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Hydraulic systems in the 1960s and 70s had the most basic monitoring systems — if any at all. If you were lucky, a fluid level switch might warn you if fluid level in the reservoir dropped dangerously low. Or maybe a temperature switch would signal if fluid temperature began to exceed a predetermined maximum temperature. Plus, many systems only had simple screens for their filtration system. Most condition monitoring was conducted using the senses of machine operators. A noise or vibration that wasn’t there yesterday usually served as a warning that a problem had arisen — and it was probably too late to correct.
We’ve learned a lot since those years. Understanding the cost to repair systems and the higher cost of lost productivity from downtime has proven the value of condition monitoring. Monitoring key parameters of a system not only can provide advance warning of an impending failure, but can also help prevent or delay a failure from occurring. The more critical a machine’s operation, the more important it is to monitor its operation.
Because of the amount of work they do, most large machines are considered critical to an operation. Time is money, so the bigger the machine, the more it costs when it is not operating. For example, large hydraulic presses and mining excavators fall into this category. Their operation is critical, so it makes sense to regularly assess the condition of their hydraulic fluid rather than just change the filters at regular intervals. These machines contain hundreds or thousands of gallons of hydraulic fluid. And even with today’s high prices, the cost of replacing their hydraulic fluid can pale in comparison to the cost of downtime.
Automated oil condition analysis using sensors working online in the hydraulic system can offer many benefits and new options. Furthermore, continuous oil control allows greater flexibility when scheduling maintenance intervals, and it is easy to adapt them on the basis of actual oil levels.
Another interesting aspect is the fact that oil condition sensors enable continuous recording and documentation with an LED status indicator of operating data, such as correctly performed oil changes and maintenance intervals in accordance with guidelines. This is an aspect that many companies are finding more and more valuable, not only from the increase in leasing contracts, but also in reducing the number of claims between the lessee and the lessor.
To aid in the monitoring of several key fluid parameters, Argo-Hytos, Bowling Green, Ohio, introduced its LubCos H2O+ oil condition sensor. It contains a humidity transducer combined with other sensors to determine the relative permittivity, oil conductivity, and temperature of hydraulic fluid. It can convert the key oil data accumulated at various temperatures to a reference temperature to improve comparability. It can also display signal trends in relation to time.
The different parameters can be read out through a serial interface or from a 4- to 20-mA output. In addition, the oil condition can be optically displayed to the operator directly at the machine via an integrated LED bar display. An integrated data storage unit can record data over a period of up to 6 months.
A sequence of LubCos H2O+ measurements were taken from a hydraulic system over several weeks. During this period the oil was subjected to a characteristic stress profile with alternating pressures and temperatures. The advancing aging process of the oil was clearly shown by the successive increase of relative permittivity and conductivity. Readings taken by the sensor matched both the values of the relative permittivity and the conductivity measured offline in the laboratory, as well as the information gi ven by the neutralization number. In addition to revealing the aging process, the example also clearly showed when fresh oil was added after 21 days, and the complete oil change after 28 days. The water content was measured at the same time. A low degree of water penetration was first noted after 4 days.
However, the water content subsided relatively quickly due to the high temperatures in the system. After 28 days, the system showed that relative humidity had increased and was fluctuating. There was even free water existing at the end of the measurement period, and the sensor showed 100% relative humidity.
This application example shows how various changes in the condition of a hydraulic system, such as oil change, oil replenishment, oil aging, or water penetration, can all be effectively recognized by the LubCos H2O+.
To learn more about the LubCos H2O+, call Argo-Hytos at (419) 353-6070, or visit www.argo-hytos.com