RIV 290 Brass Vacuum Relief Valve

The RIV 290 is a vacuum relief valve from the Ambra series of RIV's Slurry Tankers and Biogas line. It does the opposite job to a pressure relief valve: a spring holds the disc shut against atmospheric pressure, and when the pressure inside the tank falls far enough below atmosphere the disc is drawn open and air is admitted until the difference is relieved.

That protection matters because a tank barrel is far weaker in the collapsing direction than in the bursting one. A vacuum tanker that keeps pumping against a blocked suction, or a warm tank that is closed up and then cools, can pull enough vacuum to dent or collapse the shell. The vacuum relief valve is the device that stops it, and it is fitted alongside - not instead of - the pressure relief valve on the same barrel.

The valve is brass, with two drilled lugs for bolting to the tank, an open cage that exposes the stem, a male thread beneath and a black plastic cap on top. RIV also lists RIV 291, the same valve with an NPT thread, and RIV 90292, a calibrated and sealed version.

When ordering, state the size, the thread form and the vacuum setting required, and confirm the setting with RIV or the supplier - the setting is not published.