Progressing cavity pump adapted for pumping of compressible fluids

A progressing cavity pump adapted for pumping of a compressible fluid, comprising:

• an inner rotor having a number of thread-starts;
• and
• an adapted outer rotor, wherein the adapted outer rotor is provided with one extra thread-start than the number of thread-starts of the inner rotor,
• wherein a number of closed pump cavities are formed which are moved, during fluid conveyance, from an inlet side of the pump to an outlet side of the pump such that, at the outlet side of the pump, the closed pump cavities become open outlet cavities exposed to a fluid pressure downstream of the pump,
• wherein at least one passage is disposed between the outlet side and a closed pump cavity closest to the outlet side, and
• wherein the at least one passage is structured for intentional fluid back-flow from the outlet side in a measured and approximately constant volume such that pressure is approximately equalized between the outlet side and the closed pump cavity closest to the outlet side under normal operating conditions before a foremost transverse barrier of the closed pump cavity closest to the outlet side reaches an outlet plane of a helical pump section and thereby disappears.