Sheave calculator

Enter design and actual airflow, the RPMs, and the drive. The page works out the desired fan RPM, checks amps against the motor tag, and sizes a new motor or fan sheave from the charts. Nothing is saved on this page.

Variable sheaves: calculate with the MID RANGE. Don't size from the minimum or maximum of a variable sheave.

If the current sheave is variable and you don't type a measured pitch diameter, the page uses its mid-range PD, (min + max) ÷ 2 from the chart, the same way our sheave sheet does. When it recommends a variable sheave, it picks the one whose mid-range is closest to the new PD. That way the new sheave can still be adjusted either way.

Before you calculate, check that the airflow readings are right. Look for closed dampers (including fire/smoke), plugged filters, blocked or iced coils, or other restrictions, and make sure the current variable sheave has been adjusted as far as it will go.

Job (optional)

Unit (optional)

Tech (optional)

Airflow and speed

Design airflow (CFM)

Actual airflow (CFM)

Actual fan RPM

Motor RPM (actual, or tag if you can't read it safely)

Motor amps

You need these whenever the fan has to speed up.

Tag FLA (A)

Measured amps, average (A)

Drive

Belt size (e.g. A45, BX65, 2BX65, 3L33)

Belt section for the charts

Center distance, CD (in)

Fan sheave

Model (e.g. AK59, BK72) Pitch diameter, PD (in), blank = chart Bore (e.g. 1 3/16) Variable sheave

Motor sheave

Model (e.g. 1VP34, BK45)

Pitch diameter, PD (in), blank = chart

Bore (e.g. 7/8) Variable sheave

Recommend a new sheave

Change the

Motor sheaves get bigger to speed the fan up. Fan sheaves get smaller to speed it up.

New sheave series (chart)

Reference: sheave charts

These are transcribed from our Fan Sheave.xlsx chart sheets (VL -VP, LVP, AK, 2AK, BK, 2BK, B5V). Pitch diameters are in inches by belt section. Variable sheaves show min–max, and the mid-range is (min + max) ÷ 2. The calculator reads these same tables. Confirm the model and bore in the manufacturer's catalog before ordering.