The pneumatic actuator is a key final control element in automatic butterfly valve operation. Its design directly affects operating speed, stability and service life.

Many butterfly valve actuators on the market have complex construction: a cylindrical pin connects the shaft to a locating sleeve, the exhaust port is on the side of the lower flange, and a split spring clip secures the flange to the outer cylinder wall. These designs involve many parts and difficult assembly, and can cause restricted exhaust, high resistance, bearing seizure and insufficient driving force.

To address these issues, newer butterfly valve actuators incorporate systematic design improvements. This article describes 8 key changes.

1. Common weaknesses in older products

Before discussing improvements, consider the common issues in traditional designs:

  1. Complex construction and unnecessary parts: a cylindrical pin joins the shaft and locating sleeve, and the valve stem is then connected to the sleeve. This extra coupling complicates the structure.
  2. Poor exhaust-port layout: placing the port on the side of the lower flange creates an indirect exhaust path that can restrict discharge and reduce operating speed.
  3. Less secure fastening: a split spring clip connects the flange and cylinder wall, with a risk of loosening during long service or vibration.
  4. High resistance and poor stability: internal friction reduces freedom of movement and can lead to bearing seizure or insufficient drive.

2. Eight improvements in newer actuators

To address these issues, the newer design improves the following 8 areas:

Simplified transmission without the locating sleeve

The old design pins the shaft to a locating sleeve, then connects the stem to that sleeve. The new design connects the stem directly to the shaft, eliminating the extra sleeve for simpler construction and more direct transmission.

Optimized exhaust-port position for faster discharge

The port moves from the side to the face of the lower flange, and its diameter increases. Exhaust is substantially faster, improving response.

Stronger bracket mounting

Two M8 threaded mounting holes are replaced by four M5 holes. More evenly distributed fastening points make the installed bracket more stable.

Continuous flange welding for improved safety

Continuous high-frequency TIG welding with filler joins the upper and lower flanges to the outer cylinder wall, replacing split spring clips. Connection strength increases substantially for safer, more reliable long-term service.

Improved piston material and construction

The piston material changes from aluminum alloy to nylon. Aluminum alloy can oxidize during long service and may cause seizure; nylon does not oxidize and provides better reliability.

The piston's open 90° cam slot also changes to a closed, stepped, bidirectional 90° slot. This improves control of clearances between the piston, shaft, bearings and pins, strengthens the internal assembly, substantially reduces friction and improves freedom of movement.

Round guide pillars replace rolling bearings

Rolling bearings attached to both inside walls of the outer cylinder are removed. Instead, two round guide pillars on the upper flange guide piston movement.

This reduces friction and eliminates bearing seizure at its source.

Simpler shaft manufacture

The shaft is machined from round steel stock rather than made as a cup-shaped investment casting. Removing some casting stages simplifies manufacture while maintaining dimensional accuracy.

Improved spring arrangement for greater output

The two springs, one large and one small, are replaced by a single larger-diameter spring. Greater spring force increases output and is particularly suitable for reliable return in single-acting actuators.

3. Practical benefits

The direct benefits of these 8 improvements can be summarized in four points:

  1. More responsive operation: a freer exhaust path and faster discharge give a quicker valve response.
  2. More stable running: controlled clearances, reduced friction and more accurate guidance reduce the risk of seizure.
  3. More reliable construction: continuous welds, guide pillars and a nylon piston support dependable long-term use.
  4. Longer service life: wear-resistant materials such as copper at key friction points improve wear resistance.

4. Conclusion

Changes to part count, materials and connections may appear minor, but they all serve faster movement, steadier operation and longer life.

Simpler construction, lower friction and stronger connections make the actuator more reliable in the field.

When selecting a butterfly valve pneumatic actuator, examine the transmission, exhaust layout, materials and fastening methods to choose a genuinely stable, durable product.

Zhejiang HES Automatic Instrument & Valve Co., Ltd.

Established in 1989 · More than three decades dedicated to pneumatic actuators