3:36 pm
May 15, 2017
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Put Portable Filter Carts to Work

Portable filter carts play a crucial role in equipment uptime by being able to deliver lubricants at the right cleanliness level and transfer and clean oil while machinery runs. (Source: EngTech Industries Inc.)

Portable filter carts play a crucial role in equipment uptime by being able to deliver lubricants at the right cleanliness level and transfer and clean oil while machinery runs. (Source: EngTech Industries Inc.)

Don’t set up a lube program without one or more of these multi-taskers.

By Ken Bannister, MEch Eng (UK)CMRP, MLE, Contributing Editor

The ability to control contamination is an important aspect of any lubrication-management program, especially where lubricant cleanliness is concerned. A constant supply of clean oil is essential to lubricant life and, more important, bearing life.

One of the most efficient and practical tools available to ensure lubricant cleanliness is the portable filter cart. In a typical industrial environment, portable filter carts are used to transfer and clean all types of lube, gear, and hydraulic oils. The carts’ three principal applications in a lubrication-management program are:

• transferring oil from its original container into a machine reservoir
• pre-filtering and cleanup of virgin stock (new) oil in preparation for machine use
• reconditioning and cleanup of oil currently in service.

In addition, use of specialized filters on the outlet side can extract any free and emulsified water present in the oil.


The primary function of any filter cart is to filter fluids. A typical cart design will employ a two-stage filtration approach in which a gear pump is connected to both filters. The inlet, or suction, side is the first-stage, low-pressure side (approximately 5 psid) designed to capture larger contaminant particles exceeding 150 microns in size.

Oil is pumped through the inlet filter to the second-stage, high-pressure (approximately 25 psid) outlet (or delivery side) filter designed to capture much smaller particulate matter that can be filtered to less than 5 microns in size, depending on the filter rating used.

Listen to the latest in a series of monthly lubrication-related podcasts with Ken Bannister. The May podcast focuses on the selection of and best practices regarding portable filter carts.

How clean should your oil be?

Oil cleanliness is universally measured using the ISO 4406 cleanliness code rating system. This is a standard that quantifies the number of contaminant particles, 4, 6, and 14 micron in size, that are present in a 1-ml lubricant sample and compares them with a particle concentration range, resulting in an ISO-range number value.

For example, a 19/17/14 lubricant sample value (typical of new oil) translates to the presence of 2,500 to 5,000 particles >4 microns in size, 640 to 1,300 particles >6 microns in size, and 80 to 160 particles >14 microns in size present in the oil sample.

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When new or virgin stock oil is received from the supplier, many sites believe they are receiving a “ready-to-use” product. This is not always the case, as depicted in the table. New oil is typically received around a 19/17/14 ISO cleanliness level that may only be suitable for non-critical gear systems. All other applications will require the oil to be cleaned and polished by passing it through a filtration system prior to use in service.

The table also notes that “In service” oil dirtier than 19/17/14 is unsuitable for any lubrication or hydraulic system. Such oil will require replacement or cleanup using a kidney loop set-up with a portable filter cart.

The number of passes through the filter cart to achieve the appropriate cleanliness level will depend on the “start” and “finish” cleanliness level and the filter types and rating in use. Oil analysis will be required to establish cleanliness levels. Choosing a suitable combination of pump and filter size/type will require consultation with the filter-cart manufacturer who will need to understand your working environment and type/viscosity of oil(s) you use.

The rate of cleanup (speed) will depend on the reservoir size, pump flow rate, and the cleanliness-rating delta. What can be measured immediately is the time to perform one complete filter pass through the cart, as calculated using the following formula:

(Reservoir size x 7)/filter-cart flow rate =  time for a single-pass filtration

Example: 60 gal. x 7/10 gpm = 42 min. for a single-pass filtration (1 x filtration of reservoir capacity)

If the plant’s lubricants are consolidated and cleanliness levels are known, a matrix can be developed to determine how many passes are required to filter to an acceptable cleanliness level.

Best practices

As in all other facets of maintenance, there are a number of best practices associated with the use of portable filter carts:

• Work with the filter cart supplier to determine the right pump and filter choice for your plant requirements.

• To eliminate cross contamination of lubricants, each filter cart must be dedicated to a single lubricant use for transfer and cleaning of lubricants. Pilot the filter cart program with the most-critical and/or most-utilized plant-lubricant type.

• Always clean the unit after each successful transfer operation, paying particular attention to the wand ends and open drip tray under the filters and pump area. Open oil is a dirt attractant and can be transferred unwittingly if the cart and its components are not kept scrupulously clean.

• Unless specified, most filter carts are sold with open-end transfer wands fitted to the delivery and suction hose ends designed to slide easily into the reservoir openings of the donor and recipient reservoirs. In a program designed to filter contaminants from the oil, this type of delivery fitting can allow moisture and dirt contamination into the respective reservoirs during the transfer process. To combat this, and ensure a contamination-free transfer process, fit the filter cart delivery/return hose ends and reservoir fill/drain ports with quick-lock-style couplings. As the reservoir is now airtight, it will also require a quality desiccant-style breather to be fitted and, in the case of larger capacity reservoir, a closed-loop expansion tank.

• Specify kink-resistant flexible suction and delivery hose to prevent pump cavitation. Clear hoses allow a visual reference of the oil flowing through the lines.

• The cart’s electric motor will require access to electricity. Ensure that an electrical outlet is within easy reach of the unit’s electrical cord. If the cord is short in length, consider mounting a retractable electrical cord caddy on the unit with enough cord length to reach the nearest electrical outlet.

• Paint a lined box similar to a lay-down area as close as possible to the oil reservoir that’s to be serviced. This allows a cart to be positioned and used quickly without obstruction, and within reach of its hose and wand assemblies.

• Place the cart on a preventive-maintenance (PM) check program prior to every use to ensure the unit’s filters don’t go into bypass mode from being too dirty.  MT

Contributing editor Ken Bannister is co-author, with Heinz Bloch, of the book Practical Lubrication for Industrial Facilities, 3rd Edition (The Fairmont Press, Lilburn, GA). As managing partner and principal consultant for Engtech Industries Inc. (Innerkip, Ontario), he specializes in the implementation of lubrication-effectiveness reviews to ISO 55001standards, asset-management systems, and training. Contact him at kbannister@engtechindustries.com, or telephone 519-469-9173.

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“Offline Filtration: Key to Establishing and Maintaining Oil Cleanliness”