Application of Mechanical Seal on Pressure Regulating Valve

The pressure regulating valve is a pressure regulating device installed at the outlet of the pump, which is a protective device for normal operation of the pump. The valve outlet and the inlet are respectively connected with the pump inlet and the outlet. Normal work, the pressure difference between the pump inlet and outlet, valve closed. When the pump outlet pipe is clogged or the outlet pipe system pressure rises due to other reasons, the pump outlet pressure will exceed the pump outlet design pressure, causing the pump inlet differential pressure to increase does not work properly, the valve opens so that the pump outlet media returns to the inlet , Reduce the pump outlet pressure, the pressure control within the allowable range, to ensure the normal operation of the pump. Valve before the transformation of the work shown in Figure 1, K surface is the valve face, by adjusting the size of the spring A pressure adjustment, the normal work of the entrance side of the pressure and the spring force is equal to the outlet pressure. When the inlet pressure is greater than the sum of the spring force and the outlet pressure, the K surface is opened and the medium flows into the outlet end through the K surface to balance the pressure difference on both sides. Second, the control valve failure Analysis of the original valve due to structural defects, the use of shorter, analysis of the main reasons for the failure of the following points, at the same time the valve structure targeted design. (1) The valve failure performance for the pump can not be normal pressure, pump vibration is often a reason valve failure. Observed by the scene, the pump body such as vibration when the pump is large, if the vibration frequency and the natural frequency of elastic components close, the valve will wear fatigue damage, leading to end failure. (2) The original valve end surface is wedge-shaped end surface, although the work process better contact with the two end surfaces, but the end surface can not be ground (no suitable grinding tools for grinding) The analysis of the device is static two end surface contact, work without end Movement, as long as the end of the patch and good, to ensure flatness, you can work properly. Therefore, the wedge end surface can be changed to the grinding of the flat end surface. (3) After the analysis for the failure of the end face, disassembled and found that there are wounds on the end, is the pump impurities in the end surface of the crush end. Due to the original valve as a whole valve, the end face and the valve body cast together, can not be partially replaced, had to replace the whole. Maintenance costs are too high, the processing cycle is long, urgent need to transform. Third, the valve targeted transformation (1) the original wedge-type end face to flat end face, the contact area between the two ends minimize, so that the pressure is reduced in the end face between the opportunity to reduce, in case of impurities caught between the end face crush the end face , You can remove the end surface of the general seal grinding table grinding, parts can be repaired and reused. (2) The original valve body as a whole valve, the valve inside the end face in the middle of the valve, the maintenance is very inconvenient, now replaced by two-body valve body, the valve body end face sandwiched between the two parts of the valve body, by two seals The connection with the valve body not only ensures the evacuation of the end face, but also makes the end face have a certain degree of floating, and can better cooperate with the other end face. The most preferable point is that the valve body sealing end face can be detached, repairable and replaceable. (3) The original valve body is a cast part, which is an optimized production plan for mass production. However, the cost of small-batch production and casting is very high. In order to reduce the cost, the original cast part is changed into the welding part to reduce the cost. Fourth, the valve design steps and parameter selection 1. Design Basis (1) Operating conditions Nominal diameter DN50mm control valve, for example, the rated voltage range 0.2 ~ 0.8MPa, temperature: 40 ℃. (2) the original valve design theory. (3) The principle of force balance. (4) to transform the valve maintainability. (5) the original valve structure. 2. Design Procedure (1) According to the valve working principle and installation, the new modified valve shape and working principle similar to the previous. (2) According to the nature of the media, a reasonable choice of valve material, the choice of the material can fully meet the valve requirements. (3) The range of voltage regulation The original voltage regulation range is 0.2 ~ 0.8MPa. In order to ensure that the spring force does not affect the installation of the entire valve body, the free state of the spring is less than the maximum distance between the spring seat and the moving ring. The bottom of the range 0.2MPa down to 0, this does not affect the entire valve work, but also more effort when assembling the valve. (4) to determine the basic structure of the valve there are two end faces, the valve itself has an outlet and the inlet connected to the pump, the valve itself to the end face fit force provided by the spring, the spring force adjustment by the adjusting bolt adjustment. The design of the valve is designed as a removable end face design concept, the original overall valve into two parts, with bolts together to locate the pin positioning to ensure that the two flanges flatness of imports and exports, the valve is installed in conjunction with two parts of the valve The inner end face, the end face and the valve body is provided with a sealing ring (material of polytetrafluoroethylene), which can prevent the inlet pressure from extruding the end face and increase the floating of the end face so that the valve works with flexible contact between the two end faces and the sealing more reliable. The moving end is guided by the guide column, and the guide column and the moving ring are screwed together. When the maintenance is performed, the guide column is removed and the end surface can be directly ground for repair. The leading post thread tip is made sharp, tightened to a sharp corner to prevent vibration during the pump vibration. (5) the location of the end face of the valve inlet and outlet position has been determined, the flange position must be between the two, in order to ensure that the face between the two ports, in order to facilitate bolt connection, as far as possible the flange set in the middle of the two mouths, Make the spring have greater use of space, try to put the end near the entrance. 3. The main structure of the geometric dimensions to determine and technical requirements (1) the width of the end face so that the contact area between the two ends minimize, so that the pressure is reduced between the end face of the opportunity to reduce the pressure on the end face is not too high, the end face Take the width b = 3mm. (2) Confirm the size of the end face According to the size of the original body, the new body should not be larger than the original body, or it may intervene with the external pipe when installing. The wall thickness and the flange space are removed. The end face size is basically determined at φ58 .5mm or less. In order to reduce the deposition of the medium near the end face, a large chamfering size is designed near the end face to reduce the medium deposition, and the initial size is determined as φ36mm × φ30mm. (3) to determine the range of pressure regulating valve pressure regulating area End pressure area: Where S - end area, in units of mm2; R - end radius, in units of mm. Maximum spring force (valve pressure 0.8MPa when the end face should be closed): F1 = pS = 0.8 × 1017 = 813.5N where F1 --- maximum spring force in N; p --- body maximum pressure, The unit is MPa. That is, the normal working pressure of the valve to adjust the rated pressure range of 0 ~ 813.5N. (4) design of the spring length: the total length should be less than or equal to the spring space within the valve to make the installation of the screw connection effort, the calculation, L ≤ 108mm. Maximum working length: f should be less than the space within the bonnet (remove both ends of the screw head and nut), calculated that f ≤ 33mm. Outside diameter: the whole root should be installed in the valve body, so φ outside <φ58.5, temporarily set the diameter D2 = 45mm ① selected materials and allowable stress is a spring, the material used 0Cr17Ni14Mo2, "Mechanical Design Manual "Table 30.2-4 check τp = 324MPa. ② Seeking spring wire diameter according to "Mechanical Design Manual" spring design formula (30.2-6) check the "Mechanical Design Manual" spring design with C = 7.4 of Figure 30.2-4; ③ find the effective number of turns according to "Mechanical Design Manual" spring Design Formula 30.2-5 According to "Mechanical Design Manual" spring design formula 30.2-5 ④ calculate the remaining size of the total number of turns n1 = n +1.5 = 6 Maximum working load deformation and load and pressure and deformation Deformation According to Spring work area should be in the full deformation of 20% to 80% of the conditions, take f1 = 0.8fb, then f1 to meet the conditions of the work area. Compression height Hb = (n1-0.5) d = (6-0.5) × 6 = 33 mm Free height H0 = Hb + fb = 33 + 33 = 66 mm Pitch Helix angle γ = 5.13 °, satisfying 5 ° to 9 ° Requirements, spring design is completed. 4. Main Parameters The main working principle of this valve is that when the pressure difference between inlet and outlet medium and the spring pressure fluctuates, the force between the end faces is controlled by the spring. Therefore, as long as the control spring force is suitable, the valve can work normally. That is, as long as the control A size (see Figure 2) can control the entire valve work. According to the formula p = FS = Δlks was calculated from the pressure range A size size, as shown in Figure 3: According to this figure can be used directly in the valve. Fifth, the effect of the transformation (1) due to the valve sealing surface from the wedge surface into a plane, extending the operational life, the valve life after the transformation are generally above 10000h, greatly exceeding the original valve 3200h service life. (2) easy maintenance, wearing parts for the static and dynamic ring end face, such as dynamic and static ring wear, removable seal ring grinding, short maintenance cycle, saving the cost of purchasing a valve.

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