I'm having a difficult time calculating how much it's actually costing our dive center to blend Nitrox and Trimix. We use a 244 cuft cylinder of O2 and 219cuft cylinder of Helium. I understand how once I calculate the cost per psi in the large cylinder.
How to calculate the cost of blending Nitrox/trimix
- Thread starter Janean
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Not enough variables input.
Need to know exactly how you are blending the gases and how accurate you need the cost to be.
To start, you need to know the cost/cf of your compressor to run. $/kwh, $/filter cartridge, CF/cartridge, $/oil change, CF/oil change, depreciation schedule for the compressor which gets you to the $/cf of the hardware unless you consider it fully depreciated. That gets you the $/cf for air.
Then need to know how you are blending nitrox, I assume/hope it is with a stick and for that it's the $/cf of the O2 bottle including any cylinder rental fees you have, then add in the depreciation schedule of the hardware for the stick and the $/O2 sensor and cf/O2 sensor. Frankly for this I would just consider it the cost of the O2 itself and consider the O2 sensor as an annual replacement a wash.
Then we need to know what you're doing for the helium, whether you're bleeding off and PP blending, or using a booster. If using a booster, which specific booster and how is it being run? A Masterline is considerably cheaper to operate than a Haskel because it doesn't use drive gas and the cost of rebuild is considerably less, but if using a Haskel you have to consider its gas consumption rate and that is very complicated to sort out and you very much need to consider the multi-thousand dollar rebuilds every few years. If you are simply PP blending, then you have figure out whether you are charging for the gas you are bleeding off from the customers tanks and then how much is wasted by leaving it in the tank when you return it.
The $/psi is extremely complicated to get a precise number. If you just want the cost of the O2 and the He most of the blending apps out there will let you put in the $/cf of each gas and tell you the cost of raw materials, but it's the cost of moving the raw materials that complicates things.
244cf O2 cylinder is rated at 2200psi. If you are paying $100/244cf that's $100/2200psi or $0.046/psi. Obviously change the $100 to whatever you're paying
219cf of Helium is rated at 2400psi. Same math. $/2400psi.
The raw materials here are almost insignificant for nitrox and fairly small for helium. The cost of moving that gas between the compressor and/or booster is where the cost really shows up and that unfortunately is the part that most shops don't bother to calculate properly.
Need to know exactly how you are blending the gases and how accurate you need the cost to be.
To start, you need to know the cost/cf of your compressor to run. $/kwh, $/filter cartridge, CF/cartridge, $/oil change, CF/oil change, depreciation schedule for the compressor which gets you to the $/cf of the hardware unless you consider it fully depreciated. That gets you the $/cf for air.
Then need to know how you are blending nitrox, I assume/hope it is with a stick and for that it's the $/cf of the O2 bottle including any cylinder rental fees you have, then add in the depreciation schedule of the hardware for the stick and the $/O2 sensor and cf/O2 sensor. Frankly for this I would just consider it the cost of the O2 itself and consider the O2 sensor as an annual replacement a wash.
Then we need to know what you're doing for the helium, whether you're bleeding off and PP blending, or using a booster. If using a booster, which specific booster and how is it being run? A Masterline is considerably cheaper to operate than a Haskel because it doesn't use drive gas and the cost of rebuild is considerably less, but if using a Haskel you have to consider its gas consumption rate and that is very complicated to sort out and you very much need to consider the multi-thousand dollar rebuilds every few years. If you are simply PP blending, then you have figure out whether you are charging for the gas you are bleeding off from the customers tanks and then how much is wasted by leaving it in the tank when you return it.
The $/psi is extremely complicated to get a precise number. If you just want the cost of the O2 and the He most of the blending apps out there will let you put in the $/cf of each gas and tell you the cost of raw materials, but it's the cost of moving the raw materials that complicates things.
244cf O2 cylinder is rated at 2200psi. If you are paying $100/244cf that's $100/2200psi or $0.046/psi. Obviously change the $100 to whatever you're paying
219cf of Helium is rated at 2400psi. Same math. $/2400psi.
The raw materials here are almost insignificant for nitrox and fairly small for helium. The cost of moving that gas between the compressor and/or booster is where the cost really shows up and that unfortunately is the part that most shops don't bother to calculate properly.
Jack Hammer
Contributor
Don't forget to factor in potential lost gas that can happen when stick blending or unusable gas due to how low you are able to scavenge from your supply bottle. This is on top of the bleed off gasses mentioned above.
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