We recently had a customer approach us the SSPC show to discuss the differences between our compressed air drying systems and some of the others in the industry.  This particular customer spoke at great length about the size of the air motor on our 1600 CFM air dryer package.  They told us that they recently purchased a competitor's package and they were amazed to find out that our air motor was double the size of the competitor's unit.  At first, it was merely an observation, but after sending the dryer out on a few rentals, they found that it was quickly becoming a maintenance nightmare.  The smaller air motor had to work

jpcl-sizematters2harder to spin at the same RPMs and achieve the same approach temperature performance.  This additional wear and tear on the air motor caused premature failure and the customer was forced with a tough decision. To rebuild the air motor or spend the money to replace the current air motor with a larger, more suitable size. This is just one example that size does matter.

This guide was written to help you and/or your customers purchase a properly sized air dryer system for your application requirements. One of the biggest issues we come across when helping our customers is their units not working properly due to water in their airlines. Which is usually caused by an incorrectly sized unit.

The most critical part of any portable air drying package is the size of the vessel. Since the dryer vessel is the most critical part of any dryer package, it can also be the most expensive component.  Often times, manufacturers will undersize a dryer vessel or use thinner steel to remove some cost out of their portable dryer packages.  Knowing operating flow rates and pressures is essential to sizing a compressed air dryer system properly. Take a close look at the questions below before you purchase a compressed air dryer. Knowing the answers ahead of time may save you headaches later due to problems from an undersized dryer package.

  1. What is the Dew Point you need to achieve? Or What problem are you trying to solve with your Compressed Air Dryer? Dry compressed air is a concept with a wide range of meanings. Knowing your dewpoint or the application in which you will be using your dryer will help make sure its sized properly. Dew point signals how dry compressed air is. It is the temperature at which moisture begins to drop out of the air. The goal is to always keep your dewpoint temperature to be lower than your compressed air temperature. To do this you need to make sure your dryer is drying your air properly. For example dew point suppression is the primary concept behind all deliquescent dryers and deliquescent desiccants. If you maintain your dewpoint you will never have a problem with water in your lines.


  1. What size compressor do you have? Believe it or not many times, it is common to not be completely familiar with how an air dryer works.  We have had customers give us the height, width, and depth dimensions of their compressor when we ask for the size of the compressor.  If you are unsure of the size of the compressor determine the horsepower of machine. You can get up to 5 SCFM for each horsepower. From there sizing your dryer is a lot easier.


  1. What is your operating pressure? This is a very important question. You will want to know both your low and high values for this. You can size your equipment for the lowest value but it’s important to be sure that the highest value is within the design range for the for the filter and dryer. This is one of the main reasons why dryers fail If they are sized improperly for the operating pressure you will be running. Your dryer may not be large enough to handle your CFM without sacrificing performance.  Determine your flow rate at the pressure you intend to operate. Higher pressures, will be able to flow larger SCFM amounts. You will need a dryer that is capable of handling your flow at your operating pressure.

To further explain - The bigger the vessel, the more desiccant it can hold and the more SCFM you can flow through the dryer without sacrificing performance.  The longer the air remains in contact with the desiccant, the lower the dew point and the better your dew point performance will be at the outlet.  Since a larger dryer vessel will hold more desiccant, you will also be able to extend your maintenance cycles.

Below is a recommended vessel size based on your flow at 100 psig, 125 psig, and 150 psig.

Dryer Example: Van Air Blast Pak Model # Vessel
SCFM Flow Rate
@ 100 psig
SCFM Flow Rate
@ 125 psig
SCFM Flow Rate
@ 150 psig
PRO-25 16" 250 304 359
PRO-40 20" 400 487 574
PRO-50 24" 800 974 1149
PRO-75 30" 1200 1462 1723
PRO-100 36" 1600 1949 2297

Where do I find my operating pressure? Most production machinery lists air consumption in the specifications or operating manual.  Digging through old files to find a manual may be tedious, but it’s a sure way to avoid a sizing mistake for the filter and dryer.  Plan B is to put a flow meter in the line and actually measure what is going through it.  In most applications, the price to rent a flow meter is cheap insurance versus spending money for equipment that’s too big or small and not getting the job done properly.

  1. What is your air temperature at the inlet? Temperature is the final critical area.Being off by just10° or 20°F error in either direction, means that there is twice as much moisture in your system than you thought. Your brand new dryer is now too small to keep up with the moisture load.  The old time method of touching the pipe with your hand is not that accurate at best. The quickest and most effective way to measure compressed air temperature is with one of the infrared devices that are available at home supply stores for a very reasonable price.  The good part is that you do not need to get close to or actually touch that filthy compressor or piping for an accurate reading, you will have a digital result.


You Get What You Pay For:

Purchasing a properly sized dryer will save you headaches as well as money from issues caused by an undersized unit. Purchasing an air dryer system is an investment, so make sure it will outlast any application. We all have heard the old adage..."You get what you pay for" and also "Do it right, do it once".  Getting a properly sized unit may cost a little more upfront but in the long run but it will save you from breakdowns in the future.  In the rental market, longevity of the equipment translates into higher profit from your purchase. Spending a little more on the initial purchase to get a high quality dryer package with oversized components will eliminate down time, improve performance, and reduce maintenance costs.  Ultimately it will be more profitable over the 15 year life of the equipment to base your decision on quality and not price alone

As always the technical team here at Van Air Systems is more than willing to share our experiences (good and bad) so that you and your customer get the appropriate size unit for the application. Call 1-800-840-9906 or send an e-mail at any time,  we would be happy to work with you.

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