Positive displacement pump

A positive displacement pump assembly for withdrawing precisely measured, selected quantities of liquids from a supply receptacle and transferring said selected quantities of liquid to analysis receptacles for said liquids, said pump assembly comprising, in combination,

• at least one liquid cylinder and reciprocably movable plunger assembly adapted for positive displacement of a quantity of liquid upon plunger movement, said quantity displaced being proportional to the length of movement of said plunger within said cylinder,
• valve means associated with said cylinder and plunger assembly, said valve means being movable between a first position establishing a path of liquid communication between said cylinder and a cylinder inlet line and a second position establishing communication between said cylinder and a cylinder outlet line,
• a reciprocable carriage having a first carriage portion thereof adapted to engage a plunger drive unit disposed in the movement path of said first carriage portion and to move said plunger drive unit in a first direction during a portion of the movement of said carriage in said first direction,
• a second carriage portion adapted to engage a part of said plunger and to move said plunger in a second direction during a portion of the movement of said carriage in said second direction,
• a plurality of plunger drive units having different lengths,
• means for holding said plunger drive units so as to permit free but limited axial movement thereof upon engagement thereof by said first carriage portion, said means for holding said plunger drive units being mounted so as to permit selective indexing of said plunger drive units into a position within the movement path of said first carriage portion,
• a powered common drive means for reciprocating said carriage along said movement path in said first and second directions, and for moving said valve means, between said first and second positions, said first and second carriage portions being spaced from each other by a fixed distance greater than the length of said plunger drive unit, whereby said plunger is positively engaged by said carriage portions during only one part of the reciprocating movement of said carriage, upon reciprocation of said carriage, said plunger is driven in said first direction by said first carriage portion acting through said plunger drive unit, said plunger is driven in said second direction by engagement between said second carriage portion and a part of said plunger, said drive means for moving said valve means being constructed and arranged so as to move said valve means between said first and second positions only during another part of the reciprocating movement of said carriage and the quantity of liquid displaced by said plunger is determined by the length of plunger drive unit positioned within said carriage movement path.

A positive displacement pump assembly for withdrawing precisely measured, selected quantities of liquid from a supply receptacle and for transferring said selected quantities of said liquid to analysis receptacles, said pump assembly comprising, in combination,

• a pump frame and a pair of plunger and cylinder assemblies secured to said frame, said plungers including a stem portion and a flange at the bottom thereof,
• means communicating with the interiors of said cylinders enabling aspiration and discharge of liquid materials upon movement of said plungers,
• a carriage assembly and cooperating means on said carriage assembly and said frame for guiding said carriage assembly for vertical reciprocating movement along a predetermined movement path,
• a lower cross bar on said carriage,
• a drive motor secured to said frame and including a main drive element and means for forming an operative connection between said drive element and a portion of said carriage,
• a pair of turret assemblies, each including a turntable adapted to rotate in a horizontal plane, each turntable including a plurality of plunger drive metering rods disposed therein and carried for free but limited vertical movement with respect to said turntable, said turntables being mounted with respect to said frame so as to have an outer margin thereof lying within the movement path of a portion of said carriage,
• a pair of yokes forming a part of said carriage and being spaced vertically from the lower cross bar portion thereof, said yokes being adapted, in position of use, to engage the upper edges of said plunger stem flanges, whereby, upon upward movement of said carriage, said carriage lower cross bar drives said plunger drive units so as to move said plungers upwardly, and upon downward movement of said carriage said yokes on said carriage drive said plungers downwardly.