World Instrumentation Facilities and Components

1, pipe fittings

Among various pipe joints, the snap-on pipe joints are widely used due to their simple and rapid installation, convenient assembly and disassembly, and reliable sealing. At present, the domestic use is basically a single card sleeve type pipe joints, and such pipe joints already have national standards. When the single-card sleeve type pipe joint is working, the clamping sleeve is pushed into the 24° taper hole under the effect of the nut, and is deformed accordingly, so that the clamping sleeve forms a spherical contact seal with the conical surface of the joint body, and the inner edge of the clamping sleeve is embedded in the pipe. The outer wall and an annular rim are pressed on the outer wall to provide a sealing effect. The single-card sleeve type seal is a line seal, and the inner edge of the ferrule is required to have a high hardness, and the tube has a certain damaging effect when sealed. At the same time, since the ferrule uses No. 10 steel, the cutting edge is easily corroded and loses its sealing effect when exposed to corrosive fluids, and the number of assembling and disassembling operations is also limited.

In the United States in the 40's developed a double-card sleeve type pipe joints, using the front and rear ferrule structures. During assembly, the connecting nut pushes the front ferrule forward through the rear ferrule. When the front ferrule moves, it presses against the tube, and the tube and the front ferrule deform at the same time. The seal produced by this deformation serves to intercept the fluid pathway. The role. Because it is a face seal, the card sleeve can be made of stainless steel and other materials, which improves the corrosion resistance and working reliability of the entire piping system and fittings. At the end of the assembly, the rear ferrule also undergoes a certain deformation, which serves to prevent vibration and loosening. Due to the above advantages, the card type pipe joints in developed countries are currently double-casing type. Among them, the SWAGELOCK products are most widely used in the United States, with a size range of 116 to 50 mm and a leak rate of 4114×10-6 m3/s. Vacuum degree up to 01001MPa. A special plug gauge can also be used to check if the assembly is in place. The types of materials for pipe joints are also many, including aluminum, copper, nylon, stainless steel, carbon steel, and tetrafluoride. According to the user's report, the sealing of foreign pipe joints is still intact after dozens of times, and it is difficult to ensure a good seal after the domestic pipe joints are disassembled once. In addition to the processing quality, the difference in the sealing mechanism also has a certain role. In addition, the volume of the double-tubular joint is smaller than that of the single-tubular joint. Under the same caliber condition, the single-tubular joint appears to be relatively bulky.

2, valve

211 ball valve

Due to the rapid switching, ball valves are used on many devices. China's small-diameter ball valve basically adopts a floating structure, and the material of the valve seat sealing ring is PTFE. Due to the influence of ball processing quality and inherent cold flow of tetrafluoroethylene, ball valves are not effective in the medium and high pressure range. The main problem is that the internal leakage is severe.

The foreign ball valve design, structure and material application have obvious advantages compared with domestic ones. Such as HOKE's floating ball valve, the seat seal material used 3M's KEL2F (PCTFE), eliminating the cold flow of materials. At the same time, the sealing material is embedded in the metal ring to prevent bending deformation of the inlet seal seat when the ball rotates.

WHITEY's 40 series ball valve adopts a fixed structure. The valve seat seal adopts the method of fastening the upper part of the valve body. The entire valve is compact in structure. The working conditions of the valve are: temperature 5 ~ 65 °C, pressure 17MPa. The 83 series ball valve also adopts a fixed structure. The valve seat seal adopts an auxiliary disc spring to act as a pre-tightening, which reduces the seal failure caused by the cold flow. The valve can operate at 4110 MPa, 120 °C.

In addition to ball valves, there are several types of switch valves in the country. Such as P4T, P6T series plunger valve, its structure is very simple, the valve inside and outside the seal are used O-ring. To reduce the operating torque, the outer surface of the O-ring is plated with PTFE. The maximum connecting pipe diameter of the valve can reach 12mm, and it can work under 204°C and 20MPa working conditions.

There is also a toggle valve structure is also very simple, relying on the upper handle of the valve to move up and down, open and close the valve, in the low pressure system (<210MPa) using a reliable seal, the switch quickly.

212 shutoff valve

Due to the small size of the small-diameter shut-off valve, it is not possible to install the valve seat by surfacing or inlaying. Therefore, the same material is commonly used for seats and stems. When using 316 or 1828 stainless steel, due to the soft material of the valve stem and the rotating friction between the valve stem and the valve seat, improper operation force can easily cause the valve stem to scratch and cause internal leakage. The domestic cut-off valve did not take any measures to prevent this problem, and users did not respond well. The foreign cut-off valve has done a lot of work on the design, such as WHITEY's D-Series shut-off valve. When the handle rotates, the stem only moves horizontally, and the PCTFE soft seal is used. The seal effect is good when used. NUPRO company JB series globe valve adopts a ball-type structure on the stem, which also plays a role in preventing friction scratches.

Domestic valve stem seals generally use a piece of PTFE.

If the machining quality of the valve stem and the inner hole of the valve body is not good, the valve will have a large operating torque or be easily leaked. The foreign cut-off valve is a multi-layered packing structure. The addition of a rigid spacer ring in the packing facilitates the transfer of pressing force and reduces the operating torque. Some upper seal cut-off valves use a disc spring at the upper part of the seal ring to improve the self-adjusting ability of the seal force. At the same time, a seal is changed to a two-piece conical seal to improve the sealing performance.

213 filter

In many test devices, filters are used extensively to ensure the safe operation of valves and equipment. Domestic filters are straight-through and have a narrow range of filter particles. Foreign filters generally use T-shaped structure, easy to replace the filter, a wide range of adaptability (015 ~ 440μm), filter commonly used powder metallurgy sintered stainless steel.

214 pneumatic control valve

In order to adjust the parameters such as flow rate, temperature, pressure, and liquid level, general automated test devices use pneumatic control valves as actuators. There are many kinds of large-diameter pneumatic control valves in China, which basically satisfy the needs of industrial devices. However, the small-caliber, pneumatic valve used in the laboratory is basically blank and completely dependent on imports. There are many types of small-flow pneumatic control valves abroad, such as the small flow pneumatic control valve manufactured by BADGERMETER of the United States. From 6 to 25mm, the same control valve can achieve the purpose of changing the flow coefficient by replacing the valve stem and valve seat. P series control valve specific parameters, the valve basically covers the flow coefficient range of the valve used in the test chamber, the theory is relatively large. When the control requirements are high, valves can also be added, and there are various forms such as high temperature, low temperature, valve opening and valve closing.

215 pressure regulator

The pressure regulating valve is a self-operated regulating valve and has been widely used in small and medium-sized test devices. At present, the YT22 and YT24 type pressure regulating valves are the most used in China. There is a gas chamber in the valve. Two small cut-off valves on the valve are used to control the self-contained pressure of gas in and out of the air chamber, and the pressure before or after the control valve is a certain value. Because of the constant pressure of gas, the precision of pressure regulation of such valves is high, but the installation and operation are more complicated. The change or leakage of gas temperature in the air chamber has a great influence on the accuracy of constant pressure.

And can only be used for less corrosive gases.

At present, most foreign countries use spring pressure regulating pressure regulating valve, and the varieties and series are more complete, can meet the needs of different uses. Spring pressure regulating valve can be used for gas and liquid universal. TESCOM's Series 26-1000 pressure regulators are used to control the pressure of the fluid behind the valve. The valve has a pressure regulation range of 5 to 10,000 psi (01035 to 70 MPa).

In order to ensure the accuracy of pressure regulation, there are 7 types of pressure regulating springs and pressure measuring elements. Different pressure regulating ranges can be replaced with different springs and load cells. The valve is also provided with a relief valve, which is a closed container at the outlet and is vented through the valve when the outlet pressure is high. The company also has other pressure regulating valves, such as external air pressure regulation. This adjustment is somewhat similar to the domestic YT22 pressure regulator, but the constant pressure gas is introduced from the outside. There is also a pneumatically-regulated pressure regulating valve that removes the pressure regulating spring from the valve body of the ordinary valve, and adjusts the pressure of the gas on the pneumatic diaphragm at the top of the valve and the balance of the pressure in the system. The gas source pressure required for this valve is 0-100 psi (0-017 MPa), which can be automatically controlled and the adjustment accuracy is high.

With the development and application of electronic technology and computer technology, intelligent valves have emerged. For example, TESCOM recently introduced an intelligent pressure controller ER23000. This controller is actually an electronic 2 pneumatic PID controller. Its input signal can be 4 ~ 20mA, 1 ~ 5VDC analog signal, but also can input digital signal through RS2485 interface, the feedback signal is 4 ~ 20mA or 1 ~ 5VDC standard signal. Because the microprocessor is integrated in the controller, the PID parameters of the ER3000 remote controller can be adjusted and set in the field to change emergency, safety conditions and processing methods. It can also be modified or controlled by PLC or host computer. At the same time, 32 other controllers can be connected via the RS2485 interface. A typical closed-loop control system for this controller.

The computer input control signal or the controller's own internal setpoint value is compared with the signal of the pressure sensor, and then the deviation signal is output, the valve in the controller is opened, and the pneumatic actuator of the pneumatic signal input pressure regulator controls the action of the regulating valve. The valve can also send real-time signals to the upper computer to display the control results on the upper computer to correct the control parameters. The control parameters for this valve are linearity ±0105 (full scale), repeatability ±0105 (full scale), and accuracy ±0103 (full scale).

3, processing technology

The enterprises that produce instrument valves in China are generally small-scale enterprises, and the processing and detection methods are behind, resulting in lower product quality. Foreign well-known manufacturers of instrument valves are mostly automatic line production and numerical control equipment. The valve body is mostly finished after forging, which not only improves the strength of the valve body, but also makes the surface of the valve body smooth and beautiful. In-valve flow channels are electro-polished to smooth the flow path, reducing fluid resistance and dirt contamination. Special parts are specially treated. For example, some springs and O-rings are coated with a layer of PTFE to improve the corrosion resistance of these parts.

4 Conclusion

At present, China's instrumentation valves and fittings products have a certain gap compared with similar foreign products and cannot meet the requirements of scientific research and production for such products. Therefore, a large number of instrument valves and fittings need to be imported every year. On the contrary, many domestic instrument valve manufacturers do not have high grades due to their low product quality, which results in a backlog of products and difficult marketing. Therefore, we should learn from the experience of successful products from abroad, and constantly improve the level of product design, manufacturing and processing in order to improve product quality and market share.