Are You Sensing Moisture Problems? Pall's New Water Sensor Reports Dissolved Water Concentrations

Tags: water in oil, oil analysis

Did you ever wonder just how much water is in your hydraulic or lube oil? Wouldn't it be nice to have that information without sending the fluid out to a laboratory? Free water in hydraulic, lubrication, and insulating oils can impair fluid performance and adversely impact equipment effectiveness, uptime and reliability. Because concern is related to the presence of free water, equipment operators need to know when the amount of water in the fluid is approaching the saturation point so that preventative measures can be implemented before the damaging effects of water can take place.

The Pall WS03 Water Sensor allows you to obtain this information immediately in an easy to use form. The Sensor measures the temperature and relative water saturation of petroleum and synthetic fluids and fuels. By monitoring water content below the saturation level, the unit allows action to be taken prior to the formation of free water, thus preventing problems such as additive depletion, oil oxidation, corrosion, reduced lubricating film thickness, microbial growth, reduction of dielectric strength, etc.

Why Percent Saturation vs. PPM?
Most fluids can tolerate a certain degree of water contamination; but at what level is it considered excessive? The industry standard practice has been to report water in oil as percent of total volume or in PPM. In a phosphate ester based oil 200 PPM would be considered excellent. However, the same volume of water would be catastrophic in a transformer where the oil serves as an insulator. The difference between what is acceptable for one fluid and not for another relates to the particular fluid’s saturation point. Oil is saturated when it has dissolved all the water it can into its chemistry. The addition of more water leads to an emulsion or a phase separation where free water is formed in the fluid. A fluid’s saturation point is affected by a number of factors including temperature, aging, additive depletion & degradation, and cross contamination with other fluids. The saturation point (in PPM) for new oil is generally unavailable from the manufacturer and can fluctuate from lot to lot.

Because changes in fluid temperature will vary the percent saturation, a system with constant water content measured in PPM that experiences significant temperature changes creates the possibility of turning dissolved water into damaging free water. Unlike the PPM measurement that would remain constant, a percent saturation measurement will increase as the fluid temperature lowers and drop as temperature rises, making percent saturation a more practical method for reporting water content in oils. The Pall WS03 Water Sensor reports relative water level by simultaneously measuring the percent water saturation level and the temperature of fluid being tested.

Operation
The sensing element of the Water Sensor is a thin film capacitive device that changes its capacitance with the changes in the water saturation of the fluid it is submerged in. The circuitry on the sensing element converts the capacitance into a linear, amplified voltage output. Firmware in the Water Sensor box converts the voltage into percent saturation. The response of the sensor to a step change in water saturation is instantaneous, with stabilization achieved within minutes.

Results are displayed on a high visibility LED display for easy reading. As a warning of high water content, the display will flash on and off if the percent saturation is above 90%. The Pall Water Sensor contains an internal relay factory set at saturation levels of 80% (on) and 60% (off). The relay is user-settable and can be used to control an alarm, or other device. In addition, a unit with optional 4-20 milliamp outputs for the measured percent saturation and temperature is available.

With its ability to monitor water content below saturation, the Pall WS03 Water Sensor provides accurate results:
- without needing to know the fluids saturation point
- regardless of the fluids condition
- even when switching from fluid to fluid
- without requiring adjustments or recalibration

Installation & Specifications
The Sensor unit can be mounted in the side of a reservoir or in-line using a supplied 1/4" NPT fitting for pressures up to 150 psi. Bottle samples can also be evaluated. The enclosure is roughly 9" wide by 5" high by 3" deep and weighs approximately 4 pounds. It can accept input voltage from 90 to 270 volts, 50 or 60 Hz. Temperature range is 0 to 125 degrees F for the WS03 box and 0 to 185 degrees F for the probe. Standard probe cable length is 6 feet with extension cables available in 10, 20, 30, and 40-foot lengths. Water saturation is measured with accuracy within +/- 2% based on calibration per ASTM E104-85. A simple field validation process is recommended annually using a solution of table salt. Calibration is only required if validation does not yield acceptable results.

Field Experience
The best support for the use of the Water Sensor comes from the experience of a steel mill in the central United States. The unit was mounted in the main return line of their central lube system. Results were monitored for approximately one month with percent saturation readings well within acceptable levels. After about a month they noticed a sharp rise in the water content to more than 60% saturation. This prompted them to take samples from the various drip legs in the system. One drip leg showed a very high water content, which caused them to inspect the seal. Upon investigation, they found that one of the seals was beginning to wear. The seal was changed thus preventing a potentially catastrophic influx of water contamination to the system.

Conclusion
The Pall WS03 Water Sensor was designed to measure both percent water saturation and temperature in petroleum and synthetic fluids and fuels. It can be mounted in-line for continuous real-time monitoring, or can be used periodically to spot check fluids. Either way, the unit provides critical information on the presence of water contamination, thus making it a valuable tool for fluid condition monitoring.

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