Pneumatic liquid level control having either throttling of snap action

A pneumatic liquid level control having optionally available either snap action or throttling action in response to liquid level in a vessel, comprising:

• a liquid level control body having a gas supply inlet, a control gas outlet, an exhaust port, and having a single nozzle port connected to said gas supply pressure inlet by way of an inlet gas chamber, and a single nozzle closure member actuated by a float means to move said closure member towards and away from said nozzle in response to the level of liquid in a vessel;
• a snap action booster having a diaphragm controlled valve;
• a first passageway from said gas inlet chamber to said diaphragm whereby said diaphragm control valve is actuated when the pressure in said gas supply chamber exceeds a preselected level;
• a manually operated shut off screw in said first passageway which, when closed, deactivates said snap action booster;
• a second passageway from said gas supply chamber to said gas control outlet;
• a threaded opening in said level control body intersecting said second passageway;
• a throttling screw in said threaded opening providing throttling control of gas passing through said second passageway;
• and
• a third passageway from said gas supply chamber to said gas control outlet having said diaphragm controlled valve therein, whereby when said closure member is not in proximate contact with said nozzle port, gas from said gas supply chamber passes freely through said nozzle and out through said exhaust port with a resultant low pressure in said gas supply chamber, however when said nozzle closure member is in contact or proximate contact with said nozzle, gas pressure increases in said gas supply chamber, which is communicated to said control gas outlet by way of said second or third passageways depending upon the positions of said shut off screw and said throttling screw.