Protection against electrostatic discharges

At first sight only little has changed in the design of hydraulic filters within the last few years. Is this impression deceptive?

Indeed, one might get the impression that with the standard products only little has changed. However, this exterior impression is misleading because if you take a closer look it can be seen that the “interior” values have changed a lot.
The important parameters are the dirt holding capacity, the filter fineness and the pressure loss. In case that a filter element with the fineness 10 µm(c) had a specific dirt holding capacity of approx. 6 mg/cm2 in the year 2000, this capacity has been increased by more than 130 % to approx. 14 mg/cm2. At the same time the pressure loss has been reduced by approx. 50 %.
The customer benefits through this increased performance are - with filters of the same size - longer filter change intervals, improved oil cleanliness and higher nominal flow rates or - with equal filter change intervals - the possibility to use smaller and therefore more inexpensive filters. This protects the environment and the resources.

What are the characteristics of a good hydraulic filter?

Filter elements are complex hydraulic components not showing from the outside what they are capable to achieve. In addition to the afore mentioned parameters dirt holding capacity, filter fineness and pressure loss, also flow fatigue strength, differential pressure stability and resistance against all common hydraulic media play an important role.
The filtration efficiency of a filter element, characterized by the filter fineness, is essential for the oil cleanliness in the system over the entire service life.
The flow fatigue strength of the filter material ensures the required oil cleanliness also with changing volume flow.
Long filter change intervals are realized through a high dirt holding capacity in case that the flow fatigue strength and the material resistance are sufficient.
An excellent differential pressure stability guarantees intact and functioning filter elements also with frequent cold starts, stressing the material due to the low viscosity of the hydraulic oil.
Replica filter elements are – regarding the dimensions - almost an exact copy of the original filter element. The filter performances however differ considerably from the performances of the original filter elements what is impossible to see from the outside. Only in the laboratory at suitable test benches and by means of standardized tests, the differences between original and replica filter elements can be visualized.

Which demands do users nowadays dictate in the performance specifications of a filter manufacturer?

The customer requirements are varied. However, the trend is clearly going to longer filter change intervals and lower pressure loss as well as to an increased media resistance as e.g. the compatibility with biodegradable hydraulic oils.
Special requirements require special solutions e.g. filter elements for power split transmissions with an extreme flow fatigue strength, water absorbing elements in case of problems with water in the oil or electrically conductive filter elements when using oil without any or low conductivity.
For a few years now we have been observing another trend, away from standard filters, towards individual, customized filters.  By a clever functional integration into the filters or by system integration of the filters e.g. hydraulic tanks, a barrier is created, complicating the replica due to very high technical efforts or preventing it respectively due to proprietary rights. This ensures that always original spare filters are used and the required oil cleanliness is achieved over the entire service life. Only thus it is possible to extent warranties, to ensure the turnover within the After Sales and to improve customer retention.

In the recent past, new hydraulic oils have increasingly been used. In this context we keep experiencing from special problems, caused by electrostatic charges.  Would you please briefly describe us the facts.

The conductivity of the oil depends on the kind of the basic oil and the added substances. The trend is towards higher refined basic oils because of the improved technical characteristics e.g. aging resistance. However, all these oils display a lower conductivity. Besides the basic oil, additives considerably affect the conductivity. The lower the share of metal-organic additives, the lower is the conductivity of the oil.  With conventional hydraulic oils often zinc dithiophosphate (ZDDP) is used, protecting against wear and corrosion and acting as an antioxidant, but being classified as harmful. Therefore one renounces - e.g. with environment-friendly oil - from adding this additive, what reduces the conductivity and increases the danger of the electrostatic charges.
If a non- or low conductive hydraulic oil flows through a system, there will be an electrostatic charge at the interfaces between oil and non-conductive surface e.g. filter fleece and hoses. This charge is produced as a result of fast separation of two non-conductive surfaces. Thus the charge cannot be balanced and a charge separation occurs. As soon as the charge is large enough there will be discharges in the form of flashes. As the non-conductive surface in the filter elements is very large, this effect may occur and will grow with increasing flow speed of the oil.

What effects do electrostatic charges have on the filter?

Conventional filter material may be selectively destroyed due to discharge flashes and the related high temperatures. As a result, holes are created through which dirt particles may unfiltered reach the clean oil side. This results in an increased wear of the hydraulic components, ending in malfunction and failure of the machine.
The high temperatures of the discharge flashes also lead to premature oil aging, thus to a deterioration of the oil characteristics and reduction of the life time of the oil. The resulting oil aging products shorten the life time of the filter elements. Also adjacent electric components may be damaged by electric discharges.

How could this problem from the side of the filter be solved?

To ensure that the electric discharge of the oil does not exceed certain values, the charges must be balanced. For this, a special, registered for patent filter element structure has been developed which ensures charge balancing and prevents the occurrence of destroying discharge flashes.

But what about the costs?

Compared to the high costs for repair and maintenance measures, to the inconveniences related to machine downtimes as well as to the loss of earnings during the downtimes, the extra costs for the new EXAPOR^®SPARK PROTECT filter elements are low.

What is the useful value EXAPOR^®SPARK PROTECT precisely offers the customer?

100 per cent avoidance of destructive discharge flashes in the filter material guarantees an excellent oil cleanliness over the entire service life with maximum operational reliability and optimal service life of filter elements and hydraulic media.
The filter elements are compatible to standard filter elements as e.g. EXAPOR^®MAX 2 thus no modifications or extra measures at the filter and the hydraulic systems are needed. All other filter characteristics remain the same.
The EXAPOR^®SPARK PROTECT filter elements are problem solvers. Therefore we advise to use the new filter elements in case the electrical conductivity of the used hydraulic oil should be lower than 500 pS/m. If the conductivity is higher, the EXAPOR^®MAX 2 filter elements, proven for many years, should be used.

A couple of years ago there was a trend in the hydraulic filtration from the single component towards system solutions. Has this era already been finished or is it still in full swing?

The trend towards system solutions still continues. With increasing importance of the Supply Chain Managements among the machines manufacturers, there is a clear trend towards integrated solutions in the supply chain. This includes functional and system integration with particular focus on the reduction of interfaces as well as on the production of pre-assembled and tested functional units.

A customized suction filter inclusive of a pressure retention valve for the lubrication circuit, a pressure switch, a temperature sensor with modular, patented connection system, adjusted to the respective installation space situation, being supplied completely pre-assembled, reduces expense installation work.
In order to be able to react quickly to changes in the sales market, to increasing quality specifications and to the variety of new products, a close customer-supplier relationship is necessary. A long-term collaboration presumes an open information exchange and mutual trust. Sustainable success is created by continuity and results in a win-win situation.

Interview with Matthias Jung, Product manager (filter elements)  at ARGO-HYTOS and the German magazine fluid in July 2013.