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Flow Meter/Needle Valve Combo
pisanoal
Hey all,

I just wanted to share an option for monitoring/controlling gas supply to a roaster for heat control. It is a rotameter style flow meter (clear marked sight glass with a ball or "float" that rises based on the flow rate) and has an option to get it with a built in brass needle valve.

Most people opt for a pressure gauge for various reasons. I had hesitations about going with pressure based on a few factors. Those reasons being pressure at the burner and how it relates to BTU output is entirely setup dependent (BTU value is directly related to gas flow and is easily calculated), the proper pressure gauges can be expensive and/or hard to find exactly what you want and you may need to try a couple different ranges, a separate needle valve or other control method is required.

I stumbled on the Dwyer Instruments Series VF Visi-Float Flowmeters.

https://www.dwyer...a/SeriesVF

These flow meters range from LPM (liters per minute) to SCFH (standard cubic feet per hour). They come in 2" or 4" scaled versions and range from $30 ish to $62. There is also a custom option although I'm not sure how much that is, where they could make custom ranges and presumable custom sizes. There is also an option to include a brass needle valve that controls over the effective range of the flow meter (A+ option in my opinion).

To size your flow meter you need to know what BTU input you require. For propane, the heating value is around 2488 BTUs/cu. ft. (note that burner ratings are usually quoted in BTUs/hr). There are appropriate ranges available in both LPM and SCFH. To get to BTUs/liter divide by 28.32 to get 87.85 BTUs/L.

Divide your desired BTU capacity by the respective conversion to get your max flow rate. Note that if you are opting for LPM, you will first need to divide your burner rating by 60 to get to minutes. Also note that the flowmeters are designed for air, so you will need to apply a specific gravity based correction factor. Propane flows are about 82% that of air so multiply your calculated flow by .82.

Example:

(25,000 BTUs/hr) / (2488 BTUs/SCF) = 10.05 SCFH air * .82 = 8.241 SCFH propane
(50,000 BTUs/hr) / 60 / (87.85 BTUs/L) = 9.5 LPM air * .82 = 7.79 LPM propane

allenb has posted some common requirements for roasters of various sizes in another thread. Maybe he will link it for reference, but that will be an easy way to figure out what flow meter you need.

Please be aware that both btu calculations and conversion from air to gas will be different for a natural gas fired roaster. BTU information is readily available. The flow conversion is Q2=Q1*sqrt(1/SG2) where Q1 is the flow of air, Q2 is your flow of gas, and SG2 is the specific gravity of the gas you are measuring.

For my setup I went with a VFB-66-BV (BV is for brass valve). I have attached a video showing how well it controls the flame on this 100,000 BTU jet propane burner. I sized it for output of around 50k BTUs.


Edited by JackH on 10/19/2019 2:53 PM
 
allenb
Wow, great post! This is very helpful information and gives us another option for manually controlling our gas fired roasters.

I think this is the thread you were referencing regarding BTU/kw recommendations for different size roasters

https://forum.hom...post_41645
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
pisanoal
Yup, that's it. Thanks!
 
goat4hooves
Thanks for sharing what you have learned. This is a forum full of great information.

I have the same concerns as you do with the pressure gauge readings and various burner configurations.. This option kills two birds with one stone.
 
mtbizzle
Thank you for sharing! I have actually been looking at Dwyer parts as well for gas pressure measurement/control. I have been looking at Model# LPG5-D8022N, the gauge, along with Model# NVII-2B, a needle valve. This measures 0-2.5 kPa/0-10" water column (another gauge measures 0-3.5kPa) and the needle valve is for control Together they cost... slightly under $50, but another T joint would be necessary as well. I wasn't aware of the option you describe, I'll have to compare them.
Roast: Kaldi wide, SR800 + projects
Grind: Lab sweet, Bentwood, giota w/ MP burrs, Commandante
Pull: Decent, La Pavoni, Elektra Microcasa a Leva, Faemina anno 60, Kim Express
 
oldgrumpus
I realize this thread is a couple of years old... But which I'd seen it when it was more active.

I have thought this would be the best way to control a roast manually since it takes all the precise engineering of orifice sizes and pressure out of the calculations. As goat4hooves above has said,"This option kills two birds with one stone". The main focus with this is how much fuel is getting to the burner. By actually measuring through a calculated valve, you're going to get the same btu's whether its a torch, a burner or whatever at the business-end.

But... the flowmeters are calculated for air so the cubic foot numbers on the scale will not correlate to propane or natural gas. I've looked at the Dwyer site and elsewhere for a meter like this designed for propane and it doesn't exist. If anyone knows where to find one, please post the source! I suppose if the plastic holds up then no problem using it but somewhere out there you can probably find out what the difference in density is between air and propane since that is why the numbers won't correlate on the scale.

I've requested information from Dwyer to confirm whether or not an LP version is available as an option. We'll see....

Also, this may be helpful for those seeking info on whether things are chemically compatible. I've referred to it for seeing whether my particular choices for tubing might be adversely affected by propane. Some are and some aren't. Here's the PDF version: https://marketing...om-ism.pdf
Clever Coffee Dripper
Grinder: Macap M4
Roaster: Completed drum roaster project photos shown here:
Photos https://goo.gl/ph...Da6K4wfqw5
Videos https://www.youtu...Bd1NrdpSUH
 
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