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How to realize the cut-off function of the regulating valve

In modern industrial control systems, the requirements for regulating valves are getting higher and higher, and shut-off requirements are imposed on regulating valves in applications with higher requirements. Therefore, the shut-off function is an important use function and intrinsic quality index of regulating valves For the classification and standard of cut-off grade, please refer to the relevant information). In field use, faults such as poor shutoff of the regulating valve and large leakage often occur. Except for the increase in leakage caused by jamming, being allowed to open due to too small allowable differential pressure, most of them are caused by structural defects and improper selection of the regulating valve. First, the choice of structure type One of the main disadvantages of double-sealing control valves (such as double-seat valves, double-sealing sleeve valves, etc.) is large leakage. But before the 1980s, due to the prevalence of sleeve valves at that time, however, many manufacturers worked very hard on sleeve valves to improve the structure to reduce leakage and evolved into very complex structures. As a result, this has brought many shortcomings: many parts, poor reliability, difficult spare parts, difficult maintenance, unsatisfactory cutting effect, and so on. In fact, this is because the design ideas have fallen into a misunderstanding. Instead of making such a complicated change in the "heart" of the valve body, it is better to achieve it through external adjustment. Therefore, a single-seal type control valve should be selected. In this way, sealing problems, reliability problems, maintenance and spare parts problems are all solved one by one. At this time, the focus of solving the contradiction is transformed into the problem of increasing the unbalanced force of the medium on the valve, and it only needs to be equipped with a powerful piston actuator and a thicker valve stem. This external solution is obviously much easier than complex internal improvements. It is not so much a question of method as a question of ideas. In the 1990s, people began to look for cut-off valves with simpler structure and more reliable sealing. At this time, it was found that the angular stroke valve was more superior than the straight stroke valve (single seat valve, sleeve valve, gate valve), so three-eccentric shut-off butterfly valves, full-function shut-off valves, and hard-sealed shut-off ball valves were produced. Selection of sealing surface (1) Face to face seal: For common plunger spools, the sealing surface is a small tapered surface at 60 ° C, and the valve seat is also a small tapered surface at 60 ° C. The width of this small tapered surface is usually between 0.5mm and 2mm. The tapered surfaces make good contact. But in fact, it is always affected by processing errors (such as heart rate, out-of-roundness, tilt, etc.), and its sealing effect is not very satisfactory. The leakage rate of this type of valve is usually 10-4, and after precision grinding, it can reach 10-6, which can only reach a better sealing level. (2) Spherical seal: The spherical rotation of the valve core is tangent to the small cone surface of the fixed valve seat, and they are in line contact, which is better than the above-mentioned face-to-face sealing. The full-featured ultra-light valve and spherically sealed butterfly valve introduced by Hualin Company are manufactured using this idea. Its leakage rate can reach 10-6 to 10-8, and the high-performance three-eccentric butterfly valve can reach 10-8, or Zero leakage. Selection of sealing materials (1) Soft seal In addition to corrosion-resistant lined valves, general soft-sealed valves refer to valves in which either the spool or the seat is sealed with a non-metallic material (mainly polytetrafluoroethylene, but also rubber, etc.). The soft sealing valve has the best sealing effect, but may leave more or less dirty debris (such as welding slag, iron filings, etc.) in the pipeline installation and system cleaning. When they pass through the regulating valve, it is easy to remove Scratches on soft-sealed valve seats or spools increase leakage and poor reliability of the seal. Therefore, when choosing a soft seal structure, consideration must be given to the cleaning of the medium and strict rinsing of the pipeline before commissioning. (2) Hard seal Hard sealing and surfacing welding of wear-resistant alloys are the best choice for shut-off valves. This method also takes into account the service life and reliability while considering the tightness. Although the factory index is only 10-6 to 10-8, it can not achieve the effect of zero leakage of the soft seal, but it is sufficient to meet the strict and tight requirements, and it Durable, more economical from an economic point of view. Fourth, the consideration of sealing reliability (1) The soft seal has good cutting effect, but it is not suit

General requirements for regulating valve installation

Release time : 2019-11--26 Clicks: 2
Check before adjusting valve installation 1.1 Before the installation of the regulating valve, check whether the product certificate of the regulating valve, the installation instruction manual are complete. 1.2 The appearance of the control valve should be checked before installation and should meet the following requirements: a) The outer surface must be free from defects such as cracks, trachoma, mechanical damage, rust, and dirt; b) The nameplate must not fall off, and the technical parameters on the nameplate are consistent with the system design requirements; c) Both ends of the regulating valve should be protected by protective covers; d) There should be no defects such as stagnant water, rust, dirt and damage in the valve body; e) There should be no paint on the thread of the thread connection, the thread is intact, there should be no radial grooves on the sealing surface of the flange that affect the sealing performance, the groove at the welding end is intact, and there should be no mechanical damage that affects the welding; f) The inner surface of the valve body of the rubber lining, the ceramic lining of the lining and the plastic lining should be smooth and smooth, and the lining layer and the substrate should be firmly bonded without defects such as cracks and blisters. 1.3 Control valve opening and closing inspection and water pressure test Control valve (except safety valve) should be flexible to open and close, and the position indicator should be accurate. Prior to installation, the control valve should be manually turned on and off three times to check for jamming. Regulating valves (except safety valves) have been shipped for more than one year, and pressure testing is recommended under conditions. Petrochemical and related industry regulating valve tests are conducted in accordance with the provisions of JB / T9092. General industrial regulating valve tests are subject to GB / T13927. Required. 2.1 General requirements for regulating valve installation 2.1.1 Read the installation and operation manual carefully before installing the regulating valve. 2.1.2 Regulating valve with flow direction shall be installed according to the flow direction of the regulating valve. 2.1.3 Under normal circumstances, do not install the handwheel of the control valve downward to avoid valve stem corrosion. 2.1.4 The installation position of the regulating valve should be convenient for operation and maintenance. 2.2 When lifting the control valve, the lifting rope should not be tied to the hand wheel or the valve stem, and it should be tied to the lifting ear or flange of the control valve. When carrying, the handwheel or handle should not be used as a handle. Connection of control valve 2.3.1 According to the connection type of the control valve, select the connection type on the pipeline side. The pipeline flange and thread should be the same as the standard of the control valve. 2.3.2 The pipeline connected to the regulating valve should be cleaned to avoid iron chips, sand, welding slag and other debris from damaging the sealing surface of the regulating valve. 2.3.3 When installing the threaded control valve, the sealing packing (leaf hemp plus lead oil or Teflon raw material tape) should be wrapped on the external thread to prevent the valve from accumulating and affecting the medium flow. 2.3.4 When installing the flange regulating valve, pay attention to tighten the bolts symmetrically and evenly. The flange of the control valve must be parallel to the flange of the pipeline, and the clearance is reasonable to avoid excessive stress on the control valve. In particular, pay attention to the control valve with brittle materials and low strength. 2.3.5 The welding connection shall be constructed in accordance with the welding process qualified by the welding process to prevent debris such as welding slag from entering the pipeline. After the control valve and the pipeline are welded, the non-destructive inspection of the weld seam shall be performed as required. 2.4 Gasket Gasket should be reasonably selected according to the requirements of flange type, pressure level, temperature, medium, etc. 2.5 Driving device The regulating valve of the driving device is connected to the electrical, pneumatic and hydraulic pipelines according to the wiring diagram or piping diagram of the instruction manual. Before connecting, confirm the correctness of the wiring. 2.6 The regulating valve with fixed foot support shall be installed firmly. 2.7 Special requirements 2.7.1 Regulating valves with external insulation and cooling requirements shall complete the construction of the protective layer before entering the medium. 2.7.2 Safety valve installation should pay attention to the location of the discharge port to avoid facing the operator. Adjustment valve after installation 3.1 Preparation before commissioning Before commissioning the system, the hydraulic valve should be tested with the regulating valve togeth
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Changzhou Baotong Valve Industry Co., Ltd. specializes in the research, design and manufacturing of regulating valves. The company is committed to the production and operation of various gas (electric) straight-stroke, angular-stroke control valves, self-acting control valves, deformation and special products.

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