What is claimed is:
1. A bi-flow expansion device for a heat pump system in which refrigerant flow is reversed in changing from a cooling mode to a heating mode, said expansion device comprising:
a tubular member having first and second ends, and a plurality of passages extending the length of said tubular member, said plurality of passages defining means for providing a restriction of the flow of refrigerant therethrough when said heat pump is in both the cooling and the heating mode;
a cage member for supporting said tubular member in the pathway of refrigerant flow, said cage member being adapted for said tubular member moving axially therein under the force of flowing refrigerant, said cage having radially-extending stop means at said first end, said stop means being adapted to block at least one of said passages when refrigerant flows from said second to said first end, thereby providing different flow restrictions, through said tubular member, for opposite flow directions.
2. A bi-flow expansion device for refrigerant in a heat pump having a cooling mode in which refrigerant flows through said expansion device in a first direction, and a heating mode in which refrigerant flows through said device in a second direction, said expansion device comprising a tubular member having a first refrigerant entrance-exit at a first end, said first entrance-exit facing the direction from which refrigerant flows when said heat pump is in the cooling mode, a second refrigerant entrance-exit at a second end, said second entrance-exit facing the direction from which refrigerant flows when said heat pump is in the heating mode, and at least two passages extending between said first and second entrance-exit, said passages defining means for providing a restriction of the flow of refrigerant therethrough when said heat pump is in both the cooling and the heating mode, and fluid flow blocking means for obstructing at least one of said passages and leaving at least one of said passages unobstructed when refrigerant is flowing from said second to said first end, thereby providing different flow restrictions, through said tubular member, for opposite flow directions.
3. A bi-flow expansion device according to claim 2 and having means at said second end for obstructing at least one of said passages and leaving at least one of said passages unobstructed when refrigerant is flowing from said second to said first end.
4. A bi-flow expansion device according to claim 3, wherein said second end defines an entrance-exit to at least one of said passages, in which said entrance-exit has a decreasing cross-sectional area in the direction toward said first end, and said means for obstructing said at least one passage comprises a member movably housed in said entrance-exit, whereby pressure of refrigerant flowing from said second to said first end moves said member to obstruct said at least one passage.
5. A bi-flow expansion device according to claim 3 wherein said entrance-exit is cone-shaped.
6. A bi-flow expansion device according to claim 5, wherein said member movably secured in said cone-shaped entrance-exit is spherical.