Q & A

"What micron filter is frequently used to filter a 220 gear oil? We are looking into getting a pump cart to filter the oil while the machine is running, but our dealer isn't sure what we can use either?"

First determine the optimum target cleanliness level for that specific gearbox, and the do not forget to ensure adequate breathers are fitted, as any attempts at clean-up will be lost quickly.

A few tips on filter carts.
First, ensure that for each type of lubricant in use, there is a dedicated filter cart to avoid cross contamination of fluids. Second, because this is fluid power generating device, ensure it complies with all the safety requirements and has a pressure venting safety valve in the event of dead-heading the pump. Lastly, ensure the cart includes a by-pass loop to the filters, and incorporates a sampling connector for the use of online instruments or bottle sampling.

The design (pump and filter selection) of filter carts is dependent on two factors; the lubricant's viscosity grade, and the temperature at which the cart will be used. A higher viscosity, such as an ISO VG 220 oil, will require a lower flow rate in the pump to avoid high differential pressures across the filter. But this will be affected by the ambient and operating temperatures. While the use of quick connectors allow the cart to be used while the gearbox is operating (this is the optimum filtering condition), the lubricant's viscosity will also be affected by the ambient temperatures, so if this is located outdoors, assume the worst case winter temperature when looking at the viscosity issue. Of course, slowing the flow rate to avoid high differential pressures will increase the time to filter the box, and depending on the Beta ratio, the rule of thumb is to allow the volume of the gearbox to circulate seven times through the filter for effective cleanup For example, a gearbox with 50L sump capacity and a filter cart with a 10L/min flow rate will take five minutes for one pass and approximately 35 minutes to clean up. Keep in mind the flow rate versus the time available for filtering.

As to the filter rating, experience has shown a 10µm filter capable of achieving better than ISO 17/15/12. However, if your optimum target cleanliness level is lower than this, consider a 6µm filter. There are various ways to strike an optimum balance between flow rate and filter rating, and this includes the possibility of putting several filters in parallel to increase the flow area. As a simple guide, the differential pressure can be halved by doubling the length of the element or putting two elements in parallel. 3µm filters will work with ISO VG 220 oils, but check the temperature conditions, and whether your target cleanliness levels requires such fine filters. The cost of these elements should be considered.

Electrical power considerations include the use of single or three phase, and the availability of power sockets near to the equipment, as well as ensuring that the unit is intrinsically safe for use in potentially explosive areas.

Finally, consider using water-absorbing elements if the gearbox suffers from free and emulsified water, in addition to the use of desiccant breathers.

Today's Tip

• Brake fluid is highly hygroscopic, meaning, it absorbs moisture from the atmosphere. Apart form the obvious corrosion potential this presents to the master and slave cylinders, leading to rusting and pitting and seal failure, it also degrades the high temperature performance of the fluid. This results in the fluid boiling at a lower temperature leading to the loss of fluid power when pressing the brake pedal. Follow the manufacturer's recommendations and change the fluid regularly. Synthetic silicon-based brake fluid is more expensive, but does not need replacing as often, and as custom and classic car owners know, it does not damage the paint work!

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Book Bits

From the book "The Practical Handbook of Machinery Lubrication":

• Are existing full-flow filters capable of meeting the equipment manufacturer's specifications or have these filters been replaced with less expensive jobber filters, whose quality and efficiency ratings may be questionable?

• Are all lubricants pre-filtered before being added to the system?

• Are all breathers, filter bypass indicators, external seals and other contamination control devices operating properly, and are they inspected regularly and serviced when necessary?

• Are only top quality, specified fluids and lubricants used and are they stored properly in a clean environment?

• Are all leaks repaired as quickly as possible, particularly those in dirty environments?

• Is the entire system thoroughly flushed and serviced completely, after any major component failure and subsequent replacement is carried out?

• When flushing is carried out, particularly on a hydraulic system, is the reservoir opened and thoroughly cleaned by hand?

• Are all replacement components thoroughly cleaned, before they are installed?

• Is the immediate working area thoroughly cleaned, before opening up any area of a system?

For more information about the book "The Practical Handbook of Machinery Lubrication" go to:

http://www.noria.com/secure/product_detail.asp?catalogid=55

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Lube-Tips is published by Noria Corporation. Oil Analysis and Lubrication Experts