Multistage oil separator

1. A multistage oil separator, comprising a housing having a gas inlet and a gas outlet, and at least two filter elements arranged as a cascade in the housing between the gas inlet and the gas outlet,

wherein the at least two filter elements are each arranged vertically and extending upwardly from the housing such that the separated oil will run down on the filter elements under the effect of gravity, and

wherein the housing comprises:

respectively one oil passage downstream of each of the at least two filter elements, and continuous annular grooves for catching the oil and guiding the caught oil toward the oil passage in the manner of an eves gutter.

2. The oil separator according to claim 1 , wherein the housing comprises an oil passage between a last of the at least two filter elements of the cascade and the gas outlet, said oil passage being provided for returning the separated oil.

3. The oil separator according to claim 1 , wherein the at least two filter elements are attached to a common housing flange.

4. The oil separator according to claim 3 , wherein at least one oil passage extends through the housing flange.

5. The oil separator according to claim 1 , wherein the at least two filter elements include at least two cylindrical cartridges having differently sized diameters, the at least two filter elements being disposed on a common axis.

6. The oil separator according to claim 5 , wherein the at least two filter elements are arranged on the common axis on two mutually opposite sides of a flange.

7. The oil separator according to claim 5 , wherein the at least two filter elements are arranged on the common axis on the same side of the flange.

8. A multistage oil separator for separating oil from a cryogenic gas which is being compressed, the oil separator comprising:

a housing which includes a lower portion and an upper portion;

a gas inlet defined in the lower housing portion and configured to receive compressed cryogenic gas from a compressor stage;

a first filter element extending vertically upward from the lower housing portion and downstream from the gas inlet to separate oil from the compressed cryogenic gas such that the separated oil flows by gravity down the first filter element toward the lower housing portion;

a second filter element disposed to receive the compressed cryogenic gas which passed through the first filter element and separate oil therefrom, the second filter element extending vertically upward from the lower housing portion such that the separated oil flows by gravity down the second filter element toward the lower housing portion;

a gas outlet defined in the upper housing portion and configured to receive compressed cryogenic gas which has passed through the first and second filters;

a first annular groove defined in the base portion between the first and second filter elements and extending around and downstream from the first filter element to catch the oil flowing down at least the first filter element;

a second annular groove defined in the base portion around and downstream from the second filter element to catch the oil flowing down the second filter element; and

at least one oil passage which returns oil separated from the compressed cryogenic gas to the compressor stage, the at least one oil passage being connected with the first and second annular grooves.