The Comparision of BS1873 standard Globe Valve and API 623 standard Globe Valve

API 623 and BS 1873 are both important international standards for globe valves, and there are significant differences in their design concepts, technical parameters, and application scenarios.

The following comparison is made from four points:

Standard and issuance

● BS 1873 standard for globe valves was compiled and published by the British Standards Institution. The first edition was published in July 1952, and the current effective version (2nd edition) was published in April 1975.
Note: Due to the BS 1873 standard has been revised for many years, there are different situations such as the invalidation and revision of referenced standards.
● The API 623 standard is compiled and published by the American Petroleum Institute (API). The first edition was released in September 2013 and is still a valid version to this day.

Differences in main technical parameters

Size and relevant pressure rating

Table 1:Comparison BS1873 and API 623 standard’s size and pressure rating

The main difference between the two standards is that BS 1873 standard includes valves with a diameter of 2 "or less, while API 623 standard does not include small diameter valves with a diameter of 2" or less in the standard scope, and only expands the diameter on medium and low pressure valve specifications.

Runner diameter and fluid resistance

Except for the runner diameter is  the same at a pressure of Class 2500, the runner diameter  in API 623 standard is smaller than that in BS1873 standard for all other pressure rating.
For example 6’’,CL600,API 623 runner diameter is 135mm,BS1873 runner diameter is 152mm.
Differential affect:API 623 has a smaller inner diameter, higher fluid resistance, but a larger sealing contact area, which is beneficial for high-pressure sealing.

Minimum wall thickness of valve body

According to API 623 standard, except for the 4 specifications of 2 " CL150, 12" CL300, 4 " CL900, and 3" CL2500 valves, the minimum wall thickness of all other specifications of valves shall not be less than the minimum wall thickness value specified in BS 1873.
In the API 623 standard, except for the CL2500 specification valve, when the diameter of the flow channel is reduced, the minimum wall thickness of other specifications of valves actually increases. Increasing the wall thickness is beneficial for improving the pressure bearing and corrosion resistance of the valve.

Valve stem diameter and sealing reliability

API 623: Under large diameters and high pressure levels, the valve stem diameter is larger,improve sealing reliability.
BS 1873: Smaller stem diameter under the same operating conditions.May affect high-pressure sealing performance.
For example 6’’,CL600,API 623 stem diameter 48mm,BS1873 stem diameter 41.3mm.
Differential affect: The larger the diameter of the API 623 valve stem, the stronger its resistance to yielding, reducing deformation under high pressure and lowering the risk of leakage,improve sealing reliability.

Differences in Valve structure characteristics

Valve disc structure and flow direction

API 623:
● Unidirectional flow restriction: Only allows for flow direction:Flow low to high, and the valve disc design needs to be adapted to the pressure of the unidirectional medium. When closed, it is forced to seal by the pressure of the valve stem, without considering bidirectional flow scenarios
● Sealing surface design: Mainly based on flat sealing valve discs, it can be welded with metal materials or embedded with non-metallic materials (such as flexible graphite) according to working conditions to ensure sealing reliability under high pressure

BS1873:
● Bidirectional flow compatibility: supports two flow directions: "Flow low to high" (low pressure condition, ≤ 40MPa) and "From High to low" (high pressure condition,>40MPa). The valve disc needs to cope with the pressure of the reverse medium.
Large and small valve disc structure: For the "From high to low" situation, a dual valve disc design is adopted: the small valve disc first opens to balance the pressure, and then drives the large valve disc to rise, reducing the opening torque, suitable for large-diameter high-pressure valves.

Differences in guiding design of valve disc

API 623:
The API 623 standard requires the valve disc to be guided throughout the full stroke range, and when the pressure is ≥ 900 lb, the valve disc must be guided by a non stem method.

BS1873:
The BS 1873 standard only requires the valve disc to provide a guiding device, but does not specify the guiding method and stroke of the valve disc. If the guiding setting of the valve disc is not reasonable, it may cause the valve disc to seal improperly with the valve seat or the valve disc to get stuck, affecting the normal use of the valve.

Differences in the connection style of body and bonnet

The BS 1873 standard allows for a flat flange connection for the valve body and cover of a 150 lb valve, while the API 623 standard only allows for a selection from four forms: raise face, tongued and grooved flange, male and female face, and ring connection.
When the valve diameter is less than 3’’ in BS 1873 standard, the connecting flange of the valve body and valve cover is allowed to be square or rectangular, while API 623 standard stipulates that the connecting flange of the valve body and valve cover must be circular.

Summary: From the comparison results between BS1873 and API623 standards, it can be seen that valves designed and manufactured according to API 623 standards will be superior to BS 1873 standards in terms of pressure stability and sealing reliability due to their large wall thickness and thick stem. However, at the same time, the reduction of the runner diameter in API 623 standards will lead to a decrease in the Cv value of the valve, as well as an increase in fluid resistance, that cause torque value increased. Users need to consider the valve flow capacity and actuator selection when selecting valves.