These instruments are designed to check the level of liquids within vessels, to show its height on a dial and to self-regulate it by means of external regulation pneumatic valve. They operate in this way : the level increase delivers an hydrostatic lift to displacer, that causes a 0÷8° rotation to a small calibrated torque bar; this bar acts into a special device placed in the box and generates 2 different types of outputs.

• The first output, mechanical type, is sent to a linear dial to show the excursion made by displacer. The dial is placed on the front of the instrument box, is graduated 0÷100% and shows the portion of the excursion (measure field) being covered by the displacer.

• The second output is composed by a pneumatic signal that is sent by the instrument to an external regulation valve, in order to regulate loading and unloading of vessel. This pneumatic signal can be as follows :

REGULATOR ON-OFF 851 : when level reaches the preset height in the box, air signal is sent or is not sent to external valve.

PROPORTIONAL REGULATOR 852 : when level reaches the preset height, air is sent to external valve with a pressure being proportional to the difference between the level reached by the float and the level preset by user in the box : higher is the difference, higher is the output pressure and quicker is the corrective action (dirrect action). The same instrument performs the contrary action too : higher is the difference, lower is the output pressure (inverse action). The proportional dial can be preset in the range of 0÷200%, both in direct and in inverse action, and is graduated so that it shows at which % level the external valve will be completely closed or opened.

PROPORTIONAL+INTEGRAL REGULATOR 853 : air signal is sent to external valve with a pressure being proportional to the difference as above written, and also to the integral of such a difference; in this way user obtains a still quicker corrective action. The integral dial is expressed in “repetitions of operations per minute”, within values of 0,05÷15 rep/min.

TRANSMITTER 855 : as level rises, the pneumatic signal is sent out with an increasing pressure within 3÷15psi values; the pressure changes only on the basis of float position, and is not subjeted to any presetting or regulation.

The instruments realize very interesting performances :

• Pneumatic device is high precision grade, high repeatability, high linearity and high response speed.

• Proportional and Integral dials are graduated so that, after a quick calibra-tion, pressure hunting on the valve is reduced to zero. • Measure fields are very wide : 14” (356mm) to 120” (3.050mm).

• Specific gravity of liquid can be preset on the instrument, 500 to 1200kg/m³. • Pressure shown on 2 manometers : inlet (feed) and outlet (to valve).

• The instrument box can be placed on the Right of vessel (as in the sketches), or on the Left of vessel.

• Mechanical connections can be made by Flanges or Sleeves, mounting on Top or on Side-Side, as the below tables.

• A special device assurse mechanical connection between float and torsion bar, even in prsence of strongly agitated liquids; the float is connected to the bar in very easy way, so that the operator can first assemble the main chamber to vessel, and then connect the float to the bar, without any risk of damaging the lever system or the pneumatic unit.

• Technical performances of pneumatic unit :

• Type . Forces balance between the value preset by user and the value checked by displacer.

• Air feed . Pressure : 20 ±1,5psi (1,4 ±0,1bar). Flow : 3,5 Nm³/h max at 20 psi (1,4bar). Stand-by : 0,05 Nm³/h.

• Air outlet . . Pressure : 3÷15psi (0,2÷1bar), at action : ON-OFF, Proportional, Proportional+Integral. Repeatability : 0,5%. Linearity : 0,5%. Histeresys : 0,5%. Accuracy : 1%.

• Air connection . ¼” NPT-F for inlet and outlet

• Temperature . -20°C to +80°C.