This is a quick breakdown for Fetso'sThe Festo connectors are designed for gas pressure and not for liquid suction, however they are designed to handle petrol based lubricants and they are pressure rated from -0.95 to +6 bar-0.95 bar is very high, and fuel will start to evaporate at this low pressure, so it is safe to use themThe only problem by using them in the suction side is that they are more susceptible to a leak if there is something wrong like dirt, the tubing not cut squared, or the tubing not completely in etc.Regards