"初级抽气泵" can be translated as "primary vacuum pump" or "elementary vacuum pump" in English, depending on the context and specific usage.
"Primary vacuum pump" is more commonly used in technical and engineering contexts, referring to the first or main pump in a vacuum system that is responsible for initially reducing the pressure.
"Elementary vacuum pump" could also be used, though it's less common, to emphasize a basic or initial-stage pump.
In most cases, "primary vacuum pump" would be the most appropriate and widely understood translation.