How to Choose Hydraulic Fluid
Authored by Jemma Petts
There are many different types of hydraulic fluid, each with a specific purpose. Fluid is one of the most important components in any hydraulic system because it allows for smooth operation. Without fluid, your machine would not be able to function properly. Read on for more information on different types of hydraulic fluid and how to choose the right one for your machine.
What is hydraulic fluid
Hydraulic fluid is the medium by which power is transferred in hydraulic machinery. Hydraulic fluid is a type of liquid that uses pressure to move things. The fluid helps transmit and distribute force through the machine’s components to push them into action. It’s used in machines like log splitters, forestry, construction and many other specialized equipment.
3 types of hydraulic fluid
There are three basic types of hydraulic fluid: mineral oil, synthetic and water-based. Mineral oil is the most common type of hydraulic fluid. Mineral oil is used in construction, forestry and agricultural equipment because its readily available and easy to make. Synthetic oils are often used in high-performance, food grade, extreme wear resistance, fire resistance, or high temperature applications. Each type of fluid contains the same basic properties:
- They’re viscous (sticky)
- They form a seal against air or moisture so that pressure can be maintained inside the system even if it’s not being used
- Low foaming
- Acts as a heat transfer medium
- Lubricates
- Acts as sealing agent inside the system
Most common types of hydraulic oil
Mineral oil
Otherwise known as petroleum, mineral is the most common hydraulic fluid. It's an inexpensive oil made from refined crude oil with a long service life. Mineral oil has trouble performing in extreme temperatures and high pressures.
Water-based fluid
Water-based hydraulic fluid is made from water, glycol and other chemicals, including anti-corrosion to reduce rust on metal parts. Water-based fluid will freeze in cold temperatures.
Synthetic
Synthetic hydraulic fluid is made from chemically produced base fluids, allowing it to make up where mineral-based oil is lacking. Synthetic oils are used when other oils have the potential for freezing. They provide high stability and biodegradability.
Know the machine you plan on using it for
Before you decide on a type of hydraulic fluid, you should consider what kind of machine it’s going to be used in. For example, high-pressure systems require a different type of fluid than low-pressure ones. You may also need to use different types for different types of equipment.
Hydraulic fluid should not be used in shared sump applications. Shared systems that service wet brakes, transmissions, gear cases, and other components require a specific tractor fluid that contains additional additives. Anti-wear hydraulic oil is designed to operate piston, vane, and gear driven pumps. You should always consult your manufacturer’s recommendations when selecting fluid for your equipment.
Can you use different hydraulic fluid than recommended
Most machines have been designed specifically with one type of fluid in mind. Please be aware that using a fluid not recommended by your equipment manufacturer could result in equipment damage
While ISO 32, 46, and 68 all provide a similar function, they are designed to operate in different environmental conditions
- ISO 32 - Used in low temperature (winter) environments -20° to +50°F (-29° to +10°C)
- ISO 46 - Used in non-extreme ambient temperature environments +25° to +70°F (-4° to +21°C)
- ISO 68 - Used in warm ambient temperature environments. +40° to +90°F (+4° to +32°C)
Machines you may need hydraulic fluid for:
- Log splitters
- Tractors
- Excavators
- Bulldozers
- Loaders
How to choose the right hydraulic fluid
Determining the correct hydraulic oil is based on viscosity and the design of the pump. Oil viscosity measures the liquid’s resistance to flowing and different pumps will need different viscosity. You will also need to consider operating temperature and the amount of pressure being generated by your machine. Always check your owner’s manual for the viscosity requirements.
Understanding hydraulic fluids' properties and characteristics is key
There are many different types of hydraulic fluid, each with their own properties and characteristics. Your machine’s manufacturer will specify which type to use, based on its intended purpose and the type of system it has inside. If you don’t know what kind of fluid your machine uses or if you want to change it out for another type, talk with a professional first.
For most DIY or common hydraulic machines, fluid will be labeled by use at each fill point. You can find hydraulic fluid for tractors, hydraulic jacks, snow plow, as well as specific oil for anti-wear. Shopping for hydraulic fluid can be intimidating but we make it easy. If you have any questions, stop in and ask the experts at your local store – we will get your hydraulics ready for work.
