Quick-exhaust valves (QEVs for short) are ready-made piston valves or diaphragm valves, designed to quickly exhaust pneumatic cylinders. They work somewhat similarly to pneumatically modified sprinkler valves, they are more expensive and harder to find, but also perform better.
QEVs need a separate pilot valve for triggering. They can be very sensitive, triggering at a pressure drop of a few psi, so care should be taken when filling with a schrader valve or other valves that will let out air when disconnected.
Most QEVs are designed to be filled from the pilot side, and will typically work well using a 3-way valve as the fill/pilot valve. Some QEVs will also work when filled from the chamber side.
Small QEVs are sometimes used as pilots for larger valves, often to allow the use of a blowgun as the trigger.
As pressure is applied through input port 1 the poppet (yellow) shifts forward blocking the exhaust port 3 and allowing flow through output port 2.
When pressure is removed from input port 1 back pressure at port 2 unseats the poppet and allows flow through exhaust port 3.