Do I want a compressor?

[Schwob]

I really like this thread.
Many of you point out that they are happy to have a right sized set-up more for the convenience than cost savings. I certainly can see that some day, when diving more.
But could you help a compressor challenged mind with what "right sized" might be?
If I were to get a compressor while still working full time (I won't, but maybe after that...), then for me e.g even the smallest Bauer if I can rig it to auto shut off and fill a few tanks over night in parallel (if need be slow it down with a pulley change maybe to make sure nothing overheats) seems larger than what I might need. I suspect my thinking may be quite flawed or too simplistic....

Can you explain what right sized means for you?

 

[KentB]

This is my opinion and I know very little about compressors
" Right sized" is really subjective to your personal needs
Mine fills my 120/150 tanks in 30-35 min or so and they don't get warm so I don't loose too much pressure when they cool down.
faster you fill them the more pressure you loose when they cool down. So you have 2 options fill fast then top off later or fill slower.

It's at my shop so I fill the tanks while I'm getting the guys organized and out the door.
I currently bungee them to a shelving unit so if an O ring goes or the hose blows the tank won't fall over.
As soon as I slow down a bit at work I'm going to make a rack they will sit in instead of bungees.

This works Fine for me since my dive days seems to be Wednesday night dives and 1-2tank Sundays I'm at the shop for 1/2hr minimum every morning so this leaves me plenty of time to fill tanks without actually going out of my way. Or having to make special trips to shop for fills but it's close it's only 7-8 min away vs the closest dive shop which after work is 45 min there and 1.5 hours home

 

[JamesBon92007]

This is a Cornelius and is like mine. We were both born around the same time (early 50s). It takes about 40-45 minutes to fill a steel 72 to 2475. The maximum pressure is 3000. I got mine for $300. It is adequate for my needs. I rarely fill more than two tanks in one day. On the front, right, is the pressure relief valve which can be set for various pressures. Since it does not have auto-shutoff I taped a plastic bag around the valve so it fills up with air when my tank is full. I can see it from a long way off.

 

[Schwob]

This is a Cornelius and is like mine. We were both born around the same time (early 50s). It takes about 40-45 minutes to fill a steel 72 to 2475. The maximum pressure is 3000. I got mine for $300. It is adequate for my needs. I rarely fill more than two tanks in one day. On the front, right, is the pressure relief valve which can be set for various pressures. Since it does not have auto-shutoff I taped a plastic bag around the valve so it fills up with air when my tank is full. I can see it from a long way off.

View attachment 425193

Looks tiny. Which makes it interesting.

 

[2airishuman]

Can you explain what right sized means for you?

I have HP cylinders and HP twinsets and have concluded that the smaller portable units will overheat and suffer early failures for that kind of service, so the right size for me is probably one of the four-stage machines in the 8-10 scfm range. A slightly larger machine would be OK if it would run on single phase electrical power. I'm pretty sure that, if I proceed with this, I don't want a gas or diesel fueled machine.

This is a Cornelius and is like mine.

Looks tiny. Which makes it interesting.

That is similar to the flamethrower compressors of the era (and may have been manufactured for that service).

JamesBon92007, I hope you have filter towers for that -- there aren't any in the photo. I've encountered old divers who used flamethrower compressors without any filtration for shallow freshwater dives. People get away with it because the CO is not as serious a risk in the shallows and by letting the cylinders sit after filling most of the water and oils condense out. Not good for the cylinders or the diver though.

 

[TrimixToo]

<snip>
If I were to get a compressor while still working full time (I won't, but maybe after that...), then for me e.g even the smallest Bauer if I can rig it to auto shut off and fill a few tanks over night in parallel (if need be slow it down with a pulley change maybe to make sure nothing overheats) seems larger than what I might need. I suspect my thinking may be quite flawed or too simplistic....

Can you explain what right sized means for you?

I'd ask an expert before changing the compressor RPM. I'd be worried about it running out of balance, to start, since the cylinders are dynamically balanced using cylinder pressures, not statically balanced like automotive engines, and are happiest at specific speeds. (I am not home where I can look it up but I think Bauer wants mine to run at 950 RPM.)

"Right sized" for me meant "what I could afford," "something I could run," and preferably something rated for continuous duty. I got pretty lucky overall on the compressor cost, used filter towers and bank tanks, and reasonably priced replacement and upgrade parts from August Industries and Filter Techs. I got impatient after a while and bought the Haskel AG-30 new. Of course, almost immediately after opening the O2-clean sealed bag I naturally got the e-mail from High Pressure Tech about a rebuilt that would have used less drive air for much less money (a -15/30, I think). The Haskel aside, I probably have about $4K in the basic system, though I have spent more for Q/D connectors, fill whips, digital gauges, upgrades, and such since then.

There is little chance this system would ever have paid for itself if I only used air unless the closest fills were 50 miles away. A 100-mile round trip costs most people about $50 plus the cost of the fills, but that would still be a pretty long payback cycle. The savings on nitrox and (expecially!) Trimix fills, on the other hand, has more than paid for everything. As someone else posted, I expect that when I eventually stop diving I should be able to reclaim a high fraction of my investment, too. However, the convenience factor is not negligible. I can fill any time without worrying about the hours of an LDS. That's worth no money but it saves on aggravation...

I have seen better deals on compressors since, but only on things too big for me to run economically that run on 3-phase power (like K15s). The rotary phase converter cost, though, overwhelms the great deals I've seen on K15s for home use, but I did score a K15 pump and motor for the local dive club for (IIRC) $200 that will fit the existing frame as a backup.

 

[The Chairman]

Certainly, finding a good single phase compressor at an economical price is my biggest hurdle.

 

[tbone1004]

@Schwob right size is dependent on what you're doing. As mentioned above, changing RPM's is potentially really bad. In oiled compressors that are splash lubricated *most of them*, you will not have adequate oiling at slow speeds so you need them to stay fast. Something like a RIX can be slowed down, but they aren't very fast to begin with.
A lot of the size will be determined if you can bank the gas so you can get quick convenient fills if you need them, then commit half a day while doing yard work to running the compressor to refill the banks.
Electric compressors aren't quiet, easily as loud as the big 60-80gallon shop compressors, and the gas powered ones are equivalent to running a lawnmower for however many hours it needs to run.

Most home compressors are 5 ish cfm because they're big enough to fill reasonably quickly, but still small enough to have a decent footprint as well as the ability to run on a normal drier circuit if going electric

 

[The Chairman]

Saw this on ebay: 300BAR 30MPA 4500PSI High Pressure Air Compressor PCP Airgun Scuba Air Pump 220V | eBay

2.5 cf @10amp draw at 220v, but with absolutely no filters. $311 with shipping

 

[Schwob]

Saw this on ebay: 300BAR 30MPA 4500PSI High Pressure Air Compressor PCP Airgun Scuba Air Pump 220V | eBay

2.5 cf @10amp draw at 220v, but with absolutely no filters. $311 with shipping

Well, if you get it use it a good bunch for a year and let me know how it went, I may get one too...