News

Technical requirements for the purchase of imported valves

What technical requirements should be paid attention to when purchasing valves?
First, the valve specifications and categories should meet the requirements of the pipeline design documents.
1. The model number of the valve should indicate the national standard number requirement. If it is an enterprise standard, the relevant description of the model number should be indicated.
2. The working pressure of the valve requires ≥ the working pressure of the pipeline. Under the premise of not affecting the price, the working pressure of the valve should be greater than the actual working pressure of the pipeline; any side under the closed condition of the valve should be able to withstand 1.1 times. Pressure value, without leakage; valve opening condition, the valve body should be able to withstand two times the valve pressure requirements.
3, valve manufacturing standards, should be based on the national standard number, if it is an enterprise standard, the procurement contract should be accompanied by corporate documents

Second, choose the material of the valve
1. Valve material, because gray cast iron pipe is gradually not recommended, the valve body material should be mainly ductile iron, and indicate the actual physical and chemical test data of the grade and casting.
2, valve stem material, strive for stainless steel valve stem (2CR13), large diameter valve should also be stainless steel embedded valve stem.
3, nut material, cast aluminum brass or cast aluminum bronze, and the hardness and strength are greater than the valve stem
4. The material of the valve stem bushing should be no more than the valve stem, and it will not form electrochemical corrosion with the valve stem and valve body under water immersion conditions.
5, sealing surface material 1 valve category is different, sealing method and material requirements are different; 2 ordinary wedge gate valve, copper ring material, fixing method, grinding method should be explained; 3 soft sealing gate valve, valve plate lining material Physical and chemical testing data; 4 butterfly valve should indicate the sealing surface material on the valve body and the sealing surface material on the butterfly plate; their physical and chemical testing data, especially the rubber sanitary requirements, anti-aging properties, wear resistance; Dingxiang rubber and EPDM rubber are not allowed to be mixed with reclaimed rubber.
6. The valve shaft packing 1 is usually opened and closed infrequently due to the valve in the pipe network. The packing is required to be inactive for several years, the packing is not aging, and the sealing effect is maintained for a long time; 2 the valve shaft packing should also be subjected to frequent opening and closing. When the sealing effect is good; 3 In view of the above requirements, the valve shaft packing should not be replaced for life or not replaced for more than ten years; 4 If the packing needs to be replaced, the valve design should consider the measures that can be replaced under the condition of water pressure.

Third, variable speed gearbox
1. The material of the box and the internal and external anti-corrosion requirements are consistent with the valve body principle.
2. The box should have sealing measures. After the box is assembled, it can withstand the immersion of 3 meters of water column.
3. The opening and closing limit device on the box should have the adjusting nut in the box.
4, the transmission structure design is reasonable, can only drive the valve shaft to rotate when opening and closing, do not make it up and down, the transmission parts bite the appropriate degree, does not produce separation and slip when the load is opened and closed.
5. The variable speed transmission case and the valve shaft seal cannot be connected to a leak-free whole.
6. There is no debris in the box, and the gear bite should be protected by grease.

Fourth, the valve operating mechanism
1. The opening and closing direction of the valve should be closed clockwise.
2, due to the valve in the pipe network, often manual opening and closing, the number of opening and closing rotation should not be too much, that is, the large diameter valve should also be within 200-600 rpm.
3. In order to facilitate the opening and closing operation of a person, the maximum opening and closing torque should be 240m-m under the condition of pipeline pressure.
4, the valve opening and closing operation end should be square, and the size is standardized, and facing the ground, so that people can directly operate from the ground. Valves with discs are not suitable for underground pipe networks.
5, the display panel of the valve opening and closing degree
1 The scale line of the degree of opening and closing of the valve shall be cast on the outer cover of the display panel after the gearbox cover or the direction of the change, and the surface shall be facing the ground, and the scale line shall be coated with phosphor to show eye-catching;
2 indicates that the material of the disc needle can be made of stainless steel when the management is good, otherwise it is painted steel, do not use aluminum skin;
3 indicates that the disc needle is conspicuous and securely fixed. Once the opening and closing adjustment is accurate, it should be locked with rivets.
6. If the valve is buried deep, the operating mechanism and the display panel are ≥15m away from the ground, and the extension pole facilities should be provided and fixed firmly so that people can observe and operate from the ground. That is to say, the valve opening and closing operation in the pipe network is not suitable for downhole operation.

Fifth, the performance test of the valve
1. When a certain specification of a valve is manufactured in batches, an authoritative organization shall be entrusted to perform the following performance tests:
1 The opening and closing torque of the valve under the working pressure condition;
2 Under the condition of working pressure, it can ensure the tight closing and closing times of the valve;
3 The detection of the flow resistance coefficient of the valve under the condition of pipeline water delivery.
2. The valve should be tested as follows before leaving the factory:
1 When the valve is open, the valve body should be subjected to internal pressure detection twice the valve pressure value;
2 When the valve is closed, the two sides are respectively subjected to 11 times of valve pressure value, no leakage; but the metal sealed butterfly valve, the leakage value is not greater than the relevant requirements.

6. Internal and external corrosion protection of the valve
1. Inside and outside the valve body (including the variable speed transmission case), firstly, the shot blasting should be used to remove rust, and the electrostatic spraying powdery non-toxic epoxy resin should be used, and the thickness is more than 0~3mm. When a large valve is electrostatically sprayed with a non-toxic epoxy resin, it should be brushed and sprayed with a similar non-toxic epoxy paint.
2. The interior of the valve body and the various parts of the valve plate require comprehensive anti-corrosion. On the one hand, it will not rust when immersed in water, and no electrochemical corrosion will occur between the two metals. On the other hand, the smooth surface will reduce the water resistance.
3. The hygienic requirements for epoxy resin or paint for anti-corrosion in the valve body shall be tested by the corresponding authority. Chemical and physical properties should also meet the relevant requirements.

Seven, valve packaging and transportation
1. The sides of the valve should be provided with light blocking plates and solid seals.
2. The medium and small diameter valves should be bundled with straw ropes and transported by container.
3, large-diameter valves also have a simple wood frame retaining package to avoid damage during transportation

Eight, check the factory instructions of the valve
1. The valve is equipment. The following relevant data should be marked in the factory manual: valve specification; model; working pressure; manufacturing standard; valve body material; valve stem material; sealing material; valve shaft packing material; valve stem bushing material; Internal and external anti-corrosion materials; operation starting direction; number of revolutions; opening and closing torque under working pressure conditions;
2, the name of the manufacturer; date of manufacture; factory number: weight; the aperture of the connecting flange, the number of holes, the center hole distance to indicate the overall length, width, height control size; effective opening and closing times; valve flow Resistance coefficient; relevant data of factory inspection and precautions for installation and maintenance.

PREVIOUS：Mechanical seal maintenance instructionsNEXT：Brief introduction of commonly used valve sea