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Fueling with pump

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Fueling with pump

Unread postAuthor: Copperboy » Wed Aug 11, 2010 12:24 pm

I've seen the fueling meter utilizing a shock pump and a torch/lighter to fuel a hybrid but I don't find it right now. That's a great idea and maybe this is just overcomplicating it.

A regulator adjust the fuel in pressure and the check valve would allow air to enter on the down stroke. (There would be a sliding seal between the shaft and housing.)

The reg could be set with the help of a "U-tube manometer" (correct term?) or a precise normal manometer. Once it's set it should be able to provide correct mixes to any launcher, maybe getting it to fire even without venting.

What do you guys think?


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Unread postAuthor: Heimo » Wed Aug 11, 2010 2:13 pm

I have been tinkering at a similar way to fuel a hybrid but I gotta admit I am a little afraid that the premixed gas might ignite while being compressed and that would be pretty bad

I do not think that this idea is worth the risk of explosion it holds.
if anybody else thinks I am being paranoid and that the gas would not ignite from the heat generated while being compressed, feel free to correct me
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Unread postAuthor: DinerKid » Wed Aug 11, 2010 2:17 pm

Heimo is right. It just isn't worth working directly with the premixed gas. If you get some kind of static discharge it is game over for you. I would avoid this design and go for something with more safety in mind.

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Unread postAuthor: irisher » Wed Aug 11, 2010 2:46 pm

Although I understand safety concern, in my opinion it is a little overrated. I admit it would be horrible if it happened but, in my hybrid experiences it is very hard to ignite the higher mixes and if it ignited a lower mix the pump should contain it. I also think that a typical static shock would have a hard time igniting it at all. But thats just my 2 cents.
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Unread postAuthor: Heimo » Wed Aug 11, 2010 2:58 pm

irisher wrote:Although I understand safety concern, in my opinion it is a little overrated. I admit it would be horrible if it happened but, in my hybrid experiences it is very hard to ignite the higher mixes and if it ignited a lower mix the pump should contain it. I also think that a typical static shock would have a hard time igniting it at all. But thats just my 2 cents.


I did not even think about static discharge, my concern is that when you compress air, it heats up and I think there is a great risk of ignition there.
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Unread postAuthor: irisher » Wed Aug 11, 2010 3:02 pm

While it does heat up I have my doubts as to whether it would actually reach the flash point.
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Unread postAuthor: Heimo » Wed Aug 11, 2010 3:12 pm

irisher wrote:While it does heat up I have my doubts as to whether it would actually reach the flash point.


but are you willing to bet your life to that doubt?
I don't think so.
besides how about the sides of the piston in the pump how hot would those get?
It just ain't worth the risk...
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Unread postAuthor: spudtyrrant » Wed Aug 11, 2010 5:11 pm

Heimo wrote:
irisher wrote:While it does heat up I have my doubts as to whether it would actually reach the flash point.


but are you willing to bet your life to that doubt?
I don't think so.
besides how about the sides of the piston in the pump how hot would those get?
It just ain't worth the risk...
for one thing dieseling is EXTREMELY hard to get right even if you want to(I've tried with old springer pellet guns), i doubt very much it would happen in a hand pump, to shock heat the air the pump would have to go from top to bottom in an almost humanly impossible amount of time, people have used shock pumps for fueling(extremely high compression ratios) and it has yet to happen.
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Unread postAuthor: jimmy101 » Wed Aug 11, 2010 6:56 pm

Fueling via the pump really isn't a good idea. Anyone know what the dieseling compression ratio is of propane? For gasoline it is what, something like 14:1, which is doable with a good shock pump.

There's a little device called a "Fire Piston" that aboriginals in SE Asia used to light fires. With a piece of wood hollowed out to a cylinder, a wooden piston and some string (or tenon or gut or ...) for an o-ring you can, by hand, compress air enough to ignite tinder. If you can do that with a hunk of wood and tinder then a shock pump with propane+air really sounds like a bad idea.

Throw in the possibility of a spark (static or frictional) and ... you've got the pump handle blown back through your hand and imbeded in your chest. :shock:
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Unread postAuthor: spudtyrrant » Wed Aug 11, 2010 9:29 pm

jimmy101 wrote:Fueling via the pump really isn't a good idea. Anyone know what the dieseling compression ratio is of propane? For gasoline it is what, something like 14:1, which is doable with a good shock pump.

There's a little device called a "Fire Piston" that aboriginals in SE Asia used to light fires. With a piece of wood hollowed out to a cylinder, a wooden piston and some string (or tenon or gut or ...) for an o-ring you can, by hand, compress air enough to ignite tinder. If you can do that with a hunk of wood and tinder then a shock pump with propane+air really sounds like a bad idea.

Throw in the possibility of a spark (static or frictional) and ... you've got the pump handle blown back through your hand and imbeded in your chest. :shock:
those fire pistons are hardly a fair comparison they have a sealed end, the compression ratio for propane is 29:1, but with a pump the check valve will open long before any sort of compression ratio is reached, even when you have 137psi(10 x mix) behind the check valve you still only get a compression ratio of 10:1, hell the lubricants used on most pumps are highly flammable and have lower compression ratios than propane, but you don't hear about exploding pumps all the time, not to mention that unless you were using a very tiny pump the amount of heat created by friction pumping to even a 10x mix would be no where near the auto ignition temp of propane(480 degrees Celsius) :?
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Unread postAuthor: Technician1002 » Wed Aug 11, 2010 10:17 pm

As far as auto-ignition is concerned, Diesel Oil has a much lower auto ignition temperature than gasoline or propane. I believe the auto ignition compression for the oil is in the 12-15 X range and propane and gasoline is about double that for compression heating ignition. This is why gas won't work in a diesel engine. A glow engine might run but with severe pinging.

Do a Google search for auto ignition temperature for the various fuels to lean more.

Static causing ignition is the danger with the pump, not compression.
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Unread postAuthor: daccel » Wed Aug 11, 2010 11:06 pm

Have a look at this thread. I ended up giving up on it because it became unreliable. I think it was the poorly sealing rubber washer where the rod came out allowing extra air in and causing the mix to be too lean. Could be fixed with an o-ring, I just didn't pursue it.

I did try slamming the handle down to see if I could get it to auto-ignite (one of those things you realize as you're doing it should involve more safety precautions :roll:). But nothing happened, so I don't think with a normal pumping rate that the risk is very high.

With your diagram, there may be potential for too rich a mix as the pressurized fuel would move in more easily than the air at ambient which would also have to open a check valve.
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Unread postAuthor: Copperboy » Thu Aug 12, 2010 1:18 am

Nice to see some response to this. :)

The compression heating I also think is overrated (although I appreciate all your warnings and take them seriously) and the static ignition problem I also think is easy to overcome by remove the potential difference between the two moving parts.

EDIT: But yeah, it doesn't sound very smart pushing down on it with your chest in the potential fire line, instead maybe use it in a pump shotgun configuration?

As Daccel said I too can imagine the mix getting too rich...

Maybe make the fuel air mix in a tee before going into the pump?
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Unread postAuthor: POLAND_SPUD » Thu Aug 12, 2010 2:14 am

II've been thinking about something similar (probably becasue someone suggested it in some thread a while ago).
Though I just realized that it isn't any better than filling the chamebr with, let say, enough propane needed for a 5X mix and then topping it off with air from a pump (it wouldn't be a bad idea to add a short lenght of 1/2" pipe to act as a miniature air tank and a reg)

Yeah, I know it does seem a bit more complicated but it solves the issue with compression heating. What is more you can always convert it to a gun with a portable HPA tank or use a shop/fridge compressor as your air source.

Ohh and finally, it's not htat there are lots of regs that can set the exact pressure for a 1X mix... Well at least not where I live. All in all, I think it's another advantage of this idea.
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Unread postAuthor: Copperboy » Thu Aug 12, 2010 3:23 am

I agree with you Poland_Spud, and I think the reg issue is correct.

One advantage is with the pump design would be that it delivers mixtures that could be ignited even with the residue and COX that's left from the previous deflagration, even without venting and even with some initial pressure (maybe due to a valve design that closes before zero chamber pressure etc.).

This could be avoided with the standard manometric setup too I guess, but it would be nice getting this to work.

(I'm waiting for some 0-1bar meters right now.. maybe I'll just go for burstdisk manometric with onboard pump as air source.. portable..mmmm.. :) )
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