Minimum flow channel problem of valves

1. The “basic inner diameter at the valve end” is equivalent to the “nominal inner diameter at the valve end”, that is, the nominal size, such as DN100 or NPS2. 2. Taking DN100 as an example, its basic inner diameter is Φ100; the minimum allowable flow channel diameter d must not be less than Φ90.

If we go by your reasoning, then for a DN100 diameter the pressure is 2500 Lb, and according to B16.34 the minimum diameter of the flow channel is 73 mm. It does not meet the requirement you mentioned, that is, the minimum allowable channel diameter d must not be less than Φ90. How to explain this?

According to Tables 3A and 3B in 6.1.2, the inner diameter d does not have a one-to-one correspondence with the nominal size/nominal pressure. There are many series for the inner diameter d corresponding to CLASS2500, but it is not specified what value in millimeters CLASS2500LB corresponding to DN100 is. Additionally, for standards other than ASME, those that specify a minimum channel diameter d can have their standard values used directly; for example, API6D. (May I ask where it is stated in ASEM B16.34 that the minimum channel diameter for DN100, CLASS2500 is 73 mm?) ）

So if a 4-inch, 2500CL ball valve is manufactured according to B16.34, then the minimum flow channel diameter would be 90 mm?

According to national standards, the inner diameter d is defined as the basic inner diameter at the end of the valve body, rather than the nominal size of the valve. So I think the inner diameter d in B16.34 refers to the basic inner diameter at the end of the valve body

1. First, I would like to correct an issue with the incomplete wording in the reply: the nominal inner diameter changes as the nominal pressure changes, and its relationship with the nominal size is not fixed. The unclear wording in the reply can lead to misunderstandings; I’m sorry for that. 2. The determination of the valve’s inner diameter d is generally based on value B in the ASME B16.5 flange dimensions (the basic inner diameter at the valve end). For the inner diameter d of valves of CLASS600 and above, it is determined by the design (or according to the purchase order). 3. The minimum diameter of the design flow channel shall be not less than 90% of B, but not 90% of the value recommended in Table A-1.

If the inner diameter d of the valve is to be determined, it is generally based on B in the flange dimensions of ASME B16.5 (the basic inner diameter at the valve end). So, according to B16.5, for DN100 CL150, the inner diameter d is 102.1. Then, based on the requirement that the minimum diameter of the flow channel should be no less than 90% of B, does this mean that the inner diameter d for DN100 CL150 can be set at 92? 2. As stated in point 2, the inner diameter d equals B (the basic inner diameter at the end of the valve). Therefore, in the text, the inner diameter d should represent the minimum diameter of the flow channel; it is clearly specified as the minimum diameter. So, according to my understanding, this value should indeed be the smallest possible dimension. Yet later it is said that this value must be no less than 90% of the basic inner diameter at the end of the valve – doesn’t this contradict the requirement that d is the minimum diameter of the flow channel?

1. B is the “basic inside diameter at the valve end” as described in 6.1.2(a). 2. d is the minimum channel diameter adopted in the design; this value… 3. When B is 102, d must be ≥ B*90% = 91.8. 4. The recommended value of d for A-1 already represents the minimum channel diameter.

As I understand it, for valves with flange connections, the minimum inner diameter of the flow channel inside the valve is already fixed; in such cases, rule A-1 applies. The requirement that it must be at least 90% refers to valves with weld connections – the inner diameter of the weld groove cannot be too small; in other words, the inner diameter of the piping cannot be too small. What does this have to do with the valve itself? In the past, some people set the valve design standard at ASME B16.34, and then altered the design by making the valve flow channels smaller in order to save material and reduce costs. This is wrong. For example, when using a 150LB-2 inch butt-welded valve with a minimum internal flow diameter of 50.8, it is not possible to use 160-grade pipe for the connections (whose inner diameter is 60.3 – 2*8.74 = 42.82 mm), because 42.82 is less than 50.8*90%. It is permissible to use tubes with a wall thickness of 7.14, because 60.3-2*7.14=46.02 is greater than 50.8*0.9.