Desiccant air dryer cycle frequency

I am completely unfamiliar with desiccant dryers, even though we have had one running in our plasma air circuit for the last 8 years or so.

It's a Domnick Hunter DME series, although I am not sure of the exact model (it's not in a very accessible area and I'd need to disconnect it to see the plate).

It's obnoxiously loud when it cycles and I despise it being in my workshop - the plasma is in another building, but all the compressors are in the machineshop where it's clean.

I was thinking about moving it elsewhere, when I started thinking more about it. I downloaded the manual, but there is no mention anywhere in there of how frequently it should cycle.

I'm not sure this thing is even working properly, but I have no frame of reference. How frequently should a dryer like this cycle? It does it every couple of minutes currently.

I'm not sure what you mean about 'cycling'. The desiccant dryers I've seen just absorb moisture until the media is full, then its replaced or dried. Are you sure it isn't a refrigerated unit?

If refrigerated, the refer cycle should be pretty quiet but the blow-off can be pretty noisy. That's typically either an interval timer or a float switch or electronic level detector. We had a timer get flooded when a fire sprinkler went off and thereafter the timer cycled every 15 seconds or so regardless of the setting.

Is it a twin tower with regenerative drying?

Many decades ago I worked for a company that made air filtration equipment.
Yes the switch over can be loud, especially if the blow down mufflers are not installed
Computer controlled drying was just coming into being, the technology at the time for twin tower desiccant dryers used cam timers that switched between the 2 beds depending on expected moisture content. Most of the cams were set not to be adjusted, except for an occasional tweek
I would contact the manufacturer and discuss your concerns.
Are you still producing dry air?

mjk said:

Is it a twin tower with regenerative drying?

Many decades ago I worked for a company that made air filtration equipment.
Yes the switch over can be loud, especially if the blow down mufflers are not installed
Computer controlled drying was just coming into being, the technology at the time for twin tower desiccant dryers used cam timers that switched between the 2 beds depending on expected moisture content. Most of the cams were set not to be adjusted, except for an occasional tweek
I would contact the manufacturer and discuss your concerns.
Are you still producing dry air?

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Yes, and I will add....when was the desiccant last changed ?

Yes, twin tower regen.

I am not the end user of this air circuit and diplomatically, the guys that are are not the type to notice or consider if there is something wrong with it.

We have a third party who visits and services our air systems. Right now I am not sure if they have been doing anything with this dryer, accordingly I am honestly not sure if the desiccant has ever been changed. Waiting to hear from them about that.

We had a change of management recently - before now I haven't had any authority do anything about it, so I grudgingly tolerated the noise and ignored it otherwise. Now I can do something about it, and in the process have started asking these questions...

I would recommend you use a humidity meter, any that work are ok.

Check the humidity and monitor for a spell.

If the device is working the humidity is stable.

You should know what the humidity level is supposed to be controlled to.

Pathogen said:

I would recommend you use a humidity meter, any that work are ok.

Check the humidity and monitor for a spell.

If the device is working the humidity is stable.

You should know what the humidity level is supposed to be controlled to.

Click to expand...

I will have to acquire a humidity meter, don't have one on hand.

Regarding actual requirements - I have no idea. I don't know who specified this dryer, or why. I can't find any paperwork for it here. It runs a big high def plasma and the purge for the extractors filter stack. It might have been specified because of temperature. Filter stack is outdoors, and the profiler/fab shop is unheated - gets pretty cold in there in winter.

For comparison, the small, 2 cfm Balston brand pressure swing air dryers run on a 5 minute switching cycle. These dryers are designed to provide -100 deg F dew point air. The switching cycle is driven by two requirements. The first is that the running column needs to be regenerated before the water saturated zeolite reaches the last 1/4 of the column height. The second is that the low pressure regeneration needs to run sufficiently long to insure that the full length of the zeolite column has been purged of water. The columns are designed so that the dry and regeneration times are the same at the rated inlet air flow, pressure and temeperature. If the air dryer is being asked to process a higher airflow than it is designed for the outlet air will have a higher dew point.

The larger air flow models work with shorter switching intervals to limit the height of the zeolite columns.

There will be a replaceable inlet filter with a water drain to remove any liquid that may have been captured in the air stream. The filter needs to be replaced on a schedule as it becomes cloged with dust and compressor oil. There will also be a outlet filter that captures the zeolite dust.

On the Balston dryers the outlet filter has a green / yellow color indicator on the filter element to confirm that the outlet air is within specification. A humidity sensor designed for use in a room air conditioner may not have the sensitivity needed to verify that a sub zero dew point is being maintained.

On a larger dryer there will be gages that display the pressure drop across the filter elements. There may be a tag on the dryer that specifies when to change the filters based on the pressure drop.

Robert R said:

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Good information, thank you.

I prefer the style that use heaters to regenerate the desiccant. A color indicator lets you know when it needs to be done. I bought an extremely large used unit for next to nothing and only have to regenerate it once a year or so. Prior to that, I used a regenerative system. The regenerative models use a lot of air. And prior to that, water poured out of my hoses.