Which Compressor

[devjr]

Sulaco, don't feel bad about the razzing. Heck, my compressors are home built, sort of. In years past, the performance of commercial units was pathetic. You had to pay a lot of money for a clunky 100 pound portable with cast iron cylinders, crappy filter, which would only put out 2.5 cfm. So, I had my two portable units custom built from aircraft pumps(compressors); everything, frame, condensators, filling whips and manifolds, all built from scratch. Every exterior surface including the filter, muffler, cooling coils, frame, coated or plated. They're really pretty and even today, over twenty years later, there is no commercial, gas engine portable compressor that can match military performance of 4cfm and 80 lbs gross weight including a full steel frame. They can't afford to build 'em.

Incidently, the specs of commercial compressors are still rather poor and they lie about it. A compressor rated 4.2scfm is actually 3.5cfm. Just be aware.

Although there are many brands of compressors, the most popular portables are built by German, Italian and British manufacturers. Sometimes these are built overseas but most of them are assembled or partly manufactured in the USA from foreign made parts. Personally, I find the small Bauer pumps to be of fairly high quality. The filter/condensator with multi stage filter is really nice. The entire pump and filter is made from light alloy like my military compressors. The Bauers will go 5-10 years before replacement of valves and a pro can replace the 2nd and 3rd stage valves in an hour. The four stage Italian compressors are light weight but the German engineer who built my custom units doesn't like the Italians much. Says they aren't durable. I hear that the American Bristol and Austrian (poseidon?) units are fairly good quality. Easiest to find on the resale market are Bauer.

Almost any high pressure pump could be used to fill tanks but the modifications required are meticulous and expensive. For example, the "filter" alone would cost about $500. Nice to see that someone is still trying to figure things out for themselves instead of taking a course. It's more difficult but potentially less expensive, and you learn a lot more; but this may not be the right project at the right time.

Keep looking for that compressor and keep saving up your money. We're always here if you need diversified opinions.

 

[Uncle Pug]

Originally posted by devjr
Heck, my compressors are home built, sort of.

So, I had my two portable units custom built from aircraft pumps(compressors); everything, frame, condensators, filling whips and manifolds, all built from scratch.

over twenty years later, there is no commercial, gas engine portable compressor that can match military performance of 4cfm and 80 lbs gross weight including a full steel frame. They can't afford to build 'em.

Hi devjr,

Sounds like cutom fabrication that is too expensive to duplicate on a commercial scale....

Not home built, sort of....

But very interesting anyway.... got pictures and a more detailed description.... parts list.... are these pumps still available.... mil. surplus.... total cost of project (in today's $).... what pressure are you getting and is the 4cfm at rated pressure.... what power are you using?????????

TIA

 

[devjr]

Pug, the pumps are hard to find nowadays. Occasionally they show up on E Bay but the prices and condition of the item are individually or collectively subject to question. The buyer really has to be familiar with the mechanics and what questions to ask.

Many years ago, these items were commonly available from US military surplus sales and other sources. Someone who was building their own portable would usually order several pumps for installation, parts and for direct replacement in case of major failure. Overall, this route was not much cheaper but that is not the point. Nothing comes close to the quality of the military compressors, and a pump that cost the military $4000 (in 1968) could be had for $100, and that was new or almost new.

Yes, they are strictly rated by govt contract and the pumping rates are true at max pressure and normal RPM. God help the manufacturer if he tried to pull the wool over the Air Force like they do civilian divers today. These compressors were used in jet fighter aircraft.

My two portables use 5hp, 5.5hp engines; the Kidde is powered by Briggs and the SW uses a Honda. They still see service and are the hot setup on our boat trips throughout the Bahamas. Usually, the Kidde is preferred because of its compact design, low center of gravity and near total corrosion proofing. The SW is a spare and is kept in ready to travel condition.

The average mechanic should not try to work on the ultra compact and precision made Kidde pump. Some training would be required. This can be a headache. Unless certain simple precautions are taken, the Kidde may lock up or blow oil after only a few hundred hours, or a few years storage. The SW is easy to work on but rarely requires any kind of maintenance. During a routine inquiry, we discovered a SW pump at NASA that had 4000 hours on it with no problems. We were told about one that had been run for 20,000 hours.

OK, I see more questions; nominal pressure for both units is 3000 psi. Blow off is set at 3300 and 3500. We destruct tested the Kidde, same model used in my personal unit. It blew a head at 8000 psi. I've never tested the SW, too hard to find good ones at a cheap price. I don't think it will go as high as the Kidde, though.

Price is not set, it depends on sources and labor costs. We found that it is too expensive to fabricate filter canisters from scratch. Even so, the overall cost of a complete unit, today, would be about $2,000. Fortunately, the SW usually comes with a beautiful condensator, blowoff and backpressure valve, and it is only necessary to add a charcoal, dehydrator unit. These can be made by adapting a small accumulator used in aircraft and machining a plastic insert. Since the basic cost of the SW is generally higher, the overall expense turns out to be just a bit less than the entirely handmade Kidde setup.

 

[Iguana Don]

Originally posted by SubMariner
I'd like to thank all my family & friends for this wonderful award...

Wait.. that was LAST NIGHT at the OSCARS...

So who won the "not so nice n polite" award?



~SubMariner~

Sub,

We try not to have any "not so nice n polite" awards, at least that is our goal.

BTW. you gonna wear one of those Jennifer Lopez dresses to the awards??????

ID

 

[iceberg]

Has anyone heard of one of these? I found a Davey compressor at a surplus "place" for $1000. The comp is 4 stage, uses 3 phase power. has a retractable 25' whip. Unit is quite large and mounted on its own little trailer. The military tag showed last service in 1989. Hour meter shows 13 hours. No idea what this was intended for or the cfm rating. Any ideas?

 

[omar]

Three phase power is not readily available to the average consumer. Bringing in a 3 phase feed to your house/shop/garage is usually ridiculously expensive. If the equipment you want to run has a standard motor mount, it is *MUCH* cheaper to buy a new 110V or 220V motor for it. In some cases it is possible to run 3 phase equipment on ordinary power if you have a phase converter.

I ran my compressor 3 hours Friday night and 3 hours Sat night just to fill some tanks and top my bank off. So 13 hours is almost nothing. But, if the unit has only been run for 13 hours since ’89 you can most likely expect to have rust build up in the valves which will need a rebuild to run right. Also motor/compressors that sit for long periods of time generally require some work before they will run properly.

Than you will have to purchase a suitable filtration system if you want to use it for breathing gas.

Over all you would probably end up spending more to get this unit to run right than buying a new RIX, I-R, Bauer or other.

 

[devjr]

Iceberg, the Davey compressor is a familiar surplus item. You are probably looking at a 4 stage, 15 cfm model. Most of the ones that I have seen are powered by an twin cylinder Onan diesel or gas engine of, I think, about 20 hp. They were popular with dive clubs. The only one I have personally used was a gas engine trailer mount which was hauled onto a dive boat for a trip to Tortugas. That was about 30 years ago. The compressor seemed very reliable although it developed a temporary problem with the engine distributor. Salt air or something. We got it running again and pumped several tanks a day for two weeks. Throughout the trip, the air didn't taste right, kinda like burnt socks. The skipper said it was OK, but what can you do?

I'm sure there are plenty of shops that rebuild or supply parts for these. However, there are not likely to be any near you. (Just law of averages). To put in perspective, a similar E Bay compressor with SCUBA written on it would cost about $5,000 or more, and no guarantees. It really depends on what you need and the price you can afford. With used compressors, the time, effort and logistics are part of the price.

One point, the trailer is not designed to be towed by a normal hitch or at speeds above 20 mph. They will fit into the bed of a pick up, however.

 

[devjr]

Sulaco, portables are starting to show up on E Bay. There is a used Bauer Utilus 10 and a new Junior II. These are very similar 3.5 cfm units, the smallest that Bauer makes. The US retail prices run about $3500. However, I know that a couple years ago the retail in Germany for the J.II was DM3500, about half.

 

[devjr]

This is for the record only, no replys necessary. I make every effort to ensure my statements are accurate. In this regard, I stated that no small commercially made air compressor could match the performance of the military spec'd compressors dating back some 40 years. However, I found some data for the Bauer Oceanus which challenge this.

The German version of this compressor is rated 5.0 cfm at 2600 rpm and overall weight of the gas unit is 103 lbs. This is roughly equivalent to my homemade Stewart Warner and Kidde home builts which is rated at 4.0 cfm at 3600 rpm and 80 lbs overall weight. In other words, the output per unit weight has caught up. However, looking farther, I found that the US made version of the Oceanus is rated 4.1 cfm at 2100 rpm. Weight is also 103 lbs. Apparently, the Oceanus is downrated for this market in order to ensure reliability and prevent overheating in southern climes. (The German version has a thermal switch to kill the engine if the compressor overheats). Therefore, this compressor setup, nice as it is, remains challenged by certain decades old designs in terms of output per unit weight.

The Stewart Warner (and Kidde) use some very tight engineering to allow such high temp/high rpm operation. The cylinder cooling fins are very pronounced, deep and cleverly designed. The bearings and other components are sophisticated and expensive. The oil sump is twice as large as normal for this size unit. The SW is rated to operate at 100 degF and the Kidde at 160 degF!

Speaking of which, the Oceanus also has an enlarged sump and pressurized lubrication, not only for high temp but to allow safe operation at tilts up to 30 deg. This is the first Bauer unit that can do this without loss of lubrication, and is important for boat operation. The military compressors I referenced, Walter Kidde and SW, have always been capable of this. The Kidde has a dry sump system designed to operate upside down for short periods of time if necessary, as in aircraft for which it was designed. The SW sump holds a quart of oil, twice the amount used in Bauer portables such as Utilus 10 and Junior II.

The retail price of the Oceanus is $4300, a lot of compressor in a small package with a price to match. The advent of this compressor is significant in that it is no longer necessary to build your own to get decent performance and portability. Still, it's 20 more pounds and 2000 more bucks than my home builts. Can an E Bay version be so far off?