Patent ID: 6877965

Claim:
A mechanical bladder pump for collecting fluid samples from a well, comprising: an outer tubular member having a longitudinal bore; an inner member arranged within the bore of the outer tubular member for oscillating longitudinal movement of the inner member relative to the outer member; a bladder having a first end fixed relative to a lower end of the inner member and a second end fixed relative to a lower end of the outer member, the bladder being in fluid communication with an inlet passage and an outlet passage; a first check valve arranged in said inlet passage for allowing fluid to enter the bladder through the inlet passage upon expansion of the bladder and preventing fluid from exiting the bladder through the inlet passage upon compression of the bladder; a second check valve arranged in said outlet passage for preventing fluid from entering the bladder through the outlet passage upon expansion of the bladder and allowing fluid to exit the bladder through the outlet passage upon compression of the bladder; and a return spring that stores energy during a tension stroke of the inner member in an upward direction relative to the outer member and releases energy during a compression stroke of the inner member in a downward direction relative to the outer member.