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What is a Kidney Loop System?

Photo of Schroeder Filters with the caption America's most technically advanced oil filtration

To view the Schroeder Industries Kidney Loop Systems, click here.

Kidney loop systems clean hydraulic fluid and prolong the life of the fluid, filters and equipment.

Schroeder’s Kidney Loop System is an off-line stationary version of the kidney loop filter systems on portable carts. It is a compact, self-contained filtration system equipped with high efficiency, high-capacity elements capable of removing particulate contamination and/or water contamination quickly, conveniently and economically.

This off-line system can be used to supplement in-line filters when adequate turnover cannot be achieved in the system.


Keeping Hydraulic Fluid Clean

Hydraulic systems are generally equipped with system filters. The system filters are either placed on the pressure side (e.g. downstream of pumps, before system components) or on the return side (e.g. before fluid is reaching the reservoir).

In a system where only one filter is used, this one filter must remove all the dirt generated in the system.

By using both pressure and return filters in the system, the work load is shared, making it easier to maintain the recommended fluid cleanliness level  for the hydraulic system. However, the reservoir might still contain contamination accumulated over time and from the environment.

An off-line kidney loop system can be added to improve reservoir cleanliness and extend the life of the system filter elements.

In hydraulic systems, 70 to 90% of wear and failure is contamination related. Only 10 to 30% can be traced back to misuse, defects or age. Contamination cannot be stopped, only slowed down!


Watch on YouTube “Kidney Looping Filter Systems”.

How do kidney loop filtration systems differ from other filtration systems?

A kidney loop system contains a motor, a pump and a filter to form an independent filtration unit. This kidney loop system is placed on a reservoir and can run intermediately as needed or it can run continuously.

Because the kidney loop system is not exposed to the hydraulic system itself, it is very efficient in removing dirt from the fluid and holding it in the filter elements without releasing it back into the fluid.

It is important to note that the fluid might not be flowing all the time and, therefore, only needs to be filtered at certain times. Therefore, one key benefit is that an independent kidney loop system can run 24/7 and polish the fluid even when the hydraulic system is down or switched off.


  • Supplementing in-line filtration by system filters when adequate turnover cannot be attained
  • Large volume systems requiring multiple filters in different locations
  • Cleaning up a hydraulic system following component replacement

Success Story

Light bulb iconProblem: Customer was experiencing problems with external ingression of coal dust getting into the 255 gallon (965 L) lube oil reservoirs on their coal pulverizers causing degradation wear on the bearings and bull gears, which lead to premature aging of the system components.

Solution: Installation of KLD filtration skid cleaned up the system fluid from coal dust particulates and other contamination. As a result, the internal wear on system components as well as unscheduled downtime due to contamination was reduced dramatically.


Schroeder Industries offers several different types of stationary kidney loop systems, including versions with pneumatic motors in place of standard electric motors. The pneumatic motor offers the same flow capability using the same components, but without the need for an electrical outlet. The greater portability allows for field options on service trucks.

System efficiency can drop by up to 20% before an operator even detects a problem. This can appear as cylinder drift, jerky steering, erratic operation or slower performance. Overall, contamination results in shorter service intervals, higher operating costs and lost productivity.

A major portion of particulate contamination can be effectively and efficiently removed by using our kidney loop systems. This can lead to potentially saving a company production costs in the future.

The result will be improved fluid condition and consequently extended life expectancy of fluid and equipment resulting in significant cost savings.

Fluid cleanliness is a top priority for Schroeder Industries and our kidney loops can achieve that.


Find kidney loops near me


Watch on YouTube “Kidney Loop Product Extensions”.

To view the Schroeder Industries kidney loop Systems, click here.


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