The diameter of the butterfly valve is mainly determined by the flow, medium and flow rate. In general, the flow rate of liquid is not more than 5m/s and up to 7-8m/s. In general, the flow rate of water is 2-3m/s, the flow rate of low pressure gas is recommended for 2-10m/s, the flow rate of medium pressure gas is recommended for 10-20m/s; As for the flow rate of steam, the flow rate of low pressure steam is recommended for 20-40m/s, the flow rate of medium pressure steam is 40-60m/s, and the flow rate of high pressure steam is 60-80m/s.   Of course, sometimes, in order to reduce pressure loss, people will choose a larger diameter butterfly valve, so the flow rate will be slower. However, this cannot be done if the valve is operating with a low flow rate.   Liquids flow through a zone of absolute low pressure and undergo rapid evaporation and re-condensation in a very short period of time. This phenomenon is called cavitation effect. Because the gas cannot change state at low pressure, this phenomenon does not occur in the gas stream. When the fluid flows into the high-pressure area, the steam bubbles will suddenly condense, collapse or coalesce, the flow rate can reach 110m/s, the flow pressure can reach 50Mpa, causing impact damage to the pipe wall.   When the valve pressure is less than 1.5Mpa and cavitation occurs, but does not cause serious damage to the material, so no special measures are necessary.

Thanks to the development of today’s science and technology, the marine valves have been greatly improved, with better body strength, strong resistance to abrasion and corrosion and longer service life. Occasionally, however, some unexpected faults would affect the use and health of the valve. How are some common faults and relevant ways to fix it.   1. The device doesn’t work and DCS alarms timeout Possible causes: A. The power dead; B. The main loop lacks of phase; C. The control loop fails;   Solutions: A. Check the power supplier and voltage of each circuit; B. Check if the main circuit phase wire is broke; C. Check if the switch limited position or the torque switch works normally. Whether the DCS is protected by chain;   2.DCS alarms once upon it is operated Possible causes: A. The short-circuit of the main circuit leads to the protective act of the thermal relay or power switch trip; B. Fails of internal components or body cause excessive torque protection; C. The electrical equipment's torque control mechanism fails or the torque setting value is too small;   Solutions: A. Check whether the power switch trip and thermal relay ; B. Check if the transmission mechanism is stuck; C. Check the torque setting value;   Through the above analysis, we will have a general understanding of these failures and the corresponding solutions. There will be other faults in marine valves in the future, but as long as we actively analyze these faults, we will finally find a suitable solution.

1. First of all, the design of the safety valve must meet the requests from users. 2. The price of the product should be the most reasonable once upon the actual working condition. 3. The first though design should have in their mind is that making the overall performance of the valve reach the anticipation and standards. 4. More tests promise more precise and detailed parameters. 5. The spring’s stiffness should be paid more attention. Appropriate design enables the valve’s internal parts to match each other batter, making it easy to assemble, disassemble and maintain. 6.Safety valve needs to be designed to have a longer service life. Generally, the medium of safety valve can be divided into three types: steam, gas and liquid. But designers cannot do performance tests of various media at the same time. Due to heavy oil (asphalt) and other media, the qualified performance data obtained from the cold test may become unsatisfactory. Therefore, the safety valve design cannot duplicate any other mature product models. The valve should be manufactured with appropriate spring rigidity and reasonable internal structure according to different media. Of course, the design principle of the safety valve is to produce products that users satisfy, and the only design shortcut is the experience accumulated from practice.

1. Why does a double seating valve tend to oscillate at a small opening state?   When it comes to a sing-spool valve, it will have excellent stability when the medium is open-flow type, which means the medium flows towards the direction favorable to the opening of the valve. In contrast, when turn it into close-flow type, the valve’s stability falls. Based on the above, the double seat valve has a bad stability and tends to vibrate at small opening sate, because its two spools--the upper one is in flow-close situation while the lower one is bound to be in flow-open--work simultaneously.   2. Why can’t a double seal valve be used to cut off medium?   Tanks to its force-balanced structure, the double seal valve has a large differential pressure. But the leakage brought by the imperfect contact of the two sealing faces will lead to horrible consequences if it is used as a cut-off valve.   3. Why does a linear motion valve do worse in anti-blocking than rotary motion valve?   The linear motion valve cut off the flow vertically but the medium horizontally flows in and out. The flow path in the cavity, extending in twist and turns, enables the impurities to precipitate in the so-called dead zones. As time goes by, the path will be blocked. On the contrary, the rotary motion valve cut the flow off horizontally and has a relatively simple flow path. Therefore, the rotary motion valve has a better anti-blocking performance.   4.Why the stem of linear motion valve is relatively small   It refers to an easy mechanical principle: high sliding friction brings low rolling friction. The stem of the linear motion valve moves up and down. The packing, which is slightly compressed, will wrap the stem very tightly, resulting in a large backlash. To avoid that, the stem is designed to be very thin and small.   5. Why does rotary motion valve can bear high differential pressure?   That’s because the resultant force that the medium produced on the spool or plate only has a very small torque on the axis of rotation. As a result, the rotary motion valve bears high differential pressure

Q1. Why does the life of rubber lined butterfly valve and fluorine diaphragm valve will be shortened by desalinated water media? In the situation of low concentration of acid or base, desalinated water media will intensively corrode the rubber part of the rubber lined butterfly valve and make rubber expand,age and lose intensity, eventually degrading its working performance . Though another valve--rubber lined diaphragm valve has been developed with better corrosion-resisting ability, its diaphragm will easily fracture after folding. Then mechanical damage occurs and service life shortens. Q2. Why does shut-off valve should be always treated with hard seal? Soft seal can manage with the need from shut-off valve: to have a lower leakage rate, and have a great cutting function. However, valve with hard seal will not be eligible in reliability and abrasive resistance. When we add these two requests to the comparison of the two kinds of shut-off valves, the one with hard seal stands out right away. Q3. Why does sleeve valve fail to take place of single valve and double valve? Many people thought that single and double seat valve will be squeezed out by the second-generation-to-be product--sleeve valve, which born in 1960s and found its feet worldwide in 1970s. But the current situation is quite different. Although the sleeve valve has remarkable stability, its weight and leakage index don’t exceed single and double seat valves. The end result of competition of there three valves is a draw, as they’re in the market nowadays. Q4. Why are piston actuator increasingly used in pneumatic valve? Piston actuator have smaller size but bigger thrust to drive pneumatic valve thank to air pressure. Q5. Why does selection outweigh calculation? Selection is more important and complex than calculation.Because calculation is only a process of formulas, it can’t demonstrate the accuracy of the formula itself, but the accuracy of given indexes. There are many items involved in the selection. A little oversight may bring wrong choice. That not only wastes manpower, material and financial resources, but also results in unsatisfactory conditions and brings troubles in reliability, service life and operation,etc.

It is of great importance to equip the valve body with high strength. With defects in valve body, unexpected economic losses may occur someday after they are put in place. What’s more, it may put a period to the whole working system and take a exorbitant cost from the company, even the public. When it comes to material outputting, media leakage is not allowed., so do other defects like cracks, loose pores, slags to the body, cover and other parts. Besides that, to ensure the perfect performance of these apparatus, valve producers have to do do strength test to every valve. After all parts of the vale are assembled, the integrated piece will be send to do strength test. Usually, after rough machining, rough quality blanks and heat treated components will do intermediate strength test to spare unnecessary waste carried by all kinds of test failures. If all indicators are normal, further test are saved only if users insist.. The body strength tests are usually conducted under general temperature. And the testing pressure will be set 1.25 to 1.5 times higher than the nominal pressure. Valves are going to prove strong enough to pass the exam as long as these is no leakage within the allowed range. Another thing worth to be keep in mind is that air in the cavity should be output if the outputting material is water. Those above speak loudly that strength test id of great meanings and values. You could never assure its quality when its not strong enough. Therefore it is sure that the strength test is and will be the most important project in the valve producing field.