3 replies to this topic

[chemproc]

I was wondering if anyone knows what is meant by "Design for no negative tolerance on compressor capacity".

 

Thanks,

[fallah]

I was wondering if anyone knows what is meant by "Design for no negative tolerance on compressor capacity".

 

 

chempro,

 

The extra or more flow capacity consideration for a compressor than the required capacity is normally called "No Negative Tolerance" which will lead to zero negative tolerance...

[Technical Bard]

API, and other standards fo rotating equipment, allows a machine to be designed with a tolerance.  I don't recall the exact numbers, but it is typical that a standard allows for machine that performs within ±2% on head.  For instance, you specified 100 m of head for a centrifugal pump.  That manufacturer can design for that and on test, if it produces between 98 and 102 m of head, it will can be said to pass the test.  This is something many designers fail to recognize and can lead to various issues (overpressure, insufficient capacity) if not considered in the overall system design.  

 

By specifying that you want a compressor designed with no negative tolerance, it means you want a guarantee the machine will test at the specified performance or better.  Using my pump example, if I had specified the pump for 100 m with no negative tolerance, it would fail the test below 100 m.  The challenge with such a design is that it may cause the manufacturer to overdesign the machine.  My pump might now produce 104 m of head when I asked for 100.  I have seen manufacturers agree to no negative tolerance, only if we will accept higher positive tolerance on test.

 

Asking for zero tolerance is ridiculous because no engineering design is that good.

[chemproc]

Thanks Technical Bard.