Without a doubt, clean hydraulic fluid is the ultimate lifeblood of a hydraulic system. Contamination can reduce efficiency and possibly destroy machinery. That’s why many companies invest in offline filtration systems, commonly referred to as filter carts or kidney loop systems, for the external filtration of hydraulic fluids. Although traditionally used only when filtration was required occasionally—or before introducing new fluids into a system— they are now becoming a crucial part of reliability programs.
Their function is simple: they clean fluid and prevent contamination. Offline filtration supplements online filters, such as return line and pressure line filters, in conditioning and cleaning a reservoir. However, filtration does not always work the way it is supposed to. If inadequately sized or left off completely, filtration can quickly fail, allowing dirt particulates and water into the system. If there isn’t room for online filters as an aftermarket add-on, said Tony Grythe, EVP, MP Filtri, offline filtration is needed to ensure target cleanliness. Don Krause, general manager, FlowEzy Filters, added that the portability of the filter cart is what makes it so valuable to plants or machines that have improper filters.
“The beauty of a filter cart is that it is portable. You can clean one machine and then wheel it to the next machine, and so on,” Krause said. “Using portable filtration units to clean process fluids is a very economical way to go. Sure, you can keep changing filters in the system as needed, but then you would have to shut down the system to do that. If you are using a filter cart, you don’t necessarily have to shut the system down. All you have to do is keep recycling the fluid in the system to meet the cleanliness level you desire.”
Grythe added that offline filtration is becoming a stable part of most reliability and preventative and predictive maintenance programs. Here, personnel monitor systems and trend data to identify potential problems. Permanently mounted systems improve reservoir cleanliness while portable filters quickly react to a potential contamination-related issue.
“Currently, filter carts are being used on a regular basis to maintain optimal fluid cleanliness, rather than in the past when the filter cart might have only been brought out when a problem was identified,” Grythe said. “At that point, it may have already been too late to prevent a catastrophic failure if contaminants had made their way into sensitive components of the system. Filter carts remain a key tool in both identifying as well as resolving fluid issues before a major system issue occurs.”
Portable or permanent?
The portable filter cart is probably one of the most commonly used offline filtration systems, said Krause. These devices work simply by drawing the fluid out of the reservoir and running it through the filters on the filter cart and then introducing it back into the machine in a different location in the reservoir.
“You can put any filters on the cart you need to achieve the cleanliness level required for the application,” Krause said. “And sometimes you may need to have a water removal filter on your filter cart. Filter carts generally use two, or sometimes three, different size filter elements in series before re-introducing the fluid back into the system.”
Grythe added that in addition to the filter cart, permanently mounted systems are also common. These are typically mounted to a panel and then either directly on the reservoir or somewhere nearby.
Jarrod Potteiger, Des-Case educational services manager, agreed, saying he’s seen a significant increase in the use of permanently mounted kidney loop filtration compared to previous years, when people were using portable filter carts, either periodically or as needed.
“I believe this is due to the cost associated with periodically moving portable filtration units from one machine to another as well as the realization that continually maintaining fluid cleanliness provides much better results than intermittent filtration,” Potteiger said. Another growing trend, he said, is “the repurposing of portable filtration from on-demand decontamination to a standard means of transferring clean fluid from storage to service.”
Is new oil clean oil?
Just because hydraulic fluid is new doesn’t mean it’s clean. A lot of fluids suffer contamination in transport, so many manufacturers recommend filtration before putting new fluid into a system.
“Filter carts are also used to introduce new fluid to the system,” Krause said. “We know that from experience, if the filtration breaks down, the system will break down. Proper filtration is an investment and offline filtration is added security to that investment.”
This idea is termed “Roll-off Cleanliness” and is practiced more now than a few years back, said Dan Zoller, group product manager, Filter Systems at Hydac and Schroeder. “Roll-off Cleanliness is the term for cleaning a hydraulic system before it is shipped to a customer (trucks and ag equipment, for example),” he said. “Our customers have found that clean systems/fluids will reduce the breakdown rate in the first month dramatically and reduce warranty costs.”
Discover your contamination level
Kidney loop systems fitted with a contamination sensor are becoming the norm, too. This is helping users extend the service life of their equipment.
“The need to measure the actual fluid cleanliness has become more important. While portable contamination sensors provide a solution, customers like the combination of a contamination sensor with the cart or kidney loop system,” said Zoller. “We have seen an increase in filter carts and kidney loop systems that have a contamination sensor integrated. Some systems allow the automatic shutdown when target ISO codes are reached and for the collection of data for maintenance records.”
Grythe added that this goes hand-in-hand with the growing awareness by reliability departments that filtration is a key part of their reliability program. “With the addition of reliability departments, we have seen an increase in a need to meet the goals and benchmarks set by the facilities’ quality programs. This has necessitated a new addition to the offline filtration product portfolio,” Grythe said. “Filter carts and offline filter units are now being fitted with contamination monitors that can analyze the particle size and distribution in the fluid as well as the water content.
“This has become important to companies that want to track the condition of their equipment. In the past, it was just assumed that offline filtration was cleaning up the system; however, it was not known at that time what the condition of the oil actually was,” he continued. “With a contamination monitor, the operator can visually see the cleanliness class of the fluid and water concentration. He or she then knows if the filter cart has done its job and can log the condition of the fluid when complete.”
Don’t be fooled by price
Space is always a premium in any industrial setting. So smaller units are always entering the market. Smaller can sometimes mean less expensive, but these smaller units could be so loaded with extra accessories that you may be paying for more than you need. Manufacturers warn users not to base a selection on price alone.
“Fifteen years ago, a simple filter cart was used to clean and transfer fluids. Today, we see more and more companies offering filter carts with all the bells and whistles and getting away from simple, lower cost, filter carts that will get the job done efficiently,” said Krause. “Do your due diligence in shopping for filter carts. Always compare pricing to make sure you aren’t paying for something you have no use for.”
For example, he said, be careful when selecting a cart that contains a number of extras, such as various sample ports, bypass valves, cord reels, relief valves, fancy gauges, ISO quick disconnects, various pump and motor sizes and hose reels. Often on carts like these, the cost is much higher.
Grythe also cautioned against shopping based on low prices alone instead of looking at the actual specifications and whether they will work for their application. This could result in many filter carts being undersized for the application.
“It has happened many times that a customer will receive a filter cart for use with their high viscosity gearbox oils, but it has spin-on filter elements that are undersized,” Grythe said. “If the filters are already at 50%+ of indication range at clean startup, they are not even using half of the filter elements’ dirt-holding capacity and will be changing filter elements quite frequently.”
Usually, it is the companies that are conscious of the importance of a good reliability program and the ability to trend and measure data to prevent failures before they occur that have a better handle on their filtration requirements.
“These companies are aware that a larger filter means longer service interval, and that the ability to monitor the fluid condition while transferring and filtering at the same time is invaluable in their predictive program,” Grythe said. “We have seen OEM manufacturers that are able to save tens of millions of dollars per year in contamination-related warranty claims just by implementing a strictly regimented fluid cleanliness program in their manufacturing facilities, which includes contamination monitoring and offline filtration. This positive trend has made users aware of the importance of selecting the offline filter based on what is needed for the application rather than on price alone.”
1 Filter cart with ICM
The GRF502 series filter cart with inline contamination monitoring is suited for oil transfer from bulk drums to tank as well as reservoir clean up. The suction side features a 90-µm wire mesh element while the discharge side features a 10-µm absolute rated (ßx ≥ 1,000) high-capacity cartridge element. Choice of 3, 6, 10 and 25 µm elements are also available. It comes with a 1-hp, 115-Vac, 1-phase TEFC motor with motor start/stop, cord and plug. A rugged 5-gpm gear pump features an integral relief valve. Wire reinforced clear suction and discharge hose comes with stainless steel wands up to 25 ft. The frame is a steel, two-wheel cart with pneumatic tires for easy transport. Mounted inline contamination monitoring (ICM) unit measures fluid cleanliness. Water and temperature sensor is optional.
2 Hand-held filter
The OF7 hand-held kidney loop filter is suitable for transferring and filtering new fluids, maintaining fluid cleanliness and cleaning hydraulic systems after repairs. It features one spin-on element for easy change and choice of 3, 5, 10 and 20 µm elements or water absorbing elements. It is rated for 2.5 or 4 gpm flow rates and up to 4,600 SUS maximum viscosity. It weighs just 27.5 lb without the optional contamination sensor and comes standard with a 110-Vac and 24-Vdc motor; pneumatic motor is optional.
3 Portable oil transfer and filter system
The Flow Ezy filter cart easily transfers fluids from drums and storage tanks to system reservoirs for fluid conditioning. It recirculates system oil without having to shut down the system and is available with an optional third-stage 3-µm water removal filter. It easily cleans up contaminated hydraulic oils and can be moved from machinery to machinery. Standard filters include 25 and 10 µm in series with other options available. It comes with the option of a 5- or 10-gpm rated pump.
Flow Ezy Filters
4 Asset management filtration station
AMFS filter carts with integrated contamination and water saturation sensors feature an automatic shut-off of unit when selected ISO target levels are reached. They come with two filters, with 18- or 27-in. housings for high dirt holding capacity in series for staged filtration with choice of 3, 5, 10 or 25 µm elements and a water absorbing element. Modular base eliminates connections between components and minimizes leakage. Base-ported filter provides easy element service from the top. It offers a flow rate of 5 gpm and maximum viscosity of 1,000 SUS. A touchscreen terminal with pull-down menus for programming allows for automatic collection and record keeping of fluid contamination data in MS Excel spreadsheet. By-pass valve allows cart to be used as a transfer cart.
5 Portable filter cart
Portable, offline filtration system is suitable for mineral-based industrial fluids and a wide range of applications including decontaminating systems, flushing new or repaired systems, dispensing oil, pre-filtering new oil, evacuating used oil, topping off reservoirs and collecting oil samples for analysis. It comes standard with an automatic pressure relief valve and dual-stage filtration. It features 12-ft hose assemblies with various quick connect options and pneumatic wheels. Flow rates, filter bypass, hose-end connection sizes and types, and more can be customized. Micron ratings of filters are also customizable, with choices of Beta 200 at 3, 6, 12 and 25 µm, as well as water removal filters. Other micron ratings are available by request.