What type of primer is used in the water pump?

The correct choice is the electric rotary vane primer. This type of primer is commonly used in water pumps because it effectively evacuates air from the pump and allows for a quick and efficient priming process. The electric rotary vane primer utilizes a rotating mechanism that creates a vacuum to draw water into the pump from the source, ensuring that the engine can achieve optimal performance and efficiency.

The use of an electric rotary vane primer reduces the labor involved in priming compared to other methods, such as manual hand primers, which require physical effort and may not provide as consistent or quick a result. This efficiency is particularly valuable in emergency situations where speed is critical.

Additionally, while mechanical oil primers and pneumatic primers may have their applications in certain types of equipment, they are not typically used in water pumps for firefighting because they do not provide the same level of efficiency or reliability in terms of quickly establishing a water supply. The electric rotary vane primer stands out due to its combination of effectiveness and ease of use in high-demand scenarios like firefighting.