Abstract: A novel apparatus and system for developing a pressure differential in a gas flow line is provided. The apparatus comprises a flange-supported plate having a flow port formed therethrough and a pressure control valve mounted thereon for controlling flow through the port. The valve is positioned inside the gas flow line and the plate is of such dimensions so as to direct substantially all of the line's gas flow through the flow port and valve. The system comprises at least one flanged connection in the gas flow line and the apparatus, as described above, inserted into the line at the flanged connection. In another embodiment the system further comprises a well inlet separator, a gas meter and a liquid level control with a dump line downstream of the gas meter. The flanged connection is located downstream of the well inlet separator and upstream of the dump line.