PURPOSE: To prevent fluid from passing through an inlet valve and a pump barrel to cause damage thereto by providing a lock device for locking an inlet valve for a sucker rod operated reciprocating underground pump at a closure position.

CONSTITUTION: A sucker rod operated reciprocating underground pump 10 is arranged such that it is movable between a first position secured in a pumping pipe 22 and a second position not secured in the pumping pipe 22 for maintenance and repair purposes, in order to pump out fluid from a well. When a pump plunger 14 is in the second unsecured position to prevent fluid from flowing to a pump barrel 12, an inlet valve is locked with respect to the inlet. When the pump 10 is in the first secured position for pumping out fluid from a well, the inlet valve is unlocked for sealing the inlet against or opening the inlet for the pump barrel 12. In other words, a lock device is provided. In this way, the inlet valve and the pump barrel 12 will not be damaged even if fluid passes through them.