Compressor Temperatures

[pescador775]

Yeah, "twoonie", I had to look that one up. My old Purus and later, the Capitano, were each equipped with one of those hanging cartridges. Both were filled with charcoal. Never had a problem with odor with either but over time, my tanks had to be tumbled. The technology moved on and so did I. The Purus was sold ages ago. I filled the Capitano's cartridge with metal mesh, closed the filter assembly for good and added a large coalescer/filter downstream. Like Hacker said.

 

[Scubadoo72]

Another filtration system for it would be nice, as I have 3 large banks that I would like to keep filled at home...and stopping to change filtration during that fill would kind of suck.

Another thought I had was to run some sort of cool air at the compressor fan while in operation, keeping my pickup out of the way of course.

Where would one find these extra filtration systems? And would this go before or after the current one, as the water separator is in the same housing as the filter..?

 

[pescador775]

The water separator consists of a baffle or a tube with a hole in the side. Depending on which type, air is sprayed against the baffle or against the side of the canister. Neither of these work well. However, if a back pressure valve is fitted the efficiency is increased quite a bit. Orthodoxy has it that a BP valve should be located after the final filter but I have had excellent results installing this valve at the water separator canister. There are several board members who could hook you up with a filter. There is a whole thread on the subject if you just scroll down. Meanwhile, here is some reading material:
High pressure breathing air compressors, scuba air compressors, Scuba air

Shelden Sporting Goods Inc. - High Pressure Air Compressors

Jim's modified accumulator is the one to get.

 

[cool_hardware52]

The water separator consists of a baffle or a tube with a hole in the side. Depending on which type, air is sprayed against the baffle or against the side of the canister. Neither of these work well. However, if a back pressure valve is fitted the efficiency is increased quite a bit. Orthodoxy has it that a BP valve should be located after the final filter but I have had excellent results installing this valve at the water separator canister. There are several board members who could hook you up with a filter. There is a whole thread on the subject if you just scroll down. Meanwhile, here is some reading material:

Back pressure or "Priority Valves" increase filter efficacy by increasing the dwell time, i.e. the time the gas is in contact with the media.

Coalescing moisture separators work by taking advantage of the density differential between gas and liquid particles. Relatively heavy droplets of condensed moisture tend to continue to move in straight line due to their greater inertia, and the lighter gas can make a sharp turn in the separator.

Velocity and inlet temps vs ambient impact the efficacy of coalescing separators, but I don't see where a Back Pressure valve would have much impact.

My compressor is plumbed so that the outlet of the final stage passes through after coolers, to condense as much of the water and oil vapors, then it passes into a coalescing separator that has a drain valve. From the coalescing separator it passes through a check valve and into the filter towers. There is a back pressure or priority valve at the outlet of the final tower.

This allows draining of the separator without venting the pressure in the filter towers. Allowing the filter media to return to ambient pressure is undesirable and will cause CO2 spikes in the gas produced.

Are you suggesting that filters be cycled?

Tobin

 

[pescador775]

Are you suggesting that filters be cycled?

A back pressure valve placed at the separator also acts as a check valve; therefore, draining the coalescer does not empty the final filter.

Back pressure or "Priority Valves" increase filter efficacy by increasing the dwell time, i.e. the time the gas is in contact with the media.

The dwell time in a small filter is extremely small regardless of the pressure, at least as indicated by my experiments. From what I've seen, it takes a dwell of about a minute or more to produce any beneficial effect. This will never happen except in a giant canister because the air space inside a chemical cartridge is normally tiny. The desiccant counts molecules as they pass through, that is why it is called a "sieve". MS type desiccants are highly efficient even at low humidity. WRT very large filters it might be an advantage to increase dwell but since the amount of desiccant is so large to begin with the whole idea is questionable. It might provide a benefit as the desiccant is near depletion.

Coalescing moisture separators work by taking advantage of the density differential between gas and liquid particles. Relatively heavy droplets of condensed moisture tend to continue to move in straight line due to their greater inertia, and the lighter gas can make a sharp turn in the separator

Placing a back pressure valve at the moisture separator prevents heavy droplets from entering the final filter which are otherwise highly detrimental to the media. Contrary to your belief, without back pressure at the coalescer, considerable moisture may blow out of the Coalescer and into the filter at low pressures. Pressure reduction at the output of the back pressure valve allows cooler (expanding) gas to enter the desiccant increasing its efficiency. As I said, without a back pressure valve at the coalescer some neat water will be ejected out and into the final filter. However, this should be temporary as the system builds up pressure. If the coalescer is advanced with baffles and micronic separator the effect should be minimal overall. For your situation, I would suggest that you place a BP valve at the coalescer, and also the filter but that would be optional. The difference in locations of individual valves produce small effects but either seems to work well. I mean, I don't want to overplay the advantages or disadvantages of either location.

My compressor is plumbed so that the outlet of the final stage passes through after coolers, to condense as much of the water and oil vapors, then it passes into a coalescing separator that has a drain valve. From the coalescing separator it passes through a check valve and into the filter towers. There is a back pressure or priority valve at the outlet of the final tower.

I have no quarrel with this arrangement but consider it optional or even unnecessary for small compressor assemblies. All compressors should have an after cooler and, as to the location of the BP valve, I like the arrangement previously described for small compressors at least.

 

[cool_hardware52]

A back pressure valve placed at the separator also acts as a check valve; therefore, draining the coalescer does not empty the final filter.

No, but lacking a PV at the filter outlet will result in the filter pressure dropping when you connect the fill whip to an empty tank.

The dwell time in a small filter is extremely small regardless of the pressure, at least as indicated by my experiments.

Dwell time is a function of the internal volume of the filter appliance, the pressure at the outlet and the cfm of the pump. Regardless of size the dwell time will be proportional to the pressure, i.e. double the pressure, and you double the dwell time.

Placing a back pressure valve at the moisture separator prevents heavy droplets from entering the final filter which are otherwise highly detrimental to the media.

I would agree that moisture droplets are not good for MS.

Contrary to your belief, without back pressure at the coalescer, considerable moisture may blow out of the Coalescer and into the filter at low pressures.

Why would a back pressure valve be any more effective than a check valve in preventing moisture droplets from passing from the coalescer to first tower? A ball check is a ball check.

I have verified that no liquid water is reaching my first tower. I do have the added advantage of aftercooling. Look here The Deco Stop


Tobin

 

[oxyhacker]

It sounds like to are saying that pressure does not play a role in water separation. I don't think you could really mean that, but in case anyone else does, I will quibble the point.

There are two step in removing water from air. Getting as much of the water vapor dissolved in the air out of it, so it can be then separated from the air, and separating the droplets from the air. A mechanical separator can only remove liquid water - gaseous water goes right through with the air. Getting the gaseous water to condense so it can be removed by a mechanical separator can be done by lowering the temperature of the gas, which reduces the ability of the air to hold water vapor, or by increasing the pressure which increases the percentage of water above the air's ability to hold it. The water is literally squeezed from the air by the higher pressure. So a backpressure valve (or other means of keeping the pressure up in the separator stack) has a huge impact on efficiency, though just how huge depends on how efficiently the earlier steps are done. That's why a backpressure valve is more efficient in keeping droplets out than a check valve, because it increases the efficiency of the separator in removing them.

Coalescing moisture separators work by taking advantage of the density differential between gas and liquid particles. Relatively heavy droplets of condensed moisture tend to continue to move in straight line due to their greater inertia, and the lighter gas can make a sharp turn in the separator.

Velocity and inlet temps vs ambient impact the efficacy of coalescing separators, but I don't see where a Back Pressure valve would have much impact.Tobin

 

[pescador775]

The coalescer on the old Poseidon compressor is elementary. However, it can be made to work if a back pressure valve set to 2400 psi is mounted to the can itself. The rest will take care of itself, hopefully.

Yes, at, for example, 150 bar back pressure the dwell is 150 times atmospheric. However, 150 times nothing is next to nothing. The air space inside a chemical cartridge is about 1 or 2 cubic inches. The rest of the space is occupied by solid granules. With a 4 cfm compressor this would equate to 2 or 3 seconds dwell. It might help a little but it would require care to measure the improvement. Using a precision scale, I can see a difference at about 15 seconds but it is small.

As the SCUBA tank fills, the back pressure in the final filter increases anyway so the overall dwell advantage of locating the BP valve at the final filter becomes even smaller. The same could be said for the opposite arrangement so that is why I say the differences could be debatable. As to the BP valve at the coalescer and ejection of water, this refers to prevention of residual water spewing out of the coalescer as well as immediate improvement on condensation by raising pressure immediately, eg especially when the compressor is started. WRT the Poseidon system, I really believe that mounting the valve at the coalescer will help with this. I said that I added a final filter to the old Capitano and that this resulted in a big improvement, but not just due to the chemical media in the filter. I noticed that the amount of water draining from the coalescer (identical to the Poseidon) suddenly increased, more water drained after I moved the BP valve to the coalescer from its original location on the filter. I'm not sure why. It could be due to the slightly higher pressure setting I had dialed into the valve or some other factor such as I've described. In any case, not one drop of water has ever drained from the water trap on the bottom of the final filter or any of the other similar installations which I've done. The SCUBA tanks look great.

 

[cool_hardware52]

It sounds like to are saying that pressure does not play a role in water separation. I don't think you could really mean that, but in case anyone else does, I will quibble the point.

And I will quibble back. Higher pressures will increase the percentage of the water vapor that condenses, allowing the coalescor to potentially remove more water, but higher pressures do not change the efficiency of the coalescor itself.

The location of the PV valve at the outlet of the coalescor vs the outlet of the filter stack will have no impact once the filter stack is at pressure.

There are a number of benefits of using a check valve at the inlet of filter towers and a PV at the outlet. Increased dwell time, less pressure cycling of the towers, and no CO2 spikes. If the filter Towers remain at or above the pressure setting of the PV, then the check valve between the coalescor and the towers will open only when the pressure in the coalescor is equal to or greater than the PV setting + (the check valve spring)

Tobin

 

[cool_hardware52]

The SCUBA tanks look great.

I enjoy these exchanges, makes me think. I can see where your approach could result in very good moisture removal, and even possibly longer desiccant life.

If lack of tank rust is the measure of success, perhaps all is well.

I would love to see a comparison on overall air quality, HC's, CO2, CO + dew point between a system with the PV at the separator vs at the end of the stack.

For me the question is moot, as my filter stack is never below about 3500 psi even if I don't run the pump for a week.

Tobin