Most of us have seen a gate valve installed in piping, and 99% of the time, we want to see the valve handle in the VERTICAL-UPWARD position. However, when we need to install an “intervening valve” in the relief path, which ASME allows, we may/should see the valve handle(s) in the Horizontal or below Horizontal position. Here is why…
ASME Section XIII, which regulates “interning valves, states:
valve failure controls: measures taken in valve design, configuration, and/or orientation for the purpose of preventing an internal failure of a stop valve from closing and blocking the pressure relief path. An example of valve failure controls is the installation of gate valves with the valve stem oriented at or below the horizontal position.
We can also look to API 520 for some help with this requirement:
8.3.2 Inlet and Outlet Isolation Valves
...
c) When gate valves are used, they shall be installed with stems oriented horizontally or, if this is not feasible, the stem shall be oriented downward to a maximum of 45° from the horizontal to keep the gate from falling off and blocking the flow.