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K-4 K-40 K-400 O-rings. These pumps use 6 O-rings total.

For the High Volume Stage (Outer Pump).

The Larger 4" diameter o-ring (part # 6333) goes on the plunger end and creates the air seal. This o-ring requires light lubrication. The other 2 o-rings are the same size/part number. These 3.5" diameter o-rings (part # 6330) act as cushions and are located on the plunger shaft. One can be seen from the outside of the pump and acts as a bumper on the down-stroke and the other is inside the pump and acts as a bumper on the up-stroke.


For the High Pressure Stage (Inner Pump).


The Larger 3" diameter o-ring (part # 6331) goes on the plunger end and creates the air seal. This o-ring requires light lubrication. The other 2 o-rings are the same size/part number. These 2" diameter o-rings (part # 6326) act as cushions and are located on the plunger shaft. One can be seen from the outside of the pump and acts as a bumper on the down-stroke and the other is inside the pump and acts as a bumper on the up-stroke.
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