Selecting a hydraulic fluid with an optimum balance of cost and performance can be a difficult challenge.  It is relatively simple to identify a fluid that has a low price per gallon, but will it meet the OEM’s performance guidelines, will it work at the temperature extremes in your unique system, and will it minimize your maintenance costs?  How can you find meaningful answers to these questions?

A good starting point is proper fluid viscosity selection, which is a critical factor in hydraulic system performance.  The right fluid must transmit power and lubricate moving parts over the entire operating temperature range.  This requires the fluid to be thin enough to flow at cold start-up temperatures, and thick enough to maintain a protective lubricating film in the pump at peak operating temperatures. OEM’s have designed their equipment to operate with fluids having specific viscosity profiles.  A system operating with fluid that is too thick or too thin will experience sluggish response or failure.

Monograde oils are typically the low cost option when only considering the purchase price per unit volume.  Monograde oils are a good choice for systems where mild operating conditions lead to only small variations in oil temperature.  Narrow temperature operating windows are desirable, as oil viscosity will change very little and the system can operate very efficiently.  MEHF can offer the user a much wider temperature operating window (TOW), which is often required in outdoor operations or in hard working systems where the fluid absorbs and holds heat.  A typical hydraulic pump converts about 20% of its input horsepower into heat, therefore most fluids run at elevated temperatures.  There are many system design factors that determine if the fluid can properly exchange heat to maintain optimum viscosity, with other factors such as air release, foaming, water absorption and filtration playing a role as well.  A good system is designed with these considerations in mind, but aggressive operating conditions can sometimes compromise a good design.  High or low ambient air temperatures present a tough challenge, as well as demanding workloads that stress system design capabilities. 

A variety of references have been assembled which address these questions.

• Performance Details – information from industry experts
• Glossary – terms used in the industry and this website
• Conferences/Events – places to go for the latest information and training
• Industry Publications – articles from trade journals and conference papers