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Hooking up 2 refrigerant air dryers together

implmex

Diamond
Joined
Jun 23, 2002
Location
Vancouver BC Canada
Hi All:
A technical question for any of you with experience with refrigerant dryers for compressed air systems:
Here's my problem:
I have a compressed air system that I cannot seem to get completely dry.
I have a refrigerant dryer with 30 CFM capacity that is leaving water in the main down line (I have a dump valve on that line so I know it's collecting water).
I have another 15 CFM dryer I inherited and was just standing around getting in my way.

Is it reasonable to connect the two driers in series (first the 30 then the 15) in order to increase the capacity of the system?
Do I need to ditch the two smaller dryers and buy a single new bigger one.

My air consumption is estimated to be under 12 CFM unless I'm running several machines at once.
The biggest air consumer is the mill at 6 CFM and maybe 8 to 10 if I run the air blast.
Everything else requires very little...1 or 2 CFM (if that) to operate solenoids etc.

My compressor is a 5 HP Gardner Denver 2 stage recip. I'm set at between 120 and 150 PSI at the tank.
The bigger dryer was checked out by a refrigeration technician a month ago and was pronounced in good health but I've noticed it's stopped discharging water out the discharge tube, so now I'm unsure about it.
The small dryer is now in the line but it doesn't seem to be doing any better to keep the whole works dry.
It was definitely working when it was pulled from service a year ago.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
but I've noticed it's stopped discharging water out the discharge tube, so now I'm unsure about it.
The small dryer is now in the line but it doesn't seem to be doing any better to keep the whole works dry.
This kinda sounds like your problem from here, as in neither is working.
 
Your driers are not working.

Are the condensors clean with good air flow?

Is the refrigerant level in the drier correct?

Is the hot gas bypass valve working correctly?

Can almost guarantee that at least one or more of the items on my list are the issue.

Connecting in series will do little or maybe even make the problem worse with reduced compressed air flow.
 
If the dryer is not discharging water I'd pull the auto drain valve and check if it's fouled with crud.

Usually there are service kits available for them.
 
Hi All:
A technical question for any of you with experience with refrigerant dryers for compressed air systems:
Here's my problem:
I have a compressed air system that I cannot seem to get completely dry.
I have a refrigerant dryer with 30 CFM capacity that is leaving water in the main down line (I have a dump valve on that line so I know it's collecting water).

My compressor is a 5 HP Gardner Denver 2 stage recip. I'm set at between 120 and 150 PSI at the tank.

Cheers

Marcus

The 30 CFM cooler (10ish HP size compressor) should be fine if the input air's not to hot..

Driers will have trouble if the air coming in is more than 100°F. Adding an air to air after cooler BETWEEN the pump and receiver inlet usually works for most. If the 5hp pump is running near 100% and the receiver is smaller than 80gal you may need to add a fan to the radiator.

In any case, the closer you get moist air to room temp the better the refrigerant drier will work.

Good luck,
Matt
 
I have been successful in building air systems in humid climates. I have used several elements to eliminate the moisture in stages.

1. Keep the main tank drained. Auto dump or manual dump, just be sure it is working. Do the manual dump style on a daily basis.

2. The line from the tank runs UP HILL with no dips where water can collect. Any water in that line should drain BACK into the main tank.

3. A copper cooling coil. The air enters at the BOTTOM and every inch of that coil runs UP HILL. Again the water drains back toward the main tank or to a collection jar at the entrance of that coil. If possible I locate that cooling coil in an air conditioned space so it condenses more of the moisture.

4. Then on to a refrigeration dryer which has collection jars on BOTH the inlet and outlet. Again auto dump or manual, but they must be dumped at least daily.

5. The line from the dryer to the point of use, once again, runs UP HILL. And it has NO low spots where water can collect. Any water always runs backwards.

6. A final collection jar at the point of use. With a properly designed and maintained system this final jar never sees even a single drop of water. I have seen this in action over periods of YEARS in the worst of humid climates.

I developed this design in places like New Orleans, LA and Miami, FL where the humidity is very high for parts of the year. New Orleans is the absolute worst in this respect. They have been successful in that not a single drop of water got through over a period of years. The prior systems that they replaced had constant problems, even with a refrigeration dryer. One of them had, after the refrigeration dryer, a 25 foot tall water collection loop in an elevator shaft. That loop did collect water: quarts were emptied on a weekly basis. And every bit of the compressed air had to pass THROUGH that collected water after it was dried in the refrigeration dryer. DUHHHHHHHHH! Other low spots in the lines also collected water that the air had to pass THROUGH that water. This added moisture back into the air and cancelled out any prior measures used to dry the air.

So EVERY INCH of ALL LINES should run UP HILL so that the water drains backwards to a collection point that is dumped on a regular basis. Any and all low spots must be eliminated or equipped with a collection jar and drain that is dumped on a regular (daily) basis. That water must never be allowed to collect in the pipe. That is hard core law in this business.

In a properly designed system, even in the worst climates you should not need two refrigeration dryers. Just be sure the one is working.
 
Hi EPAIII:
That is a GREAT bit of advice.
Thank you very much for posting it!
Some of the elements I already have in place; some I do not.
I am going to have to do a bit of a re-think about the best way forward.
My main circuit is attached to the wall right under the ceiling so every machine has a drop.
All have extended drops with dump valves on them, but your point is well taken.
Maybe the worst of my installation, is that the line from the compressor to the dryer goes downhill, and the dryer is on the floor.
That's all correctable, but the position of the main air circuit would be a real bitch to change.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
I found cooling the air as much as possible with a water trap between the pump and tank helped the most, I get almost no water in my tank. 25' of copper coiled in a tank of water is how I did it. It's all outside so the tank of water gets nice and cold overnight.
 
A few things already mentioned in this thread, but definitely a trap in between the pump and the tank does wonders. You want the air to cool as much as possible before going through the refrigerated dryer and it will be much more efficient and work quite a bit better. A simple setup like oil-cooler/radiator style with a fan or a few vertical sections of copper with drip legs on them are an easy way to cool the air before it gets to the dryer. The system gets more and more saturated, where it's going into the tank super hot, out of the tank hot and into the dryer hot. Even if the dryer is working, it can't cool the air fast enough by the time it passes through. You remove moisture, but not enough of it.
 
Much good advice the uphill being one of the most important.
As much room or uphill length as possible between the compressor and drier.
You want to get rid of as much heat as possible before it hits the dryer.
A low buck intercooler for 5-10HP is attached.
The demon dog is optional.
Bob
 

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IF you are really using that much air all day you are pretty hard on that 5hp compressor.

I run a 7.5 into a 400 gallon tank[!] and have pretty serious ZEKS air dryer that dries it live before the tank. I can get frost on the line.

I haven't seen an ounce of water in 4 years.

I think you are overworking your compressor, my last system with a 5hp and a northern hydraulics dryer was pretty effective at keeping water out of the[ properly sloped] lines. Gallon or two of water a year out of the tank

Heat=water. You are creating so much hot air that the dryer cannot pull it down below dew point. Mostly in a one piece compressor/tank, the tank should take out the bulk water, but you are using so much air that it never cools down in the tank, and it is still too hot when it hits the dryer.
 
OOOOHH BOB!

You need to get the pump in that fridge running. The door on those things hold a case of beer & the top shelf on the door is the coolest place on a duplex type fridge.

You don't have any BEER??? C'mon man...

Matt
 
About 1990 I set up an air system that was so far from established policy that I quit telling people what I was doing so I didn't have to listen to a lot of nonsense about how it could not possibly work. I had acquired a Gardner Denver ACF compressor cheap. It had two cylinders in parallel as a high volume low pressure unit. I switched it around to a two stage connection. Before I did, I measured the rod bearing area and load, then called a friend who was regional sales manager for Shell Oil and a very knowledgeable dude. He recommended the oil to use and I never had a problem with bearings, despite the dire warnings from people who probably couldn't calculate a bearing load. That was coupled with pronouncements about how a two stage compressor with both cylinders the same size couldn't possibly achieve anything. One line was that I could never get it balanced. Balanced to what? I did flow tests on a single stage cylinder and found, as expected, the output dropped off rapidly around 100 PSI because the air drawn in would be compressed in the space above the piston and the passages, then expand back into the cylinder, occupying space that would not be available to draw in new air. By working against a low back pressure, the first stage inhaled almost its swept volume of air and once it got pushed past the first cylinder's exhaust valve, it had no choice but to go in the second cylinder.

To cool the air, I made a trap from a 5" diameter aluminum tube with the air injected peripherally at the top so it would swirl around as it made its way to the bottom where it exited by a tube coming down to a couple of inches from the bottom. It had a jacket with tap water coming in peripherally, starting at the bottom and exiting at the top. An electrical valve on the bottom opened when the compressor shut off, dumping the condensation every cycle and unloading the compressor head.

From there it went to a foot valve at the glass bead cabinet that we modified to double acting, feeding the air to the bead gun when it was pressed and dumping it when released We sized the orifice in the gun to take all the air, about 56 CFM as I recall. We never got a trace of water in the cabinet.

For shop air, we sent the exhaust air from the bead valve through a check valve to a shop made heat exchanger cooled to around 0 F by a modified locomotive air conditioner and from there to a 200 gallon tank, bought new and never fed dirty or moist air. When the pressure switch closed, the chiller started but was not fed air until it had activated a temperature switch. The chiller stopped when the compressor did or the air was diverted to the dump, allowing it to warm up and melt off the ice that formed in it, which was discharged by an automatic drain. With 200 gallons of air, the lag between the pressure switch closing and starting of air supply was not a problem. Even using air grinders, we never noticed much slowdown. I put a trap with a clear bowl on one of the shop lines with a card with three dots that turn pink when they see moisture. All three stayed dark blue all the time.

Most of the units on the market are just a way to save money, bought by people who don't know any better. The only rational way is to get the moisture out before putting it in a tank that rusts away.

If you want really dry air, get a twin tower dessicant dryer.

Bill
 








 
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