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Mixing Valve?

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Mixing Valve?

Unread postAuthor: PVC Arsenal 17 » Fri Jun 18, 2010 10:01 pm

Does anyone know of a simple, cheap way to achieve an ideal mixture of air & propane so that when connected to a propane bottle alone, I can fill balloons or plastic bags with a combustible mix?

What I'm imagining is a venturi mixing valve connected to a propane bottle that will draw in the correct amount of air from the atmosphere and put out the ideal mix through a nozzle.

The main goal is a quick filling system for noisemakers, but I suppose the idea could also be useful for rapid fire combustion launchers. Breech load your ammo, followed by a pre-filled cylindrical bag of fuel/air and fire away. Stock up on both and the process could be quite fast. The bag could even serve as it's own burst disc for increased power.
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Unread postAuthor: Crna Legija » Fri Jun 18, 2010 10:20 pm

oxy torch have mixing valve at the bottom just tune it till you get the best flame that should be the best mix.
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Unread postAuthor: Technician1002 » Fri Jun 18, 2010 10:44 pm

Unfortunately, the amount of Propane is relatively low in proportion to the air required so you will not achieve the proper mix trying to use Propane to move the required air.

A small engine Propane carburator could work with a proper custom built hand pump to draw air/fuel mix and supply it under pressure into your balloon/cylinder/etc.

As mentioned in the torch valve, that is one way to do it. Unfortunately opening the valves each time to the proper setting would be problematic.

I have been working on a solution to that very problem for a full auto combustion design that would not vent the chamber between shots but would instead purge the chamber with a fuel/air mix much like an internal combustion engine.

Air and fuel would be pressure regulated to a fixed but equal setting (like 10 PSI) and by drilling precision metering orifices, the flow rate of each gas can be supplied in correct proportion on demand. A single ball valve would cut off the supply of both fuel and air. Check valves would prevent a pressure imbalance from feeding fuel into the air and visa versa.

Delivery would simply be open the outlet valve and metered flow of both gasses would be delivered in proper mix. There would be little premix to prevent a backflash explosion. Mixing would be at the dispense valve.

The above method is very close to how they dispense softdrinks at a soda fountain. Both the syrup and carbonated water are delivered at the same pressure. (the carbonation pump and syrup pump both run off the same CO2 regulator). Electric solenoids open both the syrup and carbonated water at the same time and the two are mixed together in the nozzle as it fills your cup. Large cup or small cup, the perfect mix every time. The flow rate for each ingredient is calibrated. To calibrate the drink fountain, a two chamber measure is placed on the dispenser with the nozzle removed so syrup fills one and the water fills the other. The syrup cylinder has 1/6th the volume of the water cylinder, so on a proper dispense, the levels of syrup and water should match. If they don't, the syrup feed is adjusted until they dispense in the 6:1 ratio. The same principal can be applied to air and fuel.

For small batches, another variant would simply use two cylinders. One for air and one for Propane. They would be related in volume by the desired mix. (one 4.2% the volume of the other) When both are filled to the same pressure such as 50 PSI, then due to the expansion of both gasses as the gasses are drawn, the volumes would be drawn in the proper proportion to dispense the proper mix.

Making the cylinders for this latter one would not be difficult. A 10 Liter air cylinder for example will have a companion cylinder for Propane that is 0.42 Liter. Both are filled to the same pressure and then dispensed after mixing in a T.
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Last edited by Technician1002 on Fri Jun 18, 2010 11:19 pm, edited 2 times in total.
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Unread postAuthor: ramses » Fri Jun 18, 2010 11:09 pm

Care should be taken to avoid liquefying the propane. that would screw things up. Unfortunately, it means your air tank must also be under around 120psi.
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Unread postAuthor: POLAND_SPUD » Sat Jun 19, 2010 3:40 am

well what about hte design i posted here -> http://www.spudfiles.com/forums/valvele ... rt,30.html

that's a fairly simple system... in theory the valve will switch at a set pressure so a propane reg might not be needed at all
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Re: Mixing Valve?

Unread postAuthor: jackssmirkingrevenge » Sat Jun 19, 2010 3:41 am

PVC Arsenal 17 wrote:Breech load your ammo, followed by a pre-filled cylindrical bag of fuel/air and fire away.


interesting idea for a cartridge hybrid...
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Unread postAuthor: Lockednloaded » Sat Jun 19, 2010 6:11 am

Or a ballon filled with the correct mix. Then you screw on the cap and it pops the ballon
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Unread postAuthor: grock » Sat Jun 19, 2010 8:22 am

theres this thing called an air amplifier. its basically a big venturi. the 2" ones from exair get about the right "air it:air out" ratio when propane is used in place of compressed air. unfortunetly, ones in this size are worth about 200 dollars. while expensive, it could fill a fairly large chamber extremely quickly.

check it out
http://www.youtube.com/watch?v=XnUZFkRGCKg
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Unread postAuthor: Technician1002 » Sat Jun 19, 2010 11:35 am

ramses wrote:Care should be taken to avoid liquefying the propane. that would screw things up. Unfortunately, it means your air tank must also be under around 120psi.


Both air and fuel would be stored well below the liquification pressure. This is for vapor only. Using 50PSI and below would ensure this over most outdoor spudding temperature ranges.
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Unread postAuthor: Technician1002 » Sat Jun 19, 2010 11:39 am

Sorry for the double post. I got a server error. A retry produced a second post.

As long as this post is here, A simple way to do the metered dispense is to use a pair of BBQ grill regulators. One for fuel and one for air. A needle valve or precision drilled metering orifice would limit the flow rate of the fuel to the proper proportion. The output from both regulators would tie together and be dispensed mixed on delivery.

A quick comment on the air venturi is the ratio changes drastically with any back pressure such as feeding into a closed chamber with a limited outlet size such as a barrel. It may be good for feeding a boiler or furnace, but keeping the mix right with other dynamic downstream configurations make those pretty finicky to get working right.
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Unread postAuthor: PVC Arsenal 17 » Sat Jun 19, 2010 12:37 pm

Thanks for the replies everyone.

Technician1002 wrote:A quick comment on the air venturi is the ratio changes drastically with any back pressure such as feeding into a closed chamber with a limited outlet size such as a barrel. It may be good for feeding a boiler or furnace, but keeping the mix right with other dynamic downstream configurations make those pretty finicky to get working right.


This is what makes the process of dispensing a mixture so difficult in this case... If not for this I could probably make due with a torch head.

I've decided to use beach balls for the noisemakers. I can inflate them with air first and then add in the correct amount of propane using a conventional metering system. Beach balls are fairly spherical so it will be easy to calculate their volume.


Tech, in response to what you mentioned earlier about a rapid fire combustion launcher with an air/fuel supply to displace stale air while refilling the chamber... wouldn't that be too wasteful? By the time an acceptable amount of stale air is displaced, wouldn't quite a bit of fuel/air mixture be lost?
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Unread postAuthor: Technician1002 » Sat Jun 19, 2010 12:51 pm

PVC Arsenal 17 wrote:Tech, in response to what you mentioned earlier about a rapid fire combustion launcher with an air/fuel supply to displace stale air while refilling the chamber... wouldn't that be too wasteful? By the time an acceptable amount of stale air is displaced, wouldn't quite a bit of fuel/air mixture be lost?


In a long chamber, laminar flow can be utilized for reducing waste. A two cycle gas engine operates this way in normal operation without laminar flow and runs fine in my weed eater.

If care is taken to design it to displace the spent fuel instead of mixing it with fresh, the loss can be minimized. Look up Laminar air flow. The inlet in the design I am working on will use multiple inlet ports and baffle plates for laminar flow through most of the chamber.
http://en.wikipedia.org/wiki/Laminar_flow

Flow would be from the breech from at least 6 inlet ports so the chamber would have mostly laminar flow to the barrel. Some mixing is inevitable, just like in a 2 stroke.
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Unread postAuthor: POLAND_SPUD » Sat Jun 19, 2010 3:56 pm

get any kind of tank you can find that is rated high enough... build a typical metering system for it and fill it with a 10X mix... then use it to fill individual balloons

the method I posted earlier won't be very useful for filling balloons but it will work for hybrids
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Unread postAuthor: jimmy101 » Sat Jun 19, 2010 4:47 pm

POLAND_SPUD wrote:get any kind of tank you can find that is rated high enough...

For a tank containing premix at 10X, the rating should be the peak pressure in a 10X hybrid. Figure about 1500 PSI. Add a bit for safety and call it 10,000 PSI as the minimum tank pressure rating.

The tank is full of a combustible mix, it must be able to survive if the mix is ignited.
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Unread postAuthor: POLAND_SPUD » Sat Jun 19, 2010 5:11 pm

@jimmy
that's exactly what I had in mind
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