What are Effective Methods for Cooling Hydraulic Oil?
Most of us who work with hydraulic systems on a regular basis are well aware of the critical need for effective, efficient cooling of the hydraulic oil. Maintaining a proper oil temperature is imperative-the consequences of ignoring this factor are dramatic and often catastrophic! Elastomeric seals and hoses become hard and brittle when exposed to excessive temperatures and will begin to leak. Piston pumps and servo/proportional valves (which typically rely on tight tolerance metal-to-metal interfaces for internal moving parts) will fail due to loss of viscosity of the oil as it thins or breaks down. The hydraulic system performance will then degrade or fail completely when any of these occur.
There are several methods used for cooling of hydraulic oil in a system: oversizing of the reservoir to use the volume for cooling (the least expensive and also the least efficient option), fan and water cooled heat exchangers are also very common. While air cooling is common, it is not the most efficient means of removing heat from a system. Water-cooled systems are by far the most efficient. Temperature controlled water is circulated through the heat exchanger as hydraulic oil is also circulated, carrying heat away from the oil. The challenge comes when there is a relatively high ambient air temperature (rendering air cooling ineffective) and there is no ready source of water flow to connect to and use for cooling. Further complicating the matter, some facilities have cooling water sources from lakes or rivers, introducing the complication of pulling in water that has natural elements to it. There is a risk of harm to fish, for example, by being suctioned into a line that feeds a cooling system. Also, debris and even mollusks introduce a maintenance element to this type of water cooling system that is at the very least cumbersome and can create performance issues.
An often overlooked avenue, especially effective for larger hydraulic systems, is to use a chiller system for the cooling water. This solution provides a self-contained water source that circulates the cooling water through a standard water-cooled heat exchanger, then brings it back into a storage reservoir and refrigerates it for reuse. This is certainly not an inexpensive solution, but in the right circumstances, it is by far the most efficient way to get the job done. Chillers come in various sizes and configurations and, when properly sized can make for a very efficient, healthy and long-lasting hydraulic system.
If this method is chosen, it is critical to work with the system designer to select both the chiller and the heat exchanger together. The proper sizing of these components relative to each other is extremely important to ensure a healthy, long-lasting hydraulic system.