flex and seal off therebetween as the stem structure moves there being a flow chamber in the housing at one side of the diaphragms and a control chamber in the housing at the opposite side of the diaphragms control structure carried by the housing and extending into the control chamber to effect the movement of the stem structure the control structure being movable relative to the housing and signal structure carried by the housing to signal presence or absence of pressurized fluid leakage from the flow chamber and from the control chamber application_number US 88635597 A description the valve unit 10 shown in fig1 is connected at 11 to a high pressure gas or other fluid cylinder 12 as at upper neck 13 of the cylinder the valve unit includes a metallic housing 14 that in turn may typically include a body 14a and a cap 14b connected to the body at 15 the connection 15 may advantageously include external thread 15a on upper tubular extent 16 of the body and internal thread 15b on the cap skirt 17 telescopically received over the body upper extent 16 an o ring seal 18 is provided between 17 and 16 below the thread connection 15 to block escape of any pressurized.