Bauer Capitano improvements

[AnthonyIDB]

Hi All,

I've been using my Capitano merrily for some years without any hassles, however the lack of a water separator between stage one and two, along with the poor inter-stage cooling has bugged me, leading to this post;

Has anyone plumbed a water separator between stage one and two? ... and;

Has anyone managed to improve upon the stage one to two, and the stage two to three cooling, (those coiled up pipes alongside the block), and or that poor excuse for a fan/pulley.

Thanks in advance

 

[RayfromTX]

Compressors like this one are designed purposefully. I would not monkey with the design without knowing the reasons and intents for the decisions made by the designers. Unintended consequences could make the outcome worse than your current concerns. I am not an engineer but one may come along directly.

 

[tbone1004]

water separation isn't that common between the first and second stages. I'm sure some pumps have it, but the vast majority don't. The compression ratio isn't all that high in that stage so not a lot of water will knock out.
If you want to improve cooling, the best bet is probably to remove the fan/pulley and replace it with an electric fan. Will help quite a bit. Those fans are only running around 1500rpm which isn't bad, but you can get a lot more air flow with some electric fans.

 

[AnthonyIDB]

water separation isn't that common between the first and second stages. I'm sure some pumps have it, but the vast majority don't. The compression ratio isn't all that high in that stage so not a lot of water will knock out.
If you want to improve cooling, the best bet is probably to remove the fan/pulley and replace it with an electric fan. Will help quite a bit. Those fans are only running around 1500rpm which isn't bad, but you can get a lot more air flow with some electric fans.

Thanks for your reply tbone ... I have indeed been leaning towards a ducted air system using electric fans as suggested

Insofar as the first stage, I acknowledge your point that it only runs around six and a half Bar, however two events have prompted my wanting to improve on the design, the first event being that I left my compressor idle for a little over three months, and when serviced thereafter, found light rust in stage two's bore, which necessitated an innovated repair in the form of boring out cylinder two, hard chroming it back to 'standard', then honing, and reassembly along with new rings and valves ... This event has prompted a short monthly "blow out the cobwebs" compressor run, irrespective of any air requirements.

The second event, (albeit seemingly unrelated), is that I have a small low pressure air compressor, (approximately the same pressure as the Capitano's first stage), that I use for odd jobs / tinkering, that without going into great details of why, installed a cars oil cooler between it's first, (and only), stage and it's air storage cylinder, along with moving it's water separator, that was positioned after the regulator, to directly after the newly installed oil cooler, and ... I no longer have it's air storage cylinder filling with water, along with a cooler running system, (and a sh## load of water being "caught" in the re-positioned water separator, which previously trapped little if any water!)

I'm willing to bet that the lack of moisture removal between stage one and two was the major contributing cause of the aforementioned stage two rust issue, and ... as cooling the air is the best way to remove suspended water particles, logically the best improvement would be to both improve the inter-stage cooling, and add an additional water separator?

You raised an interesting additional point with regards fan speed that prompted a quick test too ...
You mentioned that the fan runs around 1500 RPM ... I checked the Bauer spec. and it should be running at 1280 RPM ... Mine is running just under 1000 RPM, so a primary pulley change to correct that is certainly in order, (it also explains why I have only ever managed some 110 l/min against the claimed 140 l/min ...
I don't think the additional 280 RPM will contribute much more air from the fan, and if anything, will probably be negated with the additional heat from spinning the compressor some 30% faster.

 

[tbone1004]

@AnthonyIDB I don't think a water separator would really do anything to prevent that issue from happening though. You can always just put one between the two stages and see how much water it actually separates out, but you'll be better off just running it every so often to keep it clean. Sounds like you've already replumbed an aux water cooler in another pump and since the first stage runs around the same pressure as standard shop compressors, you'll only need to use a standard water separator, probably the same one that you're using in the normal pump.
Now, there is a drawback to doing that though. I don't know about the bauer, but I believe it has a floating final stage which needs backpressure to seat before it stops hammering. If you make the volume between the first stage and the PMV longer, it will take longer to get up to pressure and cause increased hammering of the last stage piston which could result in accelerated compressor wear during startup. If you have a soft starter, you may be able to mitigate, and you may be able to pre-pressurize that water trap, but it will still increase the cycles before that final piston seats.

I seem like @iain/hsm has written some things about why there typically aren't water traps between the first and second stages, so you may want to search his posts.

If it's happy at 1000rpm then I'd focus more on getting that electric fan installed vs. trying to increase the speed

 

[RayfromTX]

@AnthonyIDB snip
Now, there is a drawback to doing that though. I don't know about the bauer, but I believe it has a floating final stage which needs backpressure to seat before it stops hammering. If you make the volume between the first stage and the PMV longer, it will take longer to get up to pressure and cause increased hammering of the last stage piston which could result in accelerated compressor wear during startup. snip

This sounds like one of those unintended consequences I referenced. I've read enough of Iain's posts to realize there is more to the engineering of a good compressor than meets the eye and if they leave something out or add something in or do things a certain way, there is usually a reason and while it may be that the design may be able to be improved with resources added, It's unlikely without a full understanding of the existing engineered design and the decisions that were made during its development.

 

[rddvet]

People with much more experience with these things design and repair compressors. If there was a need for a separator between those stages, somebody would have added it in regular production. Don’t reinvent the wheel.
Your big issue is not running it. I’m concerned over the same thing. Since moving to a rebreather I use the hell out of my booster but don’t use my compressor much at all. I run it and let if build pressure for a little while from time to time but not regularly. I just need to regularly fill a few bottles, even if I don’t use them to keep the compressor cleaned out. Thanks for the reminder to quit forgetting.

 

[tbone1004]

@rddvet have you considered doing an OC dive every few weeks? Good excuse to clean the bottles out and get updated SAC swims.

 

[rddvet]

@rddvet have you considered doing an OC dive every few weeks? Good excuse to clean the bottles out and get updated SAC swims.

That's what we're planning to start doing. We've been very focused on CC diving and now that we're finished withe crossover, I'm going to start throwing OC back in to the mix a little more. Porbably dive the spots my bm CCR won't go. Honestly though I don't like OC as much as CCR now. It's loud and the time limit sucks.

 

[tbone1004]

That's what we're planning to start doing. We've been very focused on CC diving and now that we're finished withe crossover, I'm going to start throwing OC back in to the mix a little more. Porbably dive the spots my bm CCR won't go. Honestly though I don't like OC as much as CCR now. It's loud and the time limit sucks.

I agree 100% on OC not being nearly as fun or ideal for cave diving. The other one is maybe do a SAC swim on your exit from the last dive of the trip? Helps drain the bottles, exercises the regulators, etc etc.