Hookah Compression Confusion

[Tar34]

Setting up first Hookah for shallow dive hull maintenance. I chose and off the shelf compressor, a Senco PC1010N. My regulator is an XS SCUBA RG303 rated 50-80psi. This compressor apparently has no adjustable tank regulation and cutoff is approx.130psi. One gallon tank. Tool regulation seems to operate normally. After testing my setup, I’m asking for some opinion / advice. Herein my confusion. Testing the system at a tool pressure of 80psi, the system is breathable but get labored at around 60psi. Raising tool pressure to say 1000psi keeps my draw down to a static tool and tank pressure at around 75psi. Doable but I’m not laboring and sitting in the cockpit. I’ve tried to simulate labored breathing and the pressure seems to hold. In addition, I expected my regulator to free flow if the psi was pushed pass some limit but in testing it still holds at 125psi. In my ignorance, what don’t I know? I understand the relationship between pressure and CFM. Higher pressure lower CFM. Is my regulator too high pressure for the compressor? What incompatibilities am I missing between the regulator and the compressor? Anyone with a compressor or regulator recommendation? I’d like a system that cycles and not constantly pushing air.

[s/v Thea]

I think your compressor is too small at 0.7 cfm

[Uncle Bob]

Originally Posted by s/v Thea

I think your compressor is too small at 0.7 cfm

Have to agree, mine has a 3.5 cfm free flow capacity and is adequate for boat maintenance.

[GordMay]

Please tell us you’re NOT using an industrial air compressor, with an oil bath lubrication system, to provide surface [breathing] air, along with a two-stage SCUBA regulator.

[Uncle Bob]

Originally Posted by GordMay

Please tell us you’re NOT using an industrial air compressor, with an oil bath lubrication system, to provide surface [breathing] air, along with a two-stage SCUBA regulator.

Gord, not sure if your post was directed at me but no I am not using a compressor that runs in an oil bath, it is totally oil less, 100% duty cycle 12 volt and yes it is a little hungry.

[Spot]

SCUBA Tank pressures are 500-3000+PSI (35-200+ bar).
The first stage regulator (the one on the tank) knocks tank pressure down to 150 PSI (10 bar) IP or intermediate pressure.

The second stage regulator (the one with the mouthpiece) balances IP to water pressure at depth to allow easy breathing under water.

All are meant to run on fresh dry clean air...

[Simi 60]

Originally Posted by Tar34

. I chose and off the shelf compressor, a Senco PC1010

Saw nothing to say that was oil free
Add: this ad says oil free
https://www.gettoolsdirect.com.au/se...ect-drive.html


For less money and a 3 year warranty we use an ozito 24 l oil free



https://www.bunnings.com.au/ozito-24....ds&store=8161

[Jammer]

Originally Posted by Tar34

Setting up first Hookah for shallow dive hull maintenance. I chose and off the shelf compressor, a Senco PC1010N. My regulator is an XS SCUBA RG303 rated 50-80psi. This compressor apparently has no adjustable tank regulation and cutoff is approx.130psi. One gallon tank. Tool regulation seems to operate normally. After testing my setup, I’m asking for some opinion / advice. Herein my confusion. Testing the system at a tool pressure of 80psi, the system is breathable but get labored at around 60psi. Raising tool pressure to say [100] psi keeps my draw down to a static tool and tank pressure at around 75psi. Doable but I’m not laboring and sitting in the cockpit. I’ve tried to simulate labored breathing and the pressure seems to hold. In addition, I expected my regulator to free flow if the psi was pushed pass some limit but in testing it still holds at 125psi. In my ignorance, what don’t I know?

Hello again Tar34. Sounds like you're getting ready to address your hull and prop problems. Good for you.


I dive often. I service my own regulators and had a compressor for a while, you know, the kind for filling tanks. I don't know everything but may be able to help.


As you're probably aware, the RG303 is sold as a hookah regulator and is available in several pressure ranges that use different springs. It is a downstream demand-valve style second stage with a venturi which is essentially identical in design to the regulators I use for SCUBA diving and which I have serviced and adjusted often and used at depths down to around 100 feet.


To understand regulator performance it is important to introduce the concept of "work of breathing" (WOB) which is the amount of resistance to inhaling and exhaling. It is related to the cracking pressure, that is, the amount of vacuum (usually measured in inches of water) that will cause a second stage regulator to start flowing air (or other gas e.g. nitrox). I measure it by lowering the regulator into a sink filled with water. There are more sophisticated methods. Lower cracking pressure, less WOB.



Anyway, the cracking pressure on a downstream demand-valve regulator like yours will vary with the input pressure. Higher input pressure, lower cracking pressure. At some point the regulator will freeflow, Usually a cracking pressure of around 0.75" to 1.5" provides a good balance between freeflow resistance and WOB.


Excessive cracking pressure and high WOB will lead to discomfort and early fatigue for the diver, and a sense of not being able to get enough air. Cracking pressure that is too low will give a reg that tends to freeflow too easily.


So anyway the reg should be adjusted to perform properly at a particular input pressure or a narrow range of pressures. I typically adjust mine so that they breathe the way I want at 115 PSI for example, though I have a couple that have stronger/weaker springs so I go up or down 10 PSI, sometimes that works out better overall than adjusting the second stage. Since I'm using SCUBA I set the first stage regulator output pressure (that is, the "intermediate pressure" or IP) to match what works best for the second stage.


A qualified technician (possibly you depending on your background) can adjust the regulator to perform well on the pressure to be used, but these are simple devices and you have to choose a pressure and stick with it. "Balanced" second stages exist that are more complex and that perform better on a wide range of input pressures but yours isn't like this.

I understand the relationship between pressure and CFM. Higher pressure lower CFM. Is my regulator too high pressure for the compressor? What incompatibilities am I missing between the regulator and the compressor? Anyone with a compressor or regulator recommendation? I’d like a system that cycles and not constantly pushing air.

Divers on a leisurely, very shallow bimble around the reef typically breathe about 0.4 to 0.6 cfm with thin, short, athletic women being past the lower end of the range and overweight large men with a history of cigarette smoking being past the upper end. Exertion and depth increase these figures.


Your compressor is per spec supposed to be delivering 0.7 cfm at 90 PSI. Maybe it does that, maybe not. Most people breathe less than 0.7 cfm sitting on the bench in the cockpit and so the pressure should go up above 90 PSI. Maybe you breathe more than most people, maybe you have a leak, maybe the compressor doesn't really make 0.7 cfm.


You might consider combining the output of two of those compressors, because 0.7 cfm is really pretty marginal unless you are a 22 year old female who weighs 140 pounds.


If your second stage doesn't freeflow at 125 PSI it might be out of adjustment. The real test is cracking pressure, again I measure it in the sink with a ruler, keep the diaphragm level and slowly lower it into the water until it starts to flow and measure the distance between the diaphragm and the water surface with a ruler and that's your cracking pressure.


You really want to run at a fairly constant pressure. If the tool regulator does that for you great, then use it. Either adjust the reg to perform well at that pressure or figure out what pressure the reg likes best and use that.


Hope you have dive training so you're aware of the risks and the safety practices that mitigate them. I do and I think it's valuable


Hope this helps

[Tar34]

Jammer: Thanks for following.

All: Replaced compressor. Current compressor gives 2.7 CFM @90psi. It’s is an oil less pump with 6gal tank. I’ve added an inline 5micron particulate/water separator filter. Regulator is an XS RG 303 50-80psi. I’ve dry tested with a working IP of 80psi. I seem to be getting plenty of air, enough to get wet and play around on the surface. My attention is now focused on tuning the regulator to the IP pressure to see if can improve performance. Did pre dive set up yesterday setting out lines from the bow of the boat running about 10 ft past the stern with floats. Got into wet suit and geared up. The plan is to get in the water today. Water temp 70 degrees, visibility at high tide doable. Current approaching high tide .5-1kt with a maximum outgoing current of 2.7kts. Don’t hold your breath!