Controlling the contaminant flow of your hydraulic, lubricant or fuel reservoirs is one of the simplest goals in achieving Total Systems Cleanliness.
As an equipment owner or manager, the last thing that you want to find in your system is contamination. After all, that means downtime, which ultimately costs you time and money. Contamination always somehow sneaks its way into our systems, which may leave you asking, how does it get in there and what are we supposed to do about it?
In the fascinating and fundamental field that is industrial fluid filtration, there exist many types of filter elements and many different types of media. In this article, we will briefly cover filter elements and the most common types of media they're made up of. The medias featured below include: cellulose, glass, wire mesh and water removal, coalesce and resin.
The Problem: Oil with MPC Values of 250
A coal-fired power plant in the Philippines has a scheduled shutdown. Upon shutdown, it is revealed that the turbine lube oil, Shell Turbo 32, in the system has suddenly darkened. After conducting MPC and ISO code testing, it is determined that the oil’s current state is unusable with MPC values as high as 250 and ISO codes at 20/17/10.
Accessing a System that is Currently in Place
Preventative maintenance is a program put in place in most manufacturing or production industries to ensure quality scheduled maintenance is provided. Maintenance professionals implement these routine inspections before, during and after the operation of machinery. Parts of this routine can include areas that can only be inspected by touch, not sight, to determine what is happening under the surface.
Oil analysis can be added to this routine maintenance to give a fuller picture of whats happening inside machinery and equipment. By including oil analysis in a preventative maintenance program, maintenance professionals are provided with detailed inside information that could prevent issues in the future, like unexpected downtime.
Large paper mills rely on continuous production to be profitable, thus unplanned down time is a huge financial burden. When unplanned downtime does occur and equipment must also be either repaired or replaced, the damages can feel exponential.
Throughout the first three entries in this series we've discussed the difference in two filter element testing methods, ISO16889 and DFE. We've also illustrated how many elements fall short of their stated beta ratio under dynamic flow conditions. Today we'll wrap it up with simulated cold start tests.
DFE Multi-Pass: Cold Start Contamination Retention
Once the element has captured enough contaminant to reach approximately 90% of the terminal ΔP (dirty filter indicator setting), the main flow goes to zero and the injection system is turned off for a short dwell period. Then main flow goes to maximum element rated flow accompanied by real time particle count to measure retention efficiency of the contaminant loaded element. The dynamic duty cycle is repeated to further monitor the retention efficiency of the filter element after a restart.
Last week we covered the differences between the ISO16889 Filter Test Procedure and the DFE Filter Test Procedure. This week we illustrate the difference between elements engineered to retain particles during dynamic flow conditions and those that are engineered only to pass the ISO16889 test.
Quantifying Contaminant Capture and Retention
Figure 2 compares the performance of two identical high efficiency glass media filter elements, one tested to ISO16889 multi-pass and the other to the DFE multi-pass method. The graph expresses the actual number of particles 6μ[c] and larger counted downstream of the filter element from several data points during the tests.
Filter A2 was tested at a constant flow rate and maintained a steady efficiency throughout the test. Filter A1 was cycled between max rated flow rate and half of rated flow with a duty cycle consistent with that of a hydraulic system. The downstream counts for Filter A1 varied and were highest during changes from low flow to high flow. The peaks represent counts taken during flow change and the valleys represent counts taken after each flow change. The alternating high peaks represent counts taken during changes from low flow to high flow. As the amount of contaminant captured by Filter A1 increased, the downstream counts increased most dramatically during the flow changes from low to high. Filter element A1, not properly designed to retain previously captured contaminant during dynamic system conditions, can become a dangerous source of contamination as it captures and then releases concentrated clouds of contaminated fluid.
Last week we briefly discussed how filter elements are rated by manufacturers. This week we're discussing the industry standard ISO16889 multi-pass test and Hy-Pro's standard, the DFE test.
Current Filter Performance Testing Methods
To understand the need for DFE it is important to understand how filters are currently tested and validated. Manufacturers use the industry standard ISO16889 multi-pass test to rate filter efficiency and dirt holding capacity of filter elements under ideal lab conditions.
Figure 1 depicts the test circuit where hydraulic fluid is circulated at a constant flow rate in a closed loop system with and on-line particle counters before and after the test filter. Contaminated fluid is added to the system at a constant rate. Small amounts of fluid are removed before and after the filter for particle counting to calculate the filter efficiency (capture). The capture efficiency is expressed as the Filtration Ratio (Beta) which is the relationship between the number of particles greater than and equal to a specified size (Xμ[c]) counted before and after the filter. In real world terms this test is the equivalent of testing a filter in an off-line kidney loop rather than replicating an actual hydraulic or lube system. It’s basically a filter cart test.
The Dynamic Filtration Efficiency (DFE) Test is Hy-Pro's standard for testing filter elements. Throughout this 4 part series we'll discuss what it is, why it matters and why elements engineered with this test in mind outperform others in real-life applications.
First, let's start with the basics...
Why are filters used? How are they rated?
All hydraulic and lube systems have a critical contamination tolerance level that is often defined by, but not limited to, the most sensitive system component such as servo valves or high speed journal bearings. Defining the ISO fluid cleanliness code upper limit is a function of component sensitivity, safety, system criticality and ultimately getting the most out of hydraulic and lube assets.