Spontanious identification of water and the immediate removal from hydraulic fluid

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Water in an hydraulic and lubricating oil system does not only reduce the service-life of hydraulic fluid, but also of the machining components. Investigations of different companies and institutes have clearly shown, that free water in hydraulic fluids abridges considerably the service-life of the complete system. Common damages are:

• Corrosion of metallic system parts
• Hydrolysis of the hydraulic fluid (degradation)
• Wear of bearing
• Filters block up premature (according to reaction product)
• Additive degradation in a chemical way

As a result of water ingress recognised too late, repairing costs and supply difficulties because of lost production, are possible. Is water ingress recognized, a very fast elimination of defects is necessary. The complete hydraulic fluid needs to be exchanged or it is dried in an expensive way by vacuum evaporation. With a smaller liquid volume, a cost-intensive adsorption dehydration can also be occured.

After a detailed market analysis, a new conception for water identification and removal has been developed. A demonstration system shows the function of the turbidity sensor and of the water separator (coalescer).

How can water simply be identified?
Different measuring methods and instruments are available on the market. Some recognises the water qualitatively, others quantitatively. Some analyses the dissolved water, others the not dissolved one. According to the formulation of the problem, the correct solution will be found. All systems have something in common: high purchase costs and partially additional calibration costs.

How does the new MAHLE turbidity sensor work?
A clocked light beam divides itself into two different long distances and penetrates the hydraulic fluid. Afterwards it meets two recipients. With this principle of measurement, all interference factors can be compensated e. g. light source ageing. The condition of the hydraulic fluid is valued by the operator. With a positive evaluation, it is defined as optimal and it is adopted in a fixed store of the turbidity sensor via a push-button. Further calibration measurements are not required. If water ingresses the circulation, it comes to a turbidity of the pressure fluid, moreover the light beam reduces. The datas stored are compared and therefore the electronics recognise the change and distributes a signal. The sensitivity of the turbidity sensor can be adjusted on site. At the front part of the turbidity sensor, is a G1-thread connection. The turbidity sensor can be introduced in the hydraulic circuit with this connection at the right place. It is recommendable to integrate the turbidity sensor into the return pipe or directly into the tank near to the return flow. The service-life has been designed to at least 10 years. Should the light source or an other component still fail premature, then it will be recognised and indicated from the electronics.

As not only dissolved, so emulsified water, leads to turbidity, the water solubility has to be considered depending on the temperature. In picture 3, water solubility of three hydraulic fluid groups is graphed. The water’s solubility is at the HLP very low and depending from the temperature. At HEES and HETG, unfortunately the facts are not correct. That means, that a smaller water concentration can be surely recognised only in a cold hydraulic fluid. But there are also technical questions and approaches.

What can be effected with a signal?
There is a connection plug (M 12 x 1.4 poled) with a switching outlet (200 mA) at the turbidity sensor. This signal can be used for control of different equipment and warning device. The analysis is practicable on site or/ and at a control centre. Additionally it is also possible to connect an aggregate for water separation to the turbidity sensor.

The sensor can be brought in mobile as well as in stationary systems into action. Therefore it is effected in protection type IP 65. Of course all standards specified are met, e.g. EMV-compatibility, EN 50081-2-interferience emission, EN 50082-2-interferience resistance and others.

How can water be removed?
According to VDMA-unit sheet 24568, a water content below 1.000 ppm (0.1 %) must be kept for hydraulic fluid of HE-group. There should be no free water available in HLP-group. Free water results always in turbidity, which is visually recognisable. Physically seen, a turbidity is a two-phase mixture (emulsion). There are finest water droplets in the hydraulic fluid. Because of that, it is obvious to perform a mechanical separation of the water droplets. This principle, called coalescer, was picked up and developed to a market mature product. The coalescer consists of different levels. In the first working step, the finest water droplets are collected and brought together to a larger unit. The developed, millimetre great water droplets leave the coalescer layer and meet a special hydrophobic equipped fabric. A separation of the hydraulic fluid takes place there. By sedimentation, the water reaches into the circuit. It is important for the process, that a certain differential pressure is not exceeded in the coalescer. In addition the viscosity should also be considered for an impeccable operation. Coalescer’s operation can be made fully automatic. For this, there are different possibilities of control, e.g. differential-pressure controlled volume flow with a pump or also regulation of the volume flow with a pressure limiting valve. The less emulsifying additives are available in the hydraulic fluid, the better the coalescer works. Consequence: Expensive special oils in the systems, which are often exposed by ingress of water, can be replaced by a simple inexpensive hydraulic fluid. If such a machine is equipped with a turbidity sensor, the failure is recognised immediately and a coalescer installed in the bypass-flow is connected (see picture 4). After a short period of time, the hydraulic fluid is dry again. The cause can be removed without any damages at the machine and/ or lost period of time can be caused.

Design parameters are available for hydraulic fluid groups HLP, HETG and HEES. Details must be clarified for each application.

Conclusion:
With the newly-developed turbidity sensor, an inexpensive appliance has been created in order to record the ingress of water very fast above the absorption point. In connection with the new coalescer, the ingressed water can be removed very fast and in an inexpensive way. A large number of applications of both systems are quite possible. The common use is also possible like a separate application. The system has been applied for a patent.

MAHLE Industrial Filtration has been producing high-quality industrial filters for fluid technology, dust filtration, and process technology for many years. As an innovative, reliable development partner and supplier all over the world, MAHLE Industrial Filtration is your expert partner in all areas of filtration and separation. MAHLE Industrial Filtration is an independent service area with its own engineering, production, and sales team, integrated in the MAHLE Group, and thus is backed by the strength of a worldwide market leader. The MAHLE Group is among the top 30 automotive suppliers globally and is the world market leader for combustion engine components, systems and peripherals. MAHLE employs approximately 35,000 employees in 110 production plants and eight research and development centers. In 2009, MAHLE generated sales of approximately EUR 3.9 billion.

Öhringen, 10/2010