Vibration resistant pressure actuated vacuum breaker

A pressure actuated vacuum breaker for mounting on the top of a movable tank above the level to which the tank is normally filled with product for admitting atmospheric air to the tank to relieve a reduced pressure condition occurring in the tank while substantially preventing the escape of product or product vapor from the tank via the vacuum breaker, the vacuum breaker being highly resistant to opening due to vibration associated with movement of the tank, comprising:

• a housing communicating with the interior of the tank and vented to the atmosphere;
• a downward facing closure seat disposed in the housing between the interior of the tank and the vent to the atmosphere;
• a light-weight, vertically reciprocal closure assembly disposed in the housing and including a closure member cooperable with the closure seat to close the vacuum breaker and a first permanent magnet mounted on the closure member and having an upward facing pole;
• a second permanent magnet mounted in the housing above the first permanent magnet and having a downward facing pole so that the first and second magnets attract one another with a magnetic force equal to at least about 5 times the weight of the closure assembly to hold the closure member up against the closure seat and thereby maintain the vacuum breaker closed in the absence of reduced pressure in the tank and in spite of accelerations due to vibration up to at least about 4 times gravitational acceleration tending to open the vacuum breaker, the force of attraction between the magnets being overcome and the closure assembly moving downward to open the vacuum breaker when a reduced pressure condition occurs in the tank;
• a shielding assembly disposed in the housing and substantially surrounding the first and second magnets at all times during operation of the vacuum breaker;
• and
• spring means for exerting an upward return force on the closure assembly to assist in closing the vacuum breaker after it has opened.