The stop valve has five over-flow areas that need attention. According to the flow direction sequence, they are end channel area, waist drum throat area, valve seat opening area, flow area between valve disc and valve seat when the valve is opened, and flow area of rear waist drum throat. The following describes these areas.
1) The valve end channel area valve is divided into PN series and class series, corresponding to the national standard, European standard and American Standard respectively. The end dimensions of PN series and clas series can be determined according to GB / T 12224-2015 and ASME B16.34 appendix standards respectively.
2) The flow area of the valve waist drum throat directly affects the flow capacity of the medium. If the flow area is too small, the valve flow resistance will be large, and if the flow area is too large, the material loss will be caused. The circulation area can be reasonably determined according to the following methods: first, the approximate area can be calculated according to the CAD drawing method shown in Figure 1; the second is that the area can be calculated by using three-dimensional software modeling.
In the design principle, the overflow area of the waist drum throat of the stop valve should not be less than the opening area of the valve seat, so as to ensure the good fluidity of the fluid. It can be seen from Figure 1 that the size of its overflow area mainly depends on the relationship between R (c), D, e values and valve structure length. In principle, the R (c) radius value should be expanded as much as possible without affecting the assembly space of the back of the end flange. While meeting the flow area, the value D should be reduced as much as possible, so as not to increase the overall size and weight of the valve.
3) The minimum opening area of valve seat is specified in section 188.8.131.52 of API 623-2013 and section 4.4.6 of GB / T 12235-2007. It is specified in bs1873-1975 that the area of each flow channel of globe valve shall be as close as possible to that of valve body. In the actual design, API 623-2013 is used as a reference, and whether the CV value meets the use requirements should be considered at the same time. The data in GB / T 12235-2007 will make the valve too large in actual design.
4) When the valve is opened, the flow area between the valve disc and the valve seat is determined by the maximum opening stroke of the valve, and the cylindrical outer circle area between the valve disc and the valve seat shall be greater than or equal to the area of the valve end channel. The stroke is usually the height of the cylindrical section, about 1 / 4 of the valve channel diameter, plus the distance L from the bottom of the disc to the upper shoulder of the seat (see Figure 2).
5) The calculation method of the flow area of the back drum throat is the same as that of the valve waist drum throat.