A four-valve high pressure pump having a) a drive: b) a pump part which in turn comprises: ba) a cylinder; bb) two cylinder blocks (10, 11), which are arranged on the end faces of the cylinder and through which a respective transition channel (12, 13) extends, which opens at opposing ends into an outer surface of the cylinder block and communicates in the central region with the interior of the cylinder; c) an inlet housing part, which has ca) a media channel which communicates with the inlet and in which a respective non-return valve (25, 26) is arranged on both sides of the opening point of the inlet which and communicates at its opposing ends with a respective transition channel (12, 13) of a cylinder block (10, 11); d) an outlet housing part, which has: da) an outlet for the medium to be pumped: db) a media channel which communicates with the outlet and in which a respective non-return valve (28, 29) is arranged on both sides of the opening point of the outlet and which communicates at its opposing ends with a respective transition channel (12, 13) of a cylinder block (10, 11); e) a piston which is movable back and forth in the cylinder and is in driving communication with the drive; characterised in that f) the inlet housing part and/or the outlet housing part is releasably fastened laterally on the cylinder blocks (10, 11) in such a way that it can be removed without further dismantling the pump part. a) a drive: b) a pump part which in turn comprises: ba) a cylinder; bb) two cylinder blocks (10, 11), which are arranged on the end faces of the cylinder and through which a respective transition channel (12, 13) extends, which opens at opposing ends into an outer surface of the cylinder block and communicates in the central region with the interior of the cylinder; ba) a cylinder; bb) two cylinder blocks (10, 11), which are arranged on the end faces of the cylinder and through which a respective transition channel (12, 13) extends, which opens at opposing ends into an outer surface of the cylinder block and communicates in the central region with the interior of the cylinder; c) an inlet housing part, which has ca) a media channel which communicates with the inlet and in which a respective non-return valve (25, 26) is arranged on both sides of the opening point of the inlet which and communicates at its opposing ends with a respective transition channel (12, 13) of a cylinder block (10, 11); d) an outlet housing part, which has: da) an outlet for the medium to be pumped: db) a media channel which communicates with the outlet and in which a respective non-return valve (28, 29) is arranged on both sides of the opening point of the outlet and which communicates at its opposing ends with a respective transition channel (12, 13) of a cylinder block (10, 11); da) an outlet for the medium to be pumped: db) a media channel which communicates with the outlet and in which a respective non-return valve (28, 29) is arranged on both sides of the opening point of the outlet and which communicates at its opposing ends with a respective transition channel (12, 13) of a cylinder block (10, 11); e) a piston which is movable back and forth in the cylinder and is in driving communication with the drive; f) the inlet housing part and/or the outlet housing part is releasably fastened laterally on the cylinder blocks (10, 11) in such a way that it can be removed without further dismantling the pump part.