nitrox blending

[mbsdiver]

i have a simple ? i have a 5cfm compressor and have built a blending stick. so here it is what psi or lpm do i start with? this way i know what oxygen reg to get

 

[Wookie]

Use a standard welding oxygen regulator available at the Gas Supply House and order a dwyer flowmeter in 0-20 lpm. Most flowmeters are calibrated for air, but oxygen is close enough. Set the regulator for a constant pressure and set the flowmeter to give you the nitrox concentration you desire as read on the analyzer on the outlet of the compressor. For safety, add a solenoid shutoff valve in the system so when the compressor shuts off, the oxygen shuts off too.

 

[divingtactics]

You won't need anything greater than 25 lpm and most industrial oxygen regulators will do this easily. You will find that you don't need to crank the regulator up much to get up to 40% nitrox. I am using a 25 lpm industrial oxygen regulator on a 4.9 cfm compressor with great results.

 

[mbsdiver]

so how many lpm are you putting into the 4.9cfm compressor to get ean 32. thank you

 

[Akimbo]

Just to emphasize, make sure you get a regulator cleaned and rated for oxygen service. Capt Frank’s suggestion to use a regulator sold primarily for Oxygen-Acetylene welding/cutting is the most cost effective option, comes with Oxygen service gauges, and the proper CGA adapter for Oxygen bottles. It’s a no-brainer.

 

[mbsdiver]

i plan on using a O2 reg. ether a welding 1 or a medical 1

 

[kwinter]

For safety, add a solenoid shutoff valve in the system so when the compressor shuts off, the oxygen shuts off too.

Great safety tip.

 

[divingtactics]

so how many lpm are you putting into the 4.9cfm compressor to get ean 32. thank you

I don't actually count it in lpm's, all I do is wind the regulator up until the output on the stick reads 32% - which happens very quickly. I hardly registers on the second gauge.

 

[Scuba Duck]

1 CFM is equal to 28.3 LPM.

So 5 CFM is 141.5 LPM

32% Nitrox requires a flowrate of pure oxygen equal to 14% of your compressors flowrate.
This assumes that the air your compressor takes in is dry, with no humidity.
As humidity goes up, you will require a lower flowrate of oxygen.

141.5 LPM x .14 = 19.8 LPM of oxygen

Here is a spreadsheet that I wrote that has compressor flowrates and oxygen flowrates for different EAN mixes.
http://www.envirodive.com/O2 Flowrate Spreadsheet.xls

 

[Akimbo]

… For safety, add a solenoid shutoff valve in the system so when the compressor shuts off, the oxygen shuts off too.

Any ideas on accomplishing this on a small gas or Diesel engine powered compressor? I guess a Normally Closed pneumatic valve can be used on a compressor that automatically unloads.