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Pressure test methods for several types of valves


Release time:

2018-04-16

Under normal circumstances, industrial valves in use do not do strength test, but repair after the valve body and valve cover or corrosion damage of the valve body and valve cover should do strength test. For the safety valve, the setting pressure, return pressure and other tests shall comply with the specifications and relevant regulations. The valve shall be installed for strength and tightness test. Low pressure valve spot check 20%, such as unqualified should be 100 inspection; Medium and high pressure valves should be 100 inspection. The commonly used media for valve pressure test are water, oil, air, steam, nitrogen, etc. The pressure test methods for various industrial valves including pneumatic valves are as follows:

Various valve pressure test methods

Under normal circumstances, industrial valves in use do not do strength test, but repair after the valve body and valve cover or corrosion damage of the valve body and valve cover should do strength test. For the safety valve, the setting pressure, return pressure and other tests shall comply with the specifications and relevant regulations. The valve shall be installed for strength and tightness test. Low pressure valve spot check 20%, such as unqualified should be 100 inspection; Medium and high pressure valves should be 100 inspection. The commonly used media for valve pressure test are water, oil, air, steam, nitrogen, etc. The pressure test methods for various industrial valves including pneumatic valves are as follows:

Ball valve

Ball valve (ball valve ), standard GB/T21465-2008 "valve terminology" is defined as: opening and closing parts (ball) driven by the valve stem, and around the ball valve axis for rotary motion of the valve. Can also be used for fluid regulation and control, including hard seal V-shaped ball valve of its V-shaped ball core and hard alloy surfacing metal valve seat has a strong shear force, especially suitable for containing fiber, small solid particles and other media. The multi-way ball valve in the pipeline can not only flexibly control the convergence of media, diversion, and flow switching, but also can close any channel to connect the other two channels. This type of valve in the pipeline should generally be installed horizontally. Ball valve according to the driving mode is divided into: pneumatic ball valve, electric ball valve, manual ball valve.

 

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Pressure Test Method of Ball Valve

The strength test of pneumatic ball valve shall be carried out in the state of ball half open.

Floating ball valve sealing test: the valve is in a half open state, one end of the introduction of the test medium, the other end of the closed; the ball rotation several times, the valve is closed when the closed state to open the closed end of the inspection, while checking the packing and gasket sealing performance, there must be no leakage. The test medium is then introduced from the other end and the above test repeated.

The fixed ball valve sealing test: before the test, the ball no-load rotation several times, the fixed ball valve is in a closed state, from one end of the test medium to the specified value; with a pressure gauge to check the sealing performance of the introduction end, the use of pressure gauge accuracy 0.5~1 level, the range of 1.5 times the test pressure. If there is no depressurization within the specified time limit, it is qualified; then introduce the test medium from the other end and repeat the above test. Then, the valve is in a half-open state, both ends are closed, and the inner cavity is filled with medium. Check the packing and gasket under the test pressure, and there must be no leakage.

③ The three-way ball valve shall be tested for tightness at each position.

Check Valve

Check valve is to rely on the flow of the medium itself and automatically open and close the valve flap, used to prevent the medium back flow of the valve, also known as check valve, one-way valve, reverse flow valve, and back pressure valve. Check valve is a kind of automatic valve, its main function is to prevent the medium back, to prevent the pump and drive motor reverse, and the discharge of the container medium.

 

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Pressure Test Method of Check Valve

Check valve test status: lift check valve disc axis in a vertical and horizontal position; swing check valve channel axis and disc axis in a position approximately parallel to the horizontal line.

During the strength test, the test medium is introduced from the inlet end to the specified value, and the other end is closed. It is qualified to see that the valve body and valve cover have no leakage.

For the tightness test, the test medium is introduced from the outlet end, and the sealing surface is inspected at the inlet end. No leakage at the packing and gasket is considered as qualified.

Diaphragm valve

Diaphragm valve structure and general valve is not the same, is a new type of valve, is a special form of cut-off valve, its opening and closing parts is a piece of soft material made of diaphragm, the valve body cavity and valve cover cavity and drive components are separated, is widely used in various fields. Commonly used diaphragm valve with rubber-lined diaphragm valve, fluorine-lined diaphragm valve, unlined diaphragm valve, plastic diaphragm valve.

Diaphragm valve is in the valve body and valve cover is equipped with a flexible diaphragm or combination of diaphragm, the closing member is connected with the diaphragm of a compression device. The valve seat can be weir-shaped or the wall of a straight-through flow channel. The advantage of the diaphragm valve is that its operating mechanism is separated from the medium passage, which not only ensures the purity of the working medium, but also prevents the possibility of the medium impacting the working parts of the operating mechanism in the pipeline. In addition, there is no need for any form of separate sealing at the valve stem, unless used as a safety device in the control of hazardous media. Diaphragm valve, because the working medium contact is only the diaphragm and the valve body, both can use a variety of different materials, so the valve can be ideal to control a variety of working medium, especially with chemical corrosive or suspended particles of the medium. The working temperature of the diaphragm valve is usually limited by the material used in the diaphragm and valve body lining, and its working temperature range is about -50~175 ℃. Diaphragm valve structure is simple, only by the valve body, diaphragm and valve head assembly three main components. The valve is easy to quickly disassemble and repair, and the replacement of the diaphragm can be completed on site and in a short time.

Pressure Test Method of Diaphragm Valve

Diaphragm valve strength test from either end of the introduction of media, open the valve, the other end of the closed, test pressure rose to the specified value, see the valve body and valve cover no leakage for qualified. Then depressurize to the tightness test pressure, close the disc, open the other end for inspection, no leakage is qualified.

Pressure reducing valve

The pressure reducing valve is a valve that reduces the inlet pressure to a certain required outlet pressure and relies on the energy of the medium itself to automatically maintain a stable outlet pressure. From the point of view of fluid mechanics, the pressure reducing valve is a local resistance can change the throttle element, that is, by changing the throttle area, the flow rate and the kinetic energy of the fluid change, resulting in different pressure loss, so as to achieve the purpose of decompression. Then, relying on the adjustment of the control and adjustment system, the fluctuation of the pressure behind the valve is balanced with the spring force, so that the pressure behind the valve remains constant within a certain error range.

Pressure Test Method of Pressure Reducing Valve

 

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The strength test of the pressure reducing valve is generally assembled after the single-piece test, or after the assembly test. Duration of strength test: lmin for DN<50mm; greater than 2min for dn65 ~ 150mm; greater than 3min for dn>150mm. After the bellows is welded with the component, the maximum pressure after the application of the pressure reducing valve is 1.5 times, and the strength test is carried out with air.

② The sealing test shall be carried out according to the actual working medium. When testing with air or water, the test shall be carried out at 1.1 times of the nominal pressure; when testing with steam, the maximum working pressure allowed at the working temperature shall be carried out. The difference between inlet pressure and outlet pressure shall not be less than 0.2MPa. The test method is as follows: after the inlet pressure is set, gradually adjust the adjusting screw of the valve, so that the outlet pressure can be sensitively and continuously changed within the maximum and minimum values, without stagnation and blocking. For steam pressure reducing valve, when the inlet pressure is adjusted, close the valve and block the valve. The outlet pressure is the highest and lowest value. Within 2min, the appreciation of its outlet pressure shall conform to the provisions in Table 4.176-22. At the same time, the pipeline volume behind the valve shall conform to the provisions in Table 4.18 as qualified. For water and air pressure reducing valves, 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.

Gate valve

Gate valve (gate valve) is an opening and closing parts of the gate, the direction of movement of the gate and the direction of the fluid perpendicular to the gate valve can only be fully open and fully closed, can not be adjusted and throttling. The gate valve is sealed by the contact between the valve seat and the gate. Usually, the sealing surface is surfacing with metal materials to increase wear resistance, such as surfacing 1Cr13, STL6, stainless steel, etc. The gate has rigid gate and elastic gate. According to the different gate, the gate valve is divided into rigid gate valve and elastic gate valve.

 

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Pressure Test Method of Gate Valve

The strength test of the gate valve is the same as that of the stop valve. There are two methods for sealing test of gate valve.

① Open the gate to increase the pressure in the valve to the specified value; then close the gate, immediately take out the gate valve, check whether there is leakage at the seal on both sides of the gate or directly inject the test medium into the plug on the valve cover to the specified value, and check the seal on both sides of the gate. The above method is called intermediate pressure test. This method should not be in the nominal diameter DN32mm below the gate valve to do sealing test.

② Another method is to open the gate to make the valve test pressure rise to the specified value; then close the gate, open one end of the blind plate, check whether the sealing surface leakage. Then turn the head and repeat the above test until it is qualified.

The tightness test at the packing and gasket of the pneumatic gate valve shall be carried out before the gate tightness test.

Butterfly valve

Butterfly valve is also called flap valve, is a simple structure of the control valve, can be used for low pressure pipe medium switch control butterfly valve refers to the closure (disc or butterfly plate) for the disc, around the valve shaft rotation to achieve the opening and closing of a valve.

The valve can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, mud, oil, liquid metals and radioactive media. The main role of cutting and throttling in the pipeline. Butterfly valve opening and closing parts is a disc-shaped butterfly plate, in the valve body around its own axis of rotation, so as to achieve the purpose of opening and closing or regulation.

 

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Pressure Test Method of Butterfly Valve

The strength test of pneumatic butterfly valve is the same as that of stop valve. The sealing performance test of butterfly valve should introduce the test medium from the medium flowing end, the butterfly plate should be opened, the other end should be closed, and the injection pressure should reach the specified value; After checking that there is no leakage at the packing and other seals, close the butterfly plate, open the other end, and check that there is no leakage at the butterfly plate seal. Butterfly valves used for regulating flow may not be tested for sealing performance.

plug valve

Plug valve is closed or plunger-shaped rotary valve, by rotating 90 degrees to the valve plug on the channel port and the valve body on the channel port communication or separation, to achieve the opening or closing of a valve.

Its valve plug can be cylindrical or conical in shape. In a cylindrical valve plug, the channel is generally rectangular; while in a tapered valve plug, the channel is trapezoidal. These shapes make the structure of the plug valve lightweight. It is most suitable for use as a cut-off and connection medium and as a shunt, but depending on the nature of the application and the erosion resistance of the sealing surface, it can sometimes be used for throttling.

 

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Pressure Test Method of Plug Valve

① when the plug valve strength test, the medium from one end of the introduction, closed the rest of the passage, the plug in turn to the fully open the working position of the test, the valve body found no leakage is qualified.

② During the sealing test, the straight-through cock should keep the pressure in the cavity and the passage equal, rotate the plug to the closed position, check from the other end, and then rotate the plug by 180 ° to repeat the above test; the three-way or four-way cock valve should keep the pressure in the cavity and one end of the passage equal, rotate the plug to the closed position in turn, introduce the pressure from the right-angle end, and check from the other end.

Before the plug valve test, it is allowed to apply a layer of non-acidic dilute lubricating oil on the sealing surface. No leakage and enlarged water droplets are found within the specified time. Plug valve test time can be shorter, generally according to the nominal diameter provisions for l ~ 3min.

Plug valves for gas should be tested for air tightness at 1.25 times the working pressure.

Globe valve

Stop valve (stop valve,Globe Valve) opening and closing parts is a plug-shaped disc, sealing the upper plane or sea cone, disc along the center line of the valve seat for linear motion. The form of movement of the valve stem, (generic name: dark rod), there are also lifting rotating rod type can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, mud, oil, liquid metals and radioactive media. Therefore, this type of shut-off valve is very suitable for cutting or regulating and throttling. Because of this type of valve stem opening or closing stroke is relatively short, and has a very reliable cut-off function, and because the change of the valve seat port and the stroke of the valve flap are proportional, it is very suitable for the regulation of flow.

 

Pressure Test Method for Stop Valve and Throttle Valve

For the strength test of stop valve and throttle valve, the assembled valve is usually placed in the pressure test rack, the valve disc is opened, the medium is injected to the specified value, and the valve body and valve cover are checked for sweat and leakage. Can also be a single piece of strength test. Only stop valve shall be used for tightness test. During the test, the valve stem of the stop valve is in a vertical state, the valve flap is opened, and the medium is introduced from the bottom end of the valve flap to the specified value, and the packing and gasket are checked; after being qualified, close the valve flap and open the other end to check whether there is leakage. If the valve strength and sealing tests are to be done, the strength test can be done first, then the pressure is reduced to the specified value of the sealing test, and the packing and gasket are checked. Then close the valve clack and open the outlet end to check whether the sealing surface leaks.

Safety valve

Safety valve is the opening and closing parts under the action of external force in the normally closed state, when the equipment or the medium pressure within the pipeline increases more than the specified value, by discharging the medium to the outside of the system to prevent the medium pressure within the pipeline or equipment exceeds the specified value of the special valve. Safety valves are automatic valves, mainly used for boilers, pressure vessels and pipelines, control pressure does not exceed the specified value, personal safety and equipment operation plays an important role in protection. Note The safety valve must be pressure tested before it can be used.

Pressure Test Method of Safety Valve

The strength test of the safety valve is the same as other valves, and it is tested with water. 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; when testing the upper part of the valve body and the valve cover, the pressure is introduced from the outlet El end, and the other ends are closed. The valve body and bonnet shall be qualified if there is no leakage within the specified time.

The sealing test and constant pressure test, the general use of medium is: steam safety valve with saturated steam as the test medium; ammonia or other gas valve with air as the test medium; water and other non-corrosive liquid valve with water as the test medium. For some important positions of the safety valve commonly used nitrogen as the test medium.

 

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