[Abstract] The structure, design calculation and design verification of type 1.6MPaDN300 ~ DN1000 British standard cast iron gate valve are expounded. [Key words] British Standard cast iron gate design and design verification 1 Overview BS5163, BS51501.6MPaDN300 ~ DNl000 British standard cast iron gate valve, in the United Kingdom, Singapore, Malaysia and the Middle East in some countries, water supply pipes and industrial pipes are widely used, see its structural features, see : Open gear drive gate valve shown in Figure 1; closed gear drive gate valve shown in Figure 2. This article focuses on the 1.6MPaDN300 ~ 1000 British standard cast iron gate valve body wall thickness, valve cover wall thickness, gate thickness, stem diameter design calculations and design verification - type test. 2 Design 2.1 Body wall thickness design calculations BS5163, BS5150 standard push did not give the shell minimum wall thickness data, design, the body wall thickness must be calculated. Design, the valve body cavity cross-sectional shape designed to approximate the oval, see Figure 3, the design and calculation of the wall thickness S'B1, is calculated using the formula for calculating the elliptical wall thickness formula: Where K - Approximate wall thickness coefficient of elliptical section valve body, DN300 ~ DN500, K take 1.13, DN600 ~ DNl000, K take 1.07; P - medium pressure, design, P take 1.6MPa; a - approximate oval [Mm]; [σL] - Permissible tensile stress of cast iron (HT250), [σL] 35.28 MPa; C - Allowance for corrosion, C 5 (mm). DN300 ~ DN1000 valve wall thickness of the design calculations in Table 1. Design, body wall thickness design, in addition to considering the strength of the valve body, the valve body stiffness should also be considered, that is, the valve body cavity deformation (referring to the role of medium pressure 1.6MPa) control at 0 .001DN range, otherwise, the valve body will not be able to seal due to deformation. To solve the stiffness of the valve body shown in Figure 1, in the valve body, the cavity design ribs, and the body of the external ribs and the valve body flange connected to increase the rigidity of the valve body, if necessary Designed to vary in wall thickness, ie to increase the approximate elliptical cross-section of the valve cavity in the wall thickness. 2.2 The design of the valve cover wall thickness, the valve cover wall thickness S'B2 usually no longer design calculations, the valve body wall thickness directly taken as 0.95 as the valve cover wall thickness. DN300 ~ DN1000 bonnet minimum wall thickness data in Table 2; bonnet stiffener design shown in Figure 1. 2.3 Gate thickness calculation design BS5163, BS5150 standard, also did not give the gate minimum wall thickness data, design, gate thickness S'B3 must be calculated, the formula is as follows: Where d - (Mm); P - medium pressure, designed to be 1.6 MPa; [σW] - permissible bending stress for cast iron (HT250) [σW] 56.84 MPa; C take 3 (mm). DN300 ~ DN1000 gate wall thickness of the design calculations in Table 3. 2.4 stem diameter design calculations BS5163, BS5150 standard, the same did not give the smallest diameter stem data, the design must be designed on the stem diameter calculation, which is calculated as follows: Where K - stem Design calculation coefficient, of which DN300 ~ DN500, K take 0.70 ~ 0.75; DN600 ~ DNl00. K is 0.60 ~ 0.65; Q - axial force (N) when the valve stem is opened; [σL] - allowable tensile stress of cast iron (HT250) [σL] is 35.28MPa; Formula, and is not calculated due to the small QG (weight of shutter assembly) value. Where QMF - the sealing surface to achieve the necessary pressure than the force (N); QMJ - sealing surface media hydrostatic pressure (N); d - diameter, d = DN (mm); bm - valve Body seal width (mm); qmf - Required seal pressure (MPa); P - Medium pressure, design, P take 1.6MPa. DN300 ~ DN1000 minimum diameter stem design calculations in Table 4. 3 Design verification - Type test DN300 ~ DN1000 British standard cast iron gate valve prototype, adopted by the Malaysian state quality authority SiRiM type test, the design was verified, type test in strict accordance with the British National Standard BS5163: 1986. Type testing of the pilot project are: appearance inspection, dimensional inspection, physical and chemical testing of materials, shell strength test, seal test, maximum torque test, the minimum strength torque test, cleanliness test, coating and mark inspection. Here to introduce the shell strength test, seal test, the maximum torque function test, the minimum strength torque test. 3.1 Shell strength test Shell strength test, test medium pressure 2.4MPa, to maintain the shortest duration of the test pressure 1h, no visible leakage. 3.2 Seal test Seal test, the test medium pressure 1.76MPa, to maintain the shortest duration of the test pressure 15min, no visible leakage, that is, the sealing surface of the valve body, 15min can not have any visible leakage of the naked eye, Includes small drops of water hanging on the sealing surface. Again, it is important to note that the design of the valve body must have sufficient strength and rigidity. The deformation of the housing must be controlled within the 0.001DN range of the seal test, otherwise it will be very difficult to pass the seal test. 3.3 The maximum torque test function The maximum torque test refers to the valve in the absence of media pressure and media pressure in the case of the opening and closing of the whole process, any moment of its maximum torque can not exceed the provisions of Table 5 Torque. 3.4 Minimum strength torque test Minimum strength torque test is PN1.6MPaDN300 ~ DNlO00 British standard cast iron gate valve design verification, the test steps: 3.4.1 fully open, fully closed test with the maximum torque test function of the valve Full open, full close operation test, and make full open, all off the mark of the location, at the same time record the full open, full close the valve stem rotation laps. 3.4.2 Minimum strength of the valve in the fully closed position After the torque test valve is in the fully closed position, apply a maximum of 3 times the maximum test torque in the direction of the tight direction (clockwise) on the square head of the valve stem Of the torque, that is, the minimum strength test torque, shown in Table 6; to verify the body, bonnet, gate, stem, stem nut, stuffing box and other major components and flange bolts in the strength of BS5163: 1986 Claim. 3.4.3 Minimum strength of the valve in the fully open position After the torque test valve is fully open, apply a maximum of 3 times the maximum test torque in the direction of opening (counterclockwise) on the square head of the valve stem Of the torque, that is, the minimum strength test torque, shown in Table 6; to verify the body, bonnet, gate, stem, stem nut, stuffing box and other major components and flange bolts in the strength of BS5163: 1986 Claim. 3.4.4 Sealing test Re-use the maximum torque test valve in the fully closed position, seal test again, the test medium pressure 1.76MPa, keep the test pressure minimum duration of 15min without any visible leakage to confirm the valve Whether the deformation occurs; whether the design meets the requirements of the BS5163: 1986 standard.
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