Although Concrete Batch Plants have a life expectancy of 35 – 40 years, a good plant maintenance schedule and using the correct lubricants is the key to plant longevity and production consistency.  If your plant gates seem to be “sticking” in the morning and loosing up through out the day, its probably due to lack of oil and possibly the wrong oil. 
To confirm that each air valve and ram is properly lubricated, confirm oil is exiting the exhaust side of each solenoid valve.  You should be able to visually see some residual oil, or feel a small amount of oil in the exhaust air.  In general, the oiler bowl should need to be re-filled once a week.
Marvel Mystery Oil should never be used on a Concrete Batch Plant.  Marvel oil is a cleaner and has a solvent that will overtime destroy the “O” rings in solenoid valves and dry out the cups in air rams.  To correct this, you will need to replace the Marvel oil with Air Tool Oil in all of the oiler bowls.  If the problem continues you will need to rebuild the solenoid valves with rebuild kits and prime the air rams by squirting a small amount of air tool oil directly into the ram inlet.  This will re-prime the ram and should take care of the ram dryness.