Thanks for the explanation @superkid. I was also thinking that in the first place but just need clarification.

thanks again.

Is it possible to use pneumatic valves such as pneumatic solenoid valves in hydraulic systems? I have check and they seem to have same function.

Yes, as long as you are using the same working pressure and functions. But for sure it will not last long. The valves were designed specifically for its working medium, gas or liquid. This is because they differ a lot in their properties. So difinitely, it will damage the valve for a short period (not very economical).
Therefore, it is possible but practically speaking do not use that alternative of swapping pneumatic valves for hydraulics or vice versa, it will cost you your job.