The adjustable pressure-limiting valve (APL valve) attached to a General Electric Datex-Ohmeda Aisys anaesthetic machine.
<a href="//commons.wikimedia.org/wiki/User:Kwekubo" title="User:Kwekubo">Kwekubo</a>
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>