Hi,

My company builds machinery that always includes a few blowers. When our PLC gives these blowers the “Start” signal, we want to have confirmation that each blower is actually moving air. (For example, to make sure a damper has not failed in the closed position or a belt has broken).

Currently, we use Dwyer 1910-00 Compact Low Differential Pressure Switch (with an operating range of 0.07-0.15” w.c.). These pressure switches have a high pressure port and a low pressure port. We run a metal air tube from the high pressure port into the duct at the blower exit, and we angle this air tube so that the blower blows right into it. We leave the low pressure port open to atmosphere. Even though the operating range of this pressure switch is the lowest I could find, we always have trouble getting these to work at lower blower speeds.

I was wondering if anyone could recommend a different way for me to confirm blower air flow that might be more sensitive to low air flows than the differential pressure switch that I’ve been using. (I just want a discrete switch that will tell me if air is moving or not – I don’t need an analog air flow measurement).

Any advice will be greatly appreciated.

Thanks in advance,
Paul

 

Why are you leaving the LP connection open to atmosphere? It should be connected to the duct also but just measuring static pressure.

If the velocity is really low try measuring the pressure drop before and after the fan, that will tell you if it's running, but not if it's blocked off further down.

I have an inexpensive solution to measure the velocity in low pressure ducts.

Roy

 

Hi Roy,

Thanks for your response. If I have a fan with a duct going into it and a duct going out of it, where should I expect the static pressure to be higher? In the inbound duct or the outbound duct?

I would be interested to hear about your solution to actually measure the airflow. My limitations are that the air I am moving can be high temperature. If you have something that could go up to 300-350 deg F ( 149 - 177 deg C), that would be perfect. Ideally, I'm looking for something with an adjustable setpoint that would give me a contact closure when air flow is at or above setpoint.

Thanks for your help,
Paul