A manual inflatable life jacket needs to be manually pulled the inflation device to inflate the jacket, when you fall into the water, swimming or in an emergency. So, it is more suitable for swimmers.

When you pull the manual pull cord with yellow handle, it will immediately pierce the gas cylinder and release the CO2 to inflate the chamber.

It also can be orally inflated by breathing air through the inflation tube into the chamber.
This is a backup method to inflate the lifejacket.
If after manual inflation, the lifejacket’s chamber is still without enough air, you can breathe some air into the lifejacket.

There is some manual inflatable lifejacket for you to choose.
Inflatable Lifejackets
Rescue Lifejackets
Fishing Lifejackets