Re: How come hydrolics are pressurized more than air

Doug,

The selection of the type of system to transfer energy from an energy source 
(e.g. Pump) to a device that will perform work (e.g. Linear cylinder ram) is 
based upon a number of considerations: Cost, Speed of Operations, Available 
Energy, Weight, Size, Cleanliness, etc.  Part of the design criteria 
includes the properties of the fluid (air, oil, water etc.) used to transfer 
the energy. Hydraulic oil (Mineral oil or paraffin based oil) is much more 
dense than air:
		Hydraulic Oil = 57 Lb. Per cubic foot (1)
			     Air = 0.075 Lb. Per cubic foot (2)

Either fluid can be compressed to very high pressures. Since hydraulic oil 
is not as ģelasticī as air, oil is generally used for heavy-duty operations 
such as the steel industry for forging, rolling and cold forming operations. 
Air is used generally used in lighter-duty operations such as the food 
industry, medical field and other lighter duty manufacturing applications.
.  
I hope this provides some insight on the use of fluids in transferring 
energy.

Ref: 
http://www.herguth.com/toc.htm (link defunct as of 7/20/2006)

http://www.usatoday.com/weather/wdensity.htm