Magnetic separation: A concept that will stick

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The world of separation, relating to hydronics continues to evolve and expand.

Most hydronic and HVAC contractors understand the importance of air and dirt separation. They understand the need to keep high performance equipment operating at peak efficiencies. A big part of that is keeping the piping and components air and dirt free.

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Cast iron boiler with magnetite sludge. Photo credit Richard Graves “Heatmeister”

It is well documented the importance and value of scrubbing the systems free of all dissolved and entrained air. The goal is to provide the very best heat transfer from the wall of the heat exchanger to the fluid. This is true for all fluid based systems hot or chilled.

The micro-bubble type of air removal devices have revolutionized the way we efficiently remove the smallest of air molecules. The micro-bubble removal devices are the industry standard now. They are well worth the additional cost when compared to a basic scoop type air removal device.

For dirt and particle removal, strainers have been the go-to product for decades. There are some limitations to a strainer or filter type of device. The most common Y pattern strainers present some flow resistance, even when brand spanking new. As they remove particles from the fluid stream flow is further diminished until they are cleaned and serviced.

Screen Shot 2015-03-26 at 2.55.34 PMThe same concept applies to dirt as air. Separate the particles, trap them in a lower chamber away from the fluid stream where they will not obstruct or limit flow.   A simple ball valve at the bottom allows them to be blown down or flushed out. Use a small bucket when you first blow them down to see what lurks inside your systems. You may be surprised as to what you find. Commonly pipe joint tape, solder balls, copper or steel chips or burrs that were removed are will flush out. A motorized valve could be added to program a flush for and on-going basis. This would apply to particularly dirt and rust prone systems. Cast iron radiators or steel pipe would be a good example of a prime candidate for dirt separation.

Lately we are seeing another option to dirt separation products called magnetic separation.  By adding a magnetic component to the separator we can pull out the finest of particles. One common concern is older non–barrier tube hydronic systems. Plastic, PB EPDM and PEX have been used as hydronic and radiant tube.

Oxygen molecules can enter thru the wall of the tube, that does not include a 100% O2 barrier, and support corrosion. The fine magnetic sludge you will encounter is called magnetite. It’s basically made up of the corrosion byproducts of the ferrous components in a system. Cast iron body pumps and steel expansion vessels are just a couple examples of ferrous components.

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Pump failure with magnetic particles on rotor.

Keep in mind the barrier added to some of the plastic tubing products does not stop O2 ingress 100%. Higher operating temperature systems tend to draw more O2 into the system.

One way to remove these fine particles, which are too fine to trap with a common mesh type filter, is a powerful magnet. By installing a powerful magnet or series of magnets we can attract and trap any ferrous metal particles. The magnets are either installed as a band around the outside of the separator, inside the device, or into a well in the separator.

Some brands of separators include the media to remove particles down to a 5-micron size, and use a magnet option for the finer magnetite removal.

Know magnetite by the fine, almost talcum powder consistency. It sometimes has an oily or greasy feel and will coat your fingers almost like a thick metallic paste. It reminds me of those anti-seize compounds used for engine assembly.

Screen Shot 2015-03-26 at 2.56.54 PMAnother new and exciting change in our industry is the availability of ECM motor technology for circulator pumps. This type of motor has a very strong permanent magnet inside. Under some circumstances the magnetite call travel through the bushings and seals and get trapped against the rotor of the motor. Rhyme intended.

If enough gets trapped in the small space between the rotors and can it can impede or lock the motor from spinning.

Pump manufacturers have built in protection to alleviate and minimize the potential. Samples and pictures from the field, sent to our office monthly indicate there may still a need to add magnetic separation to assure the best possible removal of the fine magnetic particles flowing thru our systems. Expect to see more and more versions and sizes of magnetic separators. Also note some products on the market offer 4 functions : air, dirt, hydraulic, and magnetic separation in one device.

Sleep well at night knowing you have taken the best steps to protect your customer’s investment. That’s my story and I’m sticking to it.

hot-rodBob ‘Hot Rod’ Rohr is currently the training and education manager for Caleffi North America. He owned his own contracting company, Show Me Radiant Heat & Solar, Rogersville, Mo. He has been a plumbing and heating contractor since 1978.

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