Question Trying to decide between an electric powered or gasoline powered MCH-6 Icon...
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there is only so slow that you can run them. The gas version goes around 2800rpm, the 3e goes about 2250rpm. I would not try going much slower than the 2250 but at that point you're down to ~3cfm from ~4cfm which is a massive drop. Like @Tracy said, you can just turn the governor down a bit on the gas motor, but now you're waiting an awfully long time to fill, over half an hour for a normal AL80 fill and you still need to wait half an hour before the next one so it's not really worth the time. If you're going to that effort, get a different pump. Treat this for what it is, a really cheap to buy, not so cheap to operate, convenient tiny compressor. Don't try to put lipstick on the pig and make it something it is not. There is a reason this pump is $4k, a Junior II is $6k, and an Oceanus is $8k. They're all small portable pumps in the 4-5cfm range. You spend twice as much for an Oceanus as the MCH6 and it's still only rated for 2x 4500psi cascade bottles....
``Well there goes the neighborhood. When Ian and T-Bone show up all semblance of a reasonable conversation goes out the door." (SurfLung.)
The Question Regarding Lowering Rotation on the Coltri MCH 6 and ICON
One of the many problems with both the Coltri MCH-6 and the new all black Icon despite all the fanboy protest is the splash lubrication design. For every rotation of the compressor a small stick dips into the small quantity 0.6L oil bath and collects a tiny amount of oil with each dip of rotation that is slung up into the upper cylinders for lubrication as described in the manual. However what is not explained to a new owner is the following:
1. The lower the RPM (revolutions per minute) the less "dips" of oil is achieved for lubrication
2. The less dips of oil the less oil is available for critical lubrication points.
3. This results in a huge increase in temperature at local contact points with a massive temperature rise
4. The huge temperature rise at local internal points "burns" the oil into breakdown
5. These overheated and burnt breakdown chemical components are dangerous to health
6. This evidence is hidden from the user and the air and oil analysis test houses by frequent oil changes.
7. Put another was by changing out the oil more frequently this potential health risk problem is obscured.
8. Resulting in suggestion what SurfLung said "nothing to see here just move along"
9. Further the 0.6L oil sump is so small only a 5 degree of inclination is allowed or the dipper dips dry
Fresh oil when new maybe clean and clear with no problem of traceable compound breakdown or nasty chemical compounds off gassing but it gets worse so a deeper look you will note in the Coltri manual this is covered over by suggesting that the low RPM single phase model is described for paintball use only.
Now I trust you can now all see what's going on here with all this cover and obfuscation of using a paintball compressor for scuba. With one question you get 10 answers.
Or for a better explanation of the above what can be better than my co conspirator T-Bone's quote
I had never previously looked at "thediveforum.com" Here is what I got today:
Hmmm, perhaps a ban isn't such a bad thing. . .
Hmmm, perhaps a ban isn't such a bad thing. . .
Gone for diving
Contributor
Thanks for a detailed explanation,
its more useful then a vague not enough oil, explanation,
There is many thoughts in my head how to fix this,
but its beyond most people's scope and abilities...
Simple one is add abit extra oil for slower speed compressor....?????
Seems it should apply for other smaller compressors that use a dipper and run slower.
No its not crazy but its not recommended
The principle is collectively known as Tribology.
The study of wear tare friction and lubrication of materials.
B9780750611954500130
I should explain further in addition to my earlier post of the problems in lowering the RPM
The second part of your question of adding more effective cooling
The Problem of Effective or Efficient Cooling with the Coltri MCH-6 and Icon
Heat created from a compressor is generated mainly at the discharge side of the head. With some secondary additional heat generated by mechanical movement bearings, crankshaft and piston diameters in addition with the actual piston diameter and the piston stroke.
With further consideration as to the inlet gas temperature, the atmospheric air temperature and the cooling medium be it ambient air fan cooled or water cooled
The RPM is converted from RPM to piston stroke length and calculated with regard to the piston stroke con rod travel length and calculated to achieve a piston speed measured in feet or meters length over time usually metres per second or minute rather than just RPM. This is required for friction calculations.
The total heat created is calculated as adiabatic P1 V1 over P2 V2 for the sake of calculation
The total heat generated is more complicated for a forum discussion.
The heat measured however is usually measured downstream of the discharge side of the head
and at that point the gas inside the tubing has achieved considerable cooling already.
The gas compressed out of the discharge side for each stage of compression is extremely hot and goes over a heat exchanger or cooling coil to cool before entering the next stage.
The hottest point inside a compressor is reached at the exit point of the discharge valve inside each of the compressor stage heads
The coolest point inside a compressor should be at the end of the cooling coils prior to entering into a coalescing filter separator tower and at the final stage discharge point prior to any chemical filtration.
At each stage of compression the gas temperature at the inlet side of each head is lower as is the pressure than its discharge side, The measurement of the inlet temperature on each stage is called the approach temperature with the discharge side called the discharge temperature.
Now this approach temperature at the point where to gas reaches the next stage of compression needs to be cooler than the original discharge temperature but not cold enough to create water condensate.
Water condensing inside the heads will create what is known as hydraulic lock and seize the compressor
due to water being non compressible and blocking up the fine holes in the valve plates the pistons can't compress the accumulated water and something will stop usually the con rod
Also oil can also be utilised as a coolant in addition to its principle purpose of lubrication.
Adding a divers built additional cooling is quite easy to do with a tube within a tube method with cold water is one what a method favoured with our Chinese friends and the paint ball folk using a bucket of cold iced water and a fish tank pump but getting it wrong is so easy to achieve and the cost described by others of the forum for the Coltri repair parts is expensive.
I note the Coltri Manual SurfLung was so keen for us all to reference makes no mention of the piston diameters or the piston stroke only the RPM. Beggars how you can make an informed choice.
No matter at least now all know why. Iain
You could add more oil with a bigger oil sump but you quickly you will come up with additional problems that cost additional money in the build and additional parts required to resolve.
With Coltri the reason for having the minimum size oil sump you can possibly get away with is IMHO to make the cost of the compressor as cheap as you can while at the same time loading the cost of maintenance higher over and across onto the customers tab while at the same time making more profit for the dive shop and distributors that sell you this stuff.
Coltri MCH-5 and Icon Oil Sump Design Against Low Oil Volume
The first question a prospective buyer of these compressors on the subject will ask is why is the oil sump so small 0.6 l and why is the oil life also so low 50 hours in the manual and around half that recommended by most users of these pumps.
1. Oil needs cooling after its journey in and around the compressor parts before re entering back into the compressor sump together with all the washed out wear material components and fragments, the burnt compounds within the oil and all the metal wear particulate from the piston liners cylinders and bearings All from that little oil slinger wacking around the place after being super heated doing its job of lubricating and cooling.
2. Excess oil volume loss known as oil carry over is lost on the upper cylinders heads and valves never returns back to the oil sump hence the loss needs to be as low as possible to extend oil duration life.
3. Further as some oil doesn't return back to the sump it makes additions problems for the gas cooling and chemical filter life side of things (we could discuss later) lowering the filter life expectancy and again with additional cost to the customer in service replacement of the chemical dehydrator chemical filter cartridges. But as. this compressor is sold mainly into the retail sports market the extra revenue generated with the sales of oil and filter is for the distributors and dive shop retailers
Keeping the divers ignorant of the reasons.
4. In addition super hot oil loss at this point gets up and into the filter towers.This is known as long chain hydrocarbons with the additional considerations for the oil chemical breakdown compounds
That are dangerous to a divers health but insignificant for a air gunner or paintballer
5. A small volume of hot oil in the sump is easier to cool than a larger volume. Try leaving different volumes of hot cooking oil in a pan at home after cooking your chips and see which pan cools down quicker the small volume of the large.
6. A larger volume of oil although beneficial to the compressor for both lubrication and cooling heat exchange but may need an additional oil cooler added and possible an oil pump to get sufficient cooled oil back up and around the running gear found in the better designed compressors for scuba applications rather than this pathetic stick on a pole poking into the oil at each rotation of the crankshaft as with the Coltri design.
7. By now you should be beginning to understand why with the small 0.6L oil sump on the Coltri why they require that the compressor be operated only on dead flat and level base hence the pathetic inclined angle of 5 degees as (opposed to others marine designs at 62 degrees) listed on the manual.
8. With beggars the question why the live aboard divers and those with yachts don't realise the danger
In conclusion having a small oil sump is cheaper to manufacture than having to have an oil pump and oil cooler and even an oil filter much more expensive. It also produces more particulate matter that damages and reduces bearing life and it reduces filter chemical life as the damaging metal particles get to go back around the compressor more often than the same amount of contamination but diluted over a larger volume of oil in the sump.
By contrast the dive shop selling you this stuff what's not to like it's a cheap compressor and easy to sell with a good margin of profit to both the importer and the distributor and to the retail dive shops who all get to sell you in addition a whole wish list of oil cans and filter tubes all you need for your diving season. Any wonder why the kick back from the fanboys on here. Iain
Understood, outside of the UK (if you still could call it "United" ), BSAC is only a mildly interesting and largely irrelevant group. FWIW, I once inquired if they would share some results of one of their surveys to expand the collective knowledge of diving accidents, only to be told that information was restricted to BSAC members only
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