Kidde 2.2 cfm bad experience

[2airishuman]

I've finally given up on my Kidde. I got maybe 25 hours out of it.

I had ongoing problems with shaft breakage. Neither I nor the experts on these compressors have been able to diagnose the root cause of the failures. My best guess is that there is some sort of internal problem with the compressor that is leading either to vibration or to unusually high instantaneous loads. The cost of replacement shafts, repair service, and round-trip shipping have led me to a point where it does not make financial sense to continue.

There are some facts I was unaware of when I started building a system around this compressor:

1. I knew these units were powered by a hydraulic motor in their original application (aircraft). There are conversion kits to allow the units to be belt driven that have been available from Jim Sheldon and other sources. What I did not know is that the shaft in these kits is a weak point. Early shafts were prone to breakage. Later shafts used a different type of steel and have a better track record, however, I had ongoing problems with shaft breakage, even though I was using the later version of the shafts with the improved steel.
   
   
2. The compressors were designed for 4000 RPM operation but are usually run at 3500 RPM using a v-belt drive with two pulleys of the same size and a 3500 RPM, 2hp electric motor. At least one person has been successful using a flexible Lovejoy coupling to eliminate the need for the belt drive. I originally assembled the system this way (a direct coupling is safer and more compact) and had shafts breaking after less than an hour of operation. One of the theories was that shaft alignment was contributing to the shaft breakage, so I switched to a belt drive where alignment is much less critical. I don't believe that was ever the problem. I think that belt slippage allowed the energy from rotational inertia of the rotor in the electric motor to be dissipated without stressing the shaft as much, when the compressor was seizing or slugged or whatever the problem was. In any case, I wouldn't recommend using a direct drive, even with a flexible coupling, based on this history.
   
   
3. Jim Sheldon provided parts, service, and conversion kits for these compressors for many years and enjoyed a reputation for being knowledgeable and providing good service. Unfortunately, he is retired and has sold his parts inventory to another organization, Elevate Systems. It was not my experience that Elevate Systems provided the level of expertise and customer service that others have received in the past from Jim. In particular, they did not respond to my emails asking for some sort of accommodation on a warranty basis when I continued to experience shaft failures after shipping my compressor to them for evaluation and repair.
   
   
4. The supply of compressors has dried up completely. I have been unable to find a complete unit for sale in working condition, to replace the one I will have to scrap. This has left me in the unfortunate situation of having a good deal of money tied up in an electric motor, base, belt drive components, filter tower, special lubricant, and other parts obtained to build a complete system around the Kidde compressor.

Any compressor is a complex machine subject to a great deal of stress. They require ongoing maintenance and support if they are operated regularly. I haven't decided whether to purchase a different compressor or just sell the remaining parts and pieces, but if I do buy another one, I think I will stick to major name-brand equipment for which service and support are widely available.

I share this so others contemplating a purchase of one of these machines can make an informed decision.

Maybe this is a failure on my part to deal with routine mechanical problems, but... I've had pretty good results on other mechanical projects I've undertaken, including engine and transmission overhauls, air conditioner repairs, hydraulic systems, ag machinery, so I don't think it's me.

 

[walkonmars]

Was the shaft breakage due to fatigue stressing on the shaft? Is the breakage always in the same spot.?
It sounds like the shafts may have a weak spot or a "notch" that may be initiating a crack. (If that is the problem.)
Maybe get rid of the notch by grinding it out so corners are round or put less lateral stress on the shaft with less tension on the belts as long as they are not slipping.

 

[2airishuman]

Was the shaft breakage due to fatigue stressing on the shaft? Is the breakage always in the same spot.?
It sounds like the shafts may have a weak spot or a "notch" that may be initiating a crack. (If that is the problem.)
Maybe get rid of the notch by grinding it out so corners are round or put less lateral stress on the shaft with less tension on the belts as long as they are not slipping.

Well, to be clear, I've decided not to experiment with this setup any further and believe that the fundamental problem is internal to the compressor.

The pump uses a relatively small spline drive. The shaft always breaks at the end of the splines. I don't think there's any way to make a better shaft. The original hydraulic-drive application used a much shorter shaft and had a comparatively low moment of inertia, which perhaps put less stress on the shaft.

 

[kelemvor]

Sorry for your loss of compression.

On the upside at least you learned something about compressors, right?

Too bad Rix isn't into selling scuba compressors anymore, 'eh?

 

[noj3333]

Speaking with almost no knowledge here... would it be possible to have a machine shop make a shaft out of a stronger metal??

 

[BRT]

Speaking with almost no knowledge here... would it be possible to have a machine shop make a shaft out of a stronger metal??

The drive on the hydraulic motor is hard, really hard. The problem is getting "one" built to that quality for an amount of money you are willing to pay. If we needed 100 it could be done.

 

[tbone1004]

@kelemvor can still find them pretty cheap though!

 

[michael-fisch]

Weren't the Kidde's originally mounted in F104 Starfighters so they could restart after a flameout and then refill the airtank? Certainly nothing to do with continuous duty.

Michael

 

[2airishuman]

Sorry for your loss of compression.

On the upside at least you learned something about compressors, right?

Too bad Rix isn't into selling scuba compressors anymore, 'eh?

Not sure where this will end up for me. I'm thinking I'll end up with one of the newer, smaller Bauers. Expensive, but good support available. I am exploring some lower cost alternatives but at this point I want a compressor, not a project.

For the rest of this year, I'm pretty much resigned to paying for fills. My kids dive, and I'm going to have 20 empty cylinders by Monday afternoon from shore diving in the Brainerd area. Fills are expensive, compressors are expensive, part of the price of diving I guess.

 

[kelemvor]

Not sure where this will end up for me. I'm thinking I'll end up with one of the newer, smaller Bauers. Expensive, but good support available. I am exploring some lower cost alternatives but at this point I want a compressor, not a project.

For the rest of this year, I'm pretty much resigned to paying for fills. My kids dive, and I'm going to have 20 empty cylinders by Monday afternoon from shore diving in the Brainerd area. Fills are expensive, compressors are expensive, part of the price of diving I guess.

True enough. With 20 tanks to manage, totally worthwhile to do your own VIPs as well. So you prefer Bauer? Just curious... I occasionally find myself interested in owning my own compressor, but the cost of entry is so high and info seems to be somewhat limited due to perceived competition from dive shops...