1. Introduction to stainless steel valve
1.1 Nominal diameter and nominal pressure
The two important indicators of the valve are nominal diameter and nominal pressure. Nominal diameter: The valve diameter is indicated by “DN + number”, but it is not the measured value of the valve diameter. According to the national standard, the measured value is greater than or equal to 95% of the nominal diameter. The general valve adopts metric system, the American standard valve is inch system, and the nominal pressure: it uses “PN+ number” to indicate the pressure, and the nominal pressure does not equal to the actual measurement value of the valve. It is the maximum working pressure allowed by the valve at the reference temperature. You should "close" to this value.
1.2 Stainless Steel Valve Features
The characteristics of the valve are mainly used in the use and structure, in which the use characteristics include the type, structure, and material of the valve. The range and performance of the valves with different use characteristics are different; and the use of structural characteristics mainly includes the valve The size, connection method, and structure of the valve stem, etc., require different maintenance and repair methods for valves of different structures. This requires selection based on actual conditions.
1.3 Performance Index
The performance indicators of the valve include flow coefficient, cavitation coefficient and sealing performance. First, the flow coefficient is a measure of the flow capacity of the valve. The larger the flow coefficient, the smaller the pressure loss when the medium passes through the valve. Second, the cavitation coefficient: must be measured according to the actual operating conditions. Finally, the sealing performance is the medium of the valve seal. An indicator of the size of the leak is classified into two kinds, endoleaks and leaks. Endoleak refers to "not strict", and external leakage refers to flowing from the valve to the outside of the valve.
1.4 Casting defects
Due to the casting process used in the valve production, sometimes some defects such as holes, air holes, porosity, slag holes, etc., borehole defects, cold and hot crack defects, and structural shape and size defects are inevitably produced.
1.5 production standards
Valve production is divided into two kinds of national standards and corporate standards, the valve must be marked with the national standard number or company logo instructions. The instructions of the valve must be marked: specifications and models, working pressure, manufacturing standards, stem material, sealing material, filler material, fluid flow, manufacturer's name, date of manufacture, factory number, and precautions for installation and maintenance.
2. Analysis of the advantages and disadvantages of the pipeline stainless steel valve
Different working conditions, different environments, different media and different requirements for use have given rise to a variety of valves in various forms. The following uses several common valves as examples to simply analyze their advantages and disadvantages.
2.1 Gate valve
The working principle of the gate valve is mainly through the pressure valve, closing and grooming the fluid. It has the advantages of small fluid pressure loss, unlimited fluid flow, simple structure, robustness, and mature manufacturing technology. However, disadvantages are large size, bulky opening height, large installation space, easy scratches on the sealing surface, easy detachment of the gate plate and the valve stem, and high-speed liquid flow causing vibration of the gate in a partially open condition. Suitable for piping systems that do not open and close frequently.
2.2 Globe valve
The working principle of the cut-off valve is mainly that the valve flap moves along the center of the valve seat and opens and closes the valve. The advantages are high temperature resistance, wear resistance, good manufacturing process, and easy maintenance. The disadvantage is that the fluid pressure loss is large and the opening speed is slow. Only one-way flow of the medium is allowed, and the sealing performance is slightly poor. Scope of application: Suitable for heating and steam systems. In the piping system, shutoff valves are generally used to shut off the flow.
2.3 Butterfly valve
The working principle of the butterfly valve is that the valve disc is a disk, and the valve stem reciprocates in the range of 0° to 90° to open and close the valve. The advantages are simple structure, small size, light weight, simple operation, and low fluid pressure loss. The disadvantage is that the flow adjustment range is not large, the sealing performance is poor, and the valve plate is subject to greater erosion of the medium. Scope of application: Suitable for small space, large diameter pipe system.
3 stainless steel valve installation and use
3.1 Check Valve Installation
Check valve is divided into lift type, swing type two. When DN<50mm, it is advisable to use lifting type; when DN≥50mm, rotary starter type should be used. Lift-type check valves can only be installed on horizontal pipes. Swing check valves can be installed on horizontal or vertical pipes. The lifting check valve should be installed with the valve vertical to ensure that the lift is flexible. When the swing check valve is installed, the pin axis must be horizontal so that the rotation can be performed flexibly. The resistance of the lift check valve is larger than that of the swing check valve; slow-closing check valves are adopted at the outlet of large-caliber pipes and pumps, and ball valves or gate valves are provided at the upper part of the check valve to facilitate overhaul; Pipe sections with pipe reverse flow preventers do not need to install check valves.
3.2 Pressure relief valve installation
Installation of a pressure reducing valve generally requires the addition of a bypass pipe. However, when the water supply system needs to increase the pressure reducing valve in the partition, it must not add a bypass pipe. Instead, two pressure relief valves of the same configuration should be provided. The pressure relief valve should be installed upright on a horizontal pipe and must not be tilted.
3.3 Stainless Steel Valves and Control Valves
Sometimes, in order to adjust the pressure, flow rate and other parameters of the control fluid, an adjustment mechanism (control valve) needs to be installed. The principle is to change the flow area between the valve flap and the valve seat to achieve the purpose of regulation. The control method is generally electric and pneumatic. Type, hydraulic type, etc. Commonly used control valves include electric control valves, pressure reducing valves, pneumatic control valves, and pressure control valves.
3.4 Selection and Use of Stainless Steel Valves
Cut-off valve is generally used in DN ≤ 50mm water supply pipe network, air-conditioning pipes as little as possible with the cut-off valve. Gate valves are often used in situations where they do not require frequent opening and closing, and keep the gate fully open or fully closed for long periods of time. The gate valve cannot be used as a regulating flow and is generally not used in pipelines for conveying mud and other media. When the gate valve is at a small opening, the closing speed must be slow, otherwise it will produce water hammer. Under normal circumstances, the handle type (D71X, D41X) is used when the butterfly valve diameter is less than 150mm, and the worm gear type (D371X, D341X) is used when the butterfly valve diameter is >150mm. When the butterfly valve is used as a regulating flow, it should not be used for a long period of time within a 15° degree of opening. This will cause vibration and cavitation. Selection of other functional valves. 1Requires closure of tighter valves: stop valves, plunger valves, ball valves; 2 valves for controlling flow: stop valves, plug valves, ball valves; 3 valves that change direction: plug valves, ball valves; 4 fluids with suspended particles Valve: ball valve and plug valve; 5 fully open, fully closed the most convenient valve: ball valve, gate valve; 6 installation space for small places should adopt the valve: butterfly valve, ball valve; 7 pump import and export should adopt the valve: butterfly valve; 8 points Valves used between the water collectors: Differential pressure bypass valves; 9 Valves with directionality: stop valves, throttle valves, pressure reducing valves, check valves; 10 valves used in variable flow systems for heating projects: Balance valve.
3.5 stainless steel valve valve installation
Water supply valve inner wall coating must be non-toxic, and the valve used for sewage works should be resistant to corrosion and difficult to plug. The quality of the valve installation directly affects the use effect. If it is improperly installed, the performance of the valve may be degraded, so it must be taken seriously.
First, before the valve is installed, you must read the valve instructions carefully; distinguish the direction and position of the valve.
Second, when the valve is hoisted, the rope should be tied to the flange connection between the valve cap and the valve body, and cannot be pinched on the hand wheel or the valve stem.
Third, when the valve is connected with the pipe counterpart, it is not allowed to pull hard and force the counterpart. The flange bolts should be tightened diagonally and tightened one after the other.
Fourth, there should not be too many corners during the entire installation of the valve.
Fifth, the installation of the valve part must ensure the stability of the flax, and reduce the rust accumulation through the coating along the wire, which will affect the safety of the valve.
Sixth, in the steam-type pipeline installation process, the installed fixed valve bracket must be set to the correct position and proper installation and use rules to ensure that the thermal expansion and contraction of the pipeline will not cause the valve to burst.