pnematic compressor selection

A Google search for "calculate+air flow+orifices" brought up many links for doing the calcultions.

BTW, 7.5 HP sounds undersized for your Blowoff frequency. However, you don't give the sie of the Blowoff Orifice/s so that is just a guess.

A general Rule of Thumb says, an Air Blow Gun uses 5-7 Compressor HP at 100 PSI.

As was indicated by BudT there is data missing to complete your request, the orifice size or cfm rating is critical to making any calculation.

"5000 rpm per hour" or Revolutions Per Minute? Never the less, the machine speed has no bearing on your air requirements unless we are going to specify or suggest an orifice type or size. The again, if thats the case MUCH more information is needed.

Here are some points necessary;

Type of varnish

Type of paper

Diameter and length of roller

Hardness or type of rubber on the roller

Picture or drawing would be really nice

You need to calculate the part you have not defined: the flow required. This will be based on the number and size of orifices, and the extent to which the paper obstructs flow through them. Once you have defined that, then you simply look for a compressor which supplies the required pressure and required flow.

Your duty cycle is almost continuous, so not much storage should be required. Your vendor should be able to supply the calculation upon which they made their recommendation.

What did you mean by 5000 rpm per hour? That series of units would usually be considered an acceleration: the speed increases by 5000rpm each hour, so it would start at zero, get to 5000 rpm after the first hour, 10,000 after 2 hours, etc.

The air storage capacity depends upon the desired duty cycle. If you want the compressor to run in short bursts, then you need a powerful compressor and a large tank. If you want the compressor to run continuously, then you can use a smaller compressor and a tank only large enough to accumulate air during the 1 second off time in your application. As an example, many paint HVLP spray systems have continuously running compressors, which are dedicated to just one use. If a compressor is installed in a shop where many things are powered by air, then the storage capacity has to be much larger, to prevent one tool from using a large portion of the air needed by another.

I have seen an arrangement on an old Heidelberg printing press where they have the piston of a large pneumatic cylinder connected to a crank on the main shaft. This acts as a compressor and is ported to "blow off" at a particular point in the cycle.

Actually thinking about it some more, the cylinder may have been used as a vacuum generator to hold the sheets of paper.

Brgds