Why should hydraulic cherry picker be air and waterproof

In the design and manufacture of hydraulic cherry picker, why should it be airproof and waterproof, the reasons are as follow：

Under normal temperature and pressure the hydraulic oil volume ratio is about 6 to 8%，when the air pressure is reduced, the air would be escaped from the oil, the collapse of bubble will create noise caused by cavitation of hydraulic components.
If too much air get into the oil, it will make the cavitation phenomenon intensified, hydraulic oil will increase compression becomes unstable, the work safety and efficiency are reduced, the hydraulic lifting platform would experience slow and delayed response and other consequences. And the air in hydraulic oil will make it oxidized and accelerate oil deterioration.

There are other reasons for hydraulic cherry picker to avoid air and water get into the system:
If oil contains excessive moisture, the hydraulic components will rust; oil emulsifying and deterioration; lubricant film strength is reduced; it will also speed mechanical wear. Therefore, more work should be done to preventing water intrusion during maintenance, like pay attention to tighten the lid when storage drums are done using, the best way is to place it upside down.
High moisture oil should be filtered several times, each filter work should be replaced with a new dry filter paper. If you don’t own the special detection equipment, try the following method: drop the oil onto a hot iron plate, if no steam coming out and it immediately burns, then it’s good to go.