BajaJim writes:

Am wondering if anyone has set up a small air compressor rig, 110V,
similar to the ones used by divers for hull cleaning services. I assume
just a small oil-less compressor and couple it directly to a stock dive
regulator?

Yes, we do this in our swimming pool. I run an old ScubaPro regulator 2nd
stage ($25 on eBay) off 90 psig shop air from a standard piston/oil type
compressor. Despite all the dire warnings (from people just reciting
paranoia they've heard, who've never tested for oil or tried it), the air
should be OK if your compressor doesn't consume oil such as from bad piston
rings. And the pressure is fine for feeding a 2nd stage.

The fear of "any oil in air will harm you" is silly. First, it is mineral
oil, which is non-toxic. Second, if were that bad, a whiff of 2-cycle
exhaust would kill you. I run this compressor for hours and hours,
thousands of cubic feet, and it loses only tiny amounts of oil, most of
which condenses in the tank.

I suppose an oilless compressor would eliminate even the possibility of
entrained oil. Although they're hideously noisy. You would want at least
a 2 cfm compressor rating, since you typically breathe about 1 cfm. But 2
cfm at 90 psi is only about a 1/2 (true) horsepower unit.
But see my essay http://www.truetex.com/aircompressors.htm on horsepower
ratings.

You need an adapter from the SAE scuba fitting to NPT pipe thread and
thence to a shop air quick-connect, which all then goes on your regulator
second stage hose where it would have connected to a first stage. You now
have a scuba regulator that terminates in an air tool quick-connect. I
made my own threaded adapter on my machine shop lathe. The only source for
such a part otherwise that I can think of is the adapters made for buoyancy
compensator connectors to shop air for filling tires or running tools from
scuba tanks (although this is the opposite direction of adaptation, it
might have the critical SAE-fitting-thread to NPT-pipe-thread conversion).
You could do it by simply splicing hoses with a hose barb if you were
willing to cut up the regulator feed hose.

Here is my drawing of the adapter essentials:

http://www.truetex.com/scuba_lp.pdf

Shallow water hookah diving is easier than most open water scuba diving.
The dive gear industry makes everything but this year's model sound like
it's going to kill you. The old 2nd stage regulators were very simple and
easy to repair yourself. They too were once the thing you had to have and
all the old models would kill you.

If anyone wonders if this is unreliable and therefore hazardous, I would
only use it for shallow diving, like working or practicing diving in a
swimming pool, or working on a boat hull, and I would insist on having a
trustworthy person for a topside tender. Being suddenly out of air is not
a problem with some simple training; we as tenders routinely disconnect the
air unexpectedly to our diving family members to help them practice the
drill (a habit I got from my first scuba instructor in the 1970s, who liked
to turn off your main valve when you weren't expecting it).

To anyone suggesting you just go full scuba instead of improvising a
topside compressor, I would say that full scuba is absurdly cumbersome and
expensive compared to hookah for shallow diving on a fixed location, and in
my opinion, no improvement in risk.

Of course this is diving, which takes training and recent diving experience
to minimize risks.

MANY Thanks to Richard Kinch and Bryan Combs for some great replies, it
was clear that they understood I am only going down 6 to 8 feet and
just need a little compressor, similar to those used for small paint
sprayers. I will also have 30A dock service to plug into.

This was my first post and participation and, while I love a little
humor as much as the next guy (see my book The Baja Bash), it was a
little hard finding the worthwhile posts while sifting through others
from people who clearly feel a need to reply to anything and
everything, under the assumption that they know all and should
therefore pass on their pearls of wisdom.

BajaJim wrote:
MANY Thanks to Richard Kinch and Bryan Combs for some great replies, it
was clear that they understood I am only going down 6 to 8 feet and
just need a little compressor, similar to those used for small paint
sprayers. I will also have 30A dock service to plug into.

This was my first post and participation and, while I love a little
humor as much as the next guy (see my book The Baja Bash), it was a
little hard finding the worthwhile posts while sifting through others
from people who clearly feel a need to reply to anything and
everything, under the assumption that they know all and should
therefore pass on their pearls of wisdom.


Jim,

I believe that the warnings you received about "oil" based compressors
are based on the concern that you might be exposing yourself to what are
admittedly small amounts of toxins but over long periods of time, all
while working underwater - an environment where one would like to avoid
encountering breathing issues.

To compound this further you will be most likely be exerting yourself
enough to raise your respiration rate which would increase any toxin
absorption rate. Also, because of the "partial pressures" of breathing
gases in increased atmospheres, the percentage of toxin absorbed by your
body goes up dramatically as you go deeper.

If you can avoid using an oil based compressor I would strongly suggest
doing so, especially since inexpensive alternatives exist.

Cheers,

Robb

Good post Robb.
The toxins are minute until the compressor pistons rings get worn (or do not
fit right from the beginning) and allow oil to enter the cylinders. With the
heat that's generated by compressing air, the oil will partially burn and
create carbon monoxide which coats the red blood cells and prohibits the
transfer of oxygen to those cells and further to the other cells in the
body.
Absolutely right about the oil free compressor!
MMC
"AMPowers" wrote in message
...
BajaJim wrote:
MANY Thanks to Richard Kinch and Bryan Combs for some great replies, it
was clear that they understood I am only going down 6 to 8 feet and
just need a little compressor, similar to those used for small paint
sprayers. I will also have 30A dock service to plug into.

This was my first post and participation and, while I love a little
humor as much as the next guy (see my book The Baja Bash), it was a
little hard finding the worthwhile posts while sifting through others
from people who clearly feel a need to reply to anything and
everything, under the assumption that they know all and should
therefore pass on their pearls of wisdom.


Jim,

I believe that the warnings you received about "oil" based compressors
are based on the concern that you might be exposing yourself to what are
admittedly small amounts of toxins but over long periods of time, all
while working underwater - an environment where one would like to avoid
encountering breathing issues.

To compound this further you will be most likely be exerting yourself
enough to raise your respiration rate which would increase any toxin
absorption rate. Also, because of the "partial pressures" of breathing
gases in increased atmospheres, the percentage of toxin absorbed by your
body goes up dramatically as you go deeper.

If you can avoid using an oil based compressor I would strongly suggest
doing so, especially since inexpensive alternatives exist.

Cheers,

Robb

MMC wrote:
Good post Robb.
The toxins are minute until the compressor pistons rings get worn (or do not
fit right from the beginning) and allow oil to enter the cylinders.
Absolutely right about the oil free compressor!

Thanks for adding your ideas here. Finally some advice based on
training, experince, and still here to give it. Unlike the other past
posts that simply said, "Ive been doing it this way for years and never
had any porblems."

Here is my question for you MMC:

A few comments earlier in this discssion I described a hand pump that
supplied diver air to about 20'. Did you ever run into anything like
that in the service? They were a little (maybe 25 lbs.) two cylinder
thing with a five foot handle that a person push-pulled too operated
the pump. The guy who made the new prototype said he got the idea from
one he saw in an old USN Dive Manual.

Thanks,
Bob

Salty Bob,
Man, that is an old set up! I remember pictures like that from the period
before those wiley divers hooked a new fangled gasoline engine to a
compressor!
The Navy used various models, without much change in design, of the Mk 5 hat
from the 1840s to the 1980s.
As I remember (got an old dive manual around here somewhere, hell if I know
where) the handle was like on the old manual rail cars, you know the ones 2
guys would stand on and pump the handle from the ends, up and down for
moving down a rail to perform maintanence?
Didn't John Wayne have a rig like that in "Wake of the Red Witch"?
As I remember a Mk 5 diver would be conscious for something like 6 minutes
if he lost his air supply, so if the supply flow replaced the air in the
suit every 2-3 minutes he'd be fine. Running a compressor like that directly
to a hat or mask, would only require a 2-3 cfrm and about 15 psi over bottom
pressure? Add depth and add cfm.
MMC
"Bob" wrote in message
oups.com...

MMC wrote:
Good post Robb.
The toxins are minute until the compressor pistons rings get worn (or do
not
fit right from the beginning) and allow oil to enter the cylinders.
Absolutely right about the oil free compressor!

Thanks for adding your ideas here. Finally some advice based on
training, experince, and still here to give it. Unlike the other past
posts that simply said, "Ive been doing it this way for years and never
had any porblems."

Here is my question for you MMC:

A few comments earlier in this discssion I described a hand pump that
supplied diver air to about 20'. Did you ever run into anything like
that in the service? They were a little (maybe 25 lbs.) two cylinder
thing with a five foot handle that a person push-pulled too operated
the pump. The guy who made the new prototype said he got the idea from
one he saw in an old USN Dive Manual.

Thanks,
Bob

MMC writes:

The toxins are minute until the compressor pistons rings get worn (or
do not fit right from the beginning) and allow oil to enter the
cylinders. With the heat that's generated by compressing air, the oil
will partially burn and create carbon monoxide which coats the red
blood cells and prohibits the transfer of oxygen to those cells and
further to the other cells in the body.

You are confusing heat and temperature, because compressing air does not
generate heat. The existing heat is concentrated into a smaller volume,
raising the temperature, but this does not rise to ignition at 90 psi.
Perhaps you are thinking of scuba tank compressors at many 1000s of psi.

If what you say were true, then working with compressed air in a closed
shop would be even more hazardous, since the air is recycled over and
over through the compressor as it is exhausted into the room. But there
is no CO or oil vapor to be concerned with in those situations.

Mineral oil is not toxic in itself.

You are breathing oil-contaminated air all the time, over a cooking
stove or around 2-cycle engines. No one thinks much of it, because it
isn't a hazard.

:
MMC writes:

The toxins are minute until the compressor pistons rings get worn (or
do not fit right from the beginning) and allow oil to enter the
cylinders. With the heat that's generated by compressing air, the oil
will partially burn and create carbon monoxide which coats the red
blood cells and prohibits the transfer of oxygen to those cells and
further to the other cells in the body.


Richard J Kinch wrote
You are confusing heat and temperature, because compressing air does not
generate heat.

Way big mistake..........! Please consult Charles Law

The existing heat is concentrated into a smaller volume,
raising the temperature, but this does not rise to ignition at 90 psi.
Perhaps you are thinking of scuba tank compressors at many 1000s of psi.
If what you say were true, then working with compressed air in a closed
shop would be even more hazardous, since the air is recycled over and
over through the compressor as it is exhausted into the room. But there
is no CO or oil vapor to be concerned with in those situations.

Mineral oil is not toxic in itself.

Now that depend on where you are breathing a contaminated gas mix that
includes Mineral Oil present. The term that MMC used is worth
researching: Partial Preasure.

You are breathing oil-contaminated air all the time, over a cooking
stove or around 2-cycle engines. No one thinks much of it,

Uhh. I do!

because it isn't a hazard.

Did I just bit on a troll?
This has got to be a troll.

If not........... for anyone wanting to breath compressed air please do
not belive anything posted here.
Bob

Bob writes:

You are confusing heat and temperature, because compressing air does not
generate heat.

Way big mistake..........! Please consult Charles Law

Charles's Law relates pressure and temperature. Not heat. Learn the
difference.

Richard J Kinch wrote:
MMC writes:


The toxins are minute until the compressor pistons rings get worn (or
do not fit right from the beginning) and allow oil to enter the
cylinders. With the heat that's generated by compressing air, the oil
will partially burn and create carbon monoxide which coats the red
blood cells and prohibits the transfer of oxygen to those cells and
further to the other cells in the body.


You are confusing heat and temperature, because compressing air does not
generate heat.

Nonsense. The "compression of air", i.e. the volume change alone, does
not change heat content(enthalpy), however mechanically "compressing
air" always does. Any mechanism that compresses air does work on the
system (consider all the frictional components), and that work is
reflected in increased temperature and enthalpy.

The existing heat is concentrated into a smaller volume,
raising the temperature, but this does not rise to ignition at 90 psi.

Ignition temperatures are not required, however, to generate volatilized
oxidation components. CO is not likely to be an issue without
ignition-high temps, but I'd just as soon not breath contaminated oil vapor.

Perhaps you are thinking of scuba tank compressors at many 1000s of psi.

If what you say were true, then working with compressed air in a closed
shop would be even more hazardous, since the air is recycled over and
over through the compressor as it is exhausted into the room. But there
is no CO or oil vapor to be concerned with in those situations.

Hardly the same context given the dilutional differences. A "closed"
shop is *not* a sealed shop.

Mineral oil is not toxic in itself.

In the gut, no. In the lungs, yes. Coat your alveoli with it and see
how long you last. The lungs have mechanisms for clearing particulates,
but not oils. And let's not forget that the oil has lots of other
charming things in it (like heavy metals from wear surfaces) by the time
it gets to your lungs.

You are breathing oil-contaminated air all the time, over a cooking
stove or around 2-cycle engines. No one thinks much of it, because it
isn't a hazard.

Well, I'd suggest that most people think more about it than you do. And
in most of those situations, you're getting particulates, not
volatilized oil. You're also breathing through your nose, which is
designed as a filter (i.e. impingement on mucosal linings of the nasal
and sinus passages), which you will not be doing underwater, unless
using a full face mask.

Using an oil sealed compressor to supply breathing air is just stupid,
unless you care nothing for your health.

Keith Hughes