An inflator for inflating an inflatable device to which it is connected via fill tubes or in which it is positioned. The inflator comprises a power module assembly and an adaptor assembly intended to be threaded into or onto the threaded neck of a gas cylinder (not shown). The power module assembly employs one or more power primers that are fired when a tether is pulled to remove the actuator cup to release a spring-loaded actuator pin to fire the power primer(s). The escaping gases from the power primer(s) then drive a pierce pin to fracture a frangible seal allowing gas in the gas cylinder to then flow into the inflatable device and inflate the same.