Design knowledge of the hottest cast iron gate val

2022-08-24
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Design knowledge of cast iron gate valve

[Abstract] this paper expounds the structural characteristics, design calculation, design verification type test of 1.6mpadn300 ~ DN1000 British standard cast iron gate valve

[key words] British standard cast iron gate valve design verification

1 overview

bs5163, BS51501.6MPaDN300 ~ DNl000 British standard cast iron gate valves are widely used in water supply pipelines and industrial pipelines in Britain, Singapore, Malaysia and some countries in the Middle East. See Figure 1 for their structural characteristics: open gear drive gate valves; See Figure 2 for closed gear drive gate valve

this paper focuses on the design calculation and design verification type test of the wall thickness of the valve body, the wall thickness of the bonnet, the wall thickness of the ram and the diameter of the valve rod of 1.6mpadn300 ~ 1000 British standard cast iron gate valves

2 design

2.1 design calculation of valve body wall thickness

bs5163 and bs5150 do not give the data of the minimum wall thickness of the shell. During the design, the wall thickness of the valve body must be designed and calculated

in the design, after the modern theory of vibration measurement and analysis and simulation analysis of the cavity in the valve body is established, the section shape is designed to be an approximate oval, as shown in Figure 3. The design calculation of its wall thickness s' B1 is the calculation formula derived from the calculation formula of the oval wall thickness: in the formula, K - the wall thickness coefficient of the valve body with approximate oval section, in which DN300 ~ DN500, K is 1.13, DN600 ~ DNl000, K is 1.07

p - medium pressure. In design, P is taken as 1.6Mpa

a - long axis of approximate elliptical section (mm)

[ σ 50] -- allowable tensile stress of cast iron (HT250)[ σ 50] Take 35.28mpa

c - corrosion allowance, C is 5 (mm)

The design and calculation results of the minimum wall thickness of DN300 ~ DN1000 valve body are shown in Table 1

it is found in the design that, in addition to the strength of the valve body, the rigidity of the valve body should also be considered in the design of the wall thickness of the valve body, that is, the deformation of the body cavity of the valve body (under the action of 1.6Mpa medium pressure) should be controlled within the range of 0.001dn, otherwise, the valve body will be unable to achieve sealing due to stress and deformation

the method to solve the rigidity of the valve body is shown in Figure 1. Stiffeners are designed on the outside and inner cavity of the valve body, and the stiffeners on the outside of the valve body are connected with the end flange of the valve body to increase the rigidity of the valve body. If necessary, they can be designed into unequal wall thickness, that is, to increase the wall thickness of the cavity part in the approximate oval section of the valve body

2.2 design of bonnet wall thickness

when designing, the bonnet wall thickness s ′ B2 is usually no longer calculated, and 0.95 of the valve body wall thickness is directly taken as the bonnet wall thickness. See Table 2 for the minimum wall thickness data of DN300 ~ DN1000 bonnet; See Figure 1 for the design of valve cover stiffener

2.3 design calculation of ram wall thickness

bs5163 and bs5150 standards also do not give the data of the minimum wall thickness of the ram. During the design, the ram wall thickness s' B3 must be designed and calculated, and the calculation formula is as follows: D - diameter (mm)

p - medium pressure. In design, P is taken as 1.6Mpa

[ σ W] -- allowable bending stress of cast iron (HT250)[ σ W] Take 56.84mpa

c - corrosion allowance, C is 3 (mm)

The design and calculation results of the minimum wall thickness of DN300 ~ DN1000 RAM are shown in Table 3

2.4 design calculation of valve rod diameter

bs5163 and bs5150 standards also do not give the data of the minimum diameter of the valve rod. During the design, the valve rod diameter must be designed and calculated, and the calculation formula is as follows: in the formula k - valve rod design calculation coefficient, in which DN300 ~ DN500, k1 Regularly replace the oil circuit filter element, taking 0.70 ~ 0.75; DN600~DNl00。 K is 0.60 ~ 0.65

q - axial force when the valve rod is opened (n)

[ σ 50] -- allowable tensile stress of cast iron (HT250)[ σ 50] Take 35.28mpa

among them, Q adopts a simple calculation formula, and because the value of QG (weight of ram assembly) is small, it will not be calculated. Where QMF -- force when the sealing surface reaches the necessary specific pressure (n)

qmj -- static pressure force of sealing surface medium (n)

d -- diameter, d=dn (mm)

bm - width of valve body sealing surface (mm)

qmf -- necessary sealing specific pressure (MPA)

p - medium pressure. In design, P is taken as 1.6Mpa

See Table 4 for the design and calculation data of the minimum diameter of DN300 ~ DN1000 valve rod

3 design verification - type test

dn300 ~ DN1000 British standard cast iron gate valve prototype has passed the type test of SIRIM, the Malaysian national quality authority, to verify the design. The type test is carried out in strict accordance with British national standard bs5163:1986. The test items of the type test include: appearance inspection, size inspection, material physical and chemical test, shell strength test, sealing test, maximum functional torque test, minimum strength torque test, cleanliness inspection, coating and mark inspection. Fluorine lined butterfly valve

here, the shell strength test, sealing test, maximum functional torque test and minimum strength torque test are mainly introduced

3.1 shell strength test

shell strength test, the test medium pressure is 2.4Mpa, the minimum duration of maintaining the test pressure is 1H, and there shall be no visible leakage with the naked eye

3.2 sealing test

sealing test, the test medium pressure is 1.76Mpa, and the minimum duration of maintaining the test pressure is 15min. There shall be no visible leakage, that is, there shall be no visible leakage on the sealing surface of the valve body within 15min, including small drops of water hanging on the sealing surface

it needs to be emphasized again that the designed valve body must have sufficient strength and stiffness. During the sealing test, the deformation of the shell must be controlled within the range of 0.001dn, otherwise it will be difficult to pass the sealing test

3.3 maximum functional torque test

maximum functional torque test refers to that the maximum torque of the gate valve cannot exceed the torque specified in Table 5 at any moment in the whole process of opening and closing without and with medium pressure

3.4 minimum strength torque test

minimum strength torque test is the verification of the design of pn1.6mpadn300 ~ dnlo00 British standard cast iron gate valves. Its test steps:

3.4.1 full open and full close test

conduct full open and full close operation tests on the valve with the maximum functional test torque, mark the full open and full close positions, and record the number of turns of the valve stem during the full open and full close process

3.4.2 minimum strength torque test when the valve is in the fully closed position

after the valve is in the fully closed position, gradually apply a torque three times the maximum function test torque along the closing direction (clockwise), that is, the minimum strength test torque, on the square head of the valve stem, as shown in Table 6; To verify whether the strength of main parts such as valve body, bonnet, ram, valve rod, valve rod nut, stuffing box and middle flange bolts meet the requirements of bs5163:1986 standard

3.4.3 minimum strength torque test when the valve is in the fully open position

after the valve is in the fully open position, gradually apply a torque three times the maximum function test torque along the opening direction (counterclockwise direction) on the square head of the valve stem, that is, the minimum strength test torque, as shown in Table 6; To verify whether the strength of main parts such as valve body, bonnet, ram, valve rod, valve rod nut, stuffing box and middle flange bolts meet the requirements of bs5163:1986 standard

3.4.4 sealing test

re use the maximum function test torque to make the valve fully closed, and conduct the sealing test again. The test medium pressure is 1.76Mpa, and maintain the test pressure for a minimum duration of 15min

there shall be no visible leakage to confirm whether the valve has deformation; Whether the design meets the requirements of bs5163:1986 standard

3.4.5 full open and full close test

carry out the full open and full close operation test on the valve with the maximum function test torque again, and check whether the positions of full open and full close are consistent with the positions of full open and full close during the test in 3.4.1; Record the number of turns of the valve rod in the process of full opening and full closing again, and check whether the number of turns of the valve rod is the same as that in 3.4.1 test, so as to confirm whether the strength and stiffness of the valve rod and valve rod nut meet the requirements of bs5163:1986 standard

3.5 part inspection

disassemble the parts, and inspect whether the valve body, bonnet, ram, valve rod, valve rod nut, stuffing box and other parts as well as the studs and nuts of the middle flange are intact, so as to confirm whether the design of the main parts such as valve body, bonnet, RAM, valve rod, valve rod nut, stuffing box and Chinese French bolts meet the requirements of bs5163:1986 standard

4 conclusion

after design verification - type test, it is confirmed that the design of BS5163, BS51501.6MPaDN300 ~ DNl000 British standard cast iron gate valves with spring washers meets the requirements of bs5163:1986 standard, has been put into mass production, and has been exported to Malaysia and Singapore in large quantities. Through the design, I deeply feel that the type test method of BS5163 standard - Minimum strength torque test is very

scientific, and should be promoted in the industry of measuring valves with dial indicators based on two force columns. This is a good way for enterprises to carry out the design verification of new valve products; It is deeply felt that the valve industry should standardize the most

functional test torque of all kinds of valves, that is, to standardize the opening and closing torque of all kinds of valves, which is a new requirement for humanized design of valves put forward by the development of the times and social progress. Reference

[1] Yang Yuanyuan, valve design manual [m] Beijing: Machinery Industry Press, 1992

[2] Hong Miancheng, Lu Peiwen, Gao organ, valve design and calculation manual [m] Beijing: China Standards Press, 1994

[3] BS technical conditions for gate valves for water supply systems

[4] BS general purpose cast iron wedge single gate plate double gate valves

[5] BS valve structure length

[6] BS part 3.2 technical conditions for cast iron flanges

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