A pump module for pressurizing control oil of a piston engine for enabling a black start of the engine, the pump module comprising - a body having a first connection surface facing a first direction and a second connection surface facing a second direction opposite to the first direction, wherein the first connection surface is configured to be connected to an oil sump or a lubricating oil tank of the engine and the second connection surface is configured to be connected to an oil pipe of a lubricating oil system of the engine, the body comprising a through-hole, the wall of the through-hole defining an oil channel for allowing oil flow between the oil pipe and the oil sump or the lubricating oil tank, - a pump chamber (27a, 27b) for pressurizing the control oil, - a fluid channel for establishing fluid communication between the oil channel and the pump chamber (27a, 27b) and for allowing flow from the oil channel into the pump chamber (27a, 27b), - a check valve that is arranged between the oil channel and the pump chamber (27a, 27b) for preventing flow from the pump chamber (27a, 27b) into the oil channel, - an outlet for discharging pressurized control oil from the pump module, - an actuation chamber (31a, 31b) that is coaxial with the pump chamber (27a, 27b), - an inlet for introducing pressure medium into the actuation chamber (31a, 31b), and - a piston device (33a, 33b) having a first piston surface (33c, 33e) delimiting the pump chamber (27a, 27b) and a second piston surface (33d, 33f) delimiting the actuation chamber (31a, 31b), wherein the pump module is configured to pressurize the oil in the pump chamber (27a, 27b) by means of the movement of the piston device (33a, 33b), when pressure is applied on the second piston surface (33d, 33f) of the piston device (33a, 33b). - a body having a first connection surface facing a first direction and a second connection surface facing a second direction opposite to the first direction, wherein the first connection surface is configured to be connected to an oil sump or a lubricating oil tank of the engine and the second connection surface is configured to be connected to an oil pipe of a lubricating oil system of the engine, the body comprising a through-hole, the wall of the through-hole defining an oil channel for allowing oil flow between the oil pipe and the oil sump or the lubricating oil tank, - a pump chamber (27a, 27b) for pressurizing the control oil, - a fluid channel for establishing fluid communication between the oil channel and the pump chamber (27a, 27b) and for allowing flow from the oil channel into the pump chamber (27a, 27b), - a check valve that is arranged between the oil channel and the pump chamber (27a, 27b) for preventing flow from the pump chamber (27a, 27b) into the oil channel, - an outlet for discharging pressurized control oil from the pump module, - an actuation chamber (31a, 31b) that is coaxial with the pump chamber (27a, 27b), - an inlet for introducing pressure medium into the actuation chamber (31a, 31b), and - a piston device (33a, 33b) having a first piston surface (33c, 33e) delimiting the pump chamber (27a, 27b) and a second piston surface (33d, 33f) delimiting the actuation chamber (31a, 31b),