VACUUM RELIEF VALVE
A spring loaded valve, mounted at the top of some tanks, designed to open and allow air into the tank if an excessive internal vacuum occurs.

VALVE STEM
A movable shaft that transmits the operating force to the valve closure member.

VAPOR TIGHT PRESSURE
The pressure measured at the inlet of a safety valve after it has closed, at which no further fluid flow is detected.

VAPOR VALVE
See "Air Valve."

VISUAL GAUGE BAR
On nonpressure tank cars, a bar mounted to the inside of the tank, and which is visible through the manway when open. Markings on the bar indicate various liquid levels.

VISUAL INSPECTION
A nondestructive test method using ordinary vision to detect surface imperfections in materials and welds.