Although not quite as advanced as the Transformer ‘Megatron’, mechanised hydraulic systems are nonetheless just as strong. Effectively deployed, efficiently maintained, this physical strength translates into profit.

With the globalized world rallying to the clarion call to go ‘green’ and, with unrelenting pressure, the continuing need to become even more competitive a constant, productivity efficiencies are all the more important because, in terms of profit, this translates into doing more in less time and at an ongoing customer satisfying quality.

Hydraulics, one of the most useful human inventions, is a means to harness the tenfold mechanical energy that can be derived from fluid in motion. But, like everything in business, it has to be properly managed and maintained.

Hydraulic systems are precision machined and operate under high pressure. Keeping the internal workings of these systems in pristine condition is crucial to the efficient and cost effective (profitable) operation of the equipment.

In a nutshell, you cannot manage want you do not measure. And, if you don’t measure it, it will catch you off guard at the most inconvenient of times. Murphy’s Law!

Oil, the big issue

There are many variables that determine the rate at which hydraulic oil degrades. However, original equipment manufacturers (OEMs), not wanting to complicate matters, simplify the decision by saying after ‘x’ hours change the oil – without any reference to the actual condition of the oil.

There are only two conditions that necessitate changing hydraulic oil – degradation of the oil or the depletion of an additive. Given the costs involved, changing oil unnecessarily will be an expensive mistake. If the hydraulic system has a large reservoir, new oil costs could be significant. In addition, equipment downtime carries with it a cost, which could take many forms i.e. additional labour, temporary equipment hire, penalties for missed delivery dates etc.

At the same time you cannot just assume your hydraulic oil does not need changing.  Poor oil quality will damage your system. Even so, if it is a minor water contamination problem, it does not mean you need to change your oil. Water can be filtered out.

Nonetheless, all being said, regular monitoring of hydraulic fluids, to measure operating quality, so that maximum efficiency is maintained, is a good idea and a recommended practice. The ‘particle count’ test detects potential wear-causing dirt and contaminants early enough to take action. Water in oil is the biggest concern because it accelerates acid formation, increases oxidation and reduces lubricity, all of which leads to system failure. Water content (%) using the Karl Fischer test provides a precise measurement of how much water is present in the hydraulic fluid.

Filters, the next priority

A similar situation applies to hydraulic filters. Changing filters too early (unnecessary expenditure) or too late (with a clogged filter forcing the bypass valve to open, raising particle levels, which cause physical damage) carries similar cost implications. Tracking the results of particle count tests serves as an indicator but the best solution is to measure pressure and/or the flow rate immediately after a filter. This can be achieved by using a differential pressure gauge or a transducer. Any drop in pressure would indicate a problem.

Where filters are fitted is crucial. Locations that must be avoided are at the pump inlet, and at the piston pump and motor case drain lines.

Not having a filter at the pump inlet may seem illogical, given that the pump draws its oil from a reservoir. Even so, the reservoir should not become a trash can. But, the more important consideration is, from a pump efficiency point of view, having a clogging or clogged filter at the pump inlet will not fill the pump chambers with freely flowing oil during every intake.  Research shows that a restricted intake reduces the life of a gear pump by as much as 56%. It’s worse still for vane and piston pumps that are less able to withstand the vacuum-induced forces created by a restricted intake. Hydraulic pumps are not designed to ‘suck’. Filters fitted to drain lines generate a different set of problems but have the same result – reduced service life.

Running too hot, or cold

Using the right oil for the prevailing climate in which the hydraulic equipment is used is critical. This refers specifically to oil viscosity, which affects both machine performance and service life.  Oil will not flow properly if the viscosity is too high for the climate the machine operates in, especially on the hotter days. If the viscosity is higher than ideal, more power is lost to fluid friction. If lower than ideal, more power is lost to mechanical friction and internal leakage.

Using the wrong viscosity oil not only results in lubrication damage, it will also lead to the premature failure of major components and increase the consumption of diesel or electricity, whichever is the energy source. As such, the importance of lubrication cannot be overstated.

Viscosity therefore defines the maximum and minimum temperatures, or what is commonly referred to as the temperature operating window (TOW), in which the machine can operate safely and productively. It is advisable to check that your machine’s actual temperature operating window falls within the temperature operating window of the oil in the machine, especially in imported machines.

The rule then is simple. An increase in oil temperature will result in a decrease in viscosity, which, if your system gets too hot, lubrication will be inadequate.

It’s important to bear in mind that a vane pump requires a higher minimum viscosity than a piston pump, another reason why a system’s components influence the system’s safe maximum operating temperature.

Hopefully your hydraulic system includes a vane pump. If so, the minimum viscosity should be 25 centistokes (cSt or mm²/s). For mineral oils with a viscosity index of around 100, this equates to a maximum allowable operating temperature of 35^oC if you are using ISO VG22 oil or 65^oC for ISO VG68. Operating temperatures above 82^oC damage most seal and hose compounds. This obviously accelerates the degradation of the oil and is something to be avoided.

Cause and effect

Some say that it is how you finish a race that is important. However, how you start, and everything that goes into starting is all important too. Fundamental to starting and finishing is the knowledge of what to do and remembering to do it. Operator education and training in hydraulics and the equipment being used is vital. For example, you would not start your car without any oil in the crankcase and you would not take off in a plane without doing a few checks first.  Starting off without everything that is needed in place and ready to go will not see you finishing the race. The same can be said of hydraulic equipment. Check and monitor the fundamentals of your system as recommended by the OEM and as discussed in this article at start up – every time. Serious problems can and will be prevented by being proactive, and time and money will be saved.

References:

Brendan Casey, Six costly mistakes most hydraulics users make, www.hydraulic supermarket.com