A pump arrangement comprising: a first piston pump having a first dispensing chamber and a first piston element reciprocally movable along a first axis in the first dispensing chamber to draw a first fluid into the first dispensing chamber from a first reservoir through a first conduit opening into the first dispensing chamber and discharge the first fluid out a first discharge outlet, wherein reciprocal movement of the first piston element discharges the first fluid from the first reservoir until the first reservoir is empty of the first fluid wherein further reciprocal movement of the first piston element creates a first vacuum condition in the first dispensing chamber axially inward of the first piston element, the first piston element including a driven member, a releasable juncture arrangement releasably coupling a driving member and the driven member together, the releasable juncture arrangement having a coupled condition and an uncoupled condition, characterized by, the first piston pump including a first inlet one-way valve across the first conduit, the first inlet one-way valve providing for flow of the first fluid from the first reservoir to the first dispensing chamber but preventing flow of the first fluid from the first dispensing chamber to the first reservoir, the driving member movable reciprocally parallel to the first axis, in the coupled condition, the releasable juncture arrangement couples the driving member and the driven member together such that reciprocal movement of the driving member parallel the first axis moves the first piston element parallel the first axis in unison, in the uncoupled condition, the releasable juncture arrangement does not couple the driving member and the driven member together such that reciprocal movement of the driving member parallel the first axis does not move the firstpiston element rendering the first piston pump inoperative to discharge the first fluid by movement of the driving member, the pump arrangement being so configures that with the releasable juncture arrangement in the coupled condition, when the first vacuum condition in the first dispensing chamber is greater than a threshold separation vacuum, the releasable juncture arrangement assumes the uncoupled condition. a first piston pump having a first dispensing chamber and a first piston element reciprocally movable along a first axis in the first dispensing chamber to draw a first fluid into the first dispensing chamber from a first reservoir through a first conduit opening into the first dispensing chamber and discharge the first fluid out a first discharge outlet, wherein reciprocal movement of the first piston element discharges the first fluid from the first reservoir until the first reservoir is empty of the first fluid wherein further reciprocal movement of the first piston element creates a first vacuum condition in the first dispensing chamber axially inward of the first piston element, the first piston element including a driven member, a releasable juncture arrangement releasably coupling a driving member and the driven member together, the releasable juncture arrangement having a coupled condition and an uncoupled condition, characterized by, the first piston pump including a first inlet one-way valve across the first conduit, the first inlet one-way valve providing for flow of the first fluid from the first reservoir to the first dispensing chamber but preventing flow of the first fluid from the first dispensing chamber to the first reservoir, the driving member movable reciprocally parallel to the first axis, in the coupled condition, the releasable juncture arrangement couples the driving member and the driven member together such that reciprocal movement of the driving member parallel the first axis moves the first piston element parallel the first axis in unison, in the uncoupled condition, the releasable juncture arrangement does not couple the driving member and the driven member together such that reciprocal movement of the driving member parallel the first axis does not move the firstpiston element rendering the first piston pump inoperative to discharge the first fluid by movement of the driving member, the pump arrangement being so configures that with the releasable juncture arrangement in the coupled condition, when the first vacuum condition in the first dispensing chamber is greater than a threshold separation vacuum, the releasable juncture arrangement assumes the uncoupled condition.