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Thread: Best way to dry compressor air?
04-06-2012, 01:52 PM #1
Best way to dry compressor air?
I'm in the process of getting a 5hp, 2 stage, reciprocating compressor. It's on a vertical 80 gal. tank. Puts out 16+ cfm at 175 psi and 17+ at 100 psi. I will have very little piping,
probably a short 1" main pipe with 3 drops coming off the top of it. One goes to to a retractable reel and two will have spring coil hoses. The drops will have ball valve drains on the bottoms. The compressor will have it's own shut-off and drain (auto or manual). Probably two sets of 2 filters: a general large size .5 micron filter feeding a similar large size 3 stage (oil,dirt and moisture) 0.01 micron with a regulator on each 3 stage. I know compressors can generate a ton of moisture, mine has an intercooler and aftercooler as part of the pump, but do I need further drying and if so what? A small refridgerated unit is not cheap and then you have running expenses. I thought about making my own aftercooler using stainless steel or copper coils 3/4" 50' to 70' in length that come in compact round or rectangles shapes, etc. These can be reasonably cheap (half the price of a used dryer) and are on ebay every so often. I would put this directly off the compressor and have a drain on it but no fan. Is this a plausible solution?
04-06-2012, 02:04 PM #2
Is the compressor in a shop that is climate controlled, if so you are a lot better off starting. A lot depends on what you are going to do with the air? Air tools and air guns, cnc machines? You probably don't need anything extra. Plasma Cutter? In that case you need DRY air. How about media blasting booth? Then you REALLY need dry air. An automatic drain really helps. I have one wired into the main motor power circuit. When the compressor kicks on the drain opens for a set time. My tank pretty much stays dry. My shop does have central AC so the air is dry in the shop already. You could put Motorguard filters on individual lines that feed things like plasma cutters or paint guns and probably not worry too much about the rest.
04-06-2012, 02:19 PM #3
Our new compressor has an integrated air dryer (we have machines that run air bearings) but before that for a while we were getting by with an aftercooler feeding into one of the harbor freight air dryer units. Worked okay, and they're not too expensive, especially with a coupon or on sale.
04-06-2012, 05:26 PM #4
I media blast and cerakote firearms so I need dry air. I ran 20' of cast iron 1" pipe into a dryer filter as mentioned above with drains at either end. The pipes are running uphill so any H2O will drain back toward the compressor. I have never had a problem with moisture in my air. I live in the south and no climate control. As long as the air has a chance to cool before entering dryer I think you should be fine. I learned this from an auto paint shop.
04-06-2012, 05:29 PM #5
If you can run an intake pipe to the outside ideally under your shop, you do a lot better if you start with cold air. Each intake stroke brings in more molecules of air and fewer of water, as cool air can hold less moisture than warmer. Compressing cold air is cheaper than compressing warm air anyway, will eventually pay back.
04-06-2012, 05:45 PM #6
04-06-2012, 10:15 PM #7
Look at the SMC Ambient dryer model AMG150, I think there is a newer model. New they are $66.
Claims to remove 99% of moisture. Then place a dessicant dryer after that. Watch the beads change
color from blue to pink and then dry them out in a oven, and reuse again.
The 50'-70' length of plumbing is extreme. The 20' sloped pipe idea is what painters use.
04-06-2012, 11:59 PM #8
Being you already have an aftercoller, next step would be to pass the air thru a desiccant dryer. They may take either activated alumnia or molecular sieve or both. Our large units at work take both.
Another item to look at installing is a timed automatic drain valve on the tank to, per timers settings, blow off and drain any moisture build up in the compressors tank.
I'd try a google search on Desiccant Air Dryers and you'll get a good selection to choose from.
Hope this helps,
04-07-2012, 01:42 AM #9
I've designed and installed systems that ran 24/7/365.25 where even a single drop of water would cause intolerable damage (2" video tape machines running air bearing headwheels). My approach was several fold. First, I always piped the air intake into an air conditioned space so there was as little moisture as possible to start. Everything was redundant, 2 or 3 compressors, 2 air tanks, dual jars at multiple points, etc. Everything was drained on a regular schedule using manual valves: auto dump valves can be counted on to fail.
From the tank, I would add a section of cooling pipe, also in an air conditioned space. A 50 or 100 foot coil/spiral of copper pipe works well. It is fed from the bottom of the spiral so that any condensate will drain back towards to the tank. A large filter jar is mounted there to collect the water.
From the top of the coil, it goes to another jar with desiccant and then to a refrigerated dryer. The jars were redundant with valves to allow maintenance while the other one was in use. The refrigerated dryer was the only non redundant element due to expense, but I had a bypass around it to allow for maintenance. And a final pair of jars after the dryer.
Distribution was overhead with a slope to drain any condensation in the pipe back toward the dryer. And a final jar at the point of delivery with a manifold to allow cutting off lines as needed.
Even though these systems were installed in the deep south where humidity is horrendous, I never saw even a single drop of water or other contaminant in the jars after the dryer. Even when the dryer was bypassed, no water at all.
04-07-2012, 04:50 AM #10
Virtues of a dryer
With summer coming fast upon us I would be leary of using a ....... well we will call it a heat exchanger that basicaly is a coil of pipe allowing the air coming thru to be cooled by air around. Remeber PV=nrT squared from physics, when air is compressed it gets hot cause we are reducing the volume. Hence water comes out especially on humid days then when leaving the compressor the air expands gets colder and more water. What i am trying to say that is if the temp in the shop where the cooling coil is is hot your not gonna get much cooling. A dedicated air dryer IMHO is only way to go especially if your running air bearings or supplying to CNC.
It is one of those pay me now or bleed me for an while then pay later. I haveseen the situation play out; die grinders depart early, cnc equipment starts faulting out and so on. So if I were buying a compressor I would budget in the dryer; not doing so is like buying a mini fridge for the home shop then never placing any beer in it.
Seriously though they are a good investment and cared for properly they will last long time, I am partial to IR. They have a small foot print and nice features. Ours senses the dew point and will shut down if not needed + you can set the dew point depending on how dry you need your air. Sutting down is great cause running one is costing basically the same as a running a small air conditioner. The front of panel of IR shows all function that working at a glance and has self dignosics as well.
Get one and you will be a happier camper with some extra cash when the unit starts to pay for itself in longer lasting air tools and less machine down time. Just be sure to put the recommended filter size between the compressor and dryer so as not to void the warranty. Also I reccomend a by pass circuit around the dryer so you can take it out of service for maintenace or for appliccations where totaly dry air is not required (like for blowing chips off; this keeps demand on the dryer lower) and keep air going to the shop. Like my blast cabinet, if ran it with dryer air there is no way it could keep up and I don't care if my blast air has a little h20 in it, but some may as above. Oh and also place a regulator before the dryer as well cause ours for example is not rated for more than 100 psi input. So estimate your pressure and CFM needs so you purchase the right sized unit.
Last edited by doug8cat; 04-07-2012 at 05:03 AM. Reason: grammer
04-07-2012, 09:52 AM #11
Best way to dry compressed air is before you compress it. I could never understand why anyone would akkoy condenced water to collect in their receiver.
A refrigerant air dryer is simplest, nearly maintenence-free, and fool-proof but expensive and you have to get one a size larger if you install it in the cimpressor inlet.
For low first cost, I suggest quick change DIY dessicant air dryers on the intake pipeing before the filter. You make three so you can have one in service while another is ready, and one in the toaster oven you have right by the compressor to recharge the dessicant for 8 hours at 250F.
Install your air filter between the dryer and the cmpressor.
Last edited by Forrest Addy; 04-07-2012 at 12:55 PM.
04-07-2012, 11:02 AM #12
Separator Filter Dryer (SFD) - SKFusa.com/Products
Take a look at this dessicant dryer. It uses compressed air to automatically regenerate one side while you run off the other side. No messing around with baking dessicant.
In my opinion the best way to dry compressed air is with a refrigerated dryer after the wet tank (you already have one on your compressor). Install an auto drain on the wet tank, this is where you will get the most water out of the air anyway. Since you have an aftercooler you shouldn't need a high temp dryer. Install a general purpose air filter between the wet tank and dryer and a coalescing filter after the dryer. A dry tank is optional then your main line regulator.
04-07-2012, 11:08 AM #13
04-07-2012, 11:20 AM #14
04-07-2012, 11:24 AM #15
Forrest I'm on board with Edster please elaborate I have never heard of or seen such configuration. Since we fighting to get a dryer for our new compressor at work I would be really interested in reading some reference on the subject. In fact I gonna google it now.
04-07-2012, 02:36 PM #16
Think about it. Degradation of a shop air system is a process over time involving the interacton of moisture, metals, time, foreign contaminants, and the 7X - 9X increase in oxygen tension in compresses air. Dehydrate the air early and you remove the means through which the other elements of degratation react. If the compressor takes in dry clean air it can pump only dry clean air. The receiver is no longer a condenser for water vapor; it's remaining function of storage and heat of compression dissipation continues but with greater efficiency. Further, corrosion in the receiver is all but eliminated. Same goes with regulators, valves, fittings, connected tooling and equipment; anyplace where dissimilar metals abut. The need for moisture traps and subsequent routine maintenence is eliminated.
In climates where ihere is often condensing humidity condensate can accumulate at unbelievable rares. In this environment, air systems are plagued with water carry trhough, recurrent cycling of water traps, water in the compressor oil and all the technical horroors attendant. In dry air delicate compresser pump components (reed valves, back-up springs, unloaders etc) are not subject to corrosion and therefore last longer. Another point is part of iron corrosion is biologoically based. In warm, moist, high oxy tension environments a family of aerobic critters exacerbate steel corrosion far beyond local corrosion cell rates and the increased oxygen tension in compresed air system accellerates it further.
Different Types of Corrosion: Microbiologically Influenced Corrosion (MIC), Microbial Corrosion or Biological Corrosion - Causes and Prevention, by WebCorr Corrosion Consulting Services, Corrosion Short Courses and Corrosion Expert Witness. corrosion
All that said there's the further point that it makes sense to condition the air to be compressed (filter, dehumidify, etc) because it takes less energy to do so at atmospheric than when elevated to line pressure. Standard practice and conventional wisdom has the air dryer downstream of the compressor but if your shop system and air tools benefit from dry air why not dry the air before it's compressed?
I've designed a few air systems based on pre-conditioned air (refrigerant air dryers have been around for a long time; cheap small ones have been around only since the late '90's) and for as long as the systems I designed were un-modified they ran perfectly without moisture carryover, pump failure, corrosion, etc; in one case (a fruit leather processor) his system ran for nearly 20 years. It wasn't until an orthodox minded maintenence man re-plumbed the air dryer downstream of the receiver that pump problems developed. That said, It must be remembered that a good air pump's operationnal life is about 15,000 hours of running time. These air punps wore on a three way alternator and had logged over 22.000 hours each. It's significant, I think, that the all three pumps failed within 1000 hours of the de-humidifier switch.
Moisture really is the enemy of compressed air systems and the earlier in the cycle you remove it the better. Here is one place you benefit by putting the traditional cart before the traditional horse.
Last edited by Forrest Addy; 04-07-2012 at 05:57 PM.
04-08-2012, 05:04 AM #17
Okay your points are making sense to me. But how would one go about estimating the size of a dryer that would be placed BEFORE the compressor ? Would you base on the final output CFM ? seems to me that you would need a bigger unit since the volume of air is going to be more in than out (cause it ain't compressed yet.).
04-08-2012, 05:31 AM #18
Thats simply not going to work well. As you run the pre dried air through the compressor your going to increase the dew point massively. Its now compressed into less than a 1/4 of the volume. Hence the dew will be nothing like as low as you can get on the output side of the compressor. Air dried to say a dew point of 15 Celsius at 120psi is a lot dryer than incoming air dried to the same dew point. More so when there uncompressed and the air chills one won't deposit its moisture the other likely will.
Add in increasing the suction pressure on the input to a compressor will have a marked reduction on its output capacity and is a real bad idea in most circumstances at the scales we deal with. Ultra large compressors and pretreatment is a diffrent ball game. But even then you have to still dry - filter post compression if you want really dry air.