The Myth of Pressure Regulators

[Stephanie Jordan]

Companion forum thread to:

The Myth of Pressure Regulators

[James Marco]

"Richard, it's not just the burner, it's the whole burner/mixer tube/jet package. Think about it:
– at the bottom of the mixer tube, the pressure inside is less than atmospheric and so air is sucked in thru the bottom holes
– at the top of the mixer tube, the pressure inside is more than atmospheric, so gas/air is forced out thru the holes in the burner"

Stuart, quite correct. Most gas burners we use simply use a series of holes around the base of the jet to adjust air inlet. Pretty obvious that air at 15000' will NOT contain as much oxygen as air at sea level. One of the lacks, for flame temperature and CO/CO2 prodiction is a simple air regulator. For those that worry about CO production, it is easy enough to simply file out the holes letting more air into the premixed gas for burning.

In practice, this means it will perform better at high outputs at sea level and better at High Altitudes on lower settings. Or, simply open the inlet holes (minding the distance to the jet (usually somewhat below midpoint) and making a sleeve adjustment for yourself out of brass shimm stock with matching holes in them. A quick and dirty adjustment for air inlets.

Idealy, a change in jet pressure will need a slight adjustment to air, also. This is usually complicated by the matter that two controlls makes it difficult for many people to use…like your gas stove at home. Adjusting gas, then adjusting air. They don't bother, usually simply supplying a sleve than is set with a screw. You do NOT normally need to change this, except if you do mostly high heat cooking, or, mostly low heat cooking, or, live at some high altitude (over 3000'.) A camp stove is about the same, but CO emisions can be greatly reduced by simply over sizing the inlet ports. The flame distance has a little to do with it, but, more importantly, it is the initial combustion mix that determines the byproducts.

Fettling this stuff is really easy.

[Jerry Adams]

"Part 2 will happen, but it will be a little while as the pile of work in front of me grows …"

I thought part 2 was next week

You are teasing us : )

[Hikin’ Jim]

Best wishes for Part 2 — and good luck, too, since it sounds like Jim is promising you a $64K payoff if you answer the question about why the Sol does well in cold.

And Jim — that's awfully nice of you!!! Better get your checkbook ready, though, since Roger probably already knows the answer.

My account is with the Bank of Zimbabwe. I trust that will be acceptable. :)

A conventional needle valve can be removed from the stove and both it and the orifice can be cleaned – in the field, easily.

You CANNOT maintain the valve on a pressure regulator stove in the field, and you probably cannot do it at home either. If it gets dirty, you buy a new stove.

Yipes. That is a significant downside. That's one to think about.

HJ
Adventures in Stoving

[Hikin’ Jim]

In all seriousness, I am of course very much looking forward to Part 2.

There have been at least two theories advanced as to why the Jetboils with regulator valves do better in cold weather than the Jetboils with conventional needle valves. One theory is that the regulated valve allows Jetboil to safely employ a jet with a larger aperture. Another theory is that the geometry of the Jetboils with regulator valves somehow causes heat to be conducted to the canister thus boosting cold wx performance. It could of course be a combination of the two. Whatever the case, it's not the regulator itself that's causing the improvement in cold wx performance. I myself lean toward the aperture size* increase as the cause of improved performance. It will be quite interesting to know what the empirical data show.

HJ
Adventures in Stoving

*The JetBoil PCS, Flash, and Zip have a jet aperture size of 0.21mm
The JetBoil Sol and Sol Ti have a jet aperture size of 0.30mm

[Jerry Adams]

95% of what Roger says is good, but : )

I have never had to clean a needle valve. I've done more than 100 nights with Coleman Exponent F1 and 20 nights with MSR Pocket Rocket.

Maybe inverting the canister is a problem – then stuff comes out of canister and goes to valve

White gas stove – that get's clogged – I have a MSR Whisperlight that got clogged a couple times, and another earlier model

If pressure regulator stoves work better because of heat conduction to canister, a better technique is to have a length of copper wire, wrap it around the canister, and then up to flame. Heat will be conducted much better to canister. I think you could get this to work much lower than 20 F.

[Adam Klags]

This is great stuff, I was thinking about this myself for the last few months – I work on carburetors as a hobby, and they function with a basic needle valve as well. I knew this would end up being the case! I can also attest to the abilities of my gnat in all seasons. Using an isobutane based canister seems to work fine, I keep them in my pocket before use just to be safe but I've never had a problem with mine in cold weather. I'd be curious to find out why the new jetboil sol titanium is so good in the winter since it obviously has nothing to do with the pressure valve… think it just stays warmer and keeps the canister warmer during use?

[Jerry Adams]

How cold does the Gnat work down to in your experience?

[James Marco]

"I'd be curious to find out why the new jetboil sol titanium is so good in the winter since it obviously has nothing to do with the pressure valve… think it just stays warmer and keeps the canister warmer during use?"

It isn't the regulator, soo, it has to be something along those lines. Really, heat/pressure are the same thing in a closed system. Measuring one without the other is sufficient in a static system, but a stove is not static. (Hint for Roger.) We will find out, Roger is pretty thurough about that stuff.

About the wire around a canister, I am sure that works. Anything that boosts the temp to above 20-25F (-3C to -6C)will work. Roger did a very god job explaining that one, previously. I think a heavy guage piece (#10) might work better than a light guage.

[Roger Caffin]

> 95% of what Roger says is good, but : )
Oh well, 95% isn't bad … :-)

You don't get much dirt out of a canister with an UPRIGHT stove because gravity is in your favour, so I would not expect many people would have this problem. However, there are a couple of cases where it can happen. Obviously, Jerry is careful.

If the canister is carried without the plastic cap over the nipple, some dirt or even fluff can get into the nipple. I have never had this problem myself because I always replace the cap, but I know of a couple of people who have had it.

The same applies to the stove: if you let any dirt or fluff get into the screw region. Putting the stove down on the dirt can do this.

Cheers

[Roger Caffin]

Part 2 may be a little while in coming, so a few comments here based on Jim's posting.

> One theory is that the regulated valve allows Jetboil to safely employ a jet with a
> larger aperture.
The early Jetboils actually had smaller jet sizes, to limit the power.

> the geometry of the Jetboils with regulator valves somehow causes heat to be
> conducted to the canister
I think this is the secret, but let's generalise that.

In some cases there is conduction back down the burner tube to the canister which helps, but this is not going to be very significant because the air inlet holes block most of the conduction. Its actually the cooling effect of the air flow through the holes which does this. Yes, I have tested this in the lab, and it happens.

Many stoves reflect some heat downwards to the canister, to the point that some vendiors (used to) include a radiation shield with the stove. Something like the MSR Pocket Rocket will be poor at this because it has a tall burner tube and a flame which goes straight up. The Snow Peak GST-100 is better at this because it has a short burner tube and the flames go out sideways, such that the canister can see the flames more.

Finally, if you operate an upright canister stove inside a tight windshield you will get a fair bit of hot air recirculating inside the windshield around the canister. Obviously this is going to help.

Feel free to experiment, but don't let the canister get any hotter than you can touch.

Cheers

[Stuart R]

In some cases there is conduction back down the burner tube to the canister which helps, but this is not going to be very significant because the air inlet holes block most of the conduction.

I don't think this effect can be ignored. One of my early attempts at making a remote canister stove utilised an aluminium mixer tube. It was a failure: without a heavy canister connected to the base, heat conduction down the aluminium tube resulted in the base of the stove quickly getting unacceptably hot (hot enough to burn skin). My current remote stove has a titanium mixer tube and burner (from the Gnat) and this runs much cooler.
So, the minimum x-sectional area (due to the air holes) will have an effect, as will the length of the tube, but the thermal conductivity of the metal has a significant effect too.

[James Marco]

"So, the minimum x-sectional area (due to the air holes) will have an effect, as will the length of the tube, but the thermal conductivity of the metal has a significant effect too."

As you say thermal conductivity cannot be ignored, especially at the near boiling point of the fuel involved. Even 1 or 2 degrees will help. Aluminum is far better at conduting heat than ti. As you say, there is a clear difference. I noted the same thing with pots: Al vs Ti. Roger pooh-poohed this because of the thickness as he is doing here with air holes. Of course, air conduction past the metal air inlet holes will cool it, also.

[Roger Caffin]

> I noted the same thing with pots: Al vs Ti. Roger pooh-poohed this because of the thickness
I am not sure I often 'pooh-poohed' an idea, although I may well disagree. :-)
My reason for doing so in this case is seen when you look at the temperature drop across a typical pot wall. I forget the exact figures, but the drop for both aluminium and titanium using typical pot wall thicknesses at typical heat fluxes was less than 1 C in each case. I submit that such a drop is not very significant.

> Of course, air conduction past the metal air inlet holes will cool it
THIS is why I placed little importance on the heat flux down the burner tube: air cooling, especially at high power when there is a lot of air flow.

In two different experiments with very different configurations I have tried to pump heat past the cooling holes in the burner tube; in each case I failed to get any significant heat flow. By moving the heat flux to another part of the fuel inlet line I was able to get considerable temperature rise for the same amount of aluminium heat shunt in the flame.

Cheers

[Stuart R]

In two different experiments with very different configurations I have tried to pump heat past the cooling holes in the burner tube; in each case I failed to get any significant heat flow.

This is the early stove I was talking about, burner and mixer tube taken from a Coleman F1. You can see that the air inlet holes are quite small, what you can't see is that the walls of the tube are also quite thick. The pot supports are titanium and the vapouriser tube is stainless steel, so not much conduction by those routes. The stove base and legs got too hot very quickly (damaging the o-ring in the valve).

[James Marco]

At a guess, the main source of heat was probably the stainless steel tubing in the flame, not the stem, though this would have contributed.

[Stuart R]

Not so. I use the same stainless tube on later designs and I can hold it in my fingers just 3" from the flame.

[James Marco]

Roger, yah, I sort of agree on the pot thing. My experiments showd a very modest increase in boil times with ti…well within the margin of error for the stove. The funny thing was it was consistent. But, 10 seconds to 200F from 40F doesn't matter a whole hell of a lot. As I remember, this was more at very low heat values, but that data is long gone…along with the hard drive that failed. Something in the order of 20sec at a 13 minute boil(200F) for two cups using the same small alcohol stove. Not all that significant.

[Roger Caffin]

Hi Stuart

> You can see that the air inlet holes are quite small, what you can't see is that the
> walls of the tube are also quite thick. The pot supports are titanium and the
> vapouriser tube is stainless steel, so not much conduction by those routes. The stove
> base and legs got too hot very quickly (damaging the o-ring in the valve).

Interesting.

Yes, those are tiny air holes. Combined with a thick Al wall I can imagine a lot more heat getting past. In my case the air holes were about 6 mm diameter, and the wall thickness was maybe 1 mm. Very different. Interesting.

I wonder … that SS tube is going to get red hot. The gas going through it will be red hot too. I wonder whether the continuous flow of very hot gas was partly responsible for the base getting so hot?

The O-ring got damaged? I wonder what sort of O-ring it was? If it was the common nitrile, yeah, that can happen. Try changing to Viton – dearer (like that matters for a couple of O-rings!) but a higher temperature rating.

And maybe thin down the wall around the air holes very slightly?

Btw: I still say that is a neat stove.

Cheers

[Tom Clark]

"I am not sure I often 'pooh-poohed' an idea, although I may well disagree. :-)"

Maybe I need to check the dictionary definition of 'pooh-poohed.' Howver, I have seen you subtly ridicule, mock, deride, disparage, and scoff at ideas. Just teasing…you have rarely been subtle.

Great article, and I agree it doesn't take long for someone experienced in this area to dismiss any significant advantage for a pressure regulartor for this application. I was surprised that you left out 3 considerations, but maybe you will address them in part II.
– relative cost
– weight penalty
– durability

Tom

p.s. Perhaps the pressure "regulator" is actually a pressure "generator"…that would be something useful!

[Roger Caffin]

Hi Tom

I must look up that new word of yours – 'subtle'. Don't think I am familiar with it. :-)

> – relative cost
> – weight penalty
> – durability

Actually, I don't really think there's much in any of them. I think the cost would be close, the weight penalty would be small, and durability would be OK.

Cheers

[Tom Clark]

I'm surprised, I would have thought that the regulator was heavier & more expensive than the valve…but that was just my first thought. Thanks!

[Roger Caffin]

Hi Tom

Well, thing is, it's very small and made of stamped bits of metal. It's not some large industrial thing. I could not imagine it costing more than 50 cents to make in volume, and possibly less.

I know my diagrams make it look large and complex, but the real thing is much smaller, and I admit the design is kinda cute.

Cheers

[James Vesely]

All things be said with Iso-butane having a range of pressure from 0 psi at 16 deg F. to 80 psi at 120 deg F. I would think a pressure regulator would make the flame a little more consistent. A more consistent output pressure would insure easier light ability, better flame and optimal air to fuel mixture so it should be more efficient.

[Hikin’ Jim]

James,

Er, couldn't you just open or close the valve to get the desired flame?

HJ
Adventures in Stoving

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