Standard_Parts_Catalogue

Page 1621 | 3.5 Controlling, Venting, Sealing of Liquids and Gases 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 GN 774 Breather Caps continued Breather caps GN 774 with double valve are normally used if the oil container is under pressure and if outside air has to flow back in to compensate for the vacuum caused by falling oil level. This is achieved by combining two valves (non-return / bypass valve). The inlet valve opens at a vacuum of 30 mbar or greater. The second valves opens at an overpressure > 350 / 700 mbar. The air filter prevents the oil from being polluted from the outside (dust). The filter is made of PU foam with a filtration of 40 µm. The overpressure inside the container ensures that the air volume flowing in or escaping owing to fluctuations of the oil level is kept to a minimum. This reduces filter fouling and substantially increases the useful filter life, especially in a dusty environment. Also, a container under pressure has a positive effect on the function of the pump and prevents foaming. The valve seal ensures that no oil can spill to the outside, neither by excessive agitation in the tank nor during trans- port. Function Pressure curve Δp [mbar] in the container as factor of the air flow rate [l/min.] at a valve opening pressure of 350 or 700 mbar.