Pump for dosing fluids

1. A pumping assembly comprising:

a pump body with a pump bore, and a sleeve fixed axially within the pump bore and having a first end, a second end and a sleeve bore; and

a plunger adapted to enter the first end of the sleeve and which reciprocates within the sleeve bore, such that a pumping chamber is partly defined by a leading face of the plunger and an interior side wall of the sleeve;

wherein the interior side wall of the sleeve has a first port and a second port which both allow fluid flow through the wall of the sleeve from a feed port into the pumping chamber,

wherein passage of fluid into the pumping chamber through the first port and the second port is blocked when the plunger advances sufficiently far into the sleeve bore to cover the first port and the second port;

wherein the first port and the second port are each elongated in a circumferential direction substantially orthogonal to a direction of reciprocation;

wherein the first port and the second port are each formed as an elongate slot, and wherein respective long edges of each of the elongate slots are substantially parallel to each other; and

wherein the first port and the second port each have a leading edge, wherein the leading edge is the long edge that is closest to the second end of the sleeve; and wherein the leading edge of one of the first and second ports is closer to the second end of the sleeve than the leading edge of the other of the first port and the second port.

2. The pumping assembly as claimed in claim 1 , wherein the sleeve and the plunger are formed of a harder material than the pump body.

3. The pumping assembly as claimed in claim 2 , wherein the harder material is a martensitic steel, wherein the pump body is formed of a ferritic steel.

4. The pumping assembly as claimed in claim 1 , wherein the pumping assembly is adapted for use in an armature pump.