GCE Gas Saver for MIG and TIG gases. 
The is one of the best gas saving devices available at this price point. There is a couple of different designs for different purposes. Please ensure you select the right version. 

Does your regulator have 2 gauges? 
Select the non-adjustable/fixed pressure one. 

Does your regulator have 1 gauge (contents) and a flow tube? 
Select the adjustable pressure version. 

If you use the wrong one it isn't the end of the world, they still work but flow adjustment will need to be adjusted and measured differently to the instructions. 

How is works 
The gas saver reduces the amount of time it takes to shut the gas off once you stop welding (or once your post gas stops) and also dramatically reduces the spike in the gas surge when you press the trigger button on your torch or foot pedal. 
Or, in GCE's words "When you close the gas flow at common pressure regulator during the welding process interruption, the outlet pressure in the connecting hose raises up much above the optimal level (acc. to ISO 2503 up to 30%). Then the volume of the gas, higher than really needed, is blowing through the system after the welding process starts again by switching on the arc on the welding torch. GS40 minimises amount of such waste gas cumulated in the connecting hose. The optimal, predefined gas flow is delivered to the welding process during all its phases." 

Technical Information
Intended Gas Use: Argon, Argon /CO Mixed, CO
Material Construction:
Bonnet: Zinc Aluminium Alloy Die Cast
Stems, Nuts and Fittings: Brass
Diaphragm: EPDM
Seat Sealing: PA
Max Inlet Pressure: 20 Bar
Outlet Pressure: 0 to 32 l/min
Operating Temperature: -20°C to 60°C
Weight: 0.4kg