How To Select And Use The Best Hydraulic Oil

Hydraulic oil is the medium through which power is transferred in a hydraulic system or unit. It also serves as a lubricant. This dual ability of hydraulic oil makes it the most important and integral part of the hydraulic system. This article seeks to enlighten you on what to consider when buying and using hydraulic oil.

How to select the best hydraulic oil

In selecting hydraulic oil, the type and capacity of hydraulic pump, operating temperature, and pressure of the hydraulic system in which the oil will be used must be considered. The base oil type, overall lubricant quality, and performance properties must be considered. However, there are two primary considerations in selecting the best hydraulic oil suited for you- the viscosity grade and the hydraulic oil type.

Pumps and Viscosity Requirements

Pump design types and their required viscosity grade is the first lubricant selection criteria to consider. Pump design types are three: Vane, Piston, and Gear.

Vane Pumps: The Vane pump has rotors with slots mounted on a rotating shaft spinning eccentrically to a cam ring. As the rotors and vanes spin within the cam ring, the friction between the cam, rotors and vanes causes wear making it more expensive to maintain. But on the flip side, they maintain a steady flow while in operation. This where the hydraulic oil as a lubricant comes in. Vane pumps require a viscosity range of 14 to 160 centistokes (CST) at operating temperatures.

Piston: Piston pumps are designed for higher durability over the vane pump. It is also more widely used with operating pressures going as high as 6,000 psi. The viscosity range for piston pumps is 10 to 160 CST at operating temperatures.

Gear: gear pumps expel fluid trapped within the gear housing and the meshed gear teeth; they can cope with a sizable amount of contamination but are the most inefficient of the three gear types. The two types of gear pumps are; internal and external.

Internal gear pumps require vast range hydraulic viscosity choices which can go as high as 2,200cSt. It operates very quietly but with high efficiency and can produce pressure of up to 3,000-3,500 psi. On the flip side, external gear pumps are less expensive, easy to maintain and repair. They are relatively less efficient but boast of a steady flow. External gear pumps can work up pressures ranging from 3,000 to 3,500 psi and require hydraulic fluids with a viscosity range of 300cSt.

Application Requirements

The performance and durability of a hydraulic system or unit are highly dependent on the quality selection of hydraulic oil. The function of the machine being powered by the hydraulic system should be assessed along with its viscosity and operation to determine what grade of hydraulic should be used.  For instance, the hydraulic oil for a constantly used bulldozer with leaky sump or hydraulic system shouldn’t be the most expensive type because of the frequent replenishment. But a hydraulic system powering machines that perform irregular but sensitive functions, require high-quality premium products. In this case, you may want to use a highly refined petroleum-based fluid an AW additive package or better still, a fully synthetic fluid.

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How to use hydraulic oil to improve the performance of your vehicle

A balanced knowledge in the use of hydraulic oil will improve the performance of your engine. You need to know some tips in the everyday use of hydraulic oil that will give optimal results obtainable in automobile service centers.

Changing the oil

To determine if the hydraulic oil is due for a change, an analysis of the oil must be carried out. Don’t just rely on hours of service, it can be misleading. Only a degradation of base oil or depletion of the additive packages should warrant a change of oil. Continued use of hydraulic oil with a degraded base oil or depleted additive package can cause damages in the hydraulic system and shorten the life span of the same. Also changing the oil that isn’t due is a waste of resources and effort.

Changing the filters 

The key to changing oil filters is to monitor the pressure drop across the filter closely. This will enable the user to determine when the dirt or debris holding capacity is reached. This is very important because if the capacity is hit and the user does not change it, the bypass valve will open and debris will get into the hydraulic system. If this happens, service life will be reduced gradually. Like the operation of an oil change, oil filters shouldn’t be changed before it is due to avoid waste of money, time and effort. Don’t change them based on hours used according to schedule just keep monitoring the flow rate through the filter.

Avoid overly high temperatures 

Hydraulic oil viscosity reduces with an increase in temperature. If the operating temperature in a hydraulic system becomes too high, the oil becomes less viscous. A drop in the viscosity of the oil below the acceptable level of that system will make the lubricating function of that oil impotent. This will lead to unacceptable levels of friction and stalling. Eventually, service life is attacked. This is one of the quickest ways to destroy hydraulic components, hoses, and seals.

Using the right oil

Hydraulic oil is not just a lubricant but a medium through which power is transmitted in the hydraulic system or unit. For this purpose, the viscosity property of the hydraulic oil is vital to the performance and service life of the engine.

Hydraulic oil viscosity must be in tandem with the climate in which the machine is operating. Preferably, hydraulic oils with high viscosity should be ideal for engines or machines operating in tropical climates because of the hot nature of such climates. This will enable the oil to perform its function of lubrication even at high machine temperatures. However, if the viscosity of the oil is too low for the prevailing climate, the lubrication function of the oil will become impotent- it won’t be able to perform its lubrication function- during the hot days of the year.

Using the wrong viscosity oil will result in damages due to lubrication and premature failure of major components in the hydraulic system. It also increases the consumption of power is it diesel or electricity which will eventually cost more to rectify.


Why do my hydraulic hoses keep bursting?

Several reasons may include a wrong application, corrosion of the ferrules, and high-pressure pulsation of the hydraulic installation, incorrect bend radius of the installed hose and expired hoses.

How hot should my hydraulic system be during operation?

You should have control over this. This is because the hydraulic oil used is a major determinant of the temperature of the system. Heat in a system is caused majorly by friction among moving parts which is intercepted by the oil and so the friction is reduced per time by the viscosity property of the oil. Most hydraulic systems use mineral-based hydraulic oil, depending on its centistokes viscosity; you can determine how hot the hydraulic system should be during operation from the oil manufacturer’s datasheet. In any case, as a guide, you have to consider the room temperature and the work cycle of your hydraulic system. Also, refer to the designer’s original allowance for heat transference.

Is hydraulic oil safe on my skin?

Just take the safety precaution of putting on protective wear or clothing till you can confirm from information provided by the oil supplier or manufacturer.

How can I troubleshoot or test my hydraulic system for faults?

The first thing to do is to break the system into the various components namely:

  • The prime mover (engine, electric motor, etc)
  • Hydraulic pump pressure & flow
  • Control gear
  • Relief valve system pressure
  • Motor or cylinder

It will be easier to troubleshoot on a component by component basis. Hydraulic systems usually come with manuals that show the user how to dismantle components for preliminary troubleshooting.

By now you should have a pretty good grasp on what to consider when buying hydraulic oils and using them.

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