Pull pumps, refill units and dispensers for pull pumps

1. A refill unit for a liquid dispenser comprising:

a container for holding a liquid; and

a post seal pump;

the post seal pump comprising

a housing;

the housing secured to the container;

a post secured to the housing;

a post seal on the post;

the housing having a pump chamber;

a base at one end of the pump chamber;

an aperture through the base;

a shaft seal secured to the housing and located proximate the aperture in the base;

a hollow piston shaft having a first end that fits over the post and engages the post seal and a second end that reciprocates within the aperture;

a fluid outlet located proximate the second end of the hollow piston shaft;

a piston located at an intermediary position on the shaft;

one or more apertures through the piston shaft located between the piston and the fluid outlet;

wherein when the piston shaft is in a first position, fluid flows into the pump chamber and the one or more apertures through the piston shaft are sealed off by the post seal; and

wherein when the piston shaft is in a second position, the piston engages a wall of the pump chamber and the one or more apertures provide a fluid path from the pump chamber to the interior of the hollow piston shaft.

2. The refill unit of claim 1 wherein the shaft seal comprises foam.

3. The refill unit of claim 1 wherein the post seal comprises foam.

4. The refill unit of claim 1 wherein one of the post guides the movement of the piston shaft.

5. The refill unit of claim 4 wherein when the piston is at either end of its stroke, the piston shaft is engaged with the post or post seal.

6. The refill unit of claim 1 wherein when the one or more apertures in the piston shaft are sealed off by the post seal, the piston is located above a top of the pump chamber.

7. The refill unit of claim 1 wherein the post is secured to the housing by a post cage having one or more legs.

8. A refill unit for a liquid dispenser comprising:

a container for holding a liquid;

a pump having a pump housing secured to the container;

the pump comprising

a pump chamber;

a stationary sealing member;

a hollow piston shaft having a first end and a second end;

a first end of the hollow piston shaft fits over the stationary sealing member;

the hollow piston shaft movable in a reciprocating motion over the stationary sealing member;

a piston extending outward from the hollow piston shaft;

one or more apertures through the hollow piston shaft located between the piston and the second end of the hollow piston shaft;

wherein fluid flows into the pump chamber when the one or more apertures through the piston shaft are sealed off by the post seal; and

wherein when the piston engages a wall of the pump chamber, the one or more apertures provide a fluid path from the pump chamber to the second end of the hollow piston shaft.

9. The refill unit of claim 8 further comprising a piston sealing member secured to the pump housing to provide a seal between the piston shaft and the pump chamber.

10. The refill unit of claim 9 wherein the piston sealing member comprises foam.

11. The refill unit of claim 8 wherein the stationary sealing member comprises foam.

12. The refill unit of claim 8 further comprising a post, wherein the stationary sealing member is secured to the post.

13. The refill unit of claim 12 wherein the post and stationary sealing member provide a guide for the movement of the hollow piston shaft.

14. The refill unit of claim 8 wherein movement of the piston shaft downward causes fluid to be dispensed and movement of the piston shaft upward for a first distance draws air and residual liquid from the hollow piston shaft into the pump chamber and further movement of the piston shaft upward allows air in the pump chamber to flow into the container and allows liquid from the container to flow into the pump chamber.

15. A refill unit for a liquid dispenser comprising:

a container for holding a liquid; and

a post seal pump;

the post seal pump comprising

a housing;

the housing secured to the container;

a post secured to the housing;

a post seal on the post;

the housing having a pump chamber;

a base at one end of the pump chamber;

an aperture through the base;

a shaft seal secured to the housing and located proximate the aperture in the base;

a hollow piston shaft having a first end that fits over the post and engages the post seal and a second end that reciprocates within the aperture;

a fluid outlet located proximate the second end of the hollow piston shaft;

a piston located at an intermediary position on the shaft;

one or more apertures through the piston shaft located between the piston and the fluid outlet;

wherein when the piston shaft is in a first position, fluid flows into the pump chamber and the one or more apertures through the piston shaft are sealed off by the post seal; and

wherein when the piston shaft is in a second position, the piston engages a wall of the pump chamber and the one or more apertures provide a fluid path from the pump chamber to the interior of the hollow piston shaft; and

wherein the pump chamber surrounds at least a portion of the hollow piston.

16. The refill unit of claim 15 wherein at least one of the shaft seal and the post seal comprises foam.

17. The refill unit of claim 15 wherein one of the post guides the movement of the piston shaft.

18. The refill unit of claim 17 wherein when the piston is at either end of its stroke, the piston shaft is engaged with the post or post seal.

19. The refill unit of claim 1 wherein when the one or more apertures in the piston shaft are sealed off by the post seal, the piston is located above a top of the pump chamber.