Relieves pressure while filtering from one keg to another while also letting you read the pressure in the receiving keg.
Note: The very end of the pressure relief valve can be adjusted by unscrewing to adjust the pressure. If tight, and not adjustable by hand, it needs to be loosened with pliers. Wrap a towel around the end piece of the pressure relief valve (about the last 1/4 in) and loosen with pliers. Then finger tighten or loosen to desired pressure.