An adjustable flow control device is provided which has a valve body containing a series of orifices of varying diameter and an indexable valve cover which includes at least one flow conduit which can be positioned and locked in a sealable manner over a chosen orifice while the remaining part of the valve cover closes off the other orifices of the valve body. Due to the device having fixed size orifices, each orifice will provide a fixed specific fluid flow rate for any predetermined pressure loss across the orifice. The device is suitable for use on all types of gas and liquid fluids.