Hookah DIY System Help

[Sunken Diver]

Hello Everyone!

I'm in the process of scrounging up some components to build a hookah dive system and I've got a couple questions that I'm hoping someone can help me out with.

Line Pressure- I've looked at a couple commercial systems and on the forums and I'm getting the sense that there are a lot of different operating pressures for these systems. I'm targeting a system that would support two divers to 45ft and up to 4 divers at 8ft or less. Would anyone recommend a good line pressure I should target and associated hookah tailored regulator model that has worked well at that target pressure?

Compressor- Right now I'm looking at a GAST PCA-10 compressor with a 1.5hp 3 phase electric motor. I want to be able to run the system off of my Honda 2200w generator and I think that is about as high as I can go. I was planning to modulate the motor speed automatically to maintain whatever the target pressure is, regardless of the system load (with this compressor, I'd be limited to a 90psi operating pressure or less). If anyone has a industrial direct drive compressor model with similar output specs, I'd really be interested to hear what it is. The drawback of the PCA-10 being I'll need to use a belt drive system.

Beyond that I was just planning a small 2 gallon accumulator the reduce the heat and then a scuba tank tied in as an emergency back-up if the system failed. I was thinking I'd regulate the tank at +10 psi to make sure it overcomes the pump pressure and forces a check valve closed to isolate the pump if the system ever activated it.

Thanks and any comments/feedback are greatly appreciated!!

 

[tbone1004]

@Sunken Diver
Compressor pressure will give you depth limits but does not determine capacity. If going to 45ft, you will want a 45psi buffer, so a 100psi compressor is fine.

Compressor capacity will determine how much you actually need to flow.
At 45ft, you have 2.5x surface consumption and with 2 divers you will want 6x a single diver breathing capacity.
At 8ft you'll want 1.5x surface consumption, so 1.5*4=6x a single diver breathing capacity.
We plan for 1cfm emergency use, and if they're working that is a reasonable consumption rate that you need to keep in mind to handle both of those situations.

The compressor you listed is rated at 6cfm and 125psi, but it is 6cfm free air. At 100psi it's only rated at 4cfm. On the deeper dives you will want some sort of SCUBA bailout system. At 8ft they can basically stand up so that's fine.
You will need a 2hp motor to run it though, 1.5hp won't give you full capacity as it calls for 1.7.

You can direct drive that compressor, but you will have an issue finding a motor that will match the target speed of 2000rpm to direct drive. No downside to belt drives for this application though, just keep a spare belt with you. That's what bailout rigs are for.
Bigger accumulators are better, but 2 gallons should be enough.
The scuba first stage acts as a check valve if you have good enough IP regulation. IP on the scuba tank has to be lower than the minimum PSI on the compressor. As soon as the compressor PSI drops below the scuba regulators IP, the regulator will automatically start feeding the system.

For the plumbing and VFD programming, you're going to have to get a bit creative.
Will want compressor-accumulator-regulator-checkvalve-manifold *compressor in, scuba in, regulator out*. The first regulator will let you set the outlet pressure to balance against the scuba tank and with the checkvalve, the scuba regulator won't try to fill the accumulation tank if the compressor fails. This way you can run the compressor and VFD at some pressure 20-30psi above target outlet to give you some buffer and have the compressor regulator set about 10psi above the scuba regulator. This is the opposite of what you talked about, but it is the least complicated way to have the scuba tank automatically and instantly takeover driving the system if the compressor can't keep up or fails. You don't want the tank to isolate the compressor because the scuba tank will be able to help the compressor in an emergency if the divers are breathing excessively hard.
Probably want the scuba regulator at 90ish psi, then the compressor to maintain at least 100psi, but as high of a pressure as it can.
You need the second regulator to handle reduction down to ~65psi for the hookah second stages
Another way to do it since you're going into VFD world with the electronics is put a normally open solenoid on the manifold from the scuba regulator and if the compressor fails or powers off it will open the scuba line. Downside to that is it can't be used as an automatic extra buffer in situations of high demand since you would have to override the solenoid manually *you could program it with the VFD and a pressure sensor, but that's getting stupid complicated*.

Now, before you get into all of this and the cost associated with it, I would look at the Brownies land based systems that are fully set up to do all of this already. I don't think you're going to save any money, and you certainly won't gain any functionality.

Brownies E250 is $1900 and is the motor/compressor. You're in for about $700 on the compressor you were talking about, at least $300 for the motor, probably $500 for the VFD to drive it, plus your time to program it. System is rated for 2x divers to 50ish ft which is what you want, and based on the math above, will support 4x at 8ft *accumulator is a MUST for the 4x divers though because if all 4 inhale at the same time that will greatly exceed the pumps capacity*.
You can still put the scuba regulator with an IP isolation system on it if you wanted to in the exact same way you would with the DIY system.

 

[Sunken Diver]

Hey Tbone1004!!

Thanks for the reply and the awesome information, much appreciated!

Sweet, I'm going to shoot for a max system pressure of around 100psi.

I'll have to dig into the HP ratings again, but I don't believe compressor HP correlates to motor power directly. It seems odd to me, but I guess a 3HP gas engine has the same power as a 1.5HP electric motor. The consumer grade compressors (with some creative figures) are claiming 3-6HP off of residential house current, so I'm not sure where this may fall into the mix. The E250 looks like it has superior airflow off of a 1HP motor, so I really need to dig into that further!

The system I was planning was the second situation you suggested. I was going to use a pressure sensor with an analog (VFD speed control) and digital (scuba tank active) output. I was thinking like you mentioned, NO valve on the scuba tank. If the system pressure dropped X below the target or electricity failure, the scuba tank would take over. I was planning the check valve on the pump because I was worried it may be a source of air loss if it was idle. If it seals tight or is running ineffectively, I really like your idea of being able to use the tank as a high demand assist! The reality is I'd rarely be down deep and it will be utilized most in 5-20ft of water.

The control loop will get a bit tricky, which was why I was planning the accumulator initially, I'll have to dampen the PID loop based on whatever I see when I plug this baby in. Based on your feedback, it sounds like to support 4 divers at shallow depth, I'll need the accumulator anyway. As far as a commercial system comparison, I'm not looking much at cost savings, I just want to build a really awesome system with real industrial components that is matched to my Honda generator. Being able to modulate the speed to eliminate excess pump wear and noise will be a big benefit. I also want to use the scuba tank as a reserve for an additional safety margin, just in case my girls decide to get their scuba certs and come diving with me. They are major Lake Superior Agate rock hounds, so I'd venture a guess that they will want to go search the lake bottoms with dad!

Thanks again! Your feedback and insight is much appreciated! I'll dig into this HP thing and let you know what I find out. I'm sticking with this generator, so if anything, I might have to resize the system accordingly.

 

[tbone1004]

@Sunken Diver
HP=torque*rpm/5252
1hp=745.7watts
Electric motors are able to produce their maximum torque ratings at 0rpm, and for motors like this are usually going to be rated at 3600rpm or so. This means that they will never get to the point that HP will exceed torque because of the formula above. Gas motors however have torque curves that skew the HP ratings so having a lower HP figure for electric motors is completely normal.

The numbers that I pulled above are "real" numbers not whatever nonsense consumer grade compressors quote, so if the manufacturer says it needs 1.7hp to run at full capacity, it means it needs to be given 1.7hp to run at full capacity, the pump needs somewhere around 1250-1300watts to run at full speed, full pressure. You can go down in HP, but you will also need to go down in speed and/or pressure and the output will go down accordingly.
There are losses associated with belt drives, losses from the VFD, losses from the phase conversion, etc. You'll need a 2hp motor to be able to give 1.7hp to the pump, and you'll also need a 3-4hp VFD to do the phase conversion for you if you are running a 3p motor.
Again, when all of this is said and done, Brownies makes a commercial grade pump for about what you're going to spend on doing this that does it all already. If you want an engineering project, go for it, but there is a system out there for the parts costs of this that is already complete.

The E250 pump from brownies is a lower pressure pump, it's also 1.5hp not 1hp. If you look at the specs for the Gast pump, there is a pretty steep falloff with pressure, as there is with every pump. The CFM ratings are free air, i.e. no backpressure.
The Gast is a "6cfm", "125psi" pump, but it's 6cfm at 0psi, and 4cfm at 125psi. To compare apples to apples, it's 5cfm at 50psi. To meet its 4cfm/125psi rating, or the 6cfm at 0 rating, it will consume roughly 1250watts.
The E250 pump is free air rated at 8.9cfm, and delivers 5.5cfm at 50psi. It needs a 1.5hp motor to do it. It's a different design than the Gast pump though since it is direct drive vs belt, and 100psi max vs 125psi max so the piston displacement is larger. Since the Gast has a higher compression ratio, it needs to spin faster to move the same amount of air. Looking at the formula above, RPM directly corresponds to HP requirements, so in a pump that has a 25% higher compression ratio, it will need to spin 25% faster to produce the same volumetric flow, and consume 25% more power to do it *obviously these are not exact numbers since I don't have the engineer docs for the pumps, but it's close enough*
Make sense?

Don't knock the Brownies system though. They are using industrial grade motors, they build the pumps themselves and they are designed for commercial use. Brownie's is focused on their commercial diving applications, the recreational market is just a perk but very few recreational divers use hookahs.

I would not emphasize the variable speed aspect of this. The pumps are rated for continuous duty regardless of which one you go with and the generator is likely going to be as loud as the pumps are so I'd just let them go. IIRC the Gast pumps we have at work are a 4000hr service interval and I think the Brownie's are somewhere up there as well. That is continuous 4000hr rated, i.e. 24/7 for 6 months then you have to do their first internal checks and they usually don't need much of anything, usually just ultrasonic the valve plates and replace a couple gaskets since you took it apart. You will want to check the filters every couple hundred hours though.
4000 hours on a hookah though is going to take you years to accumulate though so any "maintenance savings" from slowing it down is going to be washed out since you'll be rebuilding based on years long before you actually have to rebuild because of wear.

 

[Sunken Diver]

Hello again Tbone1004,

Thanks for the hp clarification, that makes sense now. I should have been factoring in the pressure when I was looking at their specs. That does look like a good system and I'll have to give it another look.

 

[Sunken Diver]

I have a bunch of older VFDs, I'll have to dig some stuff out and see what size they are. If I come across a good deal on a compressor, I'll likely give it a go. If I do, I'll post some pics and let everyone know how it works out. If nothing else, I'll have to consider the E250 this spring. I'd like to have something rigged up on my pontoon when the ice goes out!

Thanks again for all the info and help!

 

[tbone1004]

@Sunken Diver
check this thread out
$50 Harbor Freight hookah system testing

Brownie's X package is $2500. 40ft down line, 2x 20ft individual hoses, 2x regulators, tow belt, and weight belt. Add in 2x add a diver kits, and you're at $3100.

My money?
I'd buy two of these
https://www.amazon.com/California-A...8&qid=1547145352&sr=8-1&keywords=cat-2010alfc
Each rated at about 3.5cfm. These are the same type of compressors used for breathing compressors and the guy in the thread above had air analyzed and it was clean.

Puts you at $700 on the compressors. Gives you one to assist the other if you need it, but you should only ever really need to run on a single compressor. Can change the start switches to ones that give you adjustable on/off pressures. Set the first one to cut on at 65, off at 100, and set the second one to come on at say 55 and off at 70 or 80. That one it only kicks in when it has to. Add $100 for those switches. I don't believe the ones on that pump are adjustable, but could be wrong.

Still need the 4x add a diver kits, so that's $1200. Add the common hose to head down, 40ft is $110, 100ft is $225. Throw in another $100 or so for the adapters, manifolds, QD's etc to combine the two compressors and outlet to the QRS fittings, so $1500 on the hoses/adapters, blah blah blah.
That setup above gives you more cfm, redundancy under normal circumstances, saves you a grand, and is off the shelf parts.

 

[Sunken Diver]

Tbone, you're killin' me!!

I was able to rationalize building a system vs the E250, but I can't think of any half logical reason to vs the ones in the last link you sent if they are safe. Are those diaphragm compressors? Similar to the Kobalt that had the air quality testing done on?

Those babies are quiet as hell and only 35lbs each. You could probably even manipulate the primary to run in the 90-100psi range and have the back-up kick in at 80 with the factory switches, if anything, those would be cheap to get some better ones.

Yup, I think that may be the route for me. Thanks for linking that post and passing the info along, that system would be hard to beat and I can still link in the scuba tank if the kids start diving.

 

[tbone1004]

@Sunken Diver yup, oil-less, low RPM, diaphragm compressors. I use one to drive my Haskel and if I ever needed to use Hookah it would drive my system.

The nice thing with those two compressors is they are modular so if it's just you, or two of you shallow you only need one. Can also use them as generic shop compressors at home. Same technology and design as the compressors used in oxygen concentrators.

 

[Sunken Diver]

Ya, being modular is a big benefit and being able to have the trip points set different will really help with keeping the start-up current manageable, since I'll already be pushing my generators limits.

I'm going to order a couple up, thanks for the help!