Electromagnetic vacuum valve

The valves feature a solenoid, which is an electric coil with a movable ferromagnetic core in its center called the plunger. In the rest position, the plunger closes off the orifice. An electric current through the coil creates a magnetic field, which exerts a force on the plunger. As a result, the plunger is pulled so that the orifice opens.

The exhibit is METROVAC 1/2“ magnetic angle valve from the MS902 double-focusing mass spectrometer manufactured by AEI Scientific Apparatus Ltd. in 1969. It was located on the rotary pump inlet pipeline. In the case of mains failure, the valve immediately closed the line to maintain vacuum in the system.

Wikipedia: Pressure measurement