MKP fans

M.K. Plastics Direct Drive Fan Arrangements

One of our ongoing missions is to educate mechanical engineers and design professionals about our products and engineered systems. Part of the Flow Tech advantage is that we, along with our manufacturers, help develop HVAC solutions that are the most appropriate and energy-efficient for the application. Facilitating lunch and learns, exhibiting at trade shows and one-on-one meetings are all some of the ways we provide education and recommendations. More recently we’ve begun to utilize our blog for educational/design recommendation posts as well.  M.K. Plastics (MKP), our corrosion-resistant exhaust system manufacturer, periodically releases technical articles to us that feature similar design recommendations. Today’s post comes from their latest technical article which discusses designing direct drive fan arrangements…

Direct drive fan arrangements have several advantages over belt drive, and with the use of variable frequency drives to modulate speed, can offer an attractive option. Belt drive uses a combination of belts and pulleys to turn the wheel, direct drive is used where reduced maintenance is preferred.

Arrangement Types

For vertical inline direct drive fans there are two types available: Direct drive arrangement #4 where the wheel is directly mounted onto the motor shaft, and direct drive arrangement #2 where the wheel is mounted onto a shaft with bearings and a coupling on a support stand or bracket in the fan housing. Both are direct drive (no pulleys or belts), but are different in assembly.

Arrangement #4

Arrangement #2

Why is Direct Drive Arrangement #4 Preferred?

• It is the simplest in direct drive design
• It is a true ‘direct drive’ arrangement
• Wheel is directly mounted to the motor shaft
• No additional bearings or couplings required – less maintenance

Direct Drive Arrangement #2 – More Components, More Cost

• More complicated direct drive design
• Wheel is not mounted directly to motor shaft
• Requires additional shaft, bearings and coupling mounted inside the fan
• Bearings and coupling require maintenance and service costs
• Coupling alignment needs to be maintained
• Lateral wind pressure loading and fan vibration can cause the coupling to wear and prematurely fail
• Rarely used today

Operation and Maintenance

One could argue for Arrangement #2 that having the drive components in a bifurcated housing makes serviceability easy for the end user. But in fact, motor removal is the same whether it is Arrangement#2 or #4 – the discharge stack needs to be removed and a crane is required to pull the motor out. On larger fans the fan must be completely removed off its support and moved to the roof for disassembly.


Bifurcated Opening #2


Bearing Replacement on Arrangement #2

• Wheel needs to be supported to prevent shifting down during bearing replacement
• Coupling needs to be removed from the shaft
• Motor may need partial removal from its support
• Bearing unbolted and removed from shaft
• Slide new bearings onto the shaft
• Reinstall coupling bushings
• Align bearings between motor and fan shaft
• Secure bearings onto fan shaft
• Remove blocking from under the wheel, connect extended lube lines and caulk around bearing flange
• Test fan and adjust bearings and shaft/coupling alignment. Adjust if necessary


bearing replacement

Bearing replacement on arrangement #2.



While the idea of having a direct drive inline fan does have benefits over belt drive, both have their pros and cons. Direct drive Arrangement #2 assumes that having easy access to the drive-train in a fan opening will make life easier for the customer – everything is there, right in front of you. But in fact, from a practical point of view, it doesn’t. The end user now has a fan shaft, bearings and coupling to maintain. This entails more maintenance and costs for the end user. A true direct drive Arrangement #4 has the motor shaft directly mounted on the wheel. Sometimes simplicity is the best.


About M.k. Plastics

For over 45 years, M. K. Plastics has been engineering, designing, and fabricating thermoplastic and FRP ventilation components and systems for institutional and industrial applications. Founded in 1963, today M. K. Plastics has facilities and offices in Montréal, Québec, Canada; Spiez, Switzerland; Troy, OH and Mooers, NY, USA. M.K. Plastics has technical sales representatives that are in major cities throughout the globe. MKP designs and manufactures complete ventilation systems in their own facilities assuring quality, reliability and constant innovation. Their dedicated engineering and R&D teams, design, refine and test all of their fans and blowers in their 70,000 sq. ft. manufacturing facility and performance test laboratory in Montréal, Québec, Canada.

For more information about MKP and how we can provide their solutions please visit our website or email us. If you’d like to schedule a lunch and learn, or are interested in other educational opportunities please contact Nichole Petersen. Don’t forget you can stay up-to-date on all the latest industry news by following us on social media: Twitter, LinkedIn, Google+ and YouTube!

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