This invention deals with a pressure switch concerning the heat engineering control and instruments in thermal power plant. Its goal is to produce a pressure switch which is able to response the micropressure signals, has high sensitivity and combines a positive pressure switch with a negtive pressure switch. The main points of the invention are as follows: The proper quantity of mercury is filled into an insulated U-shape hole. An end of the hole is connected with controlled air pressure. When the air pressure is negtive, the mercury is raisedtowards the air inlet end and the terminal at the middle of hole is connected with the terminal at the air inlet end; when the air pressure is positive, the mercury is raised towards another end and the middle terminal is connected with the terminal at another end. As a result, the negtive or positive pressure signals or instructions are sent out. This invention can be used for monitoring the burnning in boiler and fire-extingushing protection. |