Compressed Air Dryer Trouble Shooting – A Systems Approach

I’m asked quite often to troubleshoot compressed air dryers. It’s not just Van Air Systems dryers.  I get calls on every make and model imaginable.  Over the years we have built a great reputation for helping customers solve issues with their compressed air systems regardless of what brand equipment has been installed.  I first try find a solution over the phone, but sometimes it actually requires a on-site inspection of the customer’s plant air system.

The key to helping the customer is to take your time and properly analyze the installation.  You need to develop a systems approach.  This means looking at a complex range of problems and solutions, not just what you suspect the problem to be.

Here are some descriptions of a few recent troubleshooting calls I have personally made, where the systems approach worked well. 

Case 1

Industry:         Steel Production

Application:    Dry 5000 scfm of compressed air to -40F Pressure Dew Point (PDP)

Problem:         Wet air downstream of the dryer

 This customer has a 5000 SCFM Van Air Systems, model HB-5000, externally heated blower purge dryer and a 5000 SCFM Van Air Systems, model HL-5000, heatless dryer as a backup.  When I arrived on site, the customer told me that he could not maintain the specified -40 dew point with the blower purge dryer.  The operator then put heatless dryer on line.   Still wet air was somehow getting downstream. 

 The customer insisted something was wrong with our dryers.  Had I been in his shoes, I’d have felt the same way.

 Remember always have a systems approach.  I started by looking at the compressors to confirm operating pressures, temperatures, and flow rates to the dryers.  Next, I checked the automatic condensate drains on the after-cooler separators and pre-filters.  Everything checked out. 

 Now, I watched the heatless dryer to make sure it was cycling properly.  I needed to confirm that the each tower pressure gauge read zero during regeneration.  Too much pressure in a regenerating tower of heatless dryer causes problems.

 Next, I looked at the visual moisture indicating stick on the dryer’s gauge panel.  This is a small clear tube filled with color changing silica gel crystals.  Blue crystals mean the dryer’s outlet air is dry.  Pink crystals indicate that wet air is exiting the dryer.  In this case, the moisture indicator on the dryer was blue.

So how was moisture appearing downstream of the dryer?  The puzzle was still not solved.

I then asked the customer to bring the HB-5000 blower purge dryer on line.  This dryer operates on an 8 hour cycle(4 hours drying, 4 hours regenerating) so I had to wait for an hour or so to make sure the regenerating tower was coming up to the proper temperature.  After this, I fast cycled the dryer to make sure it was sequencing properly.  Everything checked out here as well.

Now, I was on the defensive.  The customer strongly believed that our dryers were not performing.  After all, he had wet air in his plant. 

So I went back and traced all the piping between the compressors and the dryers.  That’s where I found the problem.  There was an open by-pass valve.  Wet air upstream of the dryer was escaping past the dryer, mixing with the dried air.   

 Take note: Wet Compressed air + Dry Compressed air = Wet Compressed Air.

Once I closed the by-pass valve and dried out the sample cell on the plant’s dew point meter, the dew point came back into specification.

Even though I eventually solved the problem, I should have looked at the piping and valves sooner.

Sometimes the problem is where you least expect it to be.  In this case the lack of dry air had nothing to do with the dryers.  A systems approach finally led me to the source of the trouble.

 Case 2

Industry:         Apple processing

Applications:  Dry 300 scfm of compressed air to -40 FPDP

                                   Dry 700 scfm of compressed air to +35FPDP

Problem:             Product rejections resulting from wet compressed air downstream of the dryers

 For this troubleshooting call, I visited an apple processing plant in the Shenandoah Valley region of northern Virginia.  The primary products produced at this facility are apple juice and apple sauce. Our representative in Virginia, PBE Inc., asked me to make a call with them to try and solve the customer’s compressed air problems.

 The first application we looked at included a 75 horse power screw compressor, an after-cooler with a separator and automatic condensate drain, and a Hankison 300 SCFM heatless dryer with mounted pre- and post- filters.  

All of the pipe runs are stainless steel and indoors. 

 The compressed air supplied by this installation feeds the apple juice bottling line.  We checked all the drains and the pressure and temperature conditions at the dryer inlet.  Everything looked good. 

 We then to a look at the dryer to make sure it was cycling properly. I noticed that the off stream regenerating tower pressure gauge read 30 psig.  The regenerating tower on a heatless dryer must be at 0 psig in order to get a complete regeneration of the desiccant bed. What was causing this back pressure, I next asked.  Upon further inspection I found the customer piped the purge exhaust from the dryer some 20 ft to an outside wall.  This is a fairly common strategy for managing the noise of a heatless dryer.  But if one isn’t careful, this extra piping will put a lot of back pressure on the regenerating tower.  In this case, the purge exhaust pipe size was actually smaller in diameter than the purge outlet on the dryer.  The end-user had dramatically restricted the flow of purge air.  This restriction caused the back pressure we were seeing on the regenerating tower.  We told the customer he needed increase the pipe by 2 full pipe sizes.

 We later got a report that he’d completed the re-work and the problem had been solved.

 Rule of Thumb:  When piping purge exhaust to a remote location you must increase the pipe diameter by one full size every 10 feet.

 Next we visited the bottling plant.  Here slugs of water from the compressed air system were landing directly on product.  This leads to instant project rejection.  One problem I observed here was the piping drop legs.  The drops were from the bottom of the pipe header instead of the top.  Because the heatless dryer was not working properly all of the moisture going downstream was pooling in the bottom of the pipe header and made its way to the bottling machines.

Since it would be quite costly to re-do all of these stainless steel pipe drops correctly, we recommended the customer install point of use filtration on all the bottling machine pipe drops.  Of course, this would be a stop gap measure until the root cause of the water could be addressed.

We then took a look at the 700 scfm compressed air application in the apple sauce plant.  This system has (3) 50 horse power screw compressors with after coolers, separators, a competitor’s refrigerated dryer with pre and post filters, and a dry air receiver tank.  Here again, we checked all the condensate drains to make sure they were working.  We also checked the inlet conditions to the dryer.  Everything checked out, the dryer was getting a 35F PDP according to the readout on the control panel.  Our contact said water was showing up in the apple sauce plant especially in the winter months.  What we found here is the compressor room is a separate building, and the compressed air lines run outside before entering the apple sauce plant.

In the winter months in northern Virginia temperatures can fall well below 35F.  Whenever compressed air cools below its dew point, condensation will start to form.  Since the compressed air lines run outside between the buildings they are condensing water out when the ambient drops below 35F.

Our interim suggestions were to insulate the outside pipe run that feeds the apple sauce plant and to install a moisture separator in the main header immediately after it enters the apple sauce plant.

We also informed the customer they really need to install a regenerative dryer rather than a refrigerated for the apple sauce plant.  A refrigerated dryer cannot product air lines exposed to low ambient temperatures.  Also, we informed them the bottling plant application could have used a refrigerated dryer instead of a regenerative dryer because all of the compressed air lines are indoors in a climate controlled ambient and a -40F PDP is not necessary.

The customer was very appreciative we were able to help them solve their moisture problems which will eliminate the product rejection issues.   I’m always glad to solve a problem, even when it involves a non-Van Air Systems dryer.  

Even though all the drying and filtration equipment used by this customer was from a competitor, we were able to solve the customer’s problems and we will be involved in their future expansion plans.

Whoever sold the apple processor those original dryers clearly didn’t take a systems approach.

We always do, hence the name, Van Air Systems.


  1. Emilio Morales says:

    We have a pneumatic D25 non cycling air dryer and I see lots of condensation around air lines and top of solenoids solenoids are ice cold how can i adjust temp on non cycling dryer.

  2. Keith says:

    Hi, I have a polestar smart DRD265 air dryer
    Problem high dew point AND low pressure alarm. I found the compressor ran to run irregularly if at all. I’ve seem to gotten down to the fan high pressure valve not activating…… and I on the right track? the fan does work when its contactor is pushed
    in…… thanks for any help Keith

  3. Sapta says:

    DESIGN PRESSURE : 8.8 KG / cm 2g


  4. Marcus Abela says:

    Hello we have a problem with one of the columns of the air dryer. We are writing for advise. The dew point is going up to +23Celcius and we are having these problems.
    The activated alumina is getting powdered. The dryer module consists of two duplex absorber towers containing activated alumina desiccant . When the plant is in operation one duplex tower is on stream removing water vapour from the air, the other tower is being dried and regenerated by passing a small air purge through it. No electrical heating is required.The operation and regeneration cycle is fully automatic, controlled by the plant control unit.

  5. Gaganjot Singh says:

    Hello sir,
    Really impressed with your way of solving problems and your root cause analysis.
    I have delair refrigerated type compressed air dryer model -FDI-G-290A.
    the outlet of the dryer sometimes get reduced and the flow is reduced sometimes even there is no flow.
    I think that the airline in the air to refrigerant heat exchanging unit is choked , but I am not sure if that can happen or not .Also can you guide me if that heat exchanger can be opened or is there any method for cleaning that line.

  6. Anil says:

    Hi1 we have 150 cfm heatless (PSA) dryer, line size 40 NB (1 1/2″NB), op pr 6.5~7 bar, compressed is lubricated, desiccant Activated Alumina balls 3 ~5 mm dia , qty 50 Kgs per tower tower size 8″NB pipe .

    We have desiccant dusting problem i.e. desiccant powder is comming out chocking after filter.

    I am requesting any one who can offer/ suggest corrective and preventative actions , are welcome to come forward.

  7. Siddiq says:

    Hi I’m facing a problem air dryer solned valve supply coming continues please give me solution

  8. vadivel says:

    Hello, I need one clarification about air compressor dryer unit. Compressor unit is suddenly tripped while switch on the dryer unit. Can you suggest solution for this problem please.

  9. David Atiyota says:

    hello sir, thank you for your time in providing solution to people complain n how to make our compressed air dryer work properly, i have a little problem with our dryer on site, the problem is that the fan to the dryer comes up more frequently than usual and when it does it does not blow for more than 2 sec, this is very unusual. please will be very happy to get a response from you.
    thank you .

  10. ROBERTO LUO says:

    Dear Sir.,

    Good day to you!

    Forster(FST) Pipe specializes in the superior aluminum pipework systems for compressed air, vacuum and inert gases.

    Please find our Catalogue and Price List in the attachment!

    We looking for the agent in your market!

    Anything, please feel free let us know!

  11. Daniel Caparal Abobo says:

    Good day Sir,
    Please help me. my rented atlascopco desiccant air dryer suddenly closes all the valves in the middle of the operation? why is is happened? please tell me what to do because if i call the vendor it will take 2 to 3 days. Were on drying out the cold box now. i need it to run immediately. thanks in advance

  12. Umapathy says:

    Good Day Mike,

    I am from Saudi Arabia, we had air dryer unit installed 20 years back(1998). The frequent chronic problem is the Air operated (Pneumatic) valves get struck during regeneration cycle. This leads the pressure drop on network and getting trips and blackouts. I observed on time one of the dryer change to operating cycle, lot of condensate from the outlet of dryer for a while(2 minutes). The action was frequent repair & replacement of AOV. could you please support me to get rid of this chronic issue.

  13. shafi bhatti says:

    heat less air dryer [activated alumina ] temp lower side 20 C

  14. Md. Ershadul Islam says:

    Hellow Sir
    Please note that few days ago my air dryer some problem, sudden it’s fault alarm indicated and dryer can not run. So I try to solve the problem. I find out the compressor suction pipe created a leakage so all gas out.then I repair the leakage and again fill R22 refrigerant gas. Now the discharge pressure 200 psi and suction pressure 45 psi. I know suction pressure should be 55 psi but compressor unable to get more gas. In this situation air dryer is running but auto function do not work. Compressor running long time and long time lafter it should be turn off by indicated fault alarm. I can not understand which device control air dryer compressor auto on and off. Please sir suggest me. I just waiting for your helpful answer. My air dryer Jaguar brand,made in China

  15. praveen says:

    We have heatless dryer with Alumina silicate as desiccant. The frequent problem we are facing that 4 way valve malfunction due to desiccant carryover in powdery form and damaging seat of 4 way valve.

    Why dessicant carryover and why in powder form as it was charged as small small balls.

    965-50341390 Kuwait.

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