Preventive Maintenance/Industry 4.0 Keeping Information Flowing for Preventive Maintenance of Fluid Processes

Author / Editor: Gerd R. Biller* / Dominik Stephan

From process understanding to preventive maintenance: Fluid technology in the Industry 4.0 age — Digitalisation and connectivity open new ways of understanding for fluid processes — but with that come new challenges for those involved. Only if we manage to shift our attention from alarm based punctual attention to constant information, we can create additional value. The chance is there …

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Die digitale Vernetzung bringt der Prozessindustrie viele Chancen.
Die digitale Vernetzung bringt der Prozessindustrie viele Chancen.
(Bild: © krunja -

These days, words like digitalisation and Industry 4.0 are buzzing everywhere. On closer inspection, these terms are interpreted vaguely and very differently. One explanation is networking production facilities to ensure trouble-free processes. As this includes hydraulics and lubricating systems, this article is intended to provide an example of what information about liquid level and temperature may look like in the future.

A look at the common practice to date provides a complex picture: Both with respect to liquid level and temperature monitoring you can find anything from sight glass and primitive bimetallic thermometers to bidirectional continuous communication lines via IO-Link. Trying to take a static look at the equipment for level measurement, shows: Dry-run protection for pumps is still the most popular monitoring function. Although the number of continuous monitoring sensors is increasing, it's still estimated to be in the bottom quarter.

In temperature monitoring, on the other hand, there is a decline in simple limit switches in favour of continuous signals. This shows temperature control is clearly prioritised over level monitoring, which is no surprise in temperature-sensitive elements such as hydraulics and lubricants. A further look at available equipment shows a growing percentage of combination devices, but still a large variety of plug versions and parallel wiring.

Information Becomes King in Data Driven Industry 4.0

Lacking this information the following should be considered: Going with the slogans according to which future components will all need to communicate, be connected, etc., liquid level and temperature can consequently only be monitored with continuous signals. In and of itself this is not exactly new, considering all oil-bearing systems have always carried the risk of damage caused by leaks, hence selective monitoring has never been adequate for the risk.

Based on the newly arising background of production networked according to Industry 4.0, however, this risk takes second place and information on the availability of a hydraulic/lubrication system becomes the focus. A networked production can only work if all provided data indicate the production batch can be achieved within the desired timeframe. Pump protection is no longer the primary and sole monitoring objective but will rather become a by-product of continuously signalling.

Preventive Maintenance: Monitoring Hydraulic Fluids

Intelligent correlation of the level signal not only shows that a system is ready for operation, but already detects early deviations in the sense of predictive availability analysis. As a side effect, in larger facilities, static analysis of the level curves can be used to generate or detect consumption balances or wear hotspots, thus meet potential requirements for greater environmental safety. Apart from continuously signalling that there is oil, continuously reporting its current temperature is just as mandatory.

As a result of the oil's viscosity changing based on the temperature, this information becomes vital. But it also provides additional data essential to the availability of the production system: Even a subtle temperature change can indicate the cooling system is no longer working efficiently. This can be just as much due to the cooler matrix becoming dirtier, as the coolant starting to become low or inadequate heat exchanger capacity. A relatively rapid temperature increase, in turn can indicate acute wear.

Thorough documentation of the temperature trend can also be used as a parameter to assess the remaining life of the oil. Unlike the liquid level, where visualising the level normally is not directly relevant to safety, showing the current temperature on site can aid in protecting the operators.

Connected Senors Drive Maintenance 4.0

An area where the benefits of modern communication technology become particularly evident is the connectivity of sensors. Transmitting real-time, continuous liquid level information requires less hardware than traditional switching signals. This means smaller plug connections, cables with fewer wires, and bottom line less costs. Admittedly, generating continuous signals is slightly more expensive than simple binary switching elements, however the differences are marginal, and looking at the total expense may even be positive.

This may actually be another core in the attempt to develop a sensible path to the future: With respect to the desired connectivity, isn't it important to primarily look at the total costs of the required information instead of the purchase prices of the individual components?

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Heretically speaking, one could devise that although the purchase may have been a bargain, a lot of money was thrown out on cables and installation. Just as people came to realize a long time ago that mechanics and electronics are an inextricable pair, the focus must now be shifted to the benefit generated by this mechatronic component.

Is Preventive Maintenance a Matter of Signals?

However, there is one more very crucial factor which speaks for using only continuous signals: One could easily derive from the static distribution of switching points that every oil tank is manufactured to very specific dimensions and the switching points would therefore never be the same. But is this so? Of course not. For competitive reasons alone, OEMs are forced to rationalise and standardise, and innovative suppliers have already incorporated the requirements of Industry 4.0.

But why isn't the potential to standardise continuous signals used more often, at least within the company? After all, with continuous signals it truly does not matter how far in the tank the liquid level sensor is! The relevant signals can be tailored to the system requirements in the simplest manner. Umpteen versions per company can be condensed into maybe three or four, which in turn simplify the entire supply chain. With the appropriate setup this could even be reasonably implemented on multifunctional devices and contribute to optimising the costs of signals compatible with Industry 4.0.

Technology Needed for Fluid Handling 4.0

The inherent necessities of Industry 4.0 for extensive process networking also require equipment compatible with digitalisation in fluid technology. The focus shifts to the constantly available information — not the alarm in the event of a fault. Digitalisation further opens an approach to the information required to calculate availability. And the sensor generating the information and transmitting it to the point of use is equal and as a whole constitute the cost of the required information.

Generating the information in units with a high functional density holds further, substantial rationalisation potential with respect to hardware. We should point out that providing continuous information is the best prerequisite for implementing comprehensive maintenance systems: Smart maintenance under the premise of predictive service thrives on the constant availability of “big data”.

* * The author works as a freelance consultant.