Industrial valve

Industrial valves are an important accessory for controlling the flow of medium on industrial pipelines. This lecture focuses on the practical application of valves. Detailed principles and structural sectional views refer to relevant data books. Valves are composed of valve body, opening and closing mechanism and valve cover. This time, we will introduce the structural features of the valves commonly used by the company and the precautions for proper use.

First, the role of industrial valves 1, opening and closing role: cut off or communicate the flow of fluid in the tube;
2, adjust the role of: regulating the flow of the tube, the flow rate;
3, throttling effect: make the fluid after the valve has a great pressure drop;
4, other roles: Automatic opening and closing b. Maintain a certain pressure c. Obstruction steam drainage.

Second, the types of industrial valves 1, according to the use of points: cut-off valve, regulating valve, diverter valve, check valve, safety valve;
2, according to force points: his action valve, automatic valve.

Third, the main parameters of the industrial valve PN nominal pressure (the maximum pressure to allow fluid to pass);
DN nominal diameter;
TN temperature range (temperature range of allowable fluid).

Fourth, inspection check items before use of industrial valves include:
1. Whether there are defects such as blisters or cracks on the internal and external surfaces of the valve;
2. Is the joint between the valve seat and the valve body firm or not, and if the valve plug and the valve seat are consistent, whether the sealing surface is defective or not?
3. Whether the stem and the valve plug are connected flexibly and reliably, whether the stem is bent, and whether the thread is damaged or corroded;
4. Whether the packing and gasket are aging and damaged;
5, the valve is open and flexible.

V. Frequent problems occurred during the use of industrial valves 1. Flange and thread leakage at the connection with the pipeline;
2. Leakage of filling culverts, leakage of lumbar pad, and failure to open the valve stem;
3, between the valve core and the valve seat is not strict formation of internal leakage.

Sixth, the characteristics of common industrial valves and precautions for use (a) plug valve (Cock)
Features: TN less than 150 degrees PN less than 1.6 Mpa Its advantages include simple structure, rapid opening and closing, easy operation, and low fluid resistance.

Use cautions:
1. The outer end of the valve stem is square, the vertical line marked by the diagonal line and the direction of the valve body are closed, and the valve body is in the open state.
2, the normal switch valve with a special wrench, to avoid slipping with the valve stem caused a safety accident; as far as possible without the use of adjustable wrenches resulting in slippage;
3. Open the valve and check according to the previous inspection items. After the inspection, slowly open the valve. Try not to stand in the direction of the sealing surface when opening, and wear acid-proof masks when encountering acid-base fluids;
4. If there is a sight glass in the pipe, see the fluid in the sight glass passing through before leaving.

(B) ball valve ball valve and plug valve is the same type of valve, but its opening and closing parts for the ball with a through hole, the ball Rao valve rod center line to achieve the purpose of opening and closing.
Stainless Steel Ball Valves with Collet Warming Ball Valves Stainless Steel Ball Valves Stainless Steel Ball Valves Quick Opening Ball Valves Features: The valve is simple in structure and reliable in operation. It is used in pipes with two-way flow medium, which has small fluid resistance and good sealing performance. Disadvantage: The medium easily leaks from the valve stem.

Use cautions:
a) same as the plug valve;
b) With handle valve, the handle is perpendicular to the flow direction of the medium is closed, and the direction is consistent with the open state;
c) When encountering a ball valve with jacket insulation, note the following:

I. The jacket steam insulation should be opened to melt the easily crystallized medium in the valve before opening and closing the valve. Do not force the valve to open or close if the medium is not completely melted.
Ii. When the valve cannot be opened, do not use the method of lengthening the arm to forcibly open the valve, because it will cause the valve stem to be subject to greater resistance and the valve core falls off, resulting in valve damage or damage to the wrench. safety factors.

(C) Butterfly Valve Butterfly valve uses a revolving shaft to control the opening and closing of the pipe. The rotation angle reflects the opening degree of the valve.
According to different transmission methods, the butterfly valve is divided into three types: manual, pneumatic and electric. The manual operation is manual. The rotary handle drives the valve stem through the gear transmission to open and close the valve.
Features: The butterfly valve has the advantages of simple structure, rapid opening and closing, low fluid resistance and easy maintenance, but it can not be used in high temperature and high pressure occasions, large diameter water with PN less than 1.6Mpa and t less than 120 degrees, steam, air, oil, etc. Pipeline.

Use cautions:
1, the valve can only rotate 90 degrees, the general body will indicate the CLOSE and OPEN arrow direction, hand wheel clockwise rotation is closed, otherwise open;
2, if there is a certain resistance to opening and closing sometimes, you can use a special F wrench to open the valve, but can not force open and close, otherwise it will spoil the stem gear;
3. It is forbidden to remove the hand wheel and use a spanner to pull the stem; (the same applies to the valve below)
4, open and close gradually open and close, observe whether there is an abnormal situation, to prevent leakage.

(4) Globe valve Globe valve is the most widely used type of truncated valve in chemical production. Compared with the three types of truncated valves mentioned above, it does not use its closed part to open and close the valve, but uses the stem to raise and lower the valve. The connected circular valve disc (valve head) changes the distance between the valve disc and the valve seat to control the opening and closing of the valve.
Streamline Globe Valve American Standard Globe Valve Features: The top of the globe valve has a hand wheel, stem, and a middle section of the threaded and culvert seal section. The small valve stem is threaded in the valve body, and its structure is compact, but the stem and medium There are many contact parts, especially the threaded part is apt to be corroded. The valve opening degree can be judged from the height of the valve stem exposed by the valve stem. To prevent the leakage of the medium along the valve stem, the valve stem can be sealed by filling in the valve cover part.
Shut-off valve structure is more complex, but the operation is simple, not strenuous, easy to adjust the flow and cut off the channel, starting and closing the slow dry hammer phenomenon, it is more widely used.
When the globe valve is installed, pay attention to the direction of the flow, so that the flow of the pipeline flow from the bottom up to the orifice of the valve seat, and the so-called “low-in and high-out” purpose is to reduce the fluid resistance, so that the valve stem and the filler culvert are opened in the effortless and closed state. Some parts do not come in contact with the media, ensuring that the stem and filler culvert will not be damaged or leaked.
Cut-off valve is mainly used for water, steam, compressed air and various materials of the pipeline, can accurately adjust the flow and cut off the channel, but can not be used for high viscosity, easy to crystallize the material.

Use cautions:
1. Check whether the valve has any defects before opening, especially if the filler contains no leakage;
2. When the stem cannot be turned directly by hand, use a special F wrench to open and close. When it is still impossible to open and close, do not force the wrench to open and close, thus causing valve damage or causing safety accidents;
3. When used in medium-pressure steam pipeline valves, the condensate in the pipe should be drained first after opening, and then the valve should be opened slowly with 0.2 to 0.3Mpa steam to preheat the pipe to avoid sudden increase in pressure. Damage to the sealing surface, adjust the pressure to the desired state when the inspection is normal;

(5) Gate Valves Gate valves, also known as gate valves or gate valves, control the opening and closing of valves through the raising and lowering of gates. The gates are perpendicular to the direction of flow. Changing the relative position between the gate and the valve seat can change the size of the channel.
Ming-style gate valve The gate-type gate valve is based on the different valve stem movement conditions when the gate valve is opened and closed. The gate valve is also divided into two types, the rod type and the dark type.
The stem of the stem type valve stem is exposed on the outside of the valve body. When the valve is opened, the stem extends out of the handwheel. The advantage is that the size of the valve opening can be judged according to the outside elongation of the stem, the contact length between the stem and the medium is small, and the thread portion is basically not Affected by media corrosion, the disadvantage is that the height of the extended space is large.
The lever-type valve stem screw thread in the valve stem and the internal thread on the ram plate want to cooperate, when the valve is opened, the valve stem only rotates without lifting up and down, and the ram valve rises along the stem thread.
The advantage of the lever-type gate valve is that the outrigger space is small. The disadvantage is that the opening of the valve cannot be judged according to the condition of the valve stem. The valve stem thread is prone to corrosion due to its long-term contact with the medium.
The gate valve has the advantages of low fluid resistance, constant medium flow, slow open-water hammer phenomenon, and easy adjustment of flow rate. The disadvantages are complex structure, large size, long opening and closing time, and difficult maintenance of the sealing surface. Because of its application in large-diameter water supply pipelines, it is also called watergate.

Use cautions:
1. When the valve stem is opened and closed in position, no force can be applied. Otherwise, internal threads or bolts will be broken to damage the valve.
2. When the hand can not be directly actuated when opening and closing the valve, the F wrench can be used to open and close;
3, when opening and closing the valve, pay attention to observe the valve sealing surface, especially the filling gland to prevent leakage.

(6) Throttle Throttle Valve Also known as a needle valve, its shape is similar to that of a globe valve. Its spool shape is different. It is cone-shaped or parabola-shaped. It is often used in chemical instrumentation and is often threaded.

Use cautions:
1, because of the threaded connection, so first check the open and close the threaded connection is loose;
2. Slowly open and close the valve. Because the flow area is small and the flow rate is large, the sealing surface may be corroded. Observe caution and pay attention to changes in pressure.

(7) Check valve The check valve is a valve that automatically opens and closes by using the pressure difference between the media before and after the valve and controls the medium to flow in one direction. It is also called check valve or check valve.
Check valve according to the structure is divided into lifting (jumping type) and swinging type (shake-pole type) two.
Lifting spin-type use precautions:
Pay attention to the direction of the valve, and the arrow is consistent with the direction of the flow of the medium. If the medium is susceptible to crystallization, the valve can not be pressed down and the command and non-return can not be achieved.

(8) Safety Valve The safety valve is a valve that automatically opens and closes according to the medium pressure. When the medium pressure exceeds a fixed value, it can automatically open the valve to discharge and relieve pressure, so that the equipment pipeline is protected from the danger of destruction, and the pressure is restored to normal. Can turn off automatically. Depending on the way in which the internal pressure is balanced, the safety valve is classified into two types, a lever weight type and a spring type.

Use cautions:
1. The safety valve must be used within the effective period of validity;
2. The safety valve control valve installed on pipelines and equipment is usually a stop valve that must be opened to ensure that the safety valve can work effectively;
3. Periodically lift the valve disc slightly and use the medium to blow off the valve impurities.
4. If the safety valve cannot work within the setting pressure, it must be revalidated or replaced.

(9) The trap trap is a type of valve in the system of steam pipes, heaters and other equipment that can automatically eliminate condensate intermittently and prevent the escape of steam. Commonly used bell-shaped float, thermal power and pulse several.

Use cautions:
1. Before use, use the pipeline bypass valve to eliminate the condensate. When there is steam, close the bypass and start the trap. Otherwise, the inside of the valve will not close the water.
2. Be careful not to be scalded by steam when starting or closing the valve.

(10) All kinds of sampling valve sampling valves are, as the name suggests, valves used for obtaining medium samples and thus capable of chemical analysis. Generally, they are divided into the following types on equipment or pipelines: double opening valves, flange clamp valves, and Sampling valve with insulated jacket.

Use caution method:

1. The double opening valve is generally composed of two ball valves, which is used for sampling safety and the purpose of sampling through linkage in the negative pressure device; when sampling, the second valve close to the equipment and pipeline is closed first, and the first valve is opened. Let the medium flow into the space between the two valves; then close the first valve, open the second valve, and place the sampling vessel in the sampling port.

2. The flange clip valve is generally sealed by the top cone of the valve stem and the taper hole of the valve seat. During sampling, the valve rod is rotated to disengage the valve rod from the taper hole, so that the medium can flow from the taper hole to the external sample vessel.

3, sampling valve with jacket insulation should pay attention to the following matters:
I. The jacket steam insulation should be opened to melt the easily crystallized medium in the valve, then the valve can be opened and closed. Do not force the valve to open or close when the medium is not completely melted.
II When the valve cannot be opened, the method of lengthening the arm cannot be used to forcibly open the valve, because it will cause the valve stem to be subject to greater resistance and the valve core falls off, or to damage the valve stem and the tapered hole sealing surface. The valve is damaged or the wrench is damaged, causing unsafe factors.

(11) Fluoroplastic rubber lined valves Fluoroplastic lined plastic valves are mainly used in acid-alkali and other corrosive media. Their structural principles are similar to non-lined fluorine plastic valves, except that they are used in the valve stem, valve core and valve seat. Fluoroplastic substrates are similarly used.

(12) Other Valves In addition to the eleven types of valves mentioned above, there are many kinds of valves used in industrial production such as diaphragm valves, expansion valves, pressure reducing valves, and automatic adjustment valves.