Until the 1980s the conventional d.c. machine was the automatic choice where speed or torque control is called for, and large numbers remain in service despite a declining market share that reflects the general move to inverter-fed a.c. motors.

Fisrt, I think 'call for' means require. So it can be re-written "where machine calles for speed or torque control."

I could understand the sentence, like above. But I can't understand grammatically. How preposition can be used without noun?

Until the 1980s the conventional d.c. machine was the automatic choice where speed or torque control is called for, and large numbers remain in service despite a declining market share that reflects the general move to inverter-fed a.c. motors.

First, I think 'call for' means require. So it can be re-written "where machine calls for speed or torque control."

I could understand the sentence, like above. But I can't understand grammatically. How preposition can be used without noun?