Primus/Optimus stove question

My SWAG on the Optimus would be a couple PSI. A bit more educated guess for the MSR, based on the effort to pump and size of the piston, would be around 15 PSI, at least for the XGKs. A friend of mine nicknamed mine the "Testosterone

2000" on account of all the noise it makes. I believe the MSR Whisperlites don't require as much pressure.

Ned Simmons

I cant give you an actual number, but I can tell you it ain't a heck of a lot.

All it needs do is push the fuel out of the tank. All the flame pressure is generated in a vaporizing tube below the burner, On both my optimus and my old phoebus the heat from your hand on the tank was enough to prime the works.

Both fuel tanks are quite stout and fitted with a pressure relief valve, but I think this is just for safety and not needed for normal operation.

Paul K. Dickman

Matt wrote: (clip) does anyone know what the working pressure in the tank is for "self-pressurizing" stoves similar to Optimus or Primus stoves? Just how much heat is the tank supposed to get off the burner to stay pressurized? (clip) ^^^^^^^^^^^ It has been a while since I looked at any of my little stoves, but, as I recall, they have a wick inside the brass tube, which draws fuel up near the burner by capillary action. Yoy start the action by burning a little fuel around the tube, vaporizing what has been drawn into the wick. This causes vapor to jet out of the burner, so the heat keeps the process going. It does not depend on heat actually reaching the tank,and creating pressure there. Of course, whatever pressure is creating the jet is also the other way, so I am sure the tank becomes slightly pressurized.

The rest is purely guesswork. I suspect that any pressure in the tank will be a fraction of a psi.

I don't know how much pressure you get in the tank of a Coleman type stove by pumping. But, comparing the size of the pump, the number of strokes and the volume of the tank full and empty, and comparing with what it feels like to pump up a bike tire, I would guess that it could range from 1 or 2 psi up to maybe, 20 psi for a full, freshly pumped tank.

I do know my Svea has a spring-loaded pop valve to keep the pressure below a certain level. I've never tested it, but based on the construction of the stove, and its operation, I would think no more than about 5psi.

Jim

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jim rozen wrote: (clip) my Svea has a spring-loaded pop valve to keep the pressure below a certain level. (clip) ^^^^^^^^^^ Jim, I am trying to picture the consequences of having that valve pop off while the stove is running. Sounds like it could be kind of scary.

My Optimus would pop off now and again under large pots, if turned up high for some time.

All of a sudden there would be a 6" or so flame, maybe 1/4" in diameter max licking up the side of the pot.

It had to be going and blowing pretty good for 20 min or so before it would blow. I had also built an aluminum gust gard around the inside perimeter of the stove that didn't help either.

It wasn't all that big of a deal when it did it, and the relief valve would close itself right away if the pot were removed, or burner turned down.

I used the hell out of that stove for years and years...

Erik

The presence of a wick does not imply that pressure is not necessary. The wick just makes sure that the stuff going up the tube is liqued fuel, rather than vapor.

Tom

I may be totally off the wall with this response (well, with regards to this question) but the MSR Whisperlite International has a wicking system like the Optimus Nova and Primus stoves. It doesn't look as well protected from the wind though. My Optimus is a synch to lite and priming is quite easy.

Thanks for all the replies. I found a few sources for "MSR-type" stoves putting tank pressure around 20psi. I have one of the Optimus ones and I think I'll try to rig something up to figure out what the relief valve pops off at. If anyone is interrested here is a good site which has schematics and parts break outs for all the Optimus stoves:

I was interrested to see that a lot of the newer ones have a pump either integral to the tank or which retrofits onto the filler to decrease warmup time (the "mini pump").

Thanks again,

Matt