Why is a small hole drilled in the ball of a valve in addition to the through-hole?
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I have just started working at a company that produces curing agents (methyl ethyl peroxide). In the manual ball valves and control valves used for transporting materials within the plants, in addition to the passage holes for the pipes, there is also a small hole drilled vertically above these passages. Why is this small hole drilled? Are there any relevant standards? Thank you so much!
Prevent the accumulation of medium inside the valve ball when the valve is closed, to avoid danger.
This small hole is called a pressure relief hole. In low-temperature pipelines, with media such as liquid carbon dioxide, when the ball valve is closed, the medium remaining in the chamber will vaporize due to rising temperatures; this vaporization leads to a sudden increase in pressure inside the valve, thereby damaging it. With the pressure relief hole, the pressure in the middle chamber can be released to the upstream end of the pipeline through it. Additionally, it should be noted that ball valves equipped with pressure relief holes are no longer capable of providing two-way sealing; generally, when the valve is closed, the pressure relief hole must be located on the high-pressure side of the pipeline in order to ensure proper sealing of the valve.
I personally think it is to ensure the minimum flow rate within the pipeline when the valve is closed. The specific standards require the pore size to be designed based on actual production conditions.