A PISTON PUMP

Piston pump for pumping liquidised fluids, in particular a cryogenic fuel pump for pumping liquidised fuel, such as liquid natural gas (LNG), hydrogen, methanol, ammonia or the like, said pump comprising a pump housing (1) with a piston chamber (4) formed inside and an inlet flow valve (8) and a discharge check valve (6) are provided in the pump housing; a piston having a piston head (2) and a piston rod (3), said piston being provided to reciprocate along a longitudinal axis in the piston chamber to compress fluid in the chamber to an elevated pressure, a first sealing means (21) is provided on the piston head between an inner circumferential surface of said chamber and said piston head; and a second sealing means is provided between the piston rod and a bore (10) of the pump housing, wherein the second sealing arrangement comprises a pressurised sealing means provided in the bore of the housing between at least two sealing rings (33, 34), and wherein the pressurised sealing arrangement comprises an inlet (31) and an outlet (36) for pressurised lubricating fluid, and a pressurised fluid source for the provision of pressurised fluid in a fluid flow to said inlet.