Compound lever controlled spill valve

On a liquid cargo tank of a marine vessel, and wherein there is an aperture in the top of the tank, with a mounting flange fastened and sealed to the tank around the aperture;

• a spill valve assembly comprising:
• a base plate fastened and sealed to the mounting flange and having an opening therein communicating with the interior of the tank;
• a spill valve which is seated around and closes the opening communicating with the interior of the tank;
• a valve clamp arm holding the valve closed;
• a control arm assembly having a first position retaining the clamp arm in valve closed holding condition, and having a second position with the clamp arm in a valve open condition;
• and
• a counterweight normally retaining the control arm assembly in the first position but movable with movement of the control arm assembly to a position of less clamp arm retaining control to enable increasing movement of the spill valve from closed condition;
• the clamp arm being pivotally fastened to the base plate and the control arm assembly being pivotally fastened to the base plate.

A spill valve assembly comprising:

• a base connectable to a tank as a sealing closure for an overflow aperture for the tank;
• a valve which closes an opening in the base and having a seal lying in a horizontal plane;
• a valve clamp arm holding the valve closed;
• a control arm assembly having a first position retaining the clamp arm in valve closed holding condition, and having a second position with the clamp arm in a valve open condition;
• and
• the control arm assembly in the first position being movable with movement of the valve in response to a predetermined set point pressure to a position of less clamp arm retaining control to enable increasing movement of the spill valve from closed condition.

A spill valve assembly comprising:

• a base connectable to a tank as a sealing closure for an overflow aperture for the tank;
• a valve which closes an opening in the base;
• a valve clamp arm holding the valve closed;
• a control arm assembly having a guide system and having a first position retaining the clamp arm in valve closed holding condition, and having a second position with the clamp arm in a valve open condition;
• the control arm assembly in the first position being movable with movement of the valve in response to a predetermined set point pressure to a position of less clamp arm retaining control to enable increasing movement of the spill valve from closed condition;
• and
• a roller on the clamp arm and received on the guide system of the control arm assembly and operable as the spill valve opens to move along the guide system from a position providing greater resistance to valve opening to a position providing less resistance to valve opening.

A method of holding pressure in a tank but relieving the pressure upon attainment of a predetermined maximum pressure in the tank and comprising the steps of:

• maintaining tank closure by at least two cooperating arms, the first arm of the two holding a valve closed on the tank, and the second arm of the two holding the first arm in the valve closed holding condition;
• placing the arms in a compound lever arrangement with loading points and pivot points arranged to multiply the force applied by the second arm to the first arm to produce the force applied by the first arm to the valve and thereby holding the valve closed with a much larger force than the force applied by the second arm to the first arm;
• and
• using movement of the valve from closed condition upon attainment of the predetermined pressure to reduce the closing force on the valve.