Pressure between two fans in series

[franzdrs]

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.

[Les]

Franz,

Nice to hear from Peru.

Too many variables for any answer with the info given.

[Jim Katen]

The pressure between the two systems will depend on the *volume* of air moved by each one.

[Marc]

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

[John Kogel]

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.

[kurt]

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.....

[John Kogel]

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. []