How much pressure ??

I'm guessing that, as you call it a blower, you are talking about a centrifugal compressor (forward facing, overloading impellers or rearward facing, non overloading impellers) in which case, standard fan laws apply. You will also need to assign a 'dimensionless factor' (commonly 0.3, 0.6 or 0.8) This doesn't work for a screw or reciprocating compressor. If you can give me your email address, I will send you a couple of little utilities for calculations.

I'm not sure about the cavitation. We run turbo compressors to > 300,000 RPM without cavitation (not that I would know if it did cavitate)!

Good luck with it!

I think the phenomena you are trying to determine is surging or instability that occurs to the left of the peak pressure point on a fan curve. Unfortunately, I do not know any mathematical method to determine.

Do you have any of the manufacturer's design information or fan curve data for the fan?

Original RPM and HP compared to current RPM and HP? Fan affinity laws may help determine the fan curve at different RPM.

What is the make and model number of the fan? Fan Manufacturers' often keep fan curves long after a fan is produced, but it could be hard to find the right person in technical support that can find the data you need.

If you lack that information, you might get an approximate fan curve by finding a similarly configured fan and using fan curve from that fan.

Simple method is to use a fan with an outlet damper. Slowly close the damper and measure peak pressures at different damper positions until the fan rumbles. That will provide the peak pressure point of the fan, and show you what operating point you do not want long term operations.

By the way, do you know the maximum allowed RPM for this fan?

Thank you all. If the utilities offered don't do the trick I'm sure "benchmarking" it myself will.

Cavitation is a pump issue. Blowers cannot cavitate.

Cavitate then may be the wrong word ... What I'm getting at is at what point would the blower "stall" ... or stop moving air and how would i find that point.

Most low pressure centrifugal blowers do not necessarily stall and stop delivering air, but will sugre instead. The pressure/volume curve near zero velocity has an unstable region. If you start at zero volume and slowly increase airflow the pressure will initially decline, a bit, then rise a bit to a peak pressure , and then decline to a minimum pressure/maximum volume point.

When you start a fan at wide open volume and slowly throttle the flow to increase pressure, the pressure will back up the curve to reach the peak pressure point. As you throttle back past the peak pressure point, the volume flow will become unstable and surge between two volume points and cause operating problems.

What is the power rating of the blower?

What is the inlet opening size of the blower? Single inlet or double inlet?

What is the discharge size of the blower?

How wide is the blower?

What RPM is it driven at?

thank you all I think i can work with what you've given me. My appreciations.