A pump capable of dispensing both a large volume and a small volume of colorant comprises a large reciprocating positive displacement pump having a large reciprocating part, a large pump body and a large pump inlet-outlet opening, characterized in that: a small reciprocating part fixed to the large reciprocating part is disposed in the large pump body; a small pump body is disposed on a base of the large pump body, and provided with a small pump inlet-outlet opening; and the small reciprocating part, the small pump body and the small pump inlet-outlet opening constitute a small reciprocating positive displacement pump. The reciprocating positive displacement pump provided in the present invention may achieve dispensing of both a large volume and a small volume of colorant by means of a large-section pump, and thus guarantees the accuracy of the dispensed volume of colorant, and in particular, the accuracy of dispensing of a small volume of colorant; and the reciprocating positive displacement pump, when compared with the prior art, has the advantages of high accuracy and simple structure, and when compared with the structure in patent No. US2009236367A1, has the advantages of good leakproofness, high utilization of a reciprocating pump cylinder body in the length direction, and improved stroke accuracy of the reciprocating pump due to less elastic deformation of a pump support.

A pump capable of dispensing both a large volume and a small volume of colorant comprises a large reciprocating positive displacement pump having a large reciprocating part, a large pump body and a large pump inlet-outlet opening, characterized in that: a small reciprocating part fixed to the large reciprocating part is disposed in the large pump body; a small pump body is disposed on a base of the large pump body, and provided with a small pump inlet-outlet opening; and the small reciprocating part, the small pump body and the small pump inlet-outlet opening constitute a small reciprocating positive displacement pump. The reciprocating positive displacement pump provided in the present invention may achieve dispensing of both a large volume and a small volume of colorant by means of a large-section pump, and thus guarantees the accuracy of the dispensed volume of colorant, and in particular, the accuracy of dispensing of a small volume of colorant; and the reciprocating positive displacement pump, when compared with the prior art, has the advantages of high accuracy and simple structure, and when compared with the structure in patent No. US2009236367A1, has the advantages of good leakproofness, high utilization of a reciprocating pump cylinder body in the length direction, and improved stroke accuracy of the reciprocating pump due to less elastic deformation of a pump support.

An exemplary refill unit for an dispenser includes a container for holding a liquid. The container has bottom side with a neck extending from the bottom side. A pump is connected to the neck of the container. The pump has a liquid pump portion that has a liquid pump inlet. The liquid pump inlet is located above the bottom of the container. A shroud is located over the liquid pump inlet and extends downward toward the bottom of the container. An air bleed valve is included and located in the top of the shroud.

A vented pump includes a pump housing with a fluid retention cavity, a fluid inlet, and at least one vent opening therethrough. A pump dome is secured to the pump housing to form a dome cavity. Movement of the pump dome allows material from the fluid retention cavity to enter the dome cavity through the fluid inlet, and selectively allows ambient air to enter the fluid retention cavity through the at least one vent opening.

A vented pump includes a pump housing with a fluid retention cavity, a fluid inlet, and at least one vent opening therethrough. A pump dome is secured to the pump housing to form a dome cavity. Movement of the pump dome allows material from the fluid retention cavity to enter the dome cavity through the fluid inlet, and selectively allows ambient air to enter the fluid retention cavity through the at least one vent opening.

Disclosed is a metering pump comprising a housing that extends from an inlet region to an outlet and surrounds a piston which is urged into a starting position by a compression spring. In the metering pump the stop limiting the lifting stroke of the piston is formed by the lower end of the piston coming in contact with the inlet portion.

Disclosed is a metering pump comprising a housing that extends from an inlet region to an outlet and surrounds a piston which is urged into a starting position by a compression spring. In the metering pump the stop limiting the lifting stroke of the piston is formed by the lower end of the piston coming in contact with the inlet portion.

A viscous fluid is dispensed precisely using a fluid pump, control valves configured to control both the air inlet and outlet of the fluid pump, an optional adjustable regulator further controlling the air outlet, and a control circuit that opens and closes the control valves. To further increase the precision, additional control valves can be used to control liquid inlet and outlet of the fluid pump.

A viscous fluid is dispensed precisely using a fluid pump, control valves configured to control both the air inlet and outlet of the fluid pump, an optional adjustable regulator further controlling the air outlet, and a control circuit that opens and closes the control valves. To further increase the precision, additional control valves can be used to control liquid inlet and outlet of the fluid pump.

A system comprises a variable displacement pump, a metering valve, a bypass line, a pressure regulating valve, a position sensor, and a control system. At least one fuel nozzle can be in fluid communication with the output line downstream of the metering valve, wherein the variable displacement pump is configured to supply fuel to the at least one fuel nozzle. The metering valve can be disposed in the output line for controlling outlet flow from the variable displacement pump. The system can also include an actuator line parallel to the variable displacement pump and connected to the output line to provide actuation pressure from pump output of the variable displacement pump.