What is the use of a butterfly valve in axial compressor

[MattH150197]

Homework Statement

In the image I have included it shows a diagram of the setup we used in a lab and you can see that at the right hand side there is a butterfly valve so I am wandering what would be the use of the valve in this situation. Since its after the compressor I was thinking that its there in case of surge to prevent the direction of flow reversing and going back to the compressor and maybe damaging it, is this right or is it for a another purpose. Thanks.

 

[Nidum]

The butterfly valve is there to reduce the exit flow area . As the valve is closed more the back pressure on the compressor gets higher .

Not understanding how this works may account for the low value of pressure rise described in your previous posting . If the valve were wide open during a test the pressure rise across the compressor would be very small .

Note though that if the valve is closed too much the compressor may go into surge .

 

[MattH150197]

Thanks for the quick response!

 

[Nidum]

Do you know anything about axial compressor theory and axial compressor performance charts ?

 

[MattH150197]

Only the very basics, I am new to the subject.

 

[Nidum]

OK .

 

[MattH150197]

I wonder if you could help me grasp the understanding of this, the image shows the instructions we were set for the experiment, in 4.) it says to close the butterfly valve one full revolution and in 5.) it says to continue closing it at one revolution intervals and you can see from the results set up we had in the other image we took 10 readings so does that mean at the beginning of each reading the valve would have been closed?

 

[Nidum]

Not quite sure what you are asking about here ?

The instruction sheet tells you to perform a series of tests with each test being for a different steady state running condition .

For each test you preset the butterfly valve to required position and leave it set at that position for the duration of that test .

For each successive test the valve is closed more fully but for the duration of anyone test valve remains in a fixed position .

 

[MattH150197]

Yeah that makes sense thanks, the part confusing was where it says continue closing it at one revolution intervals which sounded like turn the valve 360 degrees between each interval which didn't make any sense. Thanks for clearing it up