Need help comparing numbers with if function

I am trying to compare three cells containing numbers. I would like the result of the function to display text if any of the values differ from the others by + or - 20 points.

Example:
C1 855 This number 20 points lower than the first or second number, but could be 20 points higher.
C2 875
C3 875

I have a partial function that works comparing one of the numbers.

=IF(C1<=C2-20,"Valve Leakby",IF(C1>=C2+20,"Valve Not Open",IF(C1<>C2+20,"")))

Thanks dilipandey,
I'm not sure I am explaining the issue correctly, the numbers in column "C" will change each time the sheet is opened. The funtion I have shown does what I want comparing C1 to C2, what I am looking for is to compare each cell with the other. Any time one of the cell numbers change greater or less than 20 from the other two cells, I want the text displayed next to the cell that has the deviation.
example.jpg
Hope I explained that correctly and thank you for your response

Yes, and the function I have does that, but only compares C1 to C2. I need each cell to compare itself to the other two and give the same text.
I'm trying to upload the excel file.

I think that will do it...Thank You so much for your patience. It's wonderful to have people like yourself on here to help those of us trying to learn.

Thanks again and have a good Year!