When troubleshooting or monitoring the status of a low-pressure pneumatically powered or controlled machine — such as medical equipment or air-logic circuits — it can be next to impossible to determine if air is flowing through a particular line, even if clear tubing is being used. You could provide a flowmeter for each critical line, but that can get expensive. You could take the low-tech route and pinch the line, but that will only indicate a line is pressurized — you still don’t know if flow is actually occurring. Some might try loosening a line to let air leak out, but this unsafe practice holds potential dangers or could cause a machine