Notes from a hotel room: the true cost of pneumatic actuation

Notes from a hotel room, by Bill Knecht

Well, we made it through the holidays and it’s full speed ahead.

I was in a meeting with several engineers, and several were talking about operating costs. They were initially trying to see if they could run a plant totally autonomously. That was not acceptable. Payroll is a huge cost. They talked about equipment efficiency. Everyone in the room chimed in about various things they had seen or heard about in the last few years. I was not the only sales guy in the room and one of the other sales guys who sells very high-end products commented that “You get what you pay for”. That is the absolute truth. In the process world cheap price usually equates to short operating life. I can’t argue that. I added that looking at overall design and taking into account the day-to-day operating costs could reduce cost of ownership.

So, Compressed air cost, what is it? I’m not going to get into how to determine your compressed air cost, if you are responsible for your plant air system you are aware of your cost. But for this discussion let’s use $0.22/MCF as a base line. I suspect that is a very conservative number based on how power bills are rising these days. If you do all the math and you lose about 10,000CFM a day your annual cost per year is over $800.00. That needs to be multiplied over the entire plant.

In researching this information, it seems that some instrument/actuator/positioner manufacturers have tried to go to a ZERO bleed package. It turns out that doing such reduces the accuracy of the positioner and they comment that the cost of the bleed air is minimal compared to the cost of production issues. That is an argument for plant management. But multiply a single air bleed package times 100 or 1000 valves I think it becomes significant. Not counting that every cycle of a pneumatic actuator consumes air.

Emerson publishes air bleed rates at 80 PSI of 49SCFH. That is significant. That is just the positioner, and you must add the air exhausted from the actuator itself. Now I’m not saying change over an entire facility to electric actuation, that is cost prohibitive. But in the case of a new plant or a major piping upgrade it is worth looking at electric actuation.

I have in my career sold both pneumatic and electric actuators. And I’m certainly an advocate of making the most efficient and cost-effective choice. It’s all up to you.