Machine, hydraulics part 2.

Previously the topic of hydraulic fluid cleanliness and particulate count was discussed. Let us now bring up the ways to clean the oil and or types of filters on the market, or within your machines.

Primarily there are two types of filters used and those are of the Surface and Depth type.

Surface:
Is by direct interception of the particulate in that it captures particles larger than the pore size.  Dirt holding capacity is low and the pressure drop is great as the filter clogs up. This could be a screen with set mesh size, usually one level.
 
Depth-
This is a more complex filter than surface in that it uses both the direct interception but also adsorption to stop dirt from progressing down stream.  Particles are trapped within the matrix of the filter media. Though the pressure drop is greater to start with, in this type of filter the increase is much slower due to the massive amount of filter media. Similar to a water filter or car oil filter in that it passes through a media that has some mass to it. It thus gets the large particles at the surface and the others within, along with the possibility of water adsorption dependent on the media type.

Inline filtration
In this type of filter system, all of the oil in the system is passed through the filter. This than does create a very high flow demand on the filter and its media. Further, given that the all the oil must go through this system than the porosity of the media may be larger to allow the flow of oil. Some of these filter are only good down to 25- 40 microns. The surface will contain smaller particles as it builds up but than the flow decreases and the pressure increases. In these system there may be a by-pass value, which now allows the oil to by- pass all filtration.

By-Pass filtration
With this type of filter, a portion of the oil from the pump is routed through the filter and back to the sump.  It is determined what this volume must be to maintain the desired cleanliness level.
Overall, what kind of filtration is there on your machines? Are you following the manufactures recommendations on the maintenance?

As stated from reports in the first article on this topic up to 80% of our machine hydraulic problems can be attributed to dirty oil. Keeping that part clean and up to par only makes for good control and less downtime within our process's.

Thanks for the time.

Steven L Silvey
Senior Tech Service
General Polymers Division
Ashland Distribution