In industrial automation production, what is the principle of adjusting the opening of pneumatic valve by the liquid level gauge of reaction kettle? Ask industry experts for advice! thank you

Working principle of pneumatic control valve: Pneumatic control valve is composed of executive mechanism and regulating mechanism. The actuator is the thrust component of the regulating valve, which generates corresponding thrust according to the pressure of the control signal to push the regulating mechanism to move. The valve body is the regulating part of the pneumatic regulating valve, which is in direct contact with the regulating medium to regulate the flow of fluid.

Pneumatic valve: A valve driven by compressed air.

In the current market economy environment, it is not perfect to only specify the specifications, categories and working pressure when purchasing pneumatic valves to meet the procurement requirements. For the sake of product competition, pneumatic valve manufacturers have made different innovations under the concept of unified design of pneumatic valves, forming their own enterprise standards and product individuality. Therefore, it is very necessary to put forward technical requirements in detail when purchasing pneumatic valves and coordinate with manufacturers to obtain knowledge as an annex to the pneumatic valve purchase contract.

1. General requirements

1. 1 The specifications and categories of pneumatic valves shall meet the requirements of pipeline design documents.

1.2 The model of pneumatic valve shall be marked with the national standard number requirements. If it is an enterprise standard, it shall indicate the relevant description of the model.

1.3 The working pressure of the pneumatic valve should be equal to or higher than that of the pipeline, and the working pressure that the valve can bear should be greater than the actual working pressure of the pipeline without affecting the price; When the pneumatic valve is closed, either side should be able to withstand the valve working pressure of 1. 1 times without leakage; When the valve is open, the valve body should be able to withstand twice the working pressure of the valve.

1.4 The manufacturing standard of pneumatic valve shall indicate the national standard number on which it is based. If it is an enterprise standard, the enterprise documents should be attached to the purchase contract.

2. Pneumatic valve quality

2. 1 The valve body material should be mainly nodular cast iron, and the brand of cast iron and the actual physical and chemical test data should be indicated.

2.2 The valve stem shall be made of stainless steel (2CR 13), and the large-diameter valve shall also be made of stainless steel embedded valve stem.

2.3 The nut is made of cast aluminum brass or cast aluminum bronze, and its hardness and strength are greater than that of the valve stem.

The material hardness and strength of the stem bushing of pneumatic valve 2.4 should not be greater than that of the stem, and it will not form electrochemical corrosion with the stem and valve body under the condition of water immersion.

2.5 material of sealing surface

① Different types of pneumatic valves have different sealing methods and material requirements;

(2) For ordinary wedge gate valves, the material, fixing method and grinding method of copper ring should be explained;

(3) Physical, chemical and hygienic test data of rubber lining materials for soft sealing gate valves and valve plates;

(4) The butterfly valve shall be marked with the sealing surface material on the valve body and the sealing surface material on the butterfly plate; Their physical and chemical inspection data, especially the hygienic requirements, aging resistance and wear resistance of rubber; NBR and EPDM are usually used, and it is forbidden to mix reclaimed rubber.

2.6 valve shaft packing

(1) As the pneumatic valves in the pipe network are usually not frequently opened and closed, it is required that the packing should be inactive for several years and not aged, so that the sealing effect can be maintained for a long time;

② The packing of the valve shaft should also have a good sealing effect when it is frequently opened and closed;

(3) In view of the above requirements, the valve stem packing shall not be replaced for life or more than ten years;

(4) If the packing needs to be replaced, the design of pneumatic valve should consider the replacement measures under the condition of water pressure. Pneumatic valve diaphragm

3. Variable speed transmission box

3. 1 The box material and internal and external anti-corrosion requirements are consistent with the principle of valve body.

3.2 The box shall be sealed and can withstand the immersion of 3m water column after assembly.

3.3 The adjusting nut of the opening and closing limit device on the box body should be inside or outside the box body, but it can only be operated with special tools.

3.4 The transmission structure is designed reasonably. When opening and closing, it can only drive the valve shaft to rotate without moving it up and down, and the transmission part is well engaged, which will not cause separation and slippage when opening and closing with load.

3.5 The variable speed transmission box and the valve shaft seal cannot be connected into a leak-free whole, otherwise reliable measures should be taken to prevent leakage.

3.6 There is no sundries in the box, and the gear bite should be protected by grease.

4. Operating mechanism of pneumatic valve

4. 1 The opening and closing direction of the pneumatic valve shall be closed clockwise.

4.2 Because the pneumatic valves in the pipe network are often opened and closed manually, the opening and closing revolutions should not be too much, even the large-caliber valves should be within 200-600 revolutions.

4.3 In order to facilitate one person's opening and closing operation, the maximum opening and closing torque should be 240N-m under pipeline pressure.

4.4 The opening and closing operation end of pneumatic valve shall be square tenon, standardized in size and facing the ground, so that people can operate directly from the ground. Valves with disc are not suitable for underground pipe network.

Pneumatic valve 4.5 Pneumatic valve opening and closing degree display panel

① The scale line of the opening and closing degree of the pneumatic valve should be cast on the gearbox cover or the shell of the reversed display panel, all facing the ground, and the scale line should be painted with fluorescent powder to show eye-catching;

② Stainless steel plate can be used for indicating dial hands if they are well managed; otherwise, it is painted steel plate, not aluminum skin;

(3) The indicating needle is eye-catching and firmly fixed. Once the opening and closing adjustment is accurate, it should be locked with rivets.

4.6 When the pneumatic valve is buried deeply, and the distance between the operating mechanism and the display panel is ≥ 1.5m from the ground, telescopic rod facilities shall be provided and fixed firmly for people to observe and operate from the ground. In other words, the valves in the pipe network are not suitable for underground operation.

5. Performance test of pneumatic valve

5. 1 The valve shall be mass-produced according to certain specifications, and the following performance tests shall be entrusted to an authoritative organization:

① Opening and closing torque of the valve under working pressure;

(2) Under the working pressure, it can ensure the continuous opening and closing times of the valve to be tightly closed;

③ Detection of valve flow resistance coefficient under the condition of pipeline water delivery.

5.2 Before leaving the factory, the valve shall be tested as follows:

① When the valve is opened, the valve body should be able to withstand the internal pressure test twice the valve working pressure;

② When the valve is closed, both sides bear 1. 1 times the working pressure of the valve without leakage; However, the leakage value of metal sealing butterfly valve is not greater than the relevant requirements.

6. Internal and external corrosion protection of pneumatic valves

6. 1 inside and outside the valve body (including the variable speed transmission box), firstly, shot blasting, sand cleaning and rust removal should be carried out, and powder nontoxic epoxy resin should be electrostatically sprayed with a thickness of more than 0.3mm. When it is difficult to electrostatically spray nontoxic epoxy resin on oversized valves, similar nontoxic epoxy paint should also be painted.

6.2 The interior of the valve body and all parts of the valve plate need to be adequately protected against corrosion. On the one hand, immersion in water will not rust, and electrochemical corrosion will not occur between the two metals. On the other hand, the smooth surface reduces the resistance of water. pneumatic valve

6.3 The sanitary requirements for anticorrosion epoxy resin or paint in the valve body shall provide the inspection report of the corresponding institution. Chemical and physical properties should also meet the relevant requirements.

7. Packaging and transportation of pneumatic valves

7. 1 Light shields shall be fixed on both sides of the valve.

7.2 Medium and small caliber valves shall be bound with straw rope and transported in containers.

7.3 Large-diameter valves are also packed with simple wooden frames to avoid damage during transportation.

8. Pneumatic valve factory instructions

Pneumatic valves are equipment, and the following relevant data should be indicated in the factory manual:

Valve specifications; Model number; Working pressure; Manufacturing standards; Valve body material; Valve stem material; Sealing material; Stem packing; Material of valve stem sleeve; Internal and external anticorrosive materials; Operation start direction; Number of revolutions; Opening and closing torque under working pressure; Name of the manufacturer; Date of production; Factory number; Weight; Diameter, number and center hole spacing of connecting flanges; Graphical representation of the overall control dimensions of length, width and height; Valve flow resistance coefficient; Effective opening and closing time; Relevant data of valve factory inspection and matters needing attention in installation and maintenance, etc.

Pneumatic valves are classified by type:

One,

Main types of pneumatic valves:

1) Pneumatic V-shaped regulating ball valve

2) Pneumatic O-type cut-off ball valve

3) Torque cylinder ball valve

4) Electromagnetic diaphragm valve

Electromagnetic diaphragm valve

5) Pneumatic direct-through program diaphragm valve

6) Electric valve

Second, the pneumatic V-shaped control valve:

Uses and characteristics

A. Use

It is a right-angle rotating structure, which can be used with valve positioner to realize proportional adjustment;

V-shaped valve core is most suitable for all kinds of adjustment occasions, with large rated flow coefficient, large adjustable ratio, good sealing effect, zero sensitivity of adjustment performance, small volume and vertical and horizontal installation. Suitable for controlling gas, steam, liquid and other media.

B, features: right-angle rotating structure, consisting of V-shaped valve body, pneumatic actuator, positioner and other accessories; There is an inherent flow characteristic with approximately equal percentage ratio; Adopt double bearing structure, small starting torque, excellent sensitivity and induction speed; Super shearing ability.

C pneumatic piston actuator takes compressed air as the power source, and drives the crank arm to rotate 90 degrees through the movement of the piston, thus realizing the automatic opening and closing of the valve. Its components are: adjusting bolt, actuator box, crank arm, cylinder body, cylinder shaft, piston, connecting rod and universal shaft.

D. Working principle of pneumatic control valve: Pneumatic control valve is composed of executive mechanism and adjusting mechanism. The actuator is the thrust component of the regulating valve, which generates corresponding thrust according to the pressure of the control signal to push the regulating mechanism to move. The valve body is the regulating part of the pneumatic regulating valve, which is in direct contact with the regulating medium to regulate the flow of fluid.

Overview of pneumatic valve standards

Standard numbering standard Chinese name standard English name

JB/T6376- 19922005 Review the groove size and tolerance of rubber sealing ring for pneumatic valve.

JB/T6375- 19922005 Review the dimension series and tolerance of rubber sealing ring for pneumatic valve.

ANSI/NFPA T 3.2 1.4 R2-2000 pneumatic valve. NFPA/T 2.6. 1

R2-2000 Addendum: Pressure Class of Hydraulic Components. Pneumatic valve. Pressure rating for fatigue test and pressure determination of hydraulic pneumatic valve with metal shell.

Supplement to NFPA/T2.6. 1 R2-2000, Fluid Power Components-Verification Method

Fatigue of determining bursting pressure rating of pressure vessel

Shell of metal fluid dynamic pneumatic valve

The input signals of bs 4151-1967 are

Evaluation method of pneumatic valve positioner for 3 to 15 1b/in pressure gauge

3 to 15 psi input signal

Parameter definition:

1. Nominal diameter: (Nominal

Diameter), also known as the external mean.

Diameter), symbol DN, is a common diameter of various pipes and pipe accessories. Pipes and fittings with the same nominal diameter can be connected with each other and interchanged. It is not the actual outer diameter or inner diameter of the pipeline, although its value is close to or equal to the inner diameter of the pipeline. In order to unify the connection size of pipes and fittings, the nominal diameter (also called nominal caliber and nominal diameter) is adopted. For example, welded steel pipes can be divided into thin-walled steel pipes, ordinary steel pipes and thickened steel pipes according to their thickness. Its nominal diameter is neither outer diameter nor inner diameter, but a nominal size similar to the inner diameter of ordinary steel pipe. Each nominal diameter corresponds to an outer diameter, and its inner diameter value varies with thickness. Nominal diameter can be expressed in metric millimeters or British inches. Pipe accessories are also expressed in nominal diameter, which has the same meaning as slotted pipes.

2. Nominal pressure: (nominal)

Pressure), symbol PN, the maximum allowable working pressure when applied at a certain temperature. For the control valve with carbon steel valve body, it refers to the maximum working pressure allowed for the application below 200℃; For cast iron valve body, it refers to the maximum working pressure allowed for applications below 120℃; For the control valve with stainless steel body, it refers to the maximum working pressure allowed in the application below 250℃. When the working temperature rises, the pressure resistance of the valve body will decrease. For example, a carbon steel control valve with a nominal pressure of 6.4MPa(PN64) has a pressure resistance of 5.2MPa at 300℃, 4. 1MPa at 400℃ and 2.9MPa at 450℃. Therefore, the determination of the nominal pressure of the control valve should be based not only on the maximum working pressure, but also on the maximum working temperature and material characteristics, not just on the requirement that the nominal pressure is greater than the working pressure.