5 Considerations When Selecting a Filter Cart

Filter carts can save you time, money and effort—but only if you choose the right one. Before you place an order, make sure you’re basing your decision on your company’s needs by answering these 5 questions...

1. What’s your target cleanliness?

The most crucial aspect of any filter unit is what it filters out. Before buying a cart, you should know what pieces of equipment it will be used for, what types of contamination they’re exposed to, and how clean you need to keep the oil.  The pore size of the finest filter should be at least as small as the smallest particles you’re trying to exclude—usually 3 microns for hydraulic fluid, 6 for gear oils.

Many carts feature two filter elements, allowing the oil to pass through a coarser filter first and thus extending the life of the more expensive small-pore filter. If moisture is a problem, the first filter element could be a water filter, which also acts as a 25-micron coarse filter. If soft particles are an issue, depth media—cellulose filters designed to catch soft particles produced by oxidation—will remove them as well as some water. Finally, a unit with just one filter element is ideal if the system is sealed and unlikely to be contaminated by either water or large particles.

2. What’s your oil type?

Another key filter feature: the pump that transports the oil from machine interior to filter elements and back. Different pump mechanisms are intended for different viscosity levels, because thicker liquids can’t flow as quickly. If you try to pump a viscous oil at too fast a speed, air bubbles can form inside the machinery, damaging the pump and causing oxidation to the oil. Let your supplier know the ISO VG rating of the oil you’ll be filtering, and be aware that if you use lubricants of different viscosity levels, you’ll likely need different units to filter them.

3. What flow rate do you need?

Determining optimal flow rate is the most complex aspect of choosing a filter cart, but doing it right can save you money.  More powerful units cost more, so if you choose one with a higher flow rate than you need, you could be overspending. Conversely, if it’s too low, you’ll be unable to clean the oil thoroughly enough in the available time, leading to potential damage and premature machine failure.  

A good rule of thumb is that you should be able to pump up to 10% of the reservoir volume per minute. Another way to calculate flow rate is to determine how many times all the oil must pass through the filter to meet your targets, and how much time you have per use to achieve that. Multiply the volume of oil with the number of times you want to pass it through the filter each time it is hooked up, and divide that number by the number of minutes available. For instance, if you have a 100-gallon machine and want to pass the oil through the filter 10 times in one 10-hour shift, divide 1000 by 600 to find 1.66. This is your minimum flow rate in gallons per minute. But if you need to service 2 machines in that 10-hour shift, your needed flow rate doubles.

4. What will you use it for?

Routine filtration, in which a cart is used to clean oil externally as a machine runs, is a standard use for filter carts. But it’s not the only use. Some alternate uses require special features that don’t come standard. For instance, if you will be using the cart to perform oil changes, you will need a bypass valve to prevent dirty oil on its way out from contaminating clean oil on its way in. If you will be taking oil samples, you’ll need a sample valve that lets you remove a small amount without exposing the rest to the air.

5. Where will you use it?

All filter carts are portable in theory, but your chosen model needs to be convenient to transport to wherever you’ll be using it. If you will be using it on a machine that is accessible only by ladder, or wheeling it across uneven outdoor terrain, then the physical characteristics of the cart itself are crucial. Ask yourself if you will be better off with a cart that weighs under a certain amount, or can be carried instead of wheeled. The power source in your target location is also a key concern—most use electricity, but in areas where explosive gases or dust are present, an air-driven motor may be a better choice.



Before you place an order, make sure your chosen model...

  • has the right pump types for the oil in your machines
  • will remove what you need it to
  • can pump oil fast enough to keep your machines clean
  • has the features you need, like bypass or sample valves
  • can be easily transported to the location where you’ll be using it


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