Adjustable Speed Sheaves
Function: Variable pitch diameter for mechanical speed adjustment
Grooves: 1 to 2 (adjustable pitch)
Belt Sections: A, B, 3V, 5V (varies by model)
Mounting: QD bushing or fixed bore (varies by series)
Speed Range: Typically 3:1 to 4:1 speed ratio adjustment
Brands: Gates, Continental/ContiTech
In Stock: Same-day shipping from Houston
Adjustable speed sheaves (also called variable pitch or variable speed sheaves) let you change the output speed of a V-belt drive by mechanically adjusting the effective pitch diameter of the sheave. The two halves of the sheave move closer together or farther apart, which forces the V-belt to ride higher or lower in the groove, changing the drive ratio without swapping sheaves or installing a variable frequency drive (VFD).
These sheaves are the simplest and most cost-effective way to fine-tune fan speed, blower output, or machine speed on drives that do not require continuous speed variation under load. They are commonly found on HVAC air handlers, exhaust fans, and light industrial equipment where the speed is set during commissioning or seasonal adjustment and left until the next service interval.
How Adjustable Speed Sheaves Work
A standard V-belt sheave has a fixed groove width. The belt sits at a fixed depth in the groove, which sets a fixed pitch diameter and a fixed speed ratio.
An adjustable speed sheave has a movable flange. By turning an adjustment mechanism (typically a threaded hub or set screw), you move one flange relative to the other. This changes the groove width:
Narrower groove = belt rides higher = larger effective pitch diameter = slower driven speed (if on the motor sheave) or faster driven speed (if on the driven sheave).
Wider groove = belt rides lower = smaller effective pitch diameter = faster driven speed (if on the motor sheave) or slower driven speed (if on the driven sheave).
The adjustment is made while the drive is stopped. The belt tension must be re-checked and adjusted after changing the pitch setting. Adjustable speed sheaves are not designed for on-the-fly speed changes while the drive is running under load.
Adjustable Speed Sheave Series
| Series | Details |
|---|---|
| VP (Variable Pitch) | Mount: Fixed bore with set screw. Grooves: 1. Sections: A, B. Use: Light duty fans, blowers, and OEM equipment. Simplest and most economical adjustable sheave. ODs from 3" to 6"+. |
| 2VP | Mount: Fixed bore with set screw. Grooves: 2. Sections: A, B. Use: Dual-belt drives needing speed adjustment. Small fans and blowers with two-belt setups. |
| VS QD (Variable Speed QD) | Mount: QD bushing (removable). Grooves: 1 to 2. Sections: A, B, 3V, 5V. Use: Medium duty HVAC and industrial applications. QD mount allows shaft flexibility and faster maintenance. |
Part Number Decoder
| Example | What It Means |
|---|---|
| 1VP40 x 5/8 | 1 groove, variable pitch, 4.0" OD, 5/8" fixed bore. |
| 1VP50 x 3/4 | 1 groove, variable pitch, 5.0" OD, 3/4" fixed bore. |
| 2VP50 x 7/8 | 2 grooves, variable pitch, 5.0" OD, 7/8" fixed bore. |
| 1VP68 x 1 | 1 groove, variable pitch, 6.8" OD, 1" fixed bore. |
| VS QD 1-3V | 1 groove, variable speed, 3V section, QD bushing mount. Bushing ordered separately. |
Fixed-bore VP models include the bore size in the part number. QD-mount VS models require a separate QD bushing ordered by shaft diameter.
Speed Adjustment Range
The speed range of an adjustable speed sheave depends on the OD, the minimum and maximum groove settings, and the mating sheave on the other shaft. Most adjustable speed sheaves offer a 3:1 to 4:1 speed ratio adjustment range when used as the driver (motor) sheave with a fixed driven sheave.
| Configuration | Effect |
|---|---|
| Adjustable on motor shaft | Adjusting the motor sheave changes the output speed at the driven shaft. Closing the flanges (belt rides higher) increases driven speed. Opening the flanges (belt drops lower) decreases driven speed. Most common setup. |
| Adjustable on driven shaft | Adjusting the driven sheave also changes output speed, but in the opposite direction. Closing the flanges on the driven sheave decreases output speed. Less common but used on some machines. |
| Both sheaves adjustable | Provides the widest speed range. Both sheaves must be adjusted together to maintain proper belt tension. Used on some specialized equipment. |
Common Applications
| Application | Details |
|---|---|
| HVAC air handlers | The most common adjustable speed sheave application. Fan speed is set during commissioning to balance airflow, then left at that setting. Seasonal re-adjustment is sometimes done. |
| Exhaust fans | Speed adjustment to match ventilation requirements for different building zones or regulatory changes. |
| Cooling tower fans | Speed tuning to match cooling load. Often adjusted seasonally. |
| Small blowers | Output volume adjustment for process air, dust collection, or drying systems. |
| Light machinery | Speed tuning on drill presses, lathes, mixers, and other equipment where a fixed set of speeds is sufficient. |
| Agricultural equipment | Seasonal speed changes on fans, augers, and processing equipment. |
Adjustable Speed vs. Fixed Sheave vs. VFD
| Option | Details |
|---|---|
| Adjustable Speed Sheave | Lowest cost. Mechanical speed change by adjusting pitch. Must stop the drive to adjust. 3:1 to 4:1 range. No electrical work. Best for occasional speed tuning (commissioning, seasonal). |
| Fixed Sheave (QD) | Fixed speed ratio. Change speed by swapping sheaves. Most reliable for constant-speed drives. Widest groove and section options. Standard for most industrial applications. |
| VFD | Highest cost. Continuous speed control under load. Energy savings at reduced speeds. Requires electrical installation. Best for processes needing real-time speed control. |
Brands We Carry
| Brand | Products |
|---|---|
| Gates | VP and 2VP fixed-bore series, VS QD variable speed sheaves. Full OD and bore range. |
| Continental | Adjustable speed sheaves for A and B sections. HVAC and light industrial replacement. |
We cross-reference adjustable speed sheave part numbers between Gates, Continental, Browning, and other manufacturers. Send us any part number and we will confirm the match.
Related Pages
Frequently Asked Questions
What is an adjustable speed sheave?
An adjustable speed sheave (also called a variable pitch or variable speed sheave) is a V-belt pulley with a movable flange that lets you change the effective pitch diameter. By adjusting the groove width, the belt rides higher or lower, changing the speed ratio of the drive. This allows you to fine-tune output speed without swapping sheaves or installing a VFD.
Can I adjust the speed while the drive is running?
No. Adjustable speed sheaves are designed to be adjusted while the drive is stopped. The adjustment mechanism (threaded hub or set screw) requires the belt to be slack to change the flange position. After adjusting, you must re-tension the belt before restarting. These sheaves are not a substitute for a VFD when continuous, on-the-fly speed control is needed.
What speed range can I get from an adjustable speed sheave?
Most adjustable speed sheaves provide a 3:1 to 4:1 speed ratio adjustment range when used as the driver (motor) sheave paired with a fixed driven sheave. The exact range depends on the sheave OD, the minimum and maximum pitch settings, and the mating sheave diameter. Wider ranges are possible with adjustable sheaves on both shafts, but this requires careful belt tension management.
Do I need to re-tension the belt after adjusting the speed?
Yes. Always. Changing the pitch setting changes the effective belt path length. If you do not re-tension, the belt will be either too loose (causing slippage, heat, and wear) or too tight (causing excessive bearing load). Re-check and adjust belt tension every time you change the pitch setting.
What is the difference between a VP sheave and a VS QD sheave?
VP sheaves have a fixed bore with set screw mount, similar to BTS sheaves. VS QD sheaves use a removable QD bushing, so one sheave fits multiple shaft sizes. VS QD sheaves are the better choice for industrial applications where shaft flexibility and faster maintenance matter. VP sheaves are simpler and less expensive for light duty or OEM use.
Should I use an adjustable speed sheave or a VFD?
Adjustable speed sheaves are best for occasional speed tuning: commissioning, seasonal adjustments, or airflow balancing. They cost a fraction of a VFD and require no electrical work. A VFD is the better choice when you need continuous speed control under load, energy savings at reduced speeds, or remote/automated speed changes. For most HVAC fan applications where the speed is set once and left, an adjustable speed sheave is the more practical and cost-effective solution.
What belt type works with adjustable speed sheaves?
Adjustable speed sheaves are designed for standard V-belts. Most VP and 2VP models accept A or B section classical belts. VS QD models may also accept 3V or 5V narrow wedge belts depending on the series. Cogged V-belts can also be used for improved flexibility and heat dissipation. Do not use timing belts or flat belts on adjustable speed sheaves.
Can Texas Belting cross-reference adjustable speed sheave part numbers?
Yes. We cross-reference between Gates, Continental, Browning, and other manufacturers. Send us the part number from your existing sheave and we will confirm the equivalent in stock, or call 888-203-2358.
