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,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,Valve Pressure Test,(5) Brake Valve with Nominal Pressure less than 1.0MPa and Nominal Diameter larger than 600 mm can take strength and leak test together with process system, instead of test independently. Leak test of butt welding shall be taken separately, strength test can be taken together with the system pressure.,(6) Valves that pass the test, shall be discharged of internal water in time, coated with anticorrosive paint on sealing surface, switch off the valve, cut off the access way, wrap with plastic cloth, mark with serial number, fill with valve pressure test for store record.,(7) Unqualified valveshall be disintegrated and reassemble for pressure test.,(8) During strength and leak test, gas shall be discharged before rising pressure. Pressure for check valve pressure test shall be inducted from the inlet and the outlet shall be blocked up. During check valve test, brake valve, valve clack and valve plate shall be open.,Valve installation,1,、,General requirements for valve installation:,(1)Valves of flange threaded connection should be conducted closed.,(2)Valve and pipeline welding shall be argon-arc welding, to ensure its interior is bright and clear. When welding, valve shall be switched on to prevent partial area from overheating and deformation. When welding injection valve with high pressure, valve body shall be open, take off rubber washer incase the washer burnt out.,(3)Before valve installation, installation direction shall be determined according to the fluid flow direction.,(4)Valves installed in horizontal pipe shall be vertical, upward or downward tilt 45 degrees, the center line shall be aligned as far as possible.,(5)When installing a cast iron valve (black and silver), shall prevent the risk of damage caused by strong connection or uneven force.,(1)The relief valve installation and commissioning must be conducted according to the following requirements:,Vertical, no leaning.,When put pipeline into commissioning, relief valve shall be adjusted in time. Pressure calibration shall be conducted according to design requirements. If there is no design requirements, opening pressure shall be 1.051.15 times of working pressure. Reseating pressure shall be larger than 0.9 times of working pressure. Each relief valve shall be adjusted over 3 times before considering adjustment qualified and lead sealing again. relief valve Investigation test record shall be filled.,Relief valve installation requirements,(2)The relief valve installation must be adhered to the following requirements:,Relief valve inlet pipeline of sizes should not be less than the nominal size of the relief valve imports;,For blow down pipe of discharging air, outlet shall be 2.5 meters higher than operation level. Indoor pipe shall be lead to outdoors.,If relief valve discharge pipe is too long, it shall be fixed in case of vibration.,In case of toxic or flammable fluid, emissions, the relief valve discharge pipe should be 2 meters higher than that of the highest surrounding buildings or equipment, and no open flame in the range of 15 meters.,Valve Maintenance,valve maintenance can be divided into two conditions: store maintenance and use maintenance.,(1) store maintenance,Improper safekeeping is one of main reason of valve damage.,Valve storage can not be piled up. Small valves are kept in shelf. Bid valves can be laid neatly on the ground of store. The connection surface of flange shall be kept from the ground. Protect valve from damage.,For valves that will not be used in short time, asbestos packing shall be taken out in order to avoid electrochemical corrosion.,Valves that will be put in storage shall be checked. Any stained caused by rain or dirt in transportation shall be wrapped clean before storage.,Valves in and out of storage shall be sealed up by wax paper or PVC sheet to avoid dirt coming in.,Valves machined surface in the air shall be coated with anti-corrosive oil for protection.,Valve stored outdoors shall be covered by waterproof and dustproof materials such as felt or tarpaulin. Warehouse kept valves shall be clean and dry.,(2) Use maintenance,The purpose of use maintenance is to prolong the service life of the valve and ensure reliable valve on and off.,Stem thread often rub with stem nut. Therefore butter and graphite powder shall be applied for lubrication.,Valves that seldom open or close, hand wheel shall be often rotates. And lubricant shall be coated with stem thread in case of seizure.,For valves outdoors, valve lever shall be coated with protective casing in case of rain, snow, dust tarnishing.,As for valve mechanical drive, gear box shall be applied with lubricant frequently so as to keep the valve clean.,Valve lever, specially thread, shall be cleaned frequently and coated with new lubricant to prevent hard and sundries in the dust from wearing thread and lever and impacting its service life.,For valves, operation is as important as installation and maintenance.,(1) manual control valve switching,Manual valve is the most widely used valve, its hand wheel or handle is designed according to the ordinary labour, considering the strength of the sealing surface and the necessary closing force. those people used to use the wrench shall paid strict attention that do not push too hard, otherwise it is easy to damage the sealing surface, or break the hand wheel and handle.,switching the valve shall be smooth and no shock. Some impact high-pressure valve parts have already be considered this impact, and cannot be compared with general valve.,Steam valves shall be preheated before open to discharge condensed water. Switching on shall be slow in case of surge.,When the valve is fully open, the hand wheel should be overturned a little so that the screw thread can be tight and avoid looseness and damage.,For rising stem valve, the position of valve lever in full open and full closed to avoid striking on the dead point when full open and convenient for check the condition of full off. If crack valve falls closed, or bid debris fall between the embedded valve core, the valve lever position shall be changed when full closed.,9,、,valve operation,When pipe is put into use in the first time, it has many dirt. Valve can be open a little so that the dirt can be flush away by the high speed flow. And then close the valve slightly (no quick closing, no slamming close, avoid residual debris to damage the sealing furface ). Then open again, repeat this step several times to flush away all dirt and then put into normal operation.,Valves that open frequently might have dirt on its sealing surface. When closing the valve, the above-mentioned methods shall also be applied to clean the valves and then closing the valve tightly and officially.,Any hand wheel, handle that damaged or losing shall be supplemented. Demountable wrench is not an alternative. Otherwise it will be easy to damage the valve lever, and not smooth to open and close the valve, which might cause incident in production.,Some fluid becomes frozen after closing the valve, making valve components shrink. Operators shall close the valve once again in proper time so that there is no slit in sealing surface. Otherwise fluid flow in high speed from slit and will erode the sealing surface easily.,if operating is too hard, shall analysis reasons. If packing is too tight, shall loose properly. If valve lever inclines, shall inform personnel to repair. For some valve in closing state, its closing member is heated and expanded, making opening and closing difficult. If must open at this time, shall twist off valve bonnet thread half circle or one circle to erase valve stem stress and then move handwheel.,Notes:,high temperature valve over 200 degree stays in normal temperature during installation, while the temperature increase after normal use. Screw blot is heated and expended, gaps increase. Therefore the valve shall be tighten up again, which is called “heating tightening”. Operators shall pay high attention to this work. Otherwise leakage is easy to happen.,when cold, water valve closes in long time. Accumulated water shall be discharged. After the steam of piston valve stops, condensed water shall also be discharged. If it is plugged at the bottom of valve, valve can be open to discharge water.,non-metal valve, some are hard and brittle, some has low strength. When operating, the switching force shall not be too strong, especially no violent force. And also avoid knock from other articles.,when using new valve, packing shall not be too tight. The principle is no leakage, in case the valve lever takes too much stress, speed up wear, makes open and close hard.,Valve maintenance shall be carried on in clean environment. First of all, clean the exterior surface of valve, check the damage condition of exterior surface and take record. Dismantle each parts and clean with kerosene (gasoline is forbidden in case of fire). Check damage condition of each parts and take record.,Take strength test for valve body and valve bonnet. For high pressure valve, non-destructive testing shall also be taken, such as supersonic flaw detecting and X ray detecting.,sealing ring can be checked by red lead powder. Check the coincidence degree of valve seat and valve gate. Check whether the valve lever is bend, or eroded, the abrasion condition of screw thread. Check the abrasion degree of stem nut.,Deal with the problems in checking. weld up for valve seat. built-up welding or renew sealing ring. Alignment or change valve lever. Repair all parts and change those cannot be repaired.,Reassemble the valve. Change all spacer and packing.,Take strength test and leakage test.,Valve maintenance,（,XI,）,Common fault and prevention,1. common valve,packing box leakage.,There is several reasons for packing box leakage:,Corrosion resistance, temperature, pressure of packing and working fluid disharmony between each other.,Packing method is wrong, especially the whole packing is the most prone to leak.,machining precision and surface finish of stem machining is not enough, or has the ellipticity, or have etch mark.,Stem pitting corrosion has occurred, or rust due to a lack of protection in the open air.,Stem bending.,Packing has been aging due to being used for too long time.,Operation is too harsh.,Common fault and prevention,2. closing member leakage,Normally packing box leakage is called external leakage, closing member leakage is called internal leakage. Closing member leakage in valve is not easily to be found. Closing member leakage can be divided into two types: one is sealing surface leakage, the other is sealing root leakage.,The reasons for leakage:,Sealing surface grinding is not good.,Sealing ring and valve seat and valve crack do not match with good tightness.,valve crack and stem connection is not firm, sealing surface contact is bad or has already been damaged.,Improper material selection, cannot endure the corrosion of the fluid.,make an adjustment by using check off valve, gate valve. sealing surface cannot withstand the impact of the high-speed flow.,some fluid cools after valve is closed, making the sealing surface in thin seam, also produces erosion phenomenon.,Some sealing ring and valve seat and valve crack use threaded coupling, easy to produce the oxygen concentration cell, corrosion and loose.,Because of impurities such as embedded welding slag, rust, dust, or mechanical parts in the production system falling off and plug valve core, making valve cannot be locked tight.,Stem lift failure,The reasons are:,Operation is too harsh, making thread damaged.,No lubricate or lubricate failure.,Valve stem bend.,The degree of fineness of surface is not enough.,fit tolerance is not accurate and too tight.,Improper material selection.,Thread wave fluid corrosion. (or non-rising stem valve or valve with valve stem in the bottom,Valves stay in open air without protection, the valve stem threads are full with dust sand, or corroded by rain, dew, frost and snow, etc.,4. Others,Valve body crack: normally it is cacused by frost. When the weather is cold, the valve should have heat preservation and heat tracing measures, otherwise after shutdown water shall be discharged in the valve and pipeline. (If there are plug for any bottom valve, can open the plug and drainage),Handwheel damage: Caused by impact or harsh operation of long leverage. it can be avoided as long as the operating personnel or other related personnel pay attention.,Packing gland crack: uneven force when compression packing, or there is deficiency in gland. During compress packing, screw shall be rotated symmetrically, and cannot be twisted. For manufacture, great attention shall be paid to the bulk and key-module, also gland elements, otherwise it will affect usage.,Stem and valve brake connection failure: brake valve normally uses valve stem rectangle head and T trough connection. Sometimes there is no fabrication in T trough, therefore valve stem rectangle head worn out fast. This problem is mainly solved from the aspects of manufacture. But T trough can also be fabricated again, making it have some finish degree.,Double brake valve cannot compact the sealing surface tightly: the tension of the double brake valve is generated by upper wedge. Some upper wedge of brake valve is made by bad material (low mark cast iron), and it can be worn out or cracked very soon. Upper wedge is a small member and can replace the original cast iron pieces.,Automatic valve,1. spring safety relief valve,One of the failures: the leakage of sealing surface.The reasons are: There is debris between the sealing surface and cause damaged to sealing surface. This must be prevented by regular overhauling.,The other failureis, sensitivity is not high. The reasons are: Spring fatigue; Improper use of spring. Spring fatigue;There is no doubt that spring should be replaced. Spring has been improperly used. it is because the user do not pay attention to the nominal pressure of spring safety valve. There is several pressure section, each pressure section has a corresponding spring. For example, the nominal pressure is 16 kg/cm2, nominal pressure is 2.5 to 4 kg/cm2, and the spring is 10 to 16 kg/cm2. Though it also can be open, but the sensitivity is not good.,Check valve,Common faults are: crack is broken ; fluid flows backwards.,Reasons for crack broken: the fluid pressure in the front and at the back of the check valve is in the state of equilibrium and counterbalance with each other. Valve crack is also beating with valve seat. Some valve seat made of fragile material (such as cast iron and bronze) is easy to be broken. The preventive measure is to use check valve with tough valve crack.,Reasons for fluid flows backwards: sealing surface is damaged. Sealing surface is mixed with debris. Repair sealing surface and clean the debris so that the flow backwards can be prevented.,Above os about common fault and prevention methods, it only plays a role of inspiration, in the practical operatoin, we also have other trouble, we shall prevent the failure flexibly and the most fundamental measure is to be familiar with its structure, material and movement theory.,
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