"We frequently use filter carts as a part of our contamination control program. Do you have any information on how long we should filter the oil using this type of filtration?"

Offline filtration is a powerful asset to the lubrication technician. Without interfering with the operation of the equipment, you can keep the oil clean with full-time offline filtration, or the oil can be cleaned periodically with a portable rig, such as a filter cart.

When using a filter cart, the oil is taken from a dirty sump, filtered and returned to the dirty sump. The cleanliness of the filtered oil is diluted, so to speak, by the dirty oil residing in the tank. To overcome the dilution effect, the tank volume must pass through the filter approximately seven times to achieve the equivalent of single-pass filtration (where the oil is pumped from one container to another through a filter).

For example, if you have a 30-gallon tank and a filter cart that pumps at 5 gallons per minute (gpm), you need to run the cart for 42 minutes to equal single-pass filtration (30 gallons multiplied by 7, divided by 5 gpm). If you want to achieve two-pass filtration, you must engage the offline filter for 82 minutes or about an hour and a half.

Use this rule of thumb to manage scheduling activities where portable filtration is rotated from machine to machine within the plant.

When used properly, filter carts can be vital to the reliability of a process. The best place to combat misuse of your filter carts is to start with the design. When possible, specify that a manual filter bypass valve is plumbed into the circuit. This will allow you to bypass the filters when you are only transferring used oil and do not need to filter.

Also, specify that the hoses have quick-connects as opposed to simple drum wands. Drum wands are difficult to keep from getting contaminated. Their use requires the system to be opened to the operating environment, possibly allowing contamination to enter the system unrestricted.

Using quick-connects on the filter cart and on the system to be filtered eliminates the need to open the system for filtration or topping up. To ensure the filter carts are used only for the oils they were specified for, you need to take all guesswork out of the equation. One simple way to do this is to install different types of quick-connects on your filter carts. Place the matching ends of the quick-connect on the appropriate equipment where they will be used. Using quick-connects of different types and sizes makes it impossible to connect the filter cart to the wrong equipment and lubricant.