Approx. 30 years ago I designed and manufactured a unit that pneumatically activated a pair of mechanical fuel and nitrous valves - I was told it was outdated and a useless option even then, because electrically activated solenoids were the future.
Here's a pic of my original version (please excuse the rust and lack of anodising but it does help to prove how old this unit is, as its been neglected for 30 years)
SORRY FOR PICTURE FAILURE - TO BE FIXED ASAP
Today in the USA a product based on the EXACT same principles as my ORIGINAL (side by side valves), is the latest and greatest new idea from Combo-Flo.
Despite the fact that the Combo-Flo doesn't come close to the final version of the valve I last manufactured some 15 to 20 years ago (that was based on the same principle but a vastly superior design and a quantum step forward), some people fail to appreciate the Combo-Flo valve is a backward step not a step forward.
Here's a pic of theirs
After extensive R&D work, my original side by side design ended up as my Duo-noid (a pilot solenoid activated a piston, which activated a fuel valve, that was stacked on top of the nitrous valve, all in one unit), which had numerous safety advantages over the side by side concept, as well as over pairs of individual solenoids.
Here's a pic of my last version (approx. dimensions 1.2" diameter x approx 3" tall, so although the pic on here is bigger than the Combo-Flo valve, in actual fact it is smaller)
Since the solenoid was only a 'pilot' it did not need to flow a great deal of nitrous and therefore was only a low current draw of approx. ONE Amp. This unit did not need a pneumatic supply as it used the nitrous to activate it (which makes the unit less complicated, more reliable and weighs less), despite being able to flow in the region of 1,000 hp of both fuel and nitrous through a single unit.
Some of the UNIQUE features the Duo-Noid offers are;
1) Solenoid activated pilot valve requiring minimal current
2) Valve can NOT be activated without nitrous supply (if the bottle is not turned on the system will not flood the engine with fuel)
3) The nitrous output can NOT be activated without the fuel being activated (NO risk of the engine getting nitrous without fuel due to fuel solenoid failure)
4) The fuel flow can NOT be cut off without the nitrous also being cut off (avoiding lean outs if a nitrous solenoid stuck open)
5) Auto purge capability (no need for restrictive fittings in the pipe line and no need for additional purge solenoid)
Furthermore, although it is not originally designed this way it can be modified to;
1) Prevent nitrous flow without fuel pressure being at the valve OUTLET.
2) Have twin nitrous and fuel outlets to avoid the need for restrictive T or Y fittings that might otherwise be needed.
3) Deliver progressive flow to some degree without any extra parts.
Since ceasing production approx 15 years ago it has come to my attention that there is a growing demand for such a valve to meet stringent class regulations and by those who suffer the problems caused by multiple high Amp solenoids, so I’m seriously thinking of re-starting the manufacture of these units.