A device which allows a sampling pump to operate at low flow rates and with the optional adjustable low flow tube holders. The CPC is placed inline between the adjustable low flow tube holder and the pump inlet, and regulates the specific amount of pressure to be maintained across the needle valve(s) on the supply (pressure) end of the sampling train. During sampling a valve inside the CPC opens and pulls additional air into the train on the pump (vacuum) end of the CPC as needed, to maintain the CPC-specified pressure across the needle valve(s).