Hello. My problem is with two rather large vessels, A and B. Vessel B (rated for nearly a full vacuum) is kept at a normal vacuum of about 12” w.c. We are installing vessel A (rated for 20” w.c.) about 100’ away from B, and will connect the two together with a duct. Now, vessel B is known to have a fluctuating vacuum, so it is my mission to size a vacuum breaker for vessel A. I know with PSV’s, they recommend the pressure set point not be less than 10% less than the rated pressure, so I think for our vacuum breaker, sizing it to open at 18” w.c. should be ok.
My problem is trying to figure out what the design flow should be. Initially, I calculated what the airflow should be if somehow both outlet pumps (usually only one operates, the second is installed spare) are running, and the vessel drain is open. This loss of liquid would need to be replaced by the flow through the breaker, correct? But, if I consider if the vacuum in Vessel B drops, then how much flow is requried? Do I try to determine what theoretical airflow can travel through our 100’ long duct at a differential pressure of 18”? That seems like it would be pretty high, and I am not sure I see why the breaker would be required to pass that much. Plus, since I don't know what breaker I am going to pick yet, I don't know it's orifice size, therefore can not determine what the pressure drop through it would be.
I usually tend to try to look into things too much and am assuming I am doing the same here. Can anyone set me straight? Thanks for any and all help.
My problem is trying to figure out what the design flow should be. Initially, I calculated what the airflow should be if somehow both outlet pumps (usually only one operates, the second is installed spare) are running, and the vessel drain is open. This loss of liquid would need to be replaced by the flow through the breaker, correct? But, if I consider if the vacuum in Vessel B drops, then how much flow is requried? Do I try to determine what theoretical airflow can travel through our 100’ long duct at a differential pressure of 18”? That seems like it would be pretty high, and I am not sure I see why the breaker would be required to pass that much. Plus, since I don't know what breaker I am going to pick yet, I don't know it's orifice size, therefore can not determine what the pressure drop through it would be.
I usually tend to try to look into things too much and am assuming I am doing the same here. Can anyone set me straight? Thanks for any and all help.
