Operating fan against closed suction
Operating fan against closed suction
(OP)
Hi there,
I have an application where I am thinking of installing a fan in a vent stack. This stack is 32m high and contains gas with a SG of 3.5. The vent line is a closed system except for a number of relief valves that will vent into it in a emergency. Thus the problem is that the fan will run most of is lifetime with a "closed" suction damper. Can fans operate like this?
Regards
Alwyn
I have an application where I am thinking of installing a fan in a vent stack. This stack is 32m high and contains gas with a SG of 3.5. The vent line is a closed system except for a number of relief valves that will vent into it in a emergency. Thus the problem is that the fan will run most of is lifetime with a "closed" suction damper. Can fans operate like this?
Regards
Alwyn





RE: Operating fan against closed suction
Can you add pressure switches upstream of the relief valves set to a pressure just under the relief valve setting? Then the fan will only run when pressure approaches one of the relief valve settings. Are the relief valves used to prevent an upset in a process or protect equipment? Do you need an alarm signal to verify proper operation of the fan? What will happen if the fan is not running and a relief valve opens? Does this require the fan be installed with an uninterruptible power supply?
CRG
RE: Operating fan against closed suction
RE: Operating fan against closed suction
I will investigate your issues.
Regards
RE: Operating fan against closed suction
The fan selection should be a non-overloading wheel design (backeard inclined) so it can operate with and without airflow without overloading the motor.
RE: Operating fan against closed suction
RE: Operating fan against closed suction
1. The fan motor, may or may not overload, depending on the type of fan blading- backward curve centrifugal, forward curve centrifugal, propeller blade, radial, etc.
. Look at the fan curves for CFM/HP/SP, etc. for the answer.
For sure, a backward curve never will over load on no flow.
On the other hand, a propeller blade will overload the motor as static pressure is increased, such as when the intake gets blocked.
Another issue is the blocked intake static pressure heat that is generated [and motor heat too, if it is located in the air stream.] The fan/motor may require a minimum flow to dissipate generated heat. The higher the fan static pressure rating, the more likely this will demand attention.
Gnordo