Actuator instrumentation

[Anarchy]

Consider a pneumatic actuator with a positioner, air lock and volume booster on.

I can understand the reasoning for putting the air lock last (ie next to the actuator) so when air is locked in there is less potential leakage path.

The problem we are having is the airlock is restricting the high flow of air produced by the booster, the obvious solution is a higher capacity air lock but failing that would putting the booster after the airlock be considered bad practice, perfectly OK or just wrong?

 

[gerhardl]

I am in doubt of what your 'air booster' actually does in your circuit, a flow diagram would help.

Anyway you have to consider that through a flowpath the flow is a function of the total Cv of all components in the path. If you do not alter the amount of air or input (or output) pressure or the size of output/input flow diameters (eg. the Cv), then the order of the components will not alter the flow.

Have you checked that the pipelines and components (solenoid valves) before your described components are optimal and do not add to your problem by giving additional restrictions?

If your actuator is a 'critical for safe operation device', highest possible security should be sought: original placement of booster and larger size. (If your diagram does not convince me otherwise!)

 

[Anarchy]

The booster/relay amlifies the air out of the positioner, the booster is a relatively large Cv compared to the air lock. We have swapped the airlock and booster around and operating speed is vastly increased.

We are happy with the performance and on air failure the actuator stays put but potentially if the booster ever developed a leak the actuator would drift open in an air fail situation.

We are unsure of how reliable a booster is and if they are considered a high risk of leaking.

I have attached a quick sketch.

 

[gerhardl]

OK- I see!

And you are of course correct: the 'capacity' will increase considerably by switching, as the booster lets more air go into the system.

Regarding safety, if a booster is reliable or not, it would be difficult to decide, and you have to weigh against consequences and cost if a failure should accure, what measures to take. Options are obviously let be as it is, increase size of airlock or alternatively other back-up installations.

 

[Anarchy]

Scrap what I said above, the operating speed does increase but the air fail position is the problem. With the booster positioned after the air lock as soon as air pressure drops to below the setpoint the actuator is vented via the booster.

So to answer my own question, the air lock needs to be after the booster, it was quite obvious when we physically experimented with the components.

 

[Anarchy]

It looks like a new larger air lock, thank you for your input.