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Selecting the Right Fluid for a Hydraulic Pump

As a multi-functioning and essential component to any hydraulic system, hydraulic fluid is responsible for lubricating components such as transmissions, and also gets involved in heat transfer and wear related conveyance.

This makes choosing the correct fluid for a hydraulic system a critical decision as it could make the difference between a finely tuned system and a costly failure. A number of factors should be taken into account when choosing the right fluid for your system; these include fluid viscosity, dependent on the temperatures the system will be running at as well as taking other operating parameters into account, system requirements and environmental conditions and regulations.

Key points to take into account when selecting fluids:

  • Fluids should adhere to the hydraulic units suggested fluid specification requirements
  • Correct fluid contamination protocols should be identified which help to ensure the unit maintains a long operational life
  • Always check new hydraulic fluid for cleanliness as even new fluid can contain harmful particulate
  • Be sure to transfer the fluid into a system reservoir using a filter cart
  • If any components were to fail completely, the hydraulic system should be totally flushed and new fluid added to avoid any loose particles causing damage
  • Make sure you don’t at any time mix fluids, especially those with different viscosities as this can cause gelation, filter blockage and other potentially harmful symptoms

Fluid viscosity explained
Fluid viscosity can vary from application to application with environmental and climate factors playing a large part in this.

The lower the fluid viscosity, the thinner the fluid thickness. If this level drops too much there is the chance of metal on metal contact between componentry which is never a good sign.

Low viscosity fluid can also reduce the volumetric efficiency of hydraulic pumps and other components as it increases the chances of leakage occurring.

Effects of using the wrong hydraulic fluid
If a mistake is made and the wrong type of fluid is added to the system it is good to know the typical warning signs to look out for. For example, an oil with any variation of a set parameter can cause to damage to areas such as rubber seals, gaskets etc.

Just one of these damaged areas could put the system into shutdown and cause irreversible component damage, so it is vital that the correct oil specifications are used.

Selecting the correct fluid
After you have read up on your systems specs and the level of lubrication it requires, you can look at fluids that have the following properties which help protect system components:

·   Corrosion and rust inhibition – most hydraulic fluids on sale today have anti-corrosion qualities added and these come in the form of a thin layer of film which settles on metal surfaces, protecting them.

·  Hydrolytic stability – This is basically the chemical degradation of fluid over time due to the effects of water. This is mainly due to the additives in the fluid which react with the water. Zinc-based additives are especially bad for this and any components made from copper can react especially badly.

·  Materials compatibility – Because of the large amount of components in a hydraulic system, most of which are made from different materials such as hoses, gaskets and seals; it is imperative that the fluid used has no adverse reactions to these materials and thus ensures system reliability and performance.


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