Stewart Warner/Kidde Compressor and moisture seperator questions (Home mixing)

[pescador775]

My last post on the subj has to do with preferences. Of the two brands of commonly available military compressors, I rate any new 4 cfm Stewart Warner highest for reliability. These units are usually bulletproof and will last longer than many of the divers on this board, certainly longer than moi. However, the SW is so reliable it is not much fun to tinker with.

Generally, this is also true with the Walter Kidde 4 cfm, if new. Recently, I got a report from a friend who built and sold an electric Kidde to a small dive shop. The shop owner gave it a workout running almost continuously to maintain pressure in an HP cascade. This went on for about two years until the guy went and bought an Ingersol Rand. The Kidde compressor was not impaired in any way, he just decided to get a really big machine to match his growing business. In another case, my friend built a compressor for a yacht owner. This machine consisted of an electric motor driving TWO Kidde pumps. The machine was run all day, every day. One of the Kidde units failed within a couple months. The oil pump was defective, incorrectly assembled on the factory bench according to my friend. This seems to be a rare thing but it happens.

The SW is a three stage and can output up to 3500 psi. Going a bit higher, up to 3800 seems to be OK. However, the four stage Kidde can be operated at higher pressures if need be and this is entirely due to the four stage design. Again, due to this design, the Kidde is lighter weight and more compact. However, depending on the rotation (most are clockwise at the fan), when powering with gas, the Kidde pump must be adapted to some kind of spline/pulley arrangement and this can be a challenge. These kinds of challenges make the Kidde a bit more fun for the mechanically minded.

 

[pescador775]

Here are some images, home built Kidde first, SW last. I forgot to mention that the Kidde, although nominally rated 4.0 cfm, has an actual output of about 4.4 cfm (@ 3750 rpm). The SW is spot on 4.0 cfm @ 3500rpm, measured.

 

[pescador775]

Here is a blurb on Ultrachem's new high performance food grade compressor oils, Omnilube 32/46, etc. First available in 2004, it makes me wonder just how good is the EZ 1000 oil that I'm using in my Bauer. This EZ 1000 oil, which UBS has long touted as "premium" and safe for Nitrox within the usual limitations, has been around for years. If it turns out that the UBS oil is early generation technology, my compressor may need a different diet. Also, now thinking of pumping Nitrox through my Kidde and have already built a portable stick. Hmmm.

http://www.lubricon.ca/cgi-bin/news.cgi?rm=display&articleID=1099059487

 

[pescador775]

At this point, I'm going to continue with an anecdote that might prove useful to some person in the future who might have a technical or historical interest. In the interest of full disclosure, my memory is not perfect but I do check things for accuracy, and I always report on items which may or not agree with my opinions.

This concerns the dive shop operator mentioned in prior post. After the most recent phone call to my contact in CA, it turns out that the gent who filled his cascade storage cylinders with a 4 cfm Kidde compressor did so on a continuous basis for FOUR years before replacing the still operational Kidde with an Ingersol Rand. Furthermore, and get this, he was pumping NITROX through the Kidde. One additional detail, he lubricated the compressor with Anderol 500, a 30 weight synthetic, diester oil! Well, I've often wondered (no surprise) if the use of "food grade" oil is really necessary for pumping NITROX, particularly in high speed machines. Evidently, it has been done using a diester oil in one such high speed compressor and without reported problems. I have the phone no of the shop and hope to have the opportunity to chat. So, I'll report back with a confirmation or correction as needed and that should conclude my current investigation and belated report to JT Smith's question of long ago.

 

[pescador775]

In the meantime, here is some reading material for folks like me which one could count on one hand, heh. One factual correction and one opinion. The correction has to do with a well publicized investigation of complaints by a few commercial airline pilots, of odd odors and alleged symptoms experienced in some aircraft cockpits. The article below says that the problem was traced to jet turbine oil fumes. This is incorrect. I read the final report of the special investigatory panel which stated that jet turbine oil, degraded or otherwise, was not the source of the alleged problems.

The purpose of this generally excellent paper (link below) is to explore and make recommendations about an incident of air contamination experienced by a well known cave diver. While the approach taken is reasonable and well thought out, not to mention well written, there is some talk about carbon monoxide supposedly produced by breathing air compressors. Just keep in mind when reading this report, that extremely high temperatures are required to produce this gas, higher than would be expected to be produced by an air compressor except under the most unusual circumstances, even if pumping NITROX. However, there is a real concern about external sources such as engine exhausts and the compressor operator should be aware of this. I'm sure most are.

There are some revealing data concerning filters which use chemical media.

The writer, a Canadian physician named "swampdiver" complains about lack of data concerning the relative safety of common compressor oils under high heat conditions, diesters, triesters, PAO (food grade) oils. I agree.

http://www.neptunoworld.com/articles/toluene.html

 

[pp-1-3-5-7-9]

HI ! Pesky,

Am always with very exciting to have seeing your new valuable experience / reports regard to the little kidde . Thanks!

Peter

 

[pescador775]

Thanks, Peter.
If a single person can make beneficial use of anything we've presented here, then the board has served a good purpose.
Dennis

 

[pescador775]

To my knowledge, air compressors do not produce the cylinder head temperatures required to emit carbon monoxide. This gas is a product of incomplete combustion which implies temperatures near the flash point of the compressor oil. The specs for oils vary but the flash temps for modern synthetics range 420-510 F. This is hot enough to melt solder and weaken aluminum pistons. Although the flash point could be lowered in a NITROX atmosphere, I haven't seen data. Probably wouldn't mean much because the oil vapor inside an air compressor's cylinder is rapidly emulsified with water which is present in relatively large quantities, say 10-20 times that of the oil. How such a mixture could produce CO is not clear. Alright, alright, there was, in the stone age of the 50's, a compressor which was suspected of CO. This was the two stage General Electric (aircraft) compressor which was well known and of which several score were harnessed to SCUBA tanks. Rated at 1100 psi (?), they were used to pump to 2250 psi which caused considerable heat, and dieseling, in the tiny GE pump.With only two stages it was hardly surprising as anyone who disassembled A GE compressor could explain. It was well known at the time and these little demons (they sounded like banshees with their high speed 28 volt motors) had to kept cool.

 

[pescador775]

To anyone who wants to see (or buy) a General Electric compressor, here ya go:

http://cgi.ebay.com/ebaymotors/Gene...587057437QQcategoryZ26439QQrdZ1QQcmdZViewItem

 

[pp-1-3-5-7-9]

The story of the this G.E. Compressor can be found on the page No. 3 of the following Web with a topic of "Electric Device Prevents Gun Jamming on Aircraft".

http://www.library.ubc.ca/archives/pdfs/ubyssey/UBYSSEY_1945_03_03.pdf

At recently I have had setted up one set of same kind of compressor for test purpose. and in order to start up this compressor in a convenient way ( this stuff have equiped a 27Vdc, 17 A DC motor to drive it ) I also have DIY a 24vdc (960va) power supply to fitted this compressor use (using 24vdc power source the motor draw over 24A current for 1200 psi pressure operating ). the original compressor unit has a cornelius model 31 pressure tank piggyback, and there have a relief valve attached on this pressure tank and the original cracked pressure is setted at 1200 psi.

with regard to the runing temperature issure, I supposed the designer may consider this compressor is for aircraft operating at high altitud and cold temperature, so the whole cooling system for the compressor is just depend on the top side of the DC driving motor complex type (centrifugal plus axial ) cooling fan to forced the air down to blow the compressor with an enough of cooling, and according to my test I runing the compressor at ground (local temperature is arround in 80'F) many times until the pressure tank relief valve with actived, at this point the pressure reading are from 1200psi to 1450 psi if I keeping supply power for the driving motor ( I personal beleived this little compressor have a capability to go a higher psi ), and the pressure tank (cornelius model 31) can be get it's full charged (1200psi )within in 4.5 minutes, so, I estimated the compressor output for my case is arround 0.5 cfm.

In case of without an extra cooling fan to help the compressor to disperse the heat , I can found the compressor temperature will rise up the temperature in very quickly when the dellivery pressure start to go over arround 1000 psi , from this point my hand just can't stand on it for over 3 seconds, and I beleived this temperature may nearly reach in arround 120'F, even this temperature is still within the spec of this compressor (from 65'F below zero to 160'F), but in case of with an extra cooling fan help and blew the compressor my hand even can stand on the compressor with no problem

Finally, consider to have long last the compressor I would recommend anyone who have intended to runing this kind of compressor in a continuous working case then he better to give this compressor with an extra electric cooling fan to prevent it may go over the temperature limit also get a higher efficiency on this stuff.