening and closing, a relative friction sealing, friction is large, even at high temperature, easy to cause abrasions;

Generally, the gate valve has two sealing surfaces, which adds some difficulties to the processing, grinding and maintenance;

Opening and closing time is long.

2. butterfly valve: butterfly valve is to use disc type to open and close parts reciprocating reciprocating about 90 degrees to open, close and adjust the fluid channel of a valve.

Advantage：

The structure is simple, small size, light weight, save supplies, not used in large diameter valve;

Quick opening and closing, small flow resistance;

For medium with suspended solid particles, depending on the strength of the sealing surface, it can also be used in powder and granular media. The utility model can be applied to the bidirectional opening and closing and adjustment of the ventilation and dust removal pipelines, and is widely used in the gas pipelines and waterways of metallurgy, light industry, power, petrochemical systems, etc..

Shortcoming:

Flow regulation range is not large, when the opening to 30%, the flow will reach more than 95%.

Because of the structure of butterfly valve and the limitation of sealing material, it should not be used in the pipeline system of high temperature and high pressure. The general operating temperature is below 300 degrees, less than PN40.

Sealing performance relative to the ball valve, cut-off valve is poor, it is used for sealing requirements are not very high places.

3. ball valve: evolved from the plug valve, its opening and closing parts are a sphere, using the ball around the axis of the stem rotation 90 degrees, to achieve the purpose of opening and closing. Ball valve in the pipeline is mainly used for cutting, distribution and change the direction of media flow, designed to V shaped opening of the ball valve, also has a good flow adjustment function.

Advantage：

Minimum flow resistance (actual 0);

Because it is not stuck at work (without lubricant), it can be reliably applied to corrosive media and low boiling liquid;

Complete sealing can be achieved in larger pressure and temperature range;

The quick opening and closing can be realized, and the opening and closing time of some structures is only 0.05 ~ 0.1s, so as to ensure that the structure can be used in the automation system of the test stand. Quick opening and closing valve, operation without shock.

The spherical closure can be automatically positioned at the boundary position;

The working medium in the two-sided reliable seal;

In the fully open and fully closed, the ball and seat sealing surface and the dielectric isolation, the high-speed media through the valve will not

It has the advantages of compact structure, light weight, it could be considered for most reasonable structure of the valve system of medium low temperature;

To body symmetry, especially the welded body structure, can well withstand the stress from the pipe;

The closure of parts can withstand the pressure differential.11.

They all welded ball valve can be buried underground, so that the valve parts from erosion, the maximum life of up to 30 years, is the most ideal oil and natural gas pipeline valve.

Shortcoming:

Because the main valve seat seal material is PTFE, it has almost all the chemical substances are inert, and the friction coefficient is small, stable performance, easy to aging, temperature range and excellent sealing characteristics of a comprehensive. But the physical properties of PTFE include high expansion coefficient, sensitivity to cold flow, and poor thermal conductivity. The design of seat seals must be carried out around these characteristics. Therefore, when the seal material hardens, the reliability of the seal will be damaged. What's more, polytetrafluoroethylene has a lower temperature range and can only be used at less than 180 degrees centigrade. Over this temperature, the sealing material will age. Consider long-term use, usually only at 120 degrees Celsius use.

Its regulating performance is worse than the cut-off valve, especially pneumatic valve (or electric valve).

4. stop valve: refers to the closure of the valve (valve) along the center line of the valve to move the valve. According to this form of valve movement, the valve seat opening change is proportional to the valve stroke. Because of the valve stem to open or close the trip is relatively short, but very reliable cut off function, and because changes in the valve seat and the valve stroke is proportional, is very suitable for flow regulation. Therefore, this type of valve is ideally suited for cutting or adjusting and throttling.

Advantage：

In the process of opening and closing, the friction between the disc and the valve body is smaller than that of the gate valve, so it is wearable. The opening height is generally only 1/4 of the seat passage, so it is much smaller than the gate valve;

Generally, there is only one sealing surface on the valve body and the disc, so the manufacturing process is better and the service is easy to maintain.

Because its packing is generally a mixture of asbestos and graphite, it has a higher temperature resistance. Steam valves are normally used with stop valves.

Shortcoming:

The flow of the medium through the valve has changed, so the minimum flow resistance of the cut-off valve is higher than most other types of valves;

Because the travel is long, the opening speed is slower than the ball valve.

Plug valve: refers to the closure of the plunger into the form of rotary valve, through the rotation of 90 degrees to the valve plug on the mouth of the channel with the valve on the mouth of the mouth or separate, to achieve the opening or closing of a valve. The shape of the valve plug can be cylindrical or conical. Its principle is similar to the ball valve, the ball valve is developed on the basis of plug valve, which is mainly used in oil field production, but also used in petroleum chemical industry.

5. diaphragm: refers to the combination of a flexible membrane or diaphragm is arranged in the valve body and the valve cover, the closure member is a compression device connected with the diaphragm. The valve acne can weir shape, can also be a straight flow channel wall.

Advantage：

The operating mechanism and the media channels are separated, not only to ensure the purity of the working media, but also to prevent the possibility of the impact of media in the pipeline control mechanism components, the stem Department does not require any form of individually sealed, unless the safety facilities used in the control of harmful medium.

The working media only contact with the diaphragm and the valve body, the two can be used in a variety of different materials, so the valve can control a variety of ideal working medium, especially with chemical corrosion or suspended particles of the medium.

The utility model has the advantages of simple structure, and is composed of three parts of a valve body, a diaphragm and a valve cover assembly. The valve is easy to disassemble and maintain quickly, and the diaphragm can be completed on the spot and in a short time.

Shortcoming:

The due process and the manufacturing process of the diaphragm body lining and limit, large body lining and large diaphragm manufacturing process is very difficult, so the diaphragm should not be used for larger diameter, generally used in pipeline DN is less than or equal to 200mm the following.

Because of the restriction of membrane material