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Fan belt tension.

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Dave Faust_2
Dave Faust_2 Member Posts: 6
in THE MAIN WALL
For two decades I've tensioned v-belts by estimation but now my I'm told there not tight enough & that I should use a tensionometer. Ok, for VAV I can see why, but what about constant volume? This current project is a chilled water, forced air, constant volume unit that dosn't cool the building. This unit always uses constant air circulation (they are dorms, occupied 24 hrs./day). Dosn't no squeal on startup mean belts are tight enough?

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  • hvacfreak
    hvacfreak Member Posts: 439
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    Lucy Goosey

    https://www.emersonclimatecontractor.com/webapp/wcs/stores/servlet/ctp/cs/faq_BrowningVbelt_CS.jsp?RootNode=20_Support&OpenNode=15_Browning_V-Belt&User=false

    You know...I set up large AHU's and fans often ( new ) ...and I err on the side of " loose ". A loose belt wont trash bearings or cause alignment problems. A tight one will. I go by feel , sight , and a balance report. Above is a Browning link...they're my favorite drive manufacturer. -M

  • Unknown
    Unknown
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    I was taught...

    5/8" deflection. Adjust you belt(s) place a ruler across them, with your free thumb press on one belt pushing it toward the other belt as far as it will go. The distance you can deflect it should be ~ 5/8". I agree a little loose is better than too tight.
  • Bruce Stevens
    Bruce Stevens Member Posts: 133
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    And I was taught

    place ruler across top of pulleys and pushing down on top belt you should have an 1 inch of deflection
  • Maine Doug_65
    Maine Doug_65 Member Posts: 24
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    Squeal

    >>>Dosn't no squeal on startup mean belts are tight enough?<<<

    In the buildings I managed, on large units some squeal was appropriate as the slippage on startup allowed the motor to come up to speed with less struggle and reduced startup current. No squeal once the load was up to speed.
  • hvacfreak
    hvacfreak Member Posts: 439
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    you know

    I wanted to say that I read somewhere like 3/8 center to center ( shafts ) per ft . So , a larger unit with 2 ft center to center on drive and driven would be 3/4 inch. And I agree with the squeal...if you get a large hp motor with no soft start or vfd , something has to give on start up , and hearing the belt(s) slip on start-up , to me , is not a bad thing. Belts are usually easy to change , bearings and shafts are not.
  • Unknown
    Unknown
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    Makes sense.

    I'll admit I've always thought 5/8 was a little tight but I know I picked it up from somewhere and didn't just make it up. I've never heard of allowing belts to squeal before but I'll take you guys' word for it.

    One rule of thumb, if you adjust a belt and two weeks later it blows a bearing, you probably had it too tight. ;)
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