Vacuum valve removal flon Junior is differevt as it's mounted on top of the sight glass assembly. where as most are mounted on the boiler. see 125 Vacuum valve removal. 24 mm open end wrench needed to hold the sight glass top base as it's also connected by a pipe to the top of boiler. this pipe may flex, crack, or twist the sight glass which may also crack. hold the base firmly while using a 19 mm wrench to remove vacuum valve. there is a small o-ring that can be replaced if cracked or missing. check if there still is the white teflon seated in hole before installing the valve. Though a rubber o-ring could be used. Over tightening will squeeze out rubber. you could try heavy wraps of pipe seal tape. though this is only a temparary solution.