Definition
A protective cap fitted over a high-pressure tire or strut valve stem that incorporates a built-in tool for releasing pressure in a controlled manner. The cap can be reversed or used directly to depress the valve core, allowing trapped gas (typically nitrogen or air) to be bled off safely before servicing.
Plain English
A small cap that screws onto a tire or strut valve. As well as keeping dirt out, it has a feature that lets you let the air or gas out in a controlled way when you need to.
Context Anchor
Seen in aircraft maintenance when pressure must be released from a tire, shock strut, or other pressurized part before servicing.
Derivation
From 'deflate' (Latin 'deflare', to blow away) plus 'cap'. The name simply describes its dual job: capping the valve, and helping deflate the assembly when needed.
Why Pilots Care
High-pressure tires and struts can store enormous energy. Using the deflator cap lets a technician release that pressure in a controlled way before removing a wheel or servicing a strut, preventing sudden release that could cause injury or damage.
Intuition Check
Do not assume a deflator cap is just a dust cap. A normal cap protects a valve; a deflator cap is made to open the valve and let pressure out.
Example Sentence 1
Before removing the wheel, the technician used the deflator cap to bleed nitrogen from the tire.
Example Sentence 2
After landing, the technician used a deflator cap to reduce tire pressure to the required cold inflation value.