إِنَّمَا أَوْقَفْنَا السَّحْبَ سَاعَةً لِفَحْصِ الْمِضَخَّةِ.
We suspended pumping for only one hour to inspect the pump.
The live dispute concerns deprivation versus maintenance as the reason for the act. Innamā restricts the explanation in that conversational setting, rejecting the rival motive. It does not assert that every possible repair or every maintenance action always lasts exactly one hour.
Relative restriction (qaṣr iḍāfī) is interpreted against the alternatives under consideration. If the hearer instead denies that pumping stopped at all, the existence of the suspension must first be established.