* They generally work on oil and base their whole functioning on this liquid. Hence if there is a shortage or if this is replaced with some other automotive lubricant, it might hamper the working of the system.
* Under high pressures, there are chances for these valves to burst causing serious problems to people working with them.
* The sticky oily lubricant is little hard to handle and there are chances of constant leakage. When there are leakages the chances of valves catching fire is also high.