# How do you read a blower/compressor curve with multi-curves for inlet guide vanes?

I am trying to apply an existing blower curve in a hydraulic model for a single stage blower with variable inlet diffuser vanes. The variety of curves shown on the plot does not seem to make sense to me. In particular, I don't know which of the blower curves I should be looking at. The legend at the top-middle of the plot shows IGV: 10 etc. but then those same line-types are used in the plot with 12, 10, 08 etc. and no units are shown anywhere.

I looked up the ASME document referenced (PTC-10) but did not find anything in it to shed any light on how this curve was developed or how it is meant to be read.

Does anybody know how to interpret this or know of a resource that explains this style curve in detail?

• Is it possible that the inlet guide vanes (igv) come in different numbers? Because usually you can adjust the inclination on those (that would be the different curves with the same line-dashing, given in arbitrary units of inclination) - the straight lines of the same dahing are read on the right axis and only apply to their range of curves. Jul 27 '18 at 16:03
• Setups with different numbers of vanes then have different dashings Jul 27 '18 at 16:03
• Those numbers seem very small to be numbers of vanes. A specification that I stumbled across for a similar sized blower required a minimum of 13 vanes. Jul 27 '18 at 19:17

Old topic but... to be sure you have the correct info : The IGV positions are given by the seperate lines as indicated at the top (continious, dashed, dotted and dash-dot) At these IGV positoins, tests are done at several outlet diffuser positions (the numbers at the bottom of these lines in the curves) Example; There are several dashed lines (IGV pos 04) and these have different numbers at the bottom (outlet diffuser vane position). Basically, IGV pivots the curve around the 0 flow max head point and outlet diffusers move the whole curve horizontally.

The numbers are simply the numbers of the actuator arm position (one for the IGV and one for the diffuser), that is on the outside of the machine. You can see them in the left os the picture in the link for the IGV https://www.howden.com/Howden/media/Howden/img/products/compressors/single-stage-turbo-compressor.jpg

ASME PTC-10 is the test protocol used at this specific test for warranty on flow/pressure and power consumption.

https://www.asme.org/codes-standards/find-codes-standards/ptc-10-performance-test-code-compressors-exhausters

The curves you see here is a test curve of the machine, a KA44SV where KA44 is the size, S is for outlet diffuser vanes, V for IGV's, from testing (which was done for every machine before it left the factory) in Helsingor, Denmark. The IGV's were used to compensate isentropic head for off-design conditions (determined by pressure measurement, inlet temp measurement and diffuser position), the diffuser vanes for flow control. This way, they got a pretty constant high efficiency over the whole flow range, all the way down to ~45% from the max flow at a constant pressure, at a constant rpm.

You can not really determine flow/pressure from these to find a duty point in practice. These curves are used to program IGV position control in the PLC so when installed, the IGV goes to the optimal position automatically.

There is also another curve that comes with testing, that shows you the efficiency of the machine over the complete working range.

HV-Turbo used to be the world leader in centrifugal compressors for wastewater aeration. They made them from the KA2 (starting at ~ 45 kW) to the KA100 (max. 2.7 MW). They were taken over by Siemens (approx. 2005) and they sold of the whole package to Howden in 2018 I believe. Factory in Helsingor is gone sadly.

• Thank you for the detailed explanation Redmer. I'm glad I left the question open long enough for you to find it. Hopefully this will be helpful to someone else trying to decipher the same thing in the future. Jan 4 '20 at 2:42

This is just four separate charts drawn on one piece of paper, to save space.

For IGV:0, there are two curves (02 and 04) and the working line at the bottom left. Presumably, a higher flow rate than 04 would stall the compressor with this IGV setting (but it uses less power at low flow rates)

For IGV:4, there are four curves (02, 04, 06, and 08) because you can push the flow rate higher.

Similarly for IGV:6 and IGV:10.

For IGV:10 you can use flow rates up to 12, but the device is less efficient for flow rates less than 06 than at the other IGV settings. The curves for low flow rates at IGV:10 are not shown because nobody would use them in practice, and they would make the chart look really confusing by overlapping the "useful" curves on the chart.

• Thank you! It's starting to make sense. Does it happen to jump out to you what the 10 in "IGV:10" is and the numbers defining its curves? At first I thought it might be number of Vanes, but from my experiense, 4 fanes wouldn't really do a whole lot. Similarly, do you know what the curve designators mean (02, 04, 06, 08) since if they were just index numbers, I would think they would simply go from 1 to 4. Jul 27 '18 at 17:31
• ASME PTC-10 should define exactly what the labels mean. Sorry, I don't have a copy of it. I do work with compressors, but not the type of compressors that ASME is interested in! I would take a guess that the IGV numbers represent the vane angles somehow - but they may be the different settings available on the compressor's controls, not angles in degrees. Jul 28 '18 at 6:58

I finally found someone from the OEM that could concisely explain what is going on.

The IGV curves listed at the top are the inlet guide vanes I mentioned. The numbers are positions of those vanes and are used to control efficiency by effectively imparting spin on the incoming air.

The groups of lines that were not labeled are vane diffuser positions and are used to control capacity by opening or restricting flow.

By changing the combinations of these two features, you can hit the various curves shown on the plot. The top of the individual curves are the surge pressures.