A positive displacement pump for pumping a fluid mastic comprises a plurality of cylinders each having a piston arranged for reciprocal motion within the cylinder. Movement of the piston in a first direction draws the fluid into the cylinder and movement in a second, opposite direction pumps the fluid out of the cylinder. A variable speed electric motor is drivingly coupled to a cam arrangement providing a reciprocating drive to the pistons. The cam arrangement comprises cams shaped and arranged to drive each piston in the first direction over less than half of a rotational cycle and to drive each piston in the second direction over the remainder of the rotational cycle. The cams are arranged to drive the pistons out of phase with one another.

A positive displacement pump for pumping a fluid mastic comprises a plurality of cylinders each having a piston arranged for reciprocal motion within the cylinder. Movement of the piston in a first direction draws the fluid into the cylinder and movement in a second, opposite direction pumps the fluid out of the cylinder. A variable speed electric motor is drivingly coupled to a cam arrangement providing a reciprocating drive to the pistons. The cam arrangement comprises cams shaped and arranged to drive each piston in the first direction over less than half of a rotational cycle and to drive each piston in the second direction over the remainder of the rotational cycle. The cams are arranged to drive the pistons out of phase with one another.

A pump or compressor includes a rotating shaft, and at least a first piston rod substantially perpendicular to the rotating shaft and connecting a first pair of pistons at opposite ends of the piston rod. The piston rod moves back and forth relative to the rotating shaft. The compressor additionally includes a circular eccentric, and a circular ring connected to the circular eccentric via a bearing. A drive pin engages the circular ring at a fixed position on the circular ring and engages the at least a first piston rod. When rotational motion of the shaft rotates either the first piston rod and first pair of pistons or the circular eccentric, the drive pin and the first piston rod move back and forth relative to the rotating shaft.

A pump or compressor includes a rotating shaft, and at least a first piston rod substantially perpendicular to the rotating shaft and connecting a first pair of pistons at opposite ends of the piston rod. The piston rod moves back and forth relative to the rotating shaft. The compressor additionally includes a circular eccentric, and a circular ring connected to the circular eccentric via a bearing. A drive pin engages the circular ring at a fixed position on the circular ring and engages the at least a first piston rod. When rotational motion of the shaft rotates either the first piston rod and first pair of pistons or the circular eccentric, the drive pin and the first piston rod move back and forth relative to the rotating shaft.

A variable displacement vane pump includes: a control orifice that imparts resistance to a flow of working oil discharged from pump chambers; a flow-amount control valve that operates in accordance with an upstream-downstream differential pressure of the control orifice and controls a flow amount of the working oil discharged from the pump chambers; a variable control valve that is operated by the working oil that has passed through the control orifice and controls an amount of eccentricity of a cam ring with respect to a rotor by controlling a pressure difference between a first fluid pressure chamber and a second fluid pressure chamber; and a return passage that is connected to the flow-amount control valve and circulates a part of the working oil discharged from the pump chambers through a suction passage.

A positive displacement pump for pumping a fluid mastic comprises a plurality of cylinders each having a piston arranged for reciprocal motion within the cylinder. Movement of the piston in a first direction draws the fluid into the cylinder and movement in a second, opposite direction pumps the fluid out of the cylinder. A variable speed electric motor is drivingly coupled to a cam arrangement providing a reciprocating drive to the pistons. The cam arrangement comprises cams shaped and arranged to drive each piston in the first direction over less than half of a rotational cycle and to drive each piston in the second direction over the remainder of the rotational cycle. The cams are arranged to drive the pistons out of phase with one another.