We visit this topic again and again, the short answer is NO!
According to ASME Section VIII, Division 1 (UG-135) and API RP 520, Pressure Safety Valves (PSVs) must be installed in a vertical position with the spindle (stem) oriented upright. Installing a valve horizontally is considered a significant deviation from engineering standards and can lead to dangerous malfunctions.
Here is why vertical orientation is mandatory and the risks of a horizontal installation:
SAFTENG TIP: Check your specific Valve Data Sheet: If it doesn’t explicitly say “all-angle mounting,” assume vertical is the only safe and code-compliant option.