franzdrs Posted April 26, 2013 Report Share Posted April 26, 2013 We have two systems that need to be connected together by a flexible hose. The first system has a fan close to the intake, and afterwards comes a series of components and then the exhaust. The second system starts with a centrifugal fan, after which comes a component and then the exhaust. The idea is to connect the exhaust of the first system with the intake of the second system, thereby having two fans in series connected by the flexible hose (12 inches diameter). What pressure will develop in the connection between the two systems? Positive due to the pressure developed by the first fan? Or negative due to the suction of the second fan? Or a transition from positive to negative? In case of a negative pressure, will it be limited by the total pressure that the second fan can develop? I appreciate any answers. Quote Link to comment Share on other sites More sharing options...
Les Posted April 26, 2013 Report Share Posted April 26, 2013 Franz, Nice to hear from Peru. Too many variables for any answer with the info given. Quote Link to comment Share on other sites More sharing options...
Jim Katen Posted April 27, 2013 Report Share Posted April 27, 2013 The pressure between the two systems will depend on the *volume* of air moved by each one. Quote Link to comment Share on other sites More sharing options...
Marc Posted April 27, 2013 Report Share Posted April 27, 2013 The pressure between the two systems will depend on the *volume* of air moved by each one. And the dynamic characteristics of each fan, among other things. Les said it...too many variables. Marc Quote Link to comment Share on other sites More sharing options...
John Kogel Posted April 27, 2013 Report Share Posted April 27, 2013 We have two systems that need to be connected together by a flexible hose. The first system has a fan close to the intake, and afterwards comes a series of components and then the exhaust. The second system starts with a centrifugal fan, after which comes a component and then the exhaust. The idea is to connect the exhaust of the first system with the intake of the second system, thereby having two fans in series connected by the flexible hose (12 inches diameter). What pressure will develop in the connection between the two systems? Positive due to the pressure developed by the first fan? Or negative due to the suction of the second fan? Or a transition from positive to negative? In case of a negative pressure, will it be limited by the total pressure that the second fan can develop? I appreciate any answers. Don't listen to these guys. They are eggheads, overthinking a simple question.1) Use identical units only. Not one from your uncle's shed and one from the corner store. They've got to be equal in age as well as size. They will pump air together and the pressure in the plenum will be equal. No problemo. Quote Link to comment Share on other sites More sharing options...
kurt Posted April 27, 2013 Report Share Posted April 27, 2013 There is that nagging little question of static pressure; if the ducts are unequal length, or if one has bends and twists and the other doesn't, or if, or if..... Quote Link to comment Share on other sites More sharing options...
John Kogel Posted April 27, 2013 Report Share Posted April 27, 2013 If the connecting duct which I named the plenum is a 12" hose, then the killer is atmospheric pressure on the hose. If you have suction on the hose, negative pressure, the hose will collapse like a tons of bricks landed on it. So if there is a weak pump, it needs to go in the back. Put the best fan up front and no problemo, Franco. Bolt it all down. With engineering, it could become a jet engine. [] Quote Link to comment Share on other sites More sharing options...
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