Reciprocating compressor with vapor injection system

1. A compressor assembly comprising:

a first compression cylinder;

a first compression piston disposed within said first compression cylinder and operable to compress a vapor disposed within said first compression cylinder;

a crankshaft operable to cycle said first compression piston within said first compression cylinder;

a second compression cylinder;

a second compression piston disposed within said second compression cylinder and operable to compress vapor disposed within said second compression cylinder;

a first control piston moveable between a first state restricting passage of intermediate-pressure fluid into said first compression cylinder and a second state permitting passage of intermediate-pressure fluid into said first compression cylinder;

a second control piston moveable between a first state restricting passage of intermediate-pressure fluid into said second compression cylinder and a second state permitting passage of intermediate-pressure fluid into said second compression cylinder; and

a first gas-inlet port in fluid communication with said first compression cylinder and extending through a cylindrical wall of the first compression cylinder,

wherein said first control piston blocks said first gas-inlet port in said first state preventing fluid flow from entering said first gas-inlet port in said first state and opens said first gas-inlet port in said second state allowing fluid flow through said first gas-inlet port in said second state,

wherein, in said first state, said first control piston prevents fluid from being discharged from said first compression cylinder through any portion of said first gas-inlet port,

wherein said first control piston and said second control piston are moved between said first state and said second state by said crankshaft,

wherein the first control piston includes a window through which intermediate-pressure fluid flows into said first compression cylinder when the first control piston is in the second state,

wherein said first control piston prevents communication between the window and the first compression cylinder when the first control piston is in the first state, and

wherein the second control piston does not include a window through which intermediate-pressure fluid flows into said second compression cylinder when the second control piston is in the second state.

2. The compressor assembly of claim 1 , wherein said crankshaft includes a cam profile operable to move said first and second control pistons between said first state and said second state.

3. The compressor assembly of claim 2 , wherein said first and second control pistons are biased into engagement with said cam profile.

4. The compressor assembly of claim 2 , wherein said first and second control pistons are biased into engagement with said cam profile by said intermediate-pressure fluid.

5. The compressor assembly of claim 2 , wherein said first and second control pistons are biased into engagement with said cam profile by a biasing element.

6. The compressor assembly of claim 1 , wherein said second control piston includes a first end in contact with said crankshaft and a second end in fluid communication with said intermediate-pressure fluid, said second end exposing a second gas-inlet port when said second control piston is in said second state to permit said intermediate-pressure fluid to enter said second compression cylinder via said second gas-inlet port.

7. The compressor assembly of claim 1 , wherein movement of said first control piston and said second control piston between said first state and said second state is controlled by said crankshaft.

8. The compressor assembly of claim 7 , wherein said crankshaft includes a cam profile that controls movement of said first control piston and said second control piston.

9. The compressor assembly of claim 7 , wherein said crankshaft includes a first portion operable to move said first control piston between said first state and said second state and a second portion operable to move said second control piston between said first state and said second state.

10. The compressor assembly of claim 9 , wherein said first portion is spaced apart from said second portion in a direction extending along a length of said crankshaft.

11. The compressor assembly of claim 1 , wherein said first control piston and said second control piston are moved into said first state and into said second state at different times.

12. The compressor assembly of claim 11 , wherein movement of said first control piston and said second control piston between said first state and said second state is controlled by said crankshaft.

13. The compressor assembly of claim 1 , wherein the first gas-inlet port opens into the first compression cylinder at a location that is axially between a bottom dead center position of the first compression piston and a top dead center position of the first compression piston.

14. The compressor assembly of claim 1 , wherein an end of each of the first and second control pistons includes a lubricant drain passage disposed adjacent said crankshaft.

15. A compressor assembly comprising:

a first compression cylinder;

a first compression piston disposed within said first compression cylinder and operable to compress a vapor disposed within said first compression cylinder;

a crankshaft operable to cycle said first compression piston within said first compression cylinder;

a second compression cylinder;

a second compression piston disposed within said second compression cylinder and operable to compress vapor disposed within said second compression cylinder;

a first control piston moveable between a first state restricting passage of intermediate-pressure fluid into said first compression cylinder and a second state permitting passage of intermediate-pressure fluid into said first compression cylinder; and

a second control piston moveable between a first state restricting passage of intermediate-pressure fluid into said second compression cylinder and a second state permitting passage of intermediate-pressure fluid into said second compression cylinder,

wherein the first control piston includes a window through which intermediate-pressure fluid flows into said first compression cylinder when the first control piston is in the second state,

wherein said first control piston prevents communication between the window and the first compression cylinder when the first control piston is in the first state, and

wherein the second control piston does not include a window through which intermediate-pressure fluid flows into said second compression cylinder when the second control piston is in the second state.

16. The compressor assembly of claim 15 , wherein said first control piston and said second control piston are moved between said first state and said second state by said crankshaft, and wherein an end of each of the first and second control pistons includes a lubricant drain passage disposed adjacent said crankshaft.

17. The compressor assembly of claim 15 , further comprising:

a first port in fluid communication with said first compression cylinder; and

a second port in fluid communication with said second compression cylinder.

18. The compressor assembly of claim 17 , wherein said first control piston blocks said first port in said first state, and wherein said window is aligned with said first port when said first control piston is in said second state.