The mechanical indicator type 50 from Leutert GmbH is one of the last devices of this kind that are available on the world market.
Due to the mechanical structure, mechanical indicators can only operate at speeds of up to max. 800 … 1000 min-1 can be used. The indicator is screwed onto the indicator valve using a union nut. When the valve is opened, the pressure from the cylinder immediately enters the indicator and moves the indicator piston there.
This piston is connected to a calibrated measuring spring, so that its path, under the counterforce of the spring, is proportional to the pressure exerted on it and is recorded on the writing drum.
The writing unit is attached to the piston rod, with the pen at the tip. This records the pressure curve. The drum, in which the paper is mounted for recording, moves back and forth under the influence of the cord pull.
The variable pressure in the cylinder space over the piston stroke is recorded on the writing unit, i.e. the indicator diagram known to all of us.
From the rectangle of the same area calculated therefrom, the mean indexed pressure can be calculated with the spring scale after the scale conversion.