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Buyer’s Guide: Portable Air Dryers

MONDAY, SEPTEMBER 11, 2017


When it comes to removing moisture from compressed air for portable applications, there are many systems available. The most common is a portable deliquescent air dryer package. The following guide covers system components, advises on what to look for when buying an air dryer package, and identifies features that are worth a little extra money.

Components of a portable compressed air dryer system. image: blast pak pro-75, COURTESY van air systems

 

1. Size Matters

The most critical part of any portable air drying package is the size of the deliquescent desiccant vessel. The bigger the vessel, the more desiccant it can hold and the more standard cubic feet per minute (SCFM) can be flowed through the dryer without sacrificing performance. The longer the air remains in contact with the desiccant, the lower the dew point and the better the performance will be at the outlet. Because a larger dryer vessel holds more desiccant, maintenance cycles can be extended accordingly. 

As the most critical part of any dryer package, the dryer vessel can also be the most expensive. Oftentimes manufacturers will undersize a dryer vessel or use thinner steel to reduce some of the cost. Below is a recommended vessel size based on flow at 100 pounds per square inch gauge (psig), 125 psig, and 150 psig.

Van Air Blast
Pak Model #
Vessel Diameter 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
 

2. Receiver Tank or Deliquescent Dryer? 

It is important to understand the basic features of a deliquescent compressed air dryer. A deliquescent dryer is a pressure vessel that looks very similar to a receiver tank. The main differences between the two can only be seen on the inside of the tank.

Receiver tanks are used for compressed air storage; whereas, a deliquescent dryer vessel has a grid plate which elevates a bed of desiccant above the condensate reservoir. This allows liquid to condense and fall into the bottom of the dryer vessel. Wet air from the compressor will flow from the bottom of the vessel through the desiccant bed and out the top of the vessel. As the wet air passes through the vessel, the desiccant absorbs the moisture in the air. 

Then, as the desiccant tablets absorb water, they dissolve and the liquid condensate removed by the desiccant falls to the bottom of the reservoir in the vessel. This condensate can then be drained from the bottom of the dryer. The only maintenance needed is to top off the dryer with more desiccant when the desiccant level drops below the two sight windows.

 

3. Not All Desiccant Tablets are Created Equal

When buying a portable compressed air dryer, the buyer must consider the type of desiccant tablets needed and whether the desiccant will be included as part of the purchase.

Some customers have inquired about using water softener tablets instead of desiccant tablets in a compressed air dryer. Both of these tablets are made of sodium chloride, so it is easy to understand why a customer would think each is an option; however, there are several reasons why using water softener tablets is a bad idea. Remember that sodium chloride comes in many formulas; it is used on roads to melt ice and snow, as an oral dietary supplement, in water softener tablets and to dry compressed air.

A good water softener tablet is typically 99 percent pure sodium chloride, which allows it to dissolve in liquid water. A water softener tablet needs to be submerged in liquid to dissolve. If desiccants are elevated by the grid plate inside the deliquescent dryer, as they are in Van Air systems, they will never dissolve unless the dryer is flooded with liquid condensate.

Dessicant sizes

Deliquescent desiccants have other ingredients that allow tablets to absorb moisture from compressed air. Van Air Systems’ Dry-O-Lite desiccant, for example, has a specifically engineered chemical formula. Even if it is left on a desk in an office, it will begin to absorb the moisture in the ambient air and turn into a puddle of water. This is because the chemical formula of Dry-O-Lite is not 99% sodium chloride. After manufacturing desiccants for more than 70 years, the company says it has found no substitute for the performance of its deliquescent desiccant tablet formula.

 

4. Warranty

When investing in a portable air dryer package, it’s important to know that the unit is rugged enough to withstand the abuse of a contractor and provide years of rental revenue. A warranty says a lot about the product and whether the manufacturer will stand behind it. For example, Van Air Systems offers a 15-year prorated warranty on its dryer vessels, with full 100% replacement in the first five years. Some dryer warranties are only good for 90 days to one year. Remember, purchasing a portable air dryer package is an investment, so for your peace of mind, make sure the warranty covers the system for the long haul.

 

5. What’s Your Pressure? What’s Your Flow? 

The operating pressure plays an important role in the amount of flow a dryer package can handle without sacrificing performance. As pressure increases, so will the flow rate. Just like a water faucet at home, more gallons of water will flow per minute when pressure is increased by opening the tap all the way, as opposed to opening it only halfway.

The same logic holds true with compressed air capacities. At higher pressures, more cubic feet per minute (CFM) will be able to flow through the vessel. This is because higher-pressure air cannot hold as much moisture as low-pressure air. Since you will have less moisture in the air lines at higher pressures, you do not need to increase the size of your vessel to handle the increased flow rate. Below is a chart that shows flow rates at higher pressures.

Van Air Blast
Pak Model #
Vessel Diameter 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
 

The important thing to remember is that, if your pressures are above 100 psig, you may be able to reduce the size of your portable dryer package without sacrificing performance of the desiccant dryer. One example is the PRO-75 Blast Pak, listed above. If the operating pressure is 100 psig, this unit is rated for 1200 SCFM to achieve optimal drying performance. However, if the operating pressure is 150 psig, you can now use this same PRO-75 system to dry 1723 SCFM without sacrificing performance.

 

6. Afterfilters

An afterfilter is a critical component. It is your last line of defense on a portable air drying system and will capture particulates before going downstream to the blast pots. Particulates enter the compressed air system from the intake of the compressor. Any dust or debris floating in the ambient air surrounding the compressor will enter the compressed air stream. As the dryer system ages, this filter will also protect against pipe scale or internal corrosion that may occur throughout the years. For proper protection, make sure that the dryer package has at least a 10 micron afterfilter on the system.

 

7. More Bang for your Buck

When comparing systems, it’s always a good idea to look at what other features are included. While the dryer itself is the main component, options such as lifting lugs, tie-downs and a forklift skid will help with portability and transportation. Other options, such as air motor exhaust mufflers and filters, may help to reduce oil residue and provide quieter operation. Without a separate filter housing to capture these oils from the air motor, they will drip down the dryer vessel. That may not affect performance of the dryer, but it isn’t very friendly to the environment.

Some portable drying systems also have a removable aftercooler assembly. Being able to remove the complete aftercooler assembly makes servicing the air motor an easy task. When it comes to desiccant replacement, check to see if there are sight windows for viewing the desiccant levels and easy access to refill the vessel. As noted earlier, it's also valuable to know if the manufacturer includes desiccant with the initial purchase. Taking a close look at added options like these will help make servicing the air dryer package easier in the future.

 

8. Reputation

Reliability is essential when it comes to purchasing a compressed air dryer. Make sure you look at the manufacturer, not just the product. How long has the company been in business? How long has it been manufacturing air dryers?

Will you feel more comfortable with a unit that is built by experts in the industry, or can you live with a less-expensive product made with lower-grade materials or by a company with less experience? Van Air Systems has been manufacturing compressed air dryers and deliquescent desiccants for nearly 75 years.

 

9. Customer Service You Can Depend On

As with any big purchase, you want to know who you’ll call and who will help you if you have a problem or question. When researching products, take note of the service you receive and how long it takes to get a question answered. Do you have to press a bunch of buttons before getting to speak to someone, or are you connected with a qualified person quickly? Not all companies provide access to industry-trained professionals to answer questions, troubleshoot problems or discuss customers’ product improvement ideas. Before you decide to purchase your portable air dryer package, make sure the customer service has already surpassed your expectations. Once the sale is complete, the service should continue.

*Claims or positions expressed by sponsoring authors do not necessarily reflect the views of TPC, PaintSquare or its editors.

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