Fan Not Responding to High Pressure in Duct
Fan Not Responding to High Pressure in Duct
(OP)
Hi,
If a industrial fan inlet is blocked by a damper, will the flow decrease even if it is controlled to increase when it sees a spike in static pressure in the duct before the damper? Our fan is controlled by static pressure. We see that it is not responding to an increase in pressure (it usually speeds up). If the damper after the pressure element but before the fan is not fully open could this cause this effect (fan slowing down)?
Thank You
If a industrial fan inlet is blocked by a damper, will the flow decrease even if it is controlled to increase when it sees a spike in static pressure in the duct before the damper? Our fan is controlled by static pressure. We see that it is not responding to an increase in pressure (it usually speeds up). If the damper after the pressure element but before the fan is not fully open could this cause this effect (fan slowing down)?
Thank You





RE: Fan Not Responding to High Pressure in Duct
RE: Fan Not Responding to High Pressure in Duct
RE: Fan Not Responding to High Pressure in Duct
The pressure sensor is in the suction side of the fan.
RJB,
Positioning the sensor before the damper will not yield you the exact result you want, particularly if the damper is not activated with increased speed of the fan. This is because, at increased flowrates, considerable value of pressure is dropped across the partially closed damper and the DP across the fan may not vary much.
A description of the process and your objective will help us giving you better suggestions. Particularly, you should tell us how the pressure in the fan suction increases.
Regards,
RE: Fan Not Responding to High Pressure in Duct
Here is some more information on the process:
The fan is controlling the flow rate of air through a thermal oxidizer. The oxidizer has 3 canisters which contains heat transfer media. The air path goes through one canister, then through a combustion chamber, then out another canister. The cycles run every 2 minutes with one canister inlet damper closing and one opening. The same occurs with the outlets. The unused canister purges back into the air header. The static pressure sensor is located before the air goes through the inlet canister (measures flow). The fan is located roughly 20-30 feet after the outlet of the canisters. I don't have the fan info with me right now so I can't give what type of fan this is. There are three cycles where the dampers switch. We see that when the cycles switch from the 1st to the second, a pressure spike always occurs. This switch is where the pressure increase occurs and shuts down the oxidizer.
Right before the oxidizer shuts down, the fan amps drops and the fan starts to slow down in a stepwise fashion. The fan usually speeds up when static pressure increases in the header. This is why I asked the question in the first place.
Thanks
RE: Fan Not Responding to High Pressure in Duct
RE: Fan Not Responding to High Pressure in Duct
I fear the process is still not clear. What I understood is that air flows from a common header, in which the pressure switch is installed, into the canisters and then to the combustion chamber and then to the duct to which the fan is connected. At any time the air passes through only one canister. Correct me if I am wrong.
Is the outlet damper opening first or the inlet damper?
RE: Fan Not Responding to High Pressure in Duct
Friar Tuck of Sherwood
RE: Fan Not Responding to High Pressure in Duct