Can a fail open pneumatic actuator be converted to a fail close one?

Hey there! As a supplier of fail open pneumatic actuators, I often get asked if it's possible to convert a fail open pneumatic actuator to a fail close one. Well, let's dive right into this topic and find out.

First off, let's understand what a fail open and a fail close pneumatic actuator are. A fail open pneumatic actuator is designed to keep the valve or mechanism open when there's a loss of air pressure or power. On the other hand, a fail close pneumatic actuator will close the valve or mechanism under the same conditions. Each type has its own set of applications and advantages.

So, can we convert a fail open actuator to a fail close one? The short answer is, in some cases, yes. But it's not as simple as just flipping a switch. There are several factors we need to consider.

The Mechanics Behind It

Let's talk about the different types of pneumatic actuators. There are mainly two common types: Pneumatic Piston Actuator and Pneumatic Spring Actuator.

Pneumatic Piston Actuator

In a pneumatic piston actuator, the movement is controlled by the air pressure acting on a piston. For a fail open piston actuator, when the air pressure is removed, a spring or some other external force keeps the valve open. To convert it to a fail close, we need to reverse this setup. This might involve changing the direction of the spring force or modifying the piston mechanism so that the default position is closed when there's no air pressure.

However, this conversion isn't always straightforward. The actuator's design, size, and the materials used can all affect the feasibility of the conversion. For example, if the actuator is made of a specific alloy that's difficult to work with, it might be challenging to make the necessary modifications.

Pneumatic Spring Actuator

A pneumatic spring actuator uses a spring to provide the fail-safe action. In a fail open spring actuator, the spring is set up to push the valve open when there's no air pressure. To convert it to a fail close, we need to change the spring's pre - load and its orientation.

We have to ensure that the spring has enough force to close the valve properly under all operating conditions. This might require testing and adjusting the spring multiple times. Also, we need to check if the actuator's housing can accommodate the new spring configuration without any interference.

The Process of Conversion

If we decide that the conversion is possible, here's a general process we might follow:

1. Inspection: First, we need to thoroughly inspect the fail open pneumatic actuator. Check for any signs of wear and tear, damage, or corrosion. This will help us determine if the actuator is in a suitable condition for conversion.
2. Design Modification: Based on the type of actuator, we'll come up with a design for the conversion. This might involve creating new parts or modifying existing ones. For example, we might need to machine a new piston or change the spring seat.
3. Part Replacement: Once the design is finalized, we'll replace the necessary parts. This could include the spring, piston, or other components. We need to make sure that all the new parts are of high quality and are compatible with the existing actuator.
4. Testing: After the conversion, we'll conduct a series of tests. This includes testing the actuator under normal operating conditions, as well as simulating a loss of air pressure to ensure that it fails close as expected. We'll also check for any leaks or other issues that might affect the performance of the actuator.

Advantages and Disadvantages of Conversion

Advantages

• Cost - Saving: Converting an existing fail open actuator to a fail close one can be more cost - effective than buying a brand new Fail Close Pneumatic Actuator. This is especially true if the actuator is relatively new and in good condition.
• Time - Saving: Instead of waiting for a new actuator to be manufactured and delivered, the conversion can be done relatively quickly, reducing downtime.

Disadvantages

• Technical Challenges: As mentioned earlier, the conversion process can be technically challenging. There's a risk that the conversion might not work as expected, leading to additional costs and delays.
• Limited Compatibility: Not all fail open actuators can be converted to fail close ones. Some actuators might have a design that makes the conversion impossible or extremely difficult.

When to Consider Conversion

If you're in a situation where you have a fail open actuator that's still in good condition but you need a fail close one, conversion could be a viable option. For example, if there's a change in the process requirements at your facility, and you need the valve to close in case of a power failure instead of staying open.

However, if the actuator is old, damaged, or if the conversion process is too complex, it might be better to invest in a new fail close pneumatic actuator.

Conclusion

So, to sum it up, converting a fail open pneumatic actuator to a fail close one is possible in some cases, but it's not without its challenges. It requires a thorough understanding of the actuator's design, careful planning, and proper testing.

If you're considering a conversion or have any questions about our fail open pneumatic actuators, don't hesitate to reach out. We're here to help you make the best decision for your application. Whether it's conversion or purchasing a new actuator, we can provide you with the expertise and support you need.

References

• Pneumatic Actuator Handbook: A comprehensive guide on the design and operation of pneumatic actuators.
• Industry standards and guidelines for pneumatic actuator conversion.