Compression system

1. A method of manufacturing a compression system, the method comprising:

preparing an upper housing and a lower housing, each of the upper and lower housings comprising an impeller container and a gear train container and a flow path configured to transfer a fluid amongst a plurality of impellers, the plurality of impellers including a first impeller, a second impeller, a third impeller and a fourth impeller, the first and the second impeller provided on a first side with respect to a main drive shaft transferring power to drive the side opposite to the first side with respect to the main drive shaft, the first and second impellers attached to a first shaft, the third and fourth impellers attached to a second shaft;

installing the plurality of impellers in the impeller container of the lower housing and installing a gear train in the gear train container of the lower housing; and

coupling the upper housing with the lower housing,

wherein the preparing the upper housing and the lower housing comprises casting each of the upper and lower housings having the impeller container, the gear train container and the flow path as a one-piece casting,

wherein the impeller container, the gear train container and the flow path are formed all together using a single mold for each of the upper and lower housings in a casting process, and

wherein the first and second shafts extend through an exterior of the one-piece casting of each of the upper and lower housings along an axial direction of the first and second shafts.

2. The method of claim 1 , wherein the lower housing further comprises a support supporting the lower housing, and

wherein the impeller container, the gear train container, the flow path and the support are formed all together using the single mold.

3. The method of claim 1 , wherein the method further comprises:

providing a first connecting pipe configured to connect a first compression unit including the first impeller to a second compression unit including the second impeller;

providing a second connecting pipe configured to connect the second compression unit including the second impeller to a third compression unit including the third impeller; and

providing a third connecting pipe configured to connect the third compression unit including the third impeller to a fourth compression unit including the fourth impeller, the first, second and third connecting pipes provided at an exterior of the upper and lower housings.

4. The method of claim 1 , wherein the first and second shafts are supported by a first bearing and a second bearing, respectively, and

wherein the first and second bearings are provided in the one-piece casting of each of the upper and lower housings.