A fluid injection device (10) for injecting a dispensible fluid such as a liquid sealant (24) into an air conditioning or refrigeration system or the like, includes a tube (12, 12′, 12″) containing the fluid sealant in a storage chamber (26, 26′, 26″). Outlet valves conventionally used at the tube outlet are replaced with a rupturable membrane (28, 28′, 66). Means to rupture the membrane may comprise a puncture tool (32, 50), or the membrane may be designed to burst under pressure imposed on it in use. Use of membrane (28, 28′, 66) at the outlet of device 10 avoids problems caused by even very slight leakage of fluid sealant past an outlet valve. The fluid injection device (10) is used by connecting the tube inlet to a high pressure zone of the system and connecting the tube outlet to a low pressure zone of the system.