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

[oxyhacker]

An interesting bit of trivia: the little Coltri pump was developed for the same purpose, and used in place of the Kiddes in license-built Italian Sabres.

Afterall, when these compressors were originially selected, the military contract was for installation in the F86, America's first combat jet fighter.

 

[pescador775]

Yes, that is interesting about the Aerotechnica Coltri pump. I didn't know that. It is a light weight, 4 stage radial like the Kidde. Pump speed is about 2800 rpm and it uses a heavy oil, like Bauer, I think. I'd like to see a diagram of its innards. Google time, maybe.

 

[pescador775]

The most striking differences with the Kidde have to do with the traditional design of the Coltri with its splash lubrication. The Kidde uses a dry sump in keeping with its aircraft installation. That is, the Kidde can be operated in any position without loss of lubrication, even upside down. For this and other reasons, the aircraft Kidde has about 25 more parts despite only having a single connecting rod compared to four for the Coltri.

 

[pescador775]

The Kidde has only one connecting rod, to the first stage. The other three stages are driven by cams and a "keystone". It's an interesting design and must have been pretty innovative back in the day. The pic below is an exploded diagram of the 4 cfm Kidde that was installed in a piece of ground support equipment, essentially a two wheeled cart with 2 cyl engine to which the four cylinder Kidde pump was bolted in a direct drive configuration. Main differences from the aircraft type compressor are the block, and oil pump which was compatible with left hand rotation of the crank (looking at fan). This mod has fewer parts than the aircraft compressors with its combined crankcase/first stg/2nd stg main casting. In the aircraft unit these are cast separately and bolted together. Even so, this unit is a bit more complex than the Coltri. Nevertheless, it is remarkable that the Coltri can be sold on the civilian market for little money. The Kidde's select fit, blueprinting, run in requirements and exotic materials (the crankcase is magnesium--the keystone is made of aluminum bronze, pistons made of niconel or chromalloy, valves of stainless steel), spell big bucks.

 

[pescador775]

Erratum: this is a short note and correction. The 3rd and 4th stage pistons of the Kidde compressor are not fabricated of niconel, these ringless plungers are made of INCONEL and are precipitation hardened. The valves are also made of this alloy.
Pesky

 

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

My opinion is that noise is difficult to compare, but..... The larger, slower turning compressors make knocking and clicking sounds and shake a lot where the Kidde produces a smooth "burrrr". Overall, the Kidde seems a bit softer and nicer because it has no vibration. Unlike the Bauers, and three stages in general, the Kidde is dynamically balanced and one knows it must be designed just so because otherwise the vibrations would be transmitted in the aircraft where many are installed. Afterall, when these compressors were originially selected, the military contract was for installation in the F86, America's first combat jet fighter.

Otherwise, gas engine installations DO have significant vibration and are quite noisy. Vibration is caused when the engine pulses and the compressor pulses are not aligned. After all, the typical engine has ONE cylinder and the compressor has FOUR. Vibration is significantly reduced at high engine/pump speeds and, of course, increased at low speeds, so one should run the engine at about 3400 rpm. (Just think of a polygon, the more sides that it is given, the more it resembles a smooth circle). Anti vibration measures are this: Attach bracket from engine cylinder head bolt to frame. Attach bracket from compressor mounting bolt to engine side bolt. Install rubber "feet" on frame. Some may wonder why I stay with the old style Briggs engine. (The Kidde does need somewhat more than 5 hp). It has to do with the low profile of the engine and the ease of attaching the anti vibration brackets. The brackets are just strips of 1/8" stainless steel, bent to the correct angle but they make a difference. Less chance of something coming loose or braking. The frame itself is all steel, welded. Total weight of setup is about 85 lbs.

I fully agreed with your statement, these kidde was made with a very well balanced ( I can feel it's almost no vibration on these kidde which are driven by way of electric motor ), install a rubber feet is a good ideal to absorb a vibration, I also have installed four rubber pads underneath the base wooden frame but just simulated as a cushion only. for your information that I have weight my 4 cfm kidde unit, it's about 63lbs.

 

[pescador775]

Peter,
just heard from a friend who enjoys reading your posts. How about that? Heh, always good to hear from a Kidde fan.

 

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

Pesky ,

Supposed he is a Kidde fan also, In actually, I became as a kidde fan in about 25 years ago, and at the beginning I have tried to found out a used high presure air compressor for filling my scuba tank use. but even I have screened a certain unmber of local compressor shops but no one have been seeing or familarize with these stuffs. after about 3 years later when I traveled to the south area for business, the god gave me a chance to seeing a military surplus high pressure compressor, it's navy used one with a vertical structure driven by a 2HP, 27.5 DC motor, and it rated with 3000 psi & 2cfm ouput and made by some thing like "Rouid---- , I just forgot the whole name ", this model pump I have total acquired 5 units back home for rebuild, but unfortunately, because of the materail used to built this compressor is not so good ( most of the 3 & 4 stage valves were get rusted and stucked ) so finally I only rebuilt one unit in working order, since it's not my ideal HPA compressor therefore I just sold it out in several months later, after that I have found out a cornelius HPA compressor rated 3000 psi /2cfm driven by 2hp 400 hz motor, but I am still not lucky becaused of the second stage with damaged so I treated it as spare part ( I have used the moisture separator in my current 4 cfm kidde ), then kidde happened and compared all these three brands of pumps I would said the kidde is the best designed also just used the highest quality material to make it. and most impressive to me is the keystone design - just so sample but work so well.

I personally beleived there should be have a certain nunmber of kidde fan still alive in the world, since these stuff need some knowledge to be able to use it. but I can feel with all the resouces seems became little and less at now, so, I deeply expect if some one who is the kidde expert (i.e. like you) can be stand up and set up a "kidde group" in the internet and create a plateform to help all the kidde fan to get or sharing all the valueable experience.

An interesting item, they called HIPPAG (High Pressure Pure Air Generator -http://www.uews.co.uk/hippag.asp) made by a U.K. company named "Ultra Electronic Limited ", max to 18 SL/Min but 5100 psi rated. I even have a dream to get one to study it.

 

[pescador775]

In the past, I've posted regarding a conversion of a Paintball yoke into a useable diver's tank filler yoke and the problems that had to be solved which were several. I'm happy to report that the little stainless steel Proline quick disconnect, made for the paintball industry, is a much better product and easily adaptable to a diving compressor. I've attached a QD to my home assembled Kidde 4 cfm portable compressor. The result eliminates the need to scrounge for a wrench when connecting the whip to the compressor. It has the added feature of revolving 360 deg. The stud (nipple) is 1/8 npt male and the connector is 1/8 female. Nice, little 15 minute DIY effort.

 

[pescador775]

Peter, the "HIPPAG" is designed to be in direct competition with the Kidde (Meggitt Airdynamics) compressor; Missile cooling and like that. It looks different from anything I've seen.