and into an outlet passage 38 which communicates with the cavity 29 in the aspirator assembly 26 in the lower end of the device 20 the aspirator assembly 26 and the jet assembly 37 are so designed that the flow of oil out of the degassing chamber 32 exceeds the flow in through the aspirator port 23 thus when the valve 34 is open the oil level in the degassing chamber 32 will fall and will tend to leave a vacuum above itself air in the oil entering through the jet assembly 37 will be readily separated from the oil in this near vacuum and will accumulate in the degassing chamber 32 at a relatively constant pressure since any tendency for the pressure to increase will increase the flow through the outlet passage 38 and thereby lower the oil level in the chamber when the oil level in the degassing chamber drops to a low level the valve 34 closes automatically and the level begins rising again since the flow in through the degassing port remains relatively constant as the level rises separated air above the oil is compressed and expelled through the vent port 25 when its pressure slightly exceeds the.