In some customer inquiries about electric butterfly valves, reducers are recommended. This concept might be unfamiliar to customers. In fact, it’s a crucial component that’s easily overlooked. The main function of a reducer is to reduce speed and increase torque, protect the motor, solve the problem of motor-valve load mismatch, and reduce costs.
This article will analyze the following questions from the perspectives of engineering principles and practical applications: Why is a reducer needed when the electric actuator already has a motor?
How to rationally select a reduction device based on torque?
And how to achieve optimal matching between the electric butterfly valve and the reducer?
1. Why do we recommend configuring electric butterfly valves reducers?
And electric butterfly valve reducer: Essentially a power transmission device, it utilizes the gear meshing principle (commonly worm gears, planetary gears, or multi-stage spur gears) to achieve “speed reduction and torque increase.”
1.1 Torque Requirement Much Higher Than Motor Output
1.1.1 Factors Affecting Torque
During the opening and closing process, a butterfly valve needs to overcome various resistances, which are also called “torque”:
Valve Diameter (DN) – The larger the diameter, the greater the torque.
Nominal Pressure (PN) – The greater the pressure, the greater the torque.
Differential Pressure of the Medium (the force exerted by the medium pressure on the valve plate) – The greater the pressure difference, the greater the torque.
Sealing Pre-tightening Force between the Valve Seat and the Valve Plate – The greater the pre-tightening force, the greater the torque (especially for soft-seal structures, where PTFE requires about 10% more than EPDM).
Friction of the Valve Shaft and Bearings – The greater the coefficient of friction, the greater the torque.
Deposits or jamming after long-term operation.
These factors combined often result in the starting torque of a butterfly valve being much higher than the torque required to maintain operation.
1.1.2 Typical Characteristics of the Motor:
High speed (typically 1400 rpm, 1500 rpm, 3000 rpm or higher) but low torque.
Directly driving a butterfly valve often results in insufficient torque, leading to a situation where the valve rotates quickly but cannot be pushed. Therefore, a speed reducer is necessary to amplify the torque.
Torque Amplification: The reduction ratio i (input speed/output speed) directly amplifies the motor torque. Output torque ≈ motor torque × i × transmission efficiency η (η is typically 60%~90%, worm gears have lower efficiency but stronger self-locking).
1.2. Achieving Smooth Opening and Closing, Preventing Water Hammer
Butterfly valves are 90° rapid opening and closing valves. If the opening or closing speed is too fast, it will cause:
-Sudden acceleration or stopping of fluid in the pipeline
-Water hammer phenomenon
-Impact damage to pipelines, valves, and even pump equipment
The speed reducer reduces the high motor speed to a suitable low output speed for the butterfly valve (typically a few seconds to tens of seconds for the full stroke), enabling the valve to achieve smooth “slow opening and slow closing,” thereby significantly improving the safety and service life of the system. 1.3. Protecting the Actuator and Extending its Service Life
The speed reducer is not only an “amplifier” but also a “buffer”:
-Reduces motor load
-Absorbs some impact
-Prevents reverse drive
Prevents overload operation
The worm gear reducer has irreversible direction, which can prevent external forces from driving in reverse and protect the electric actuator. In addition, the speed reducer automatically stops when the torque exceeds the limit, protecting the motor and valve; this is of great significance for improving the reliability and service life of the electric actuator.
2. How to select a suitable electric butterfly valve reducer based on torque?
The core of speed reducer selection lies in: performing reverse calculation based on the butterfly valve torque.
2.1. Determining the Required Torque for the Butterfly Valve
The following methods are usually used in engineering:
(1) Check the manufacturer’s data (recommended)
This is the most accurate method. For example, the following is our company’s torque table:
| DN | PN6 | PN10 | PN16 |
| Torque,Nm | |||
| 40 | 9 | 11 | 15 |
| 50 | 9 | 12 | 16 |
| 65 | 15 | 17 | 20 |
| 80 | 23 | 29 | 34 |
| 100 | 35 | 43 | 52 |
| 125 | 60 | 70 | 84 |
| 150 | 100 | 110 | 118 |
| 200 | 168 | 180 | 220 |
| 250 | 280 | 320 | 380 |
| 300 | 360 | 490 | 510 |
| 350 | 600 | 620 | 960 |
| 400 | 800 | 920 | 1500 |
| 450 | 1120 | 1200 | 1800 |
| 500 | 1380 | 1680 | 2200 |
| 600 | 2280 | 2600 | 3600 |
| 700 | 4800 | 5016 | 5208 |
| 800 | 5280 | 5400 | 6668 |
| 900 | 8900 | 9800 | 10908 |
| 1000 | 9980 | 11000 | 12720 |
| 1200 | 18000 | 20000 | 20856 |
(2) Add a safety factor
Considering operating condition fluctuations, aging, and jamming:
> Recommended safety factor: 1.3 ~ 2.0
2.2. Calculate the motor output torque
Motor torque formula:
> T = 9550 × P / n
Where:
P: Power (kW)
n: Speed (rpm)
For example:
0.75 kW motor, speed 1400 rpm
→ Output torque approximately 5 Nm
Obviously far below the butterfly valve’s requirements.
2.3. Checking the Reduction Ratio for Electric Butterfly Valve Reducer
Reduction Ratio Calculation Formula:
> i = Valve Torque / Motor Torque
Example:
Valve Requirement: 600 Nm
Motor Output: 6 Nm
→ i = 100
Considering efficiency (approximately 0.8):
> Actual reduction ratio should be selected: 120–150
2.4. Common Electric Butterfly Valve Reducer Type Selection
2.4.1 Worm Gear Reducer (Most Mainstream)
Features:
Good self-locking performance (prevents reverse rotation)
Compact structure
Low cost
Suitable for:
On/off type electric butterfly valves
Most industrial scenarios
2.4.2 Multi-stage Reduction Structure
For large-diameter butterfly valves (DN≥400):
Commonly uses “electric actuator + external worm gear box (two-stage head valve reducter)”
3. Matching Principles for Electric Butterfly Valves and Reducers
Proper matching not only affects performance but also directly relates to cost and lifespan.
3.1. Torque Matching Principle
The following must be met:
> Actuator output torque ≥ Valve maximum torque × Safety factor
However, two extremes of an electric butterfly valve reducer must be avoided:
Too low torque → Valve cannot open or close
Too high torque → Wasted cost + poor control
3.2. Balance of Speed and Torque
The reduction ratio determines two key parameters:
Torque (increases with increasing reduction ratio)
Speed (decreases with increasing reduction ratio)
3.3. Differences in Different Sealing Structures
3.3.1 Soft-Seal Butterfly Valve (EPDM / PTFE)
High starting torque
Sealing depends on clamping force
Selection recommendation:
High reduction ratio
Low speed operation
3.3.2 Hard-Seal Butterfly Valve (electric Double Eccentric butterfly valve / electric Triple Eccentric butterfly valve)
Low friction
Stable torque variation
Selection recommendation:
Appropriately increase speed
Relatively small reduction ratio
3.4. Control Method Matching
On/Off Type: Ordinary reducer is sufficient
Adjustable type: Requires a high-precision reduction gear structure
3.5. Cost Optimization Strategy
Common Misconceptions:
Increasing motor power while ignoring the reducer
Over-selection leading to system redundancy
The best solution is usually:
> Small-power motor + reasonable reduction ratio
This satisfies torque requirements while controlling costs.
4. Engineering Practice Recommendations
In actual projects, the following experience can be referenced:
DN200 and below: Prioritize integrated electric actuators (built-in reduction mechanism)
DN300 and above: External worm gear box structure is recommended
High-pressure or long-term inactive conditions: Select a reducer with a torque of at least 1.5 times the rated torque
Outdoor or harsh environments: Select a reducer with good sealing performance (IP67 or above)