nitrox blending

[mbsdiver]

Thanks for the info it is exactly what i was looking 4.

[Scuba Duck]

If you are using this for surface supplied, and you have a power source on board (12 volt DC, 120 volt AC),
you could use a barkesdale or similar pressure switch monitoring the pressure between the ouput of the
compressor and the unloader valve (load genie). When the valve shifts and idles the compressor, the pressure in that
leg of piping gets vented to air. So if you set the switch to 50 psi or so, when the unloader was sending air to the
tank, the switch would be closed. When the unloader shifts to idle the engine and vent the output from the compressor,
the switch would open. Then you could tie this switch into a solenoid valve that operates with whatever power source
you have on your boat (12 volt DC, 120 volt AC, etc). It also helps to have a pressure guage monitoring this leg of piping
so you know what to set the switch to. Remember this piping gets pretty hot and has lots of vibration, so plan accordingly
(glycerin filled guage, use brass vice plastic body switches, etc). I've done this before for a couple commercial diving (harvest) applications.

[Akimbo]

Scuba Duck: Why not just use a NC (Normally Closed) pneumatic valve if you have an automatic unloader?

[Scuba Duck]

I suppose you could use a Normally closed pneumatic one, SMC might carry something. You'd have to get something that works in the proper pressure range, something that opened at around 50 psi, otherwise the valve might clycle and let oxygen leak by, I think there is some residual pressure in that line even when the compressor is unloaded. The electrical switches are adjustable (within a range) to resolve this...

something like this might work.... but then again, it might leak by as you get that pressure surge from the compressor.
SMC Pneumatics Direct Air Operated Valve Pilot VXA2260 | eBay

here's a similar one.
http://www.ebay.com/itm/SMC-Direct-A...item5adec0f92e

and technical information for the above valves.
http://www.coastpneumatics.com/pdfs/smc/70VVXA.pdf

[Peter_C]

We got a O2 welding reg off of fleabay that already had a metering valve after the regulator. This allows the pressure to be set at roughly 32 psi (Which roughly correlates to 32% O2 mix), then the fine adjustments for mixture are done with the welding reg. In fact the knob was removed for the metering valve. Everything is done by pressure, not LPM. The important meter is the O2 analyzer mounted at the bottom of the Oxyhacker nitrox stick. Put 32% in and I expect to get 32% out. If not as much oxygen then I would be checking for CO and in fact recommend a CO meter. (We had a bad experience on a dive boat where over half the people onboard got CO poisoning.) I just wonder why you can buy a home CO meter for $32, yet a dive related one costs $400?? (Accuracy I know, but still...) I also have a second, and well a third, and fourth O2 meter for checking tanks etc. Bought the other O2 meters for $15.

To shut off the flow of O2 these were put together and installed right at the mixing stick.
Solenoid Valve, 2 Way, NC, 1/8 In, Brass - Solenoid Valves - Valves - 2CZZ6 : Grainger Industrial Supply
Solenoid Valve Coil, 120 Volts - Solenoid Valve Coils - Valves - 4A706 : Grainger Industrial Supply

If you don't already have it I would strongly recommend the Oxyhackers book from Airspeed Press.

[KWS]

does this engine have electric start. if so it has a charger for battery shouldnt be hard to rig a charge sensor to the engine and use it to switch a relay to close the o2 valve.

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.