The Clarke Pressure Limiting Driver (PLD)-equipped engine is a UL/FM certified diesel engine fire pump driver that reduces pump speed to limit the maximum pump discharge pressure to prevent over-pressurization of the sprinkler system. The PLD senses sprinkler system water pressure via a sensing line connected at the pump discharge pipe (between the pump flange and the discharge check valve) and physically moves the engine throttle to manage engine speed. Clarke Fire Protection Products.