Pipeline pig with pressure-equalizing transmitter cavity system

A method for pressure-equalizing a transmitter cavity of a pipeline pig when the pipeline pig is traveling through an interior of a pipeline by way of differential pressure due to pipeline product flow, the method comprising:

• providing a pipeline pig (10) including:
• a transmitter cavity (13) located between a forward end (29) and a rearward end (31) of the pipeline pig and arranged coaxial a central longitudinal centerline (23) of the pipeline pig, the transmitter cavity having a forward end (39) and a rearward end (41), the forward end being a closed end;
• a flange (17) located at the rearward end of the transmitter cavity, the flange including a central opening (45) and having a first hardness;
• a plug (15) sized for engagement with the central opening of the flange, the plug including a thru passageway (25) and having a second hardness different than that of the first hardness;
• wherein, when the plug is engaged with the flange, the transmitter cavity is in fluid communication with the thru passageway of the plug.
• the method further comprising, equalizing a pressure of the transmitter cavity with that of the pipeline product flow as a portion of the pipeline product flow fills the transmitter cavity during the traveling.