The chemical, materials handling, and transportation fields preferably require containers having only a minimal number of ports and other openings thereon for safety, cost and other reasons. It is therefore advantangeous to provide containers such as cargo and storage tanks and bulk shipping containers having single openings which can be used for multiple purposes such as for filling and cleaning, for venting or relieving normally occurring pressure and vacuum conditions, and also for preventing dangerous pressure build-up in the container in the event of fire and the like. Government regulations can also require tanks, vessels and other containers for the transportation and storage of chemicals and other substances to have means providing prescribed flow rates for pressure and vacuum relief under predetermined pressure conditions, and also means providing temperature actuated pressure relief and depressurization at or above predetermined temperature conditions. Such relief means should be rugged and durable so as to be able to withstand abuse in industrial environments, should operate under severe adverse conditions, and should also be leak-resistant even in the event the container tips or overturns.
The device disclosed in U.S. Pat. No. 5,165,445, referenced above, mounts on or over a single opening or orifice on a container and can provide both pressure relief and vacuum relief for the container through the container opening. Such device, however, provides no means for temperature actuated pressure relief. Furthermore, such device does not include mounting means adapted for replacing container caps and covers and so does not readily facilitate using the same port or opening for alternative purposes such as for filling and cleaning the container.
Numerous other devices attempting to satisfy one or more of the above discussed requirements are also known in the art. Reference is made to U.S. Pat. No. 5,031,790, which discloses a removable vented cap for fuel tanks including a self-actuating valve for pressure relief, an open vent for vacuum relief, and fusible plugs for temperature actuated pressure relief. Reference is also made to U.S. Pat. No. 3,385,468, which discloses a safety vent device for mounting over the vent hole of a gasoline tank, which device has passages for pressure and vacuum relief venting and a releasable member held in place with a thin band of fusible alloy to provide emergency pressure relief at a particular temperature. Such prior art devices are limited, however, as they include open passages and fusible means which can leak and allow contamination and such devices may also be damaged if the tank is overturned. Such devices can also expose the interior of a tank and the contents thereof to toxic fusible substances such as a solder substance containing lead alloy or like substances.
Contrasted to the relatively limited prior art devices discussed above, the subject invention relates to a durable and leak-resistant relief vent apparatus which mounts as a removable cover or cap over an opening on a container and can provide pressure relief and vacuum relief for the container at precise predetermined pressure and vacuum conditions and rapid fusible pressure relief at and above a precise predetermined temperature.