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Cautions for selecting valves in the chemical industry

发表时间:2019-08-19 15:15:52 Article source: Publication time: 2019-08-19 15:15:52

Points for attention in the chemical industry when choosing electric gate valves :

1. The operating temperature of the soft-seal electric gate valve is restricted by the sealing material.

2. Electric gate valve with reverse effect board, suitable for automatic shutdown system operation. With regard to these valves, simple push-pull operators can be used, thus avoiding the messy joystick cams required for general ball valves and plug valves. All moving parts with power manipulators on electric gate valves can be closed, eliminating contamination caused by paint and corroded products.

3. Unprotected bright-pole electric gate valve is not recommended. Because the marine environment will corrode the exposed stem and threads, making the valve difficult to operate and easy to endanger the stem packing.

4. Regarding DN50 (2 in) or larger standard manually operated electric gate valves, they should be equipped with elastic or expansion gates. Tapered gate valves generally do not have overpressure protection in the valve cavity.

5. Electric gate valve cannot be used for saving operation. Especially with fluids containing sand, savings can damage the seal appearance.

Electric gate valves are suitable for most switching operations, vibration-free hydrocarbons, and common facilities in all temperature ranges. During vibration operations, electric gate valves may open or close from their normal orientation. Unless the valve stem packing is carefully adjusted, the torque characteristics of electric gate valves are better than those of ball valves and plug valves, but they do not have 90-degree rotating action and convenient operating characteristics.

Suitable valves for the chemical industry are:

Check valve

Check valves come in a variety of forms: including swing check, lift, ball, piston, and separable circle swing twist check valves. In the meantime, the fully open swing check valve is suitable for most non-stable situations. Swing check valve is also used on vertical pipes (moving direction upwards). At this time, there is a stop block in the valve to prevent the valve flap from opening above the top dead center.

Swing check valve can not be used on vertical pipelines with downward movement direction. If it is used in places with low and unsteady flow rates, the swing check valve will vibrate and eventually endanger its sealed appearance. In order to extend the service life, the disc can be coated with a layer of tungsten chromium cobalt alloy. In order to reduce valve seat leakage, an elastic seal should be used. Detachable valve seats should be preferred because they are easy to repair and allow easy replacement of seals in the valve.

Swing check valves should be fitted with a screw or bolted bonnet in order to view and repair the disc and seat. In many cases, high pressure swing check valves that can be repaired on the pipeline.

Diaphragm valve (disc)

At the top of this kind of valve, a diaphragm made of synthetic rubber is connected to the valve stem. The valve is closed by pressing the diaphragm on a metal boss (which is part of the valve body).

Diaphragm valves are primarily used in low-pressure water at 1400 kPag (200 psig or less). They are particularly suitable for systems containing sand and other solid particles.

Electric butterfly valve

Ordinary electric butterfly valves are suitable for approximate savings and low-pressure, hydrocarbon-free, and non-hazardous operations. They are not suitable as important shut-off valves for containers and tanks. In the case of temperatures higher than 65oC or pressure levels higher than ASME 150 or hazardous fluids, wireless electric butterfly valves should be used. Because only a small amount of torque is required to cause the electric butterfly valve to vibrate open, the handle should be equipped with a confirmation device.

Shut-off valve

When good saving control is required (such as a bypass line for a control valve or a small vent hole), a shut-off valve is most suitable.

Ball valve

When the operating temperature is between -29oC and 200oC, most of the manual (opening and closing) ball valves are suitable for the operation of hydrocarbons and common systems. Ball valves used above 100oC should carefully consider the temperature constraints of the soft sealing material during use. Above 100oC. In high temperature and severe abrasion operations, the use of metal sealed ball valves should be considered.

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