PRESSCON FX PREVENT, User Manual

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4.  Functioning of the safety valves 

4.1 Operation of a vacuum-overpressure safety valve  

If the pressure of the nitrogen above the water rises above the maximum operating pressure for any reason, 
the operating pressure side of the vacuum pressure relief valve opens. This creates an open connection to 
the outside air. The excess nitrogen can flow away through the opening. The working pressure valve 
remains open until the pressure equals the operating pressure.  

If the pressure keeps rising and reaches the maximum overpressure, the overpressure safety valve will also 
open. The vacuum relief valve remains open until the pressure falls below the maximum overpressure.  

When the pressure drops and a vacuum is created between -2 and -4 mbar, the vacuum relief valve on the 
vacuum side opens. Due to the pressure difference between the outside and inside air, outside air flows in. 
The pallet is lifted until the pressure difference is equalised. 

By using a PRESSCON vacuum-overpressure safety valve the possibility of an unacceptable over- or under 
pressure altering the lasting shape of the tank is prevented. To guarantee a correct operation of the vacuum-
overpressure safety valve it is prohibited to change the lead weights in the safety valve in any way. 

4.2 Operation of a vacuum safety valve 

If water flows from the buffer tank and causes a decrease in the water level, then the water level will 
foremost decrease in the vacuum safety valve. If the water in the housing of the vacuum safety valve drops 
more, a vacuum will be created. When a vacuum exists between -2 and -2 mbar, the pallet of the seating will 
be lifted. This causes an open connection with the outside air. Because of the differential pressure between 
outside and inside, outside air will flow into the buffer tank. The differential pressure is settled. By applying a 
PRESSCON vacuum-overpressure safety valve the possibility of an unacceptable over- or under pressure 
altering the lasting shape of the tank is prevented. To guarantee a correct operation of the vacuum safety 
valve it is absolutely prohibited to turn the adjusting screw on the downside of the valve. The adjusting screw 
is adjusted and secured in the factory. 

5.  Construction 

PRESSCON has aimed to make the construction of the vacuum-overpressure safety valve as simple as 
possible. Except for the flange for the mounting on the tank, only the gasket under the pallets is capable of 
leaking. A very durable rubber is chosen as the material for the gasket. As a seal between the inside and the 
outside, a combination of a stainless steel seating with a special rubber has been chosen. An important 
feature of this special rubber is its lack of permit for dirt to attach itself to the rubber. The rubber is also very 
heat resistant. The vacuum-overpressure and vacuum safety valve are constructed in such a way that after 
assembly they are completely resistant to a plurality of pressures that can occur at a vertical or horizontal 
buffer tank.