The Barksdale 0403-105 Mechanical Pressure Switch is a device used to monitor the pressure of a fluid within a system and to control safety or regulating devices based on certain predefined pressure values. The operation of the Barksdale 0403-105 mechanical pressure switch occurs via a pressure-sensitive element, such as a diaphragm or a Bourdon tube, which in turn acts on an electrical or pneumatic contact. When the pressure reaches a certain level, the sensing element deforms and activates the contact, tripping an electrical or pneumatic switch. The Barksdale 0403-105 mechanical pressure switch can be used in various industries, such as in plumbing, chemical industry, heating and air conditioning systems. In summary, the mechanical pressure switch works by ensuring that the pressure of a fluid within a system remains within certain limits, and by activating safety or regulation devices if these limits are exceeded.