A pressure vessel apparatus according to exemplary aspects includes: a branched tube comprising a tube main body and three branches, wherein a side branch of the branches comprises a flared out portion connected to the tube main body; a liquid inlet opening disposed at a first branch of the branched tube; a liquid outlet opening disposed at a second branch of the branched tube; a gas inlet opening disposed at a third branch of the branched tube, wherein the third branch is the side branch; and a cover plate configured to mount a valve actuating mechanism in the branched tube, the cover plate configured to be joined to the branched tube at the third branch.