Patent ID: 7458787

Claim:
A downhole pump, comprising: a) a barrel having first and second ends, with a first one-way valve located adjacent to the second end, the barrel comprising a vent port at a location intermediate the first end and the first one-way valve; b) a plunger having first and second ends and being located inside of the barrel such that the first one-way valve is closer to the plunger second end than to the plunger first end, the plunger capable of reciprocating inside of the barrel, the plunger has a second one-way valve, a compression chamber being formed between the first one-way valve and the second one-way valve; c) a seal between the plunger and the barrel, the seal located between the vent port and the barrel first end; d) a clearance between the plunger and the barrel, the clearance located between the seal and the plunger second end so as to communicate with the compression chamber and so as to communicate with the vent port, wherein gas in the compression chamber can escape the barrel through the clearance and the vent port, the clearance forming a seal to liquid in the compression chamber.