Abstract: An emergency shut down device for a gate valve utilizes a pre-assembled spring cartridge assembly which includes a container and a compression spring pre-loaded therein. Suitable openings are provided in the end plates of the cartridge to permit the remaining components, including a ram cup, a piston and cylinder arrangement, a base mounting member and a stem for connection to the valve gate, to be assembled within the cartridge without fear of a spring-initiated explosion of parts as the spring is safely contained within the container before final assembly begins. The device is operable to rapidly close a gate valve when there is a loss of fluid pressure within the device.