How are various industrial valves tested?
In general, industrial valves are not used for strength testing, but after repair of the body and bonnet or corrosion damage of the body and bonnet should be tested for strength.For the safety valve, its fixed pressure and return seat pressure and other tests shall comply with the specification and the relevant regulations.Valve strength test and valve seal test should be done on the valve hydraulic test bench before valve installation.Low pressure valve spot check 20%, if unqualified should be 100% inspection;Medium and high pressure valves shall be inspected 100%.The commonly used media of valve pressure test are water, oil, air, steam, nitrogen, etc. The pressure test methods of all kinds of industrial valves including pneumatic valves are as follows:
Pressure test method for globe and throttle valves。Strength test for globe and throttle valves, usually assembled valves placed in a pressure rack, disc opened, medium injected to specified value, check body and bonnet for sweat and leakage.Strength test can also be carried out on a single piece.Seal test for globe valve only.When tested, the stop valve stem is in a vertical state, the disc is open, the medium is introduced from the bottom end of the disc to the specified value, check the packing and gasket;When qualified, close the disc and open the other end to check for leakage.If valve strength and sealing tests are to be done, do the strength test first, and then reduce the pressure to the sealed test specification, check the packing and gasket;Close the disc again and open the outlet end to check the sealing surface for leakage.
Test method for gate valves。Gate valves are tested for the same strength as globe valves.There are two methods of sealing test for gate valves.
Gate open, so that the pressure in the valve to the specified value;Then close the gate, take out the gate valve immediately, check for leakage in the seals on both sides of the gate or inject the test medium directly into the plug on the valve cover to the specified value, check the seals on both sides of the gate.The above method is called intermediate pressure test.This method is not suitable for seal testing of gate valves of nominal size DN32mm or less.
Another method is to open the gate, so that the valve test pressure to the specified value;Then close the gate and open one blind end to check the sealing surface for leakage.Repeat the above test until qualified.
Pneumatic gate valve packing and gasket sealing test shall be conducted before the gate sealing test.
Pressure test method for ball valves.Pneumatic ball valve strength test should be carried out in the ball valve ball half-open state.
(1) floating ball valve sealing test: the valve in a half-open state, one end of the test medium, the other end closed;Turn the ball several times, open the closed end when the valve is in the closed state, check the sealing performance at the packing and gasket, no leakage.Then introduce the test medium from the other end and repeat the experiment.
(2) fixed ball valve sealing test: before the test will turn the ball for several times without load, the fixed ball valve in the closed state, from one end of the test medium to the specified value;Check the sealing performance of the inlet end with the pressure gauge. The accuracy of the pressure gauge is 0.5 ~ 1, and the range is 1.6 times of the test pressure.In the specified time, no hypotension phenomenon is qualified;Then introduce the test medium from the other end and repeat the experiment.Then, leave the valve half open, both ends closed, the cavity filled with medium, check the packing and gasket under test pressure, no leakage.
The tee ball valve should be in each position for sealing test.
Test method for plug valves.When the plug valve strength test, the medium from one end of the introduction, closed the rest of the road, the plug in turn to rotate to the full open each working position for the test, the valve body did not find leakage as qualified.(2) during the sealing test, the straight through cock should keep the pressure in the cavity equal to the path, rotate the plug to the closed position, check from the other end, and then rotate the plug 180° to repeat the test;Three-way or four-way plug valves shall keep the pressure in the chamber equal to that at one end of the passage, rotate the plug to the closed position in turn, and the pressure shall be introduced from the right Angle end, and shall be inspected from the other end at the same time.In front of the test stand of the cock valve, a layer of non-acid thin lubricating oil is allowed on the sealing surface.The test time of the plug valve can be shorter, generally l ~ 3min according to the nominal size.Gas cock valves should be tested for air tightness at 1.25 times working pressure.
Pressure test method for butterfly valve.The strength test of pneumatic butterfly valve is the same as that of globe valve.The sealing performance test of butterfly valve should be conducted by introducing the test medium into the end of the flow of medium. The butterfly plate should be opened and the other end closed. The injection pressure should reach the specified value.After checking the packing and other seals for no leakage, close the butterfly plate, open the other end, check the butterfly plate seal for no leakage is qualified.Butterfly valves used to regulate the flow rate do not do sealing performance tests.
Pressure test method for diaphragm valves.Diaphragm valve strength test from either end of the introduction of media, open the disc, the other end closed, test pressure to the specified value, see the valve body and bonnet no leakage is qualified.Then step down to the sealing test pressure, close the disc, open the other end for inspection, no leakage is qualified.
Pressure test method for check valves.Check valve test status: lifting check valve disc axis is in a position perpendicular to the horizontal position;Swing check valve channel axis and disc axis are approximately parallel to the horizontal line.
During the strength test, the test medium shall be introduced from the inlet end to the specified value, and the other end shall be closed. The valve body and bonnet shall be qualified if there is no leakage.
The sealing test introduces the test medium from the exit end, and it is qualified to check the sealing surface at the inlet end, and there is no leakage at the packing and gasket.
Pressure test method of the safety valve the strength test of the safety valve is the same as that of other valves.When testing the lower part of the valve body, the pressure is introduced from the inlet I=I end and the sealing surface is closed.Test upper body and bonnet with pressure introduced from the El end and closed at other ends.Qualified for no leakage of valve body and bonnet within specified time.(2) sealing test and constant pressure test, the general use of the medium is: steam with the relief valve to saturated steam as the test medium;Ammonia or other gas valves with air as the test medium;Valves for water and other non-corrosive liquids shall be tested in water.Nitrogen is commonly used as the test medium for some important safety valves.
The seal test shall be carried out with nominal pressure as the test pressure, and the number of tests shall be no less than two times.There are two methods for leak detection: one is to seal the joints of the safety valve, with butter to seal the thin paper on the El flange, thin paper bulging for leakage, not bulging for qualified;The second is to use butter to thin plastic board or other board seal on the lower part of the outlet flange, fill water seal the disc, check the water does not bubble as qualified.The number of tests for the fixed pressure and return pressure of the safety valve shall be no less than 3 times.
Refer to GB/T 12242-1989 safety valve performance test method for safety valve performance tests.
Pressure reducing valve test method the strength test of pressure reducing valve is generally assembled after a single test, can also be assembled after the test.Duration of intensity test: DN<Lmin 50 mm;DN65 ~ 150mm larger than 2min;DN>150mm is greater than 3min.After the bellows are welded to the assembly, the strength test shall be conducted with air at 1.5 times of the maximum pressure after applying the pressure reducing valve.(2) sealing test according to the actual working medium.When air or water is used, 1.1 times of nominal pressure is used;In the case of steam testing, the maximum operating pressure allowed at the operating temperature is applied.The difference between inlet pressure and outlet pressure shall not be less than 0.2mpa.The test method is: after the inlet pressure is adjusted, gradually adjust the adjustment screw of the valve, so that the outlet pressure in the maximum and minimum range can be sensitive, continuous change, no stagnation, jam phenomenon.For the steam reducing valve, when the inlet pressure is adjusted away, the outlet pressure is the highest and lowest value after the shutoff valve cut-off valve. Within 2min, the increase of the outlet pressure should comply with the provisions in table 4.176-22. Meanwhile, the volume of the pipeline after the valve is qualified according to the provisions in table 4.18.For water and air pressure reducing valve, when the inlet pressure is adjusted and the outlet pressure is zero, close the pressure reducing valve for sealing test, no leakage within 2min is qualified.