Does anyone know if tweaking the one-way valve would have any effect on the flow of water coming through? My machine works but the extraction time is very short, below 10 seconds for 1.5 oz of coffee. I've been changing the grind size, amount of coffee and tamping differently but nothing increased the extraction time. I read a comment saying to increase the extraction time “you should use the group tightener to tighten the screw on the underside of the group head”. I'm not sure what that exactly is, best I can tell it's referring to the one way valve.