Vacuum assisted loading system

A vacuum assisted system for loading a liquid product containing vapor into a tank comprising:

• means for loading the liquid product under pressure into said tank;
• means for disposing of vapor recovered from said tank during loading;
• conduit means for interconnecting said tank and said vapor disposing means;
• a blower in said conduit means for applying a predetermined vacuum to said tank, whereby the loading means pressure and the blower vacuum act to move vapor from the tank to the vapor disposal means;
• a by-pass conduit formed between the outlet and the inlet sides of said blower;
• and
• valve means in said by-pass conduit and responsive to the vacuum at the inlet side of said blower for progressively opening to permit by-pass flow of vapor from the outlet side to the inlet side of said blower, whereby maximum by-pass is provided when the vacuum approaches a predetermined maximum level;
• said valve means comprising a valve seat, a valve stem extending through said valve seat, a valve at one end of said stem, a spring at the other end of said valve stem for biasing said valve against said valve seat, and a diaphragm interposed between said spring and said valve seat for pulling said valve stem away from said spring to progressively open said valve in response to an increasing vacuum.