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Maintaining the hydraulic fluid and hydraulic system

If you want a hydraulic system that works well and reliably, good order is key. Thankfully, keeping your hydraulic system in good condition doesn’t have to take a lot of time or effort. Something as simple as keeping it clean pays for itself very quickly.

Hydraulic systems are sensitive to contamination in the shape of water and particles, for example. You may think that large, well-dimensioned hydraulic systems should be able to take a lot – and indeed that’s true when it comes to load and weight – but small particles and other contaminants can cause all kinds of problems. So cleanliness is absolutely crucial when it comes to a smoothly functioning hydraulic system.

Even small amounts of impurities can cause wear on the system, both mechanically and chemically. Not only that, but the hydraulic fluid can age far more quickly as well. Changes in pressure and temperature can also cause problems. That’s why it pays to continuously maintain your hydraulic system and make sure it’s always as clean as possible.

Maintenance - how to

Water can often get into the hydraulic system in the shape of condensation, especially if there are temperature variations. However, water reduces the hydraulic fluid’s lubrication properties. There is also a risk of corrosion and lower hydrolytic stability. If you suspect that there may be water in the hydraulic fluid reservoir, it may therefore be worth trying to drain it. Since water generally settles underneath the oil, many reservoirs have a drainage plug in the bottom where you can drain off any water. In certain cases though, you may need to change the oil instead.

To avoid problems with water/condensation:

  • If you suspect water – try draining the water from the oil reservoir.
  • Check the oil – if it looks milky, this often means there’s water in it.
  • Ideally, fit the system with a respiratory filter with a desiccant cartridge to prevent condensation.
  • Never pressure-wash sensitive parts in a hydraulic system.

It is equally important to keep dirt and particles out of the hydraulic system, since they can quickly increase the risk of wear and operational stoppages. Always handle hydraulic fluid as cleanly as possible to help prevent costly repairs. For example, always use a clean container when topping up with hydraulic fluid. Also, make sure that the area around the fluid drum and the refill hole on the hydraulic system are completely clean.

Since all hydraulic systems contain some amount of particles (they could come from inside, outside or be generated by wear in the system), oil filters are used to continuously filter the system during operation, just as in a car engine. Breather filters are also often used, which not only combat condensation but also help to keep dust particles etc. out. Remember that filter maintenance is essential, i.e. checking the filters and replacing them as recommended. Oil analyses are another means of keeping an eye on the hydraulic fluid’s condition; these reveal whether the oil is clean and is working as it should, or if it’s time to change it. Contact your lubricant supplier for assistance with oil analyses.  

To keep dirt and particles out:

  • Always think cleanliness when refilling and handling hydraulic fluid.
  • Use clean containers when topping up.
  • Ideally, use a filter when topping up.
  • Clean the machine’s refill points carefully.
  • Also remember cleanliness when changing hoses or repairing the hydraulic system.
  • Keep an eye on the hydraulic system’s filters and make sure they’re in good condition.

Pressure changes in a hydraulic system can give rise to free air bubbles (also called ‘entrained air’) and reduce operational reliability. In low pressures, these air bubbles can lead to cavitation and the diesel effect, and can spoil the hydraulic fluid. Pressure drops in the hydraulic system can also generate heat, which reduces the life of the fluid. Low pressure can arise if the oil is of too high viscosity, if the pump suction pipe is under-dimensioned, or if the pump is too high up in relation to the hydraulic reservoir.

To avoid changes in pressure and temperature:

  • Seal the suction pipe, gaskets and couplings, etc.
  • Check that the hydraulic fluid level in the reservoir is not too low.
  • Check the reservoir’s position in relation to the pump.
  • Don’t use a thicker oil than necessary.
  • Ensure the suction pipe is correctly dimensioned.
  • Check the overflow valve to make sure it is not left open.
  • Check the hydraulic fluid and filters to assure the system’s status and quality.

Just as water can cause problems in hydraulic systems, residues from degreasing, for example, can also cause major complications. Degreasers are emulsifiable, and even very small amounts can disrupt the hydraulic fluid’s ability to separate water.

When cleaning hydraulic systems and their components:

  • If possible, avoid using degreaser. If necessary, use degreaser cautiously – rinse and wipe carefully to ensure that no residues remain.
  • Never pressure-wash sensitive parts in a hydraulic system.

There is much to be gained by storing and handling hydraulic fluids in the right way. Putting a bit of thought into it beforehand is a simple way of reducing the risk of contaminants and operational stoppages, while also extending the life of the oil, as well as your machinery.

To store and handle hydraulic fluid correctly:

  • Store in a dry place under cover, ideally indoors where temperature variations are minimal.
  • Store drums lying down, sealed with a plug or tap below the fluid level.
  • Do not store drums directly on the floor or ground.
  • Store drums in as clean a place as possible – and clean them as required.
  • Handle drums carefully to avoid dents and the resultant flaking.
  • Clean the pack before opening – and always reseal an opened pack carefully.
  • Label drums clearly so as not to risk confusing different hydraulic fluids; also label containers used to handle the fluids.
  • Consider fire safety when storing! Grinding dust, welding residues and so on can contaminate or ignite the hydraulic fluid.

Did you know that elevated temperature affects an oil’s life span?

A mineral-based hydraulic oil that’s correctly maintained – and works at a maximum temperature of 40 degrees Celsius – can have a useful life of around 20 years. The useful life is halved for every ten degrees the temperature in the system increases.  So there is much to be gained by keeping the temperature down. This is most easily done by regulating the cooling with a thermostat, but also by ensuring that the air or water cooling system is clean and working properly. 

Did you know that the diesel effect can ruin hydraulic oil?

Low pressure in a system can cause what’s known as a diesel effect and ruin the oil. If the pressure is low, gas bubbles can form in the oil. In the diesel effect, these bubbles then ignite and cause a micro-combustion, forming nitrogen oxides. Over time this darkens the oil, it starts to smell acrid and perform worse. Low pressure can arise if the oil is of too high viscosity, if the hydraulic pump suction pipe is under-dimensioned, or if the pump is too high up in relation to the hydraulic reservoir.

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