What expels the extinguishing agent from a pump tank water extinguisher?

In a pump tank water extinguisher, the extinguishing agent is expelled through manual effort. This type of extinguisher relies on a hand-operated pump to create pressure within the tank, which forces the water out of the nozzle when the operator depresses the handle. The action of manually pumping creates the necessary pressure to disperse the water to extinguish a fire.

This method gives the user control over the flow and direction of the water, allowing for effective targeting of the fire. The design is straightforward, making it effective for use in various firefighting situations, especially in environments where immediate manual intervention is practical.

In contrast, other options like gravity or compressed air involve different mechanisms that do not apply to pump tank water extinguishers. Gravity would depend on the weight of the water alone and would not provide the control needed for effective extinguishment. Compressed air typically relates to extinguishers that use gas under pressure to propel the agent, which does not occur in a manually operated pump tank extinguisher. A pressure cartridge is specific to extinguishers that utilize pre-filled pressure cartridges rather than manual pumping.