Purge valves are activated above a set pressure. Bleed valves are activated by hand. (Car brakes, for example, have bleed valves that one opens to remove air from the brake lines or to replace the brake fluid.)

Here are some pictures from a Polish web site:
http://www.amet.com.pl/zawory-swagelok
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1) Bleed

Hy-Lok USA, Inc. bleed valves can be used on instrument fluid handling products, such as manifolds or gauge/root valves, in order to vent signal line pressure to the atmosphere before disassembling of an instrument or to facilitate in the calibration of control devices. End connection options include male NPT and SAE from 1/8″ to 1/2″.

https://www.hylokusa.com/bleed-and-purge-valves/

2) Purge valve

Vent hole bleeds excessive liquid or gas from system lines.
https://www.hylokusa.com/catalog/purge-valve