How to Choose an Oil Filtration System

A common question that I am often asked is about how to select the right filtration skid for offline kidney-loop oil filtration. This is one of the most neglected and least understood issues in the industry, costing companies billions of dollars in losses.

The question usually is asked by people who are having problems with their bulk lubricants in the reservoirs of critical machines. Most of these large machines have no redundancy and require the highest availability in the plant.

The bulk lubricants should not be replaced on a time-based schedule but rather only on condition. However, before replacement, it is important to consider the possibility of getting the lubricants back to a healthy state by using a filtration system. 

Since there is no straightforward answer to the above question, I usually start by saying that one size doesn't fit all. Many things must be considered. For example, if this question is asked to someone who sells oil filtration skids, you can expect he or she will try to push their off-the-shelf items, which may not be suitable for your application.

Don't just blindly trust the marketing guys. Dig into the specifications of the product that has been proposed to you. The brochures distributed by the filtration skid suppliers typically lack technical specifications, which are essential in selecting the right system for your application.

I have seen companies spend thousands of dollars on filtration skids that either do not work for their specific purpose or are too expensive to operate due to frequent filter element replacements. After a few months of use, these skids are often set aside.

Varnish Removal Technologies

When choosing an oil filtration skid, you must understand the different varnish removal technologies. These technologies can be divided into two main categories: particulate removal filters and dissolved breakdown product removal technologies.

Remember that varnish is the consequence of dissolved breakdown products accumulating past the point of saturation. Since the key to prevent varnish is to prevent saturation, only varnish removal technologies that remove dissolved oxidation products and return the oil to an unsaturated state can actually prevent varnish.

Be sure to find out if the proposed skid will work during normal operation when the varnish is dissolved in the oil. Some systems use a cooler on the inlet to force dissolved varnish precursors out of solution before they go through the filter. These types of systems only work above the saturation point and are unable to pick up deposited varnish from the system.

Operating Temperature

Is the proposed skid able to remove dissolved varnish at the oil’s operating temperature in the reservoir? In the Middle East, I have commonly seen gas turbine oil temperatures of 165-169 degrees F in the reservoir during peak summer months.

Soluble vs. Insoluble Varnish Content

Another important consideration is whether the system is capable of removing both soluble and insoluble varnish content from the oil. Many varnish removal units on the market can only remove insoluble varnish content, but it is actually the dissolved varnish content that damages the machine. Therefore, the system you select should be able to remove both soluble and insoluble varnish content.

Flow Rate

What is the flow rate of the filtration system? A system that can remove dissolved varnish content from oil should cycle the entire reservoir volume through the system more than once per day for efficient cleaning.

Some varnish removal systems may take 30-60 days to cycle the reservoir volume just one time. Don’t be persuaded to purchase a system that is a few thousand dollars cheaper when the flow rate is insufficient. Size matters.

Cost of Ownership

What is the system’s cost of ownership over its lifespan? For a varnish removal system, the cost of ownership includes the initial cost of the system, maintenance and consumables over its lifetime. The latter can be calculated by the volume of the dissolved varnish removal filter element.

You will find that some systems can be up to five times more expensive to operate than others. Again, the volume of the varnish removal filter also determines the system’s flow rate, so attention must be paid to the filter size.

Technical Support

Will the skid supplier be able to provide technical support on short notice, e.g., 48-72 hours? What experience and qualifications do the technical support team have for troubleshooting problems? I have often seen end users struggle to get support from their skid suppliers or even get them onsite in time. Time is money. 

When selecting your next oil filtration system, be sure to keep all of these considerations in mind and remember that one size will not fit everyone.