Ken Fox wrote:Exactly what additional information would a flow meter give to someone roasting coffee, than he or she would easily get from a simple pressure gauge?

Hi Ken:

If your pressure gauge is of reasonable quality, and it is properly located in the gas train (as I believe yours is now), then I doubt there would be much advantage is using a flowmeter vs the pressure gauge. I assume that with some trial and error, one learns what gas pressures one wants to use in order to hit one's roasting waypoints in the proper time frame.

On the other hand, I was very surprised to read that your old gas roaster had the pressure gauge located in the wrong place (ie, before the control valve). Had I known that, I surely would have recommended you install a flowmeter such as the one that Kendall is considering. It would have been more repeatable and more intuitive.

Meanwhile, if Kendall builds this thing, he will be saving hundreds or thousands of dollars over the cost of a commercially-made roaster. The flowmeter (rather than a simple pressure gauge) would be a nice addition. Sort of like having xenon vs conventional halogen headlights on your Bimmer -- not a necessity, but an aid and a comfort.

[edit] BTW, and just to set the record straight -- I don't own a Bimmer. I drive a lowly Prius.

Actually, a flowmeter would allow for much easier estimates for gas settings to roast loads of different charge size. Gas flow can readily be converted to heat consumption whereas gas pressure cannot.

Pressure is linearly related to flow, but (the relationship between pressure and flow is) also dependant on system variables like piping type, fittings, etc.

.

I haven't read this whole thread and probably shouldn't comment here but I use to work in the gas valve industry and it's very common to adjust/set burners by just using the gas pressure (" W.C) and the burner orifice size to determine BTU's using a chart like below.

http://www.joppaglass.com/burner/lowp_chrt.html

AndyS wrote:
On the other hand, I was very surprised to read that your old gas roaster had the pressure gauge located in the wrong place (ie, before the control valve). Had I known that, I surely would have recommended you install a flowmeter such as the one that Kendall is considering. It would have been more repeatable and more intuitive.

Meanwhile, if Kendall builds this thing, he will be saving hundreds or thousands of dollars over the cost of a commercially-made roaster. The flowmeter (rather than a simple pressure gauge) would be a nice addition. Sort of like having xenon vs conventional halogen headlights on your Bimmer -- not a necessity, but an aid and a comfort.

BTW, and just to set the record straight -- I don't own a Bimmer. I drive a lowly Prius. [/size]

Hi Andy,

Firstly, we all know that the Soy Boy drives a Maserati, and that the Prius is just parked outside to fit in with the Bohemian ethos you aim to project; we were not fooled.

Secondly, we have no idea of what sort of roaster Kendall is planning to build; it might be more intended to replace a Behmor than a Probat. I would be very surprised if after it is all said and done that there would be very much money to be saved, given that Jon's 1lb roaster (US Roasters) costs around $4500 and the Diedrich 1kg roaster costs around $6500. Knowing what goes in to making these sorts of roasters leads me to believe that trying to duplicate something in that range at a lower cost would not be worth the effort, financially speaking.

I think a flow meter might be a "cool addition," however I doubt it will give any useful information above and beyond what would be supplied by a pressure gauge.

As to my old roaster, I actually did not understand when I got the gauge, that it would read out the back pressure rather than the actual pressure, and only when I got it installed did I appreciate that rather obvious fact I would have considered replacing it with a flow meter, and in fact that might be a fun project to do now, however from the standpoint of actually using it, the readings it gives are entirely consistent with a given level of burner height, so once I got used to its inverse behavior, it did not matter other than esthetically.

Can you run a Prius on soy oil or tofu? That's what I want to know!

ken

JonR10 wrote:Actually, a flowmeter would allow for much easier estimates for gas settings to roast loads of different charge size. Gas flow can readily be converted to heat consumption whereas gas pressure cannot.

Pressure is linearly related to flow, but (the relationship between pressure and flow is) also dependant on system variables like piping type, fittings, etc.

.

Hi Jon,

I question your logic here. This is both from a theoretical and a practical sense. The amount of heat (BTUs, or CFM of gas supplied) will only be somewhat proportional to the bean load in a drum, because of course one has to heat everything else (e.g. the drum, the outer shell, the air, etc. etc.) regardless of how much the charge load weighs. I would regard the needed input as requiring some sort of complex formula in regards to bean load, and not being even close to being proportional to the bean load.

From a practical standpoint, I've roasted different amounts of charge weight in both my old sample roaster and my new Diedrich IR-1. There is no question that all other things being equal, one needs less of a heat input when the bean charge weight is reduced, however I have never found that I lacked enough information to work with simply having an inline gas pressure gauge. In addition, with a roaster having active ventilation and/or a damper set up, one is probably more likely to have to adjust both the airflow and the gas input in relationship to changing charge weights.

Unless one is using a different burner when one roasts differing weights of beans, the gas pressure gauge gives all the information that I can possibly use when it becomes necessary to reduce or increase gas heat inputs in relationship to charge weight. I am curious to know what additional and "useful" information that you think a flow meter would give in that situation, over that supplied by a simple pressure gauge.

ken

Ken Fox wrote:Meaning no disrespect, engineering types do tend to to take something simple and to muck it up with complexity when it comes to hobbies, often times doing so only for the (apparent) sake of complexity itself.

This is such bs. If it weren't for "engineering types," you would be roasting your DP-only beans in a deer skull over a wood fire (that's if you could even figure out how to start a fire). And this is after you rowed yourself over to Africa to buy the beans.

You certainly wouldn't be waking up every morning to find your GS3, one of the most highly-engineered coffee machines ever, already warmed up and ready to go. Instead, you'd be pounding your beans into fragments with a club and filtering the brown muck through a cloth.

The other issue with a flow meter, which is obvious but which I did not consider before, is that the propane or nat. gas must flow through it, in order to get a reading. This creates some plumbing and ergonomic issues.

If one puts the flow meter directly in-line, in the gas flow path, then the gas piping will either have to be made somewhat circuitous, or the meter will not be placed where it can be easily read. This is obviously because the burner/heat source is unlikely to be located at eye level or above.

If the idea is to be able to roast coffee while referring to the flow meter to guide the roast, and if one doesn't want to continually contort one's body to know the gas flow, then the gas piping must go up to eye level, pass through the flow meter that is located there, then the piping must go back down to where the control valve is located, then out to the burner. This is much more complicated than the plumbing required for a simple pressure gauge, which can come up off a "T" in a single pipe to eye level, while the actual gas flow goes through the other 2 ports on the "T."

Since, as has been pointed out previously, if one has a fixed orifice size for the burner, the heat produced/consumed/ flow of gas will be proportional to the pressure, one can see why the manufacturers have gone this route with pressure gauges, rather than to install flow meters.

ken

Ken Fox wrote:Hi Jon,

I question your logic here.

As always, anyone is free to question. But until one experiences such a thing for one's self then it would be impossible to make any sure judgement as to the relative veracity of such an idea.

In my opinion, a flowmeter is a more direct measurement of actual heat input to the roasting system (given a known offset for gas density). And (again, only my opinion) such a measurement would be more readily interpreted for predicting the behaviour of the roaster using different bean loads.

Of course there are other factors as you point out, and there would certainly be a learning curve involved for changing charge load mass as we both know.

Thankfully we each get to choose our own path, and we can each "get there" in any number of ways.



Edit note - ball-type flowmeters like the one shown earlier install inline, much like a simple "T" and (so in my roaster's design) one could easily be added very close to my existing gauge with no re-routing of plumbing required. I have no idea how your roaster gas line is routed so I won't comment on ease of installation for your setup.

Ken Fox wrote:The other issue with a flow meter, which is obvious but which I did not consider before, is that the propane or nat. gas must flow through it, in order to get a reading. This creates some plumbing and ergonomic issues.

If one puts the flow meter directly in-line, in the gas flow path, then the gas piping will either have to be made somewhat circuitous, or the meter will not be placed where it can be easily read.

You are correct when referring to the particular type of flowmeter in the picture, which is called a "rotometer." I thought it was an appropriate choice because it is simple and inexpensive. Not only must the meter be inline, but it must be mounted vertically, and the gas must enter at the bottom and exit out the top. This means, as you say, that the gas piping must be designed to accommodate it. Really this is trivial to accomplish, but takes a little extra effort and costs a little more.

Also, because the rotometer depends on the earth's gravity in order to function, this flowmeter would be a poor choice for roasting on the International Space Station. Roasters on the moon or Mars will have to recalibrate their rotometers in order to hit their waypoints properly (which is the least of their problems, actually).

With respect to ease of use, there are other types of flowmeters that are two part devices: a sensor in the gas line, and a remote readout that can be located anywhere. But these are more expensive and more complicated, and I know how you feel about engineering complexity....

Ken Fox wrote:If the idea is to be able to roast coffee while referring to the flow meter to guide the roast, and if one doesn't want to continually contort one's body to know the gas flow, then the gas piping must go up to eye level, pass through the flow meter that is located there, then the piping must go back down to where the control valve is located, then out to the burner.

I was under the impression that you didn't refer to your pressure gauge continually throughout the roast; I thought one referred to it only a few times when a change in the heat output was deemed necessary. It would seem to me that the contortions about which you speak would occur at a tolerable frequency; a mere one or two chiropractor visits a year should suffice to iron out whatever kinks are produced by flowmeter contortions.

Ken Fox wrote:Since, as has been pointed out previously, if one has a fixed orifice size for the burner, the heat produced/consumed/ flow of gas will be proportional to the pressure, one can see why the manufacturers have gone this route with pressure gauges, rather than to install flow meters

Manufacturers are keenly (kenly?) interested in reducing costs, otherwise they wouldn't be able to send their kids to college. So for them the pressure gauge, rather than a flowmeter, is functional and cost effective.

As with a custom tamper, however, Kendall, Jon, and all the rest of us are free to spend a little extra on a fancier gizmo if it gives us satisfaction. Or if we think it makes the job easier. It is not necessary to justify the expense to you or anyone else...although that may not be true for those folks who are married.

AndyS wrote:...It is not necessary to justify the expense to you or anyone else...although that may not be true for those folks who are married.

That is if one intend to stay married!