How to calculate the flow coefficient of low Reynolds number liquid
Re is the dimensionless number indicating the flow state of the fluid in the pipe. The characteristics of fluid flow in a tube depend on a combination of four parameters (diameter, viscosity, density, and velocity). The Reynolds number can be used to determine whether the liquid flow is laminar or turbulent. The flow coefficient Kv is measured at the appropriate Reynolds number and turbulence conditions. As Re number increases, Kv value does not change much. However, when the Reynolds number decreases, the effective Kv value decreases. In extreme cases, the Reynolds number is very low. For example, for viscous fluid, the flow of liquid has become laminar flow state, and its flow rate is proportional to the valve pressure drop, but not proportional to the inverse of the square root value of the valve pressure drop. If Kv is calculated according to the above formula, the error must be large. Therefore, the Kv value of less than 104 fluid is calibrated. In the formula K 'v------, the revised flow coefficient K' v=Kv/FR (3-28); Kv-------- according to the above formula, namely the flow coefficient calculated according to the turbulence condition; FR---------- Re number correction coefficient, which can be obtained from FIG. 3-11 according to the size of Re number. Re number can be obtained from the following formula according to the valve structure, viscosity and other factors. With two parallel flow regulating valve, such as direct two-seater valve, butterfly valve, eccentric rotary valve, the Reynolds number for (3-29) for only a flow control valve, such as direct single seat valve, sleeve valve, ball valve, Angle valve, diaphragm valve, etc., the Reynolds number is (3-30) type v -- -- -- -- -- - liquid flowing temperature viscosity, was/s can be seen from the figure 3-11 curve, when the Reynolds number Re is more than 3500, correction is not big, so the Reynolds number is larger than 3500 generally do not need to correct the low Reynolds number.
Working principle and fault analysis of pneumatic valve
Working principle of pneumatic valve
The so-called pneumatic valve, specifically refers to the cylinder as an actuator, to compressed air as a source of power to achieve the valve drive, in order to achieve the switch for regulation. When the regulating pipe receives the control signal sent by the automatic control system, it will adjust the temperature, pressure, flow and other related parameters. In general, pneumatic valves have the characteristics of safe and reliable, rapid response and simple control. In the process of specific operation, the adjusting chamber will be input 0.02-0.10mpa signal pressure, the film will appear thrust, in the process of thrust plate moving down the spring will be compressed to achieve the valve stem, push rod and spool moving down, to achieve the purpose of valve regulation.
The product of each country of the world detects attestation mark to enumerate your home product to pass which a few
What are the security codes required for export products in other countries? What are the meanings of these certification marks? Let's take a look at the top 20 international brands and what they mean.
The CE mark is a security certification mark and is considered a passport for the manufacturer to open and enter the European market. CE stands for CONFORMITE EUROPEENNE. All products with the "CE" mark can be sold in the eu member states without meeting the requirements of each member state, thus realizing the free circulation of goods within the eu member states.
ROHS is the abbreviation of the Restriction of the use of certain hazardous substances inelectrical and electronic equipment. ROHS lists six hazardous substances in total, including: lead Pb, cadmium Cd, mercury Hg, hexavalent chromium Cr6+, PBDE and PBB. The eu began to implement ROHS on July 1, 2006. Electrical and electronic products that use or contain heavy metals, PBDE, PBB and other flame retardants are not allowed to enter the eu market. ROHS for all the production process and raw materials that may contain the above six kinds of harmful substances in electrical and electronics products, mainly including: white home appliance, such as refrigerators, washing machines, microwave ovens, air conditioners, vacuum cleaners, water heaters, etc., black appliances, such as audio and video products, DVD, CD, TV receiver, IT products, digital products, communication products, etc.; Power tools, power electronic toys, medical electrical equipment.
Remark: when the customer asks whether there is rohs, he should ask whether he wants the finished product rohs or the raw material rohs. Some factories cannot make the finished product rohs. The price with rohs is generally about 10%-20% higher than that of ordinary products.
UL is short for Underwriter Laboratories Inc. UL safety testing institute is one of the most authoritative safety testing and certification organizations in the United States. It is an independent, nonprofit, professional organization that tests for public safety. It USES scientific testing methods to study and determine whether all kinds of materials, devices, products, equipment, construction, etc. are harmful to life and property and the degree of harm; To determine, compile and publish relevant standards and data that can help reduce and prevent loss of life and property, and to carry out fact-finding research. In short, it is mainly engaged in product safety certification and operating safety certificate business, its ultimate purpose is to get a fairly safe level of goods for the market, and to make contributions to ensure the safety of human health and property. In terms of product safety certification as an effective means to eliminate technical barriers to international trade, UL also plays a positive role in promoting the development of international trade.
Remark: it is not mandatory for UL to enter the United States.
The Food and Drug Administration (FDA). FDA is one of the executive agencies set up by the us government in the department of health and human services (DHHS) and the department of public health (PHS). The FDA is responsible for ensuring the safety of food, cosmetics, medicines, biologics, medical devices and radiological products produced or imported in the United States. In the wake of September 11, there was a real need to improve security in the food supply. After congress passed the public health, safety and bioterrorism prevention and response act of 2002 last June, it allocated $500 million to authorize the FDA to write specific rules to implement the act. Under the rule, the FDA will assign a special registration number to each applicant, and foreign food exports to the United States must be notified to the U.S. food and drug administration 24 hours before arrival at a U.S. port, or they will be denied entry and detained at the port of entry.
Valve market analysis: valve market turnover as high as 150 billion yuan
At present, China's annual valve market turnover is as high as 150 billion yuan, of which more than 30 billion yuan market is occupied by foreign valve enterprises. And according to China's "eleventh five-year" development plan, China's valve industry, especially focusing on water and construction of the two major market valve enterprises, in energy saving, environmental protection, safety, sustainable development strategy and the international advanced enterprises still have a gap.
Compared with international advanced valve enterprises, Chinese valve enterprises are mainly characterized by small scale, low technical level and weak competitiveness of Chinese valve brands. If these problems are not solved in time, not only greatly affect the overall level of China's valve industry, but also restrict the healthy growth of China's valve industry. Valve enterprise integration and reorganization is the current Chinese valve industry must go through the process. Chinese valve enterprises only through a large range, large-scale integration of quality assets, can quickly set up a strong valve group.
During the eleventh five-year plan period, the total demand for domestic valves is predicted to be 300 billion yuan. In addition, according to the needs of China's national economic development, valve development focuses on the development of thermal power, nuclear power, hydropower, large-scale petrochemical, oil and natural gas pipelines, coal liquefaction and metallurgy and other major engineering construction supporting valve new product development. In the development of new products of the above valves, attention should be paid to the promotion and application of new valve technology, such as the development of high temperature and high pressure power station valves and nuclear power plant valves using forging welding structure when the application of vacuum electron beam welding technology and shear extrusion technology; Develop large diameter integral ball valve of long pipeline and apply integral welding technology.
Valves are indispensable fluid control equipment in petroleum, chemical industry, power station, long-distance pipeline, shipbuilding, nuclear industry, various cryogenic engineering, aerospace and offshore oil production, etc.