Hydraulic oil you can cook with?
Have you ever driven through a bad puddle of water only to have your wretched engine stall after gulping down a full cylinder? This is known as hydraulic lockout and is an expensive illustration of the hydraulic power transmitted by hydraulic oils.
In this commentary I will focus on hydraulic fluids rather than brake fluids, which are a very specialized subgroup.
functions and properties
The crucial function of hydraulic oils is to transmit power. On the other hand, there are other significant functions of today’s hydraulic fluids.
The following table lists the primary functions of hydraulic oil and the fluid properties that shape its ability to perform that function:
Hydraulic Performance Properties
• Low compressibility (high bulk modulus)
• Quick air release
• Low tendency to foam formation
• Low volatility
thermal performance
• Good thermal function and conductivity
sealing properties
• Appropriate viscosity and viscosity index
• Shear stability
Lubrication
• Satisfactory viscosity for film maintenance
• Low temperature fluidity
• Thermal and oxidative stability
• Hydrolytic stability / water tolerance
• Purity and filterability
• Demulsibility
• Wear reduction features
• Corrosion control
pump efficiency
• Proper viscosity to reduce internal leakage
• Higher viscosity index
special requirements
• Fire resistant
• Friction modifiers
• Radiation resistance
Environmental Impact Properties
• Low toxicity when new or decomposes
• Biodegradability
make up
Since ancient Egypt, the mode of hydraulic fluid was water. It was not until the 1920s that mineral oil began to be used. This was due to the oils inherent lubricating properties and performance at temperatures above the boiling point of water. Today, most hydraulic fluids are based on mineral base oils and, more recently, synthetic alternatives.
Today’s hydraulic oils can contain a wide range of chemical compounds, such as: mineral oils, butanol, esters (eg, phthalates, such as DEHP and adipates), polyalkylene glycols (PAGs), phosphate esters (eg, tributylphosphate), silicones, alkylated aromatic hydrocarbons, polyalphaolefins (PAO) (for example, polyisobutenes), corrosion inhibitors, etc.
For environmentally sensitive applications such as farm tractors and marine dredging (where there is the consequence of an oil spill from a ruptured oil line), biodegradable rapeseed (Canola) vegetable oil-based hydraulic oils (often blended with custom synthetic esters). ). These oils are generally available as ISO 32, ISO 46 and ISO 68 specification oils.
Other base oils are used for special applications such as fire resistance and extreme temperature applications. Some examples include: glycol, esters, organophosphorus ester, polyalphaolefin, propylene glycol, and silicone oils (for brake fluids).
aircraft hydraulic systems
As aircraft performance improved, the force required to activate the mechanical flight controls increased, and hydraulic systems were introduced to relieve pilot effort. Hydraulic power is also used to start the auxiliary power unit (APU) for automatic starting of the aircraft’s main engines. While several aircraft equipped with the M61 family of guns, take advantage of hydraulic power to drive the weapon system, allowing for reliable high rates of fire.
Below are some of the more common phosphate ester base hydraulic oils for aircraft.
• Skydrol 500B-4 (Type IV class 2)
• Skydrol LD-4 (Type IV class 1)
• Skydrol 5 (Type V)
• Skydrol PE-5 (Type V)
As with other modern oils, new synthetic hydraulic oils are blended to optimize the product for precise circumstances, such as Skydrol.
With the rising costs of crude oils, synthetic hydraulic oils are gaining more and more favor for their superior performance. While there has always been a stark price difference, unit costs for mineral and synthetic hydraulic oils are now very similar, but with synthetic hydraulic oils lasting longer than mineral equivalents, real cost savings are realized.