What is the purpose of the ball valves installed at the inlet and outlet of the safety valve?
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Is it to facilitate disassembly during the maintenance of the safety valve?
That’s right. This ball valve is usually kept open; it is only closed when maintenance requires the removal of the safety valve
There is no need to install it for export; it might have other uses. I’m not sure what operating conditions it is intended for
Gate valves are commonly used; ball valves might be chosen because of their better sealing performance. Whether a valve needs to be installed downstream of the valve depends on the specific circumstances. For example, in cases where gas is vented to the main pipe, a valve must be present downstream; otherwise, when the safety valve is removed for maintenance, gas from the main pipe will leak out, so a valve is necessary to prevent this from happening.
The issue regarding LZ has been discussed many times on the forum; please refer to the relevant posts: 1. The purpose of installing a shut-off valve at the inlet of the safety valve: http://bbs.hcbbs.com/viewthread.php?tid=234160, http://bbs.hcbbs.com/viewthread.php?tid=208522. 2. Requirements related to the installation of valves at the inlet of the safety valve: http://bbs.hcbbs.com/thread-410261-1-6.html, http://bbs.hcbbs.com/viewthread.php?tid=193800. Please use these as references!