Compressor Question

"a common header pipe"

Trying to visualize your setup, the only thing that comes to mind is the level of the outlet piping. If the discharge line is running up hill maybe water is condensing in the pipe and running back to the filter. Total guess.

I experienced a similar issue at a power plant (only with 3 compressors). Everything appeared to be running ok to us; That is if we compared operational data there was little difference in any operational temperatures or pressures. We found the root cause in our case to be a faulty interstage drain (our compressors were 2 stage). "Faulty" meaning the orifice that allowed water to drain was slightly gunked up, so it would drain, just not fast enough to keep up with what was condensing.

I agree with ChaoticIntellect, the dry filters are just not working. It would be a good idea to have a check valve after each filter and trap before the common line, too.

We don't have 2 stage comps. Each unit goes to a moisture seperator which mechanically removes most condensate and has a float drain with a ball valve that allows a visual check of the float drain. if to much condensate is present while doing a manual check this indicates a bad float which won't open and needs servicing.

The 1um and 0.01um filters each have a float drain and ball valve check system. Each compressor has a seperate refrigerated dryer that dries to -30* to -40* dew point, with electric drain valves with manual test buttons.

The compressors then tie into a header pipe which then goes to the resevoir tank which has a float drain with ball valve to check it. The from the tank it goes through a pilot valve to regulate plant pressure.

So filtration is fine, float drains are fine. What has me scratching my head is one comp. 'makes' water, one does not. Just an oddity I guess.

crazy question... How do you know the "wet" compressor's dryer is functional?

How do I know the dryer is functional? The suction pressure gauge level. The manual test function on the auto drain which feeds into a transparent tubing allows me to see how much condensate comes out under a manual test. If this amount exceeds 2-3 seconds before I get air then I know it is time to service the auto drain and or replace it.

Neither unit is closer to a wall or 'high' humidity air inlet source to account for one making more condensate than the other. Neither one has it's piping 'draining' back to it.

Just was wondering if anyone ran into a similar situation before as it is rather odd.

Well, I'm out of ideas.

Compressors don't make water, there's something either different or not working properly on that compressor. Good luck. Let us know if you get it figured out.

I strongly agree with pritam in comment #16.

Your "test" for determining the dryer is functional is not what you should be looking at--it might be good for determining the condition of the auto drain.

You need to do a test that confirms the other dryer is actually drying--measure the dew points and so forth as others have suggested, or maybe collect the condensate in a bucket or similar separately for each dryer. The one that produces less condensate is probably not functioning properly.

It could be as simple as the compressor creating condensate being closer to a source of moisture/humidity i.e.- a concrete wall, a door to the outside, etc.

Is there any source of moisture that could be closer to that particular compressor?

If for some reason the feed air was just slightly more damp around that unit, it might explain things.

swap the dryer for two days.and watch the result.

You said that the air receiver is the last item in the circuit. I believe the two compressors should first feed into the receiver and from there on to the filters and dryers and a final filter before moving to the points of use. This is how our own circuit is designed.

Any chance that one compressor is closer to a wall or source of temperature differential?

The other compressor also should drain lot of water. Please check these points & tabulate:

1. In-let & out-let water temperatures of both compressors at inter-coolers & after-coolers.
2. also flow rate of water of above
3. Is water piping same for both?
4. are you using same cooling tower for both or different? if different what is the temperatures difference at out let & inlet/

all the best!

My simple thought process is that compressing air heats it, and any moisture will stay in the air for this part of the process. Then when it is expanded it cools and moisture can then condense out (this could be post any restriction or into an increased pipe size). So it follows from this that you must have a point on the exit side of your offending compressor where there is "expansion", and where perhaps more for the offending compressor, there is additional cooling of the compressed air up to that expansion point - so that the expansion-cooling phase becomes critical and causes water to condense out.

If the problem is not the above then it can only be as others have suggested, water draining back on one side, or from the other, or failing to drain away as quickly on one side.

1 simple answer: no 2 items in the world are created equal. With 2 identical machines, 1 perfect (never happens) 1 that acts up (always). Several posts on here looks at plumbing. My guess is, that is the problem. There is something very different or the proximity of the distances that is creating the wet issue. I don't believe you gave us the differential distance between the 2 comps yet.

1) No 2 installations are perfectly the same.

2) Since the filters have Mechanical Float drains and the dryers have auto-drains they must function and prevent water going through from one stage to the other. The air reaching the storage tank should be dry enough like the other compressor.

3) If the Air intake have the same conditions of temperature and RH% for both compressors when working, then the Wet line is more efficient in drying since it is draining more water out: Check the cooling temperatures and the air pressures on both lines. Even a small temperature difference (1 or 2 degrees) is enough to shed more water on one line than the other!(you are saying 160 to 180 = 20 degrees possible fluctuation!!). Therefore, the wet line could be running cooler and producing more water out of the air!

I hope that is the case. Then adjust the dry line to cool the same way. if the dry line was working better, it should be draining more water than the wet line, since the same air conditions are there, both airs should contain the same amount of humidity (RH% and Absolute H i.e. the same weight of water per Volume of air) and therefore, the dry line is not shedding enough water (??).

If not then the auto-drains are not working on the wet line! The water comes from the air intake and nowhere else.

Good job guest! Didn't even think of that. The filters and or dryers are malfunctioning on the dry one and allowing moisture into the system.

Sorry for not getting here sooner. I have not tested the discharge temps, as soon as I can I will, however by the 'hand' method there is little difference.

No the filters are not malfunctioning on the 'dry' compressor as the 'excess' condensate it 'might' produce would show up in the tank.

Both units are in a room inside a production building and have the same filtered air coming into to the room.

Both compressors run in the same temp range and each dryer's suction pressure gauge reads in the same range when it's comp is running.

Air holds water like a sponge. You squash the sponge and the water runs out. Compressing the air is much the same squashing the sponge. Except in this case the water (not as a liquid) is in the atmosphere as vapour - in molecular form.

But different from the sponge, air heats up as it is compressed, and in doing so the water stays as a vapour - until such time the vapour condenses as the air cools.

Thus the water in your system is directly linked to the means of cooling. Either naturally due to cooling throughout the pipework system as the air cools to ambient temperature -or artificially forced by inter-coolers (if multi-stage compressors), after-coolers and fridge dryers.

The condensed water then has to be collected at each cold point by separators and filters, and then dumped by the drains.

Lots of water at the filters and dryers suggests the cooling system is working, whereas little water suggests the cooling system has failed.

In the latter case, the hot air with vapour (still as molecules) passes straight through the separators and filters (and maybe overload the dryer) where the air then gradually cools to ambient in the receiver and rest of the pipework - to appear as if by magic at the point of use.

Fridge dryers (typically) provide a pressure Dewpoint of +3C. Thus any subsequent pipework exposed to an ambient temperature below is likely to have condensed water vapour in it.

With one compressor seemingly dry and one wet, it might be a simple case of the dry one not having any work to do. It runs nice and cool off-load most of the time compared to the wet one that is probably on full-load all the time - which means it runs hot (and could over-load the fridge dryer) either by heat alone, or possibly by oil contamination in the heat exchangers.

Proper cooling at each appropriate stage is critical.

Could it be that one of the compressors, the "wet" one, is doing the lions share of the work? This could cause more moisture in the one that is working the hardest and, possibly, very little in the one that is simply loafing along doing very little.

Work load for the comps is so light only one runs daily. So we switch every 1000 hours. Oil is tested at that time and oil filter changed. The 'dry' unit produces what I consider a normal amount of condensate for SD at this time of year. The 'wet' one produces more. This is evident in the drains of the moisture seperator, 1um, dryer, 0.01um filter traps and the tank's trap.

As it is all I can come up with is it's an oddity. They are within 1000 hours of each other at this time. Same oil, same filters, same all around.

And actually the "Water by Karl Fisher" test shows the units to be +- 10ppm of each other.

You say that you switch them over at 1000h interval. If the switching is done manually, are the hours clocked on an hour meter? and is it the number of hours the unit is connected to power or when the compressor is running?

In any case, the 1000h could be anything from 2 month to 4 month apart. There could be atmospheric changes and different conditions. To make a usefull comparison, you should switch from one unit to the other within the same day and see the results.

I refer you to my previous contribution (and others with the same comments ... nearly):

- With the same air conditions of humidity and temperatures at the inlet, and the same dryer cooling temperatures, with the same approximate volume of consumption, the amount of condensate should be the same on both lines.

- A small difference in cooling temperature can result in more or less condensation quantity that can be detected.

- Any uncondensed water due to higher (hotter) cooling temperature will carry over even beyound the air receiver and into the pneumatic devices or wherever the compressed air is going. Therefore, When the seemingly Dry line is running with the same atmospheric conditions,If there are water traps further down, you should also be experiencing more condensate there. That is Normal and there is no magic here.

You are slowly opening up your cards. All along I was thinking that you are running both the comressors in parallal because you say every thing is same all around for both. If your running time is different then every thing is not at all same. moisture content before and after compressor may vary with the variation in following parameters:

Suction Temperature, RH of atmospheric air,

Differential pressure across suction air filter, flow rate(at NTP),

Discharge pressure, Discharge temperature,

Efficacy of moisture trap and dryers etc.

So, When you say every thing is same all around for both, please check that these parameters are also same.

Also there is confusion over the flow circuit. A simple bock diagram showing equipments and flow direction would have been better than hundreds of words.

I heard a thumb-rule once...

For compressed air systems, 3/4 of the moisture should be removed by the inter/after coolers and the remaining 1/4 removed by the air dryers.

I'm not sure of it's validity. But perhaps you could measure the condensate production rates at various points in your system to give you a better picture of how each system is operating.

Just a thought...

The other thing that comes to mind is the size of the filters... The experience I have with sub-micron filters is for water filtration. The ones I have used are very rapidly consumed (clogged) even with a larger pre-filter. This might suggest to me that the moisture that is found in the receiver might still be vapor as it makes its way past the filters and then condenses afterward... perhaps there is fouling in the cooler and thus overloading the dryers.

Compressor inner coolers tend to leak into the air stream even if the air pressure is greater than the cooling water pressure. I would tend to think the compressor cooling system has an issue. An inner cooler pressure gauge should tell the tail or the pressure differential between the two compressors could signal this problem.