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Electric to Propane Gas Conversion • Updraft • Pressure Gauge Type & Location


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Hi there,

Thank you for all the wonderful info this forum, it is truly great and a HUGE help to everybody.

I am writing from Dominican Republic. Here we do not have stores for ceramic materials and equipment like in the US. A lot of things need to be imported paying high freight forwarding fees. I have fired electric before and gas raku. Here the electricity is NOT AT ALL reliable and VERY expensive and we have regular power outages, which makes firing electric a big problem. I know most folks her recommend the conversion to a downdraft, but I wanted to try it this way as the downdraft conversion will be an added expense, chimney, etc... 

I am in the process of preparing a refurbished electric kiln onto gas updraft propane. Propane is more affordable here. I have read MANY of the posts on here and online about conversions and I anticipate the challenges ahead. also, Olsen's the Kiln Book, Mel's 21stcentury firing, and looking for the Art Of Firing by Nils Lou (very difficult to get), and many many more info online.

A profesional potter friend is selling me an electric kiln to covert to gas (below the layout and some pics). He also used refractory cement on the inside walls (shown in the pics). It will have a layer of INSBLOK-19 1.5'' thick after the brick for added insulation, and then the stainless steel jacket. 

I would like the system to have a pressure gauge so that I can include the pressure info in my firing log and be able to learn as I go and become more efficient with my firings. I am planning to have as my max temp cone 5-6 (stoneware). Did a lot of earthenware before (electric) but would like to experiment / learn stoneware. I will have this kiln located in my 5th floor rooftop terrace outside. At the moment there is no roof, so I will be covering the kiln when not in use with tarp and a pice of corrugated zinc roofing. . I also have a pyrometer (dual thermo) and thermocouple that I will be placing in the kiln interior, 2-2.5 inches in (not shown in the layout). I only have 1 thermocouple for the moment and will wait to see if I need a 2nd one if I get too much temp difference between top & bottom.

I wanted to ask, what is the pressure gauge in psi that I need? 0-15 psi? 0-30 psi? and the location of the pressure gauge, what should it be?  According to this post which I have found that is VERY popular online about conversion:

http://www.sebastianmarkblog.com/2018/07/gas-kiln-conversion-downdraft.html

He advises to have the pressure gauge at the regulator in the tanks and control the flow form there. But I remember that I liked (in my old Raku kiln) to control the flow of the burner in the valve located on the galvanized steel pipe. I would like to have my gauge after that MAIN VALVE, to be closer to the kiln and be able to notice any changes (big and small) in realtime, and not be 8 feet away where the tanks are going to be. I wanted to check with you. Any help would be greatly appreciated. I have never used a gauge before but feel it will be great for my learning curve. 

If you notice the layout, I have 2 valves before each of the burners and before the MAIN VALVE. I am thinking that since this will be my main kiln, I will be single firing, from green to glazed, that I may want to start of with ONE (1) burner in the beginning and then turn BOTH (2) of them on as I progress. I imagine that the 2 RED valves before the burners would be both completely open for the large duration of the firing and I would control the flow with the BLUE MAIN VALVE

Many thanks in advance for taking the time to read this and if you have info, even general that yo think will help me, it would be great.

Sincerely,

Gus

PS: Thank you again for all the info here, I have gathered / saved lots of info theory. Now I will be putting all of that theory to practice. Hope to eventually build an oxygen probe using a car oxygen sensor, as I found some instructions online.  Big shout out to: @neilestrick @Mark C.  @Marcia Selsor  @Bill Kielb   Thank you for all your info, have seen your names a lot combing the forums and your advice has given me a sense of grounding when I finally do it. :)

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Amau_B.jpg.f674adfbfb5f6f308704b05905bec755.jpg

Edited by Gusf
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  • Gusf changed the title to Electric to Propane Gas Conversion • Updraft • Pressure Gauge Type & Location

Absolutely great you are planning in advance, so let me see if I can ask the right questions to spark some thoughts.

your burners with a #50 orifice are rated to work approximately 16000 btuh to let’s say conservatively  65000  btuh so when I look at an orifice table you will be operating 0” - 28” of gas pressure. 
9205A785-961B-4BBC-9692-69CC5A0C227E.jpeg.0bb6714dc2c3635e11957e4c20188f0d.jpeg

Gas pressure is often measured in inches of water column so much less than 1 PSI. (It takes over 28” of water column to make 1 PSi)

so a gauge like this is more suitable

139514BF-50CC-4F9F-85E1-1342BDC215C8.jpeg.4f01cec153f982d424de03bc26d3b6de.jpeg

In reality, the common pressure for propane regulators is 14” of water column so we should find out what your regulator is rated at. If it is rated at 14” then the gauge above is overkill and will only make your adjustments less accurate. 0-15 inches of water column would be typical.

4987C74B-6D3F-412B-8403-6744AB3A9604.jpeg.4863572e6495abea76582becb81ed9fb.jpeg

 

So to start, a gauge reading PSI will never move with a proper regulator that maxes out at 14 inches which matches your burner and orifice specification.

First question: What will your regulator be rated at? You will need a two stage to go from tank pressure down to the inches of pressure your burners are designed for. Typical propane tank pressure is 100 - 200 PSI to ensure the propane remains liquid. Your first stage regulator needs to be able to withstand this pressure, so typical ratings are 250 PSI max inlet pressure. It also means you  generally cannot simply put a second stage regulator on the tank directly, it will only be max rated at about 10 PSI inlet.

here is a typical 2 stage tank regulator

FAB41308-AF3D-4BC7-BAAC-AB9E59ED6370.jpeg.d7f55c02d6f0c6b1cce6e8499a7ddadf.jpeg

 

Notice, this regulator stops at 11 inches which is quite common actually so when we figure this out we will move on to checking the size burner and orifice combination.

The  gauge itself  is typically installed downstream of the adjustment valve and before the burner. Generally no other valve  is inserted between the gauge and burner but I get his use of a simple pilot and additional isolation. We try never to trap gas at any pressure though so that later even when the main gas is off someone cannot unwittingly discharge raw gas by opening any valve other than the main gas.

Just a late note to add, you can do this with a single stage regulator and work in PSI but it is less safe and ought to require orifices in the drill # 70 range (really small). The potential for leaks is why PSI pressures are not common for these types of burners.

If this were an electric kiln we would find the equivalent of 45,000 btuh is the capacity of a decent powered kiln.  This is gas and since you have two burners 25000 btuh each  or 50000 btuh total can be achieved with less than 7 inches of gas pressure with quite a bit of extra capacity to 11 inches. You also have  the ability if needed to increase the orifice to a number 40 drill which gets this in the 140,000 btuh range.  Keeping in mind you have already added insulation to the outside of this kiln.

I find the sizing to be a mystery in the article actually and his firing chart doesnt appear to have been done with a PSI guage actually. I would  encourage you to operate this as low pressure as a safe best practice.

Actually reading through the narrative on this kiln, firing too fast, cone ten in four hours, tap on the gauge to see small pressure changes, logged pressure changes of a few tenths of a psi, all seem to indicate this was likely overpowered and run on a single stage regulator. All very common errors BTW when it comes to gas.

I will stop now and suggest you pick your intended regulator and operating pressure first.

 

Edited by Bill Kielb
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Propane pressure is much more than natural gas pressures-I would get a guage that is up to 100#s or better still is the gauge that Bill shows in 1st photo that shows water column presure to 30 inches

Propane I think is usually in pounds here in USA and tanks can be as high as 70-100#s

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28 minutes ago, Mark C. said:

Propane I think is usually in pounds here in USA and tanks can be as high as 70-100#s

Tank pressure is 100  - 200 PSI to keep the propane liquid. …… dependent on fill and temperature of course. His burners are designed to operate on inches of pressure. Operating these burners and orifices on PSI pressure I believe is a mistake and will be difficult to dial down. Propane service in the US is usually limited to 14 inches of water column  and most often regulated to 11 inches. Propane has about double the btuh content of natural gas so it stands to reason it generally operates on the same pressure as natural gas for burner service and requires smaller orifices than natural gas as well. Tank pressures are in PSI, service pressures are in inches of water column in the US.

The orifice chart above is for propane and is basically in inches. The chart extends to 2PSI as this is medium pressure service in the US and has very specific applications it is used for. Often folks confuse this and call it high pressure gas.

Edited by Bill Kielb
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Posted (edited)

Hi there and THANK YOU so much for your help, this has been very enlightening. I am still a bit confused as to what I need to buy for my setup, but will proceed to answer your questions.

Sorry for the late reply. I have been busy visiting MANY hardware stores here in the country and I have not been able to find a second stage regulator. Just for context, propane gas is the MAIN fuel used in the country for urban, buildings and houses. There are even cars that run on propane here. It is very common. But no second stage regulators here. My brother is actually coming to visit from Maryland, US. I will ask him to bring the equipment that you recommend from there so that I can save in shipping and have quality equipment. 

The only one they sell here is very similar to this one (pic below) at my home, It has a lever to switch between tanks, it is a 1st stage (now I know):

From your explanation I can have a 2-stage regulator installed at the tank, OR one 1st stage at the tanks (like below) and then a 2nd stage  down the line and at the start of the galvanized 1/2'' pipe in the line but I don't know yet. 

Unknown-2.jpeg.b7f568f854640a8e971676a1e3485292.jpeg

I now understand what you explained so clearly that 28+ WC is equal to 1 psi. 

For the gauge I will need a T I imagine to put it in the line?  is this correct?

If I have two (2) tanks (25lb or 50lb), and two Venturi MR-750. The tanks will be roughly 20 feet from the kiln but in the same terrace / space.

On 7/4/2021 at 6:30 PM, Bill Kielb said:

Operating these burners and orifices on PSI pressure I believe is a mistake and will be difficult to dial down.

When you say "dial down" you mean, get the burners, their flame under control instead of having a too big of flame, is this correct? is it related to efficient combustion?

 

On 7/4/2021 at 4:45 PM, Bill Kielb said:

The  gauge itself  is typically installed downstream of the adjustment valve and before the burner. Generally no other valve  is inserted between the gauge and burner but I get his use of a simple pilot and additional isolation.

Yes, is my thinking correct that I should be able to start with only one (1) burner? thats the reason I thought of putting a small valve on each burner located before the burner and before the gauge that I will be using. Is this correct? Even If I use them completely open most of the time, andI would only close one at the start? might there be a better way of doing this? I also have read in previous posts that it is important to move the gas around in the kiln, so I have found it as an advice to stalling. 

On 7/4/2021 at 4:45 PM, Bill Kielb said:

This is gas and since you have two burners 25000 btuh each  or 50000 btuh total can be achieved with less than 7 inches of gas pressure with quite a bit of extra capacity to 11 inches.

How do I know I will not exceed this? On the Axner website: https://www.axner.com/mr-750venturiburner.aspx for the burner it says that "The BTU values listed above can be increased with increases in pressure, however this burner may be subject to less efficiencies at pressures greater than 10 psi.  The BTU they have listed at 10psi is 171,910 but It is rated at 77,400 BTUs operating on propane at 11" WC. Confused still. 

 " BTW on their website they have a table for BTU/LP (#38 orifice) this is a mistake. I called Axner directly to ask for the orifice number (as I had already ordered one of the burners) and they confirmed by phone that the orifice is 0.07'' #50

I have read that these burners are not the best, but since I already had one for my small raku kiln I used in the past, my friend suggested that I order another one (which I did 3 weeks ago, have it here, from axner. The more expensive ones cost almost what the kiln is costing me . 

Just to be sure, what regulator do you recommend for my setup?

Whatever you recommend I will buy, he will look for them in the states. Remember I want to be able to connect two (2) tanks of 25lp, or 50 lp to prevent freezing, this is called pigtail? or do I need to buy one with a lever to switch between tanks? 

Does the regulator need a gauge also in case I need to UP the pressure?

and then the what gauge? 

 that I know understand is related to the 2-stage regulator I use, which one would you recommend? I just want to be sure before I invest and order the parts I need so that my brother can bring everything over on the 15th of July :) I calculated the internal size of my kiln and apparently it is 4 CF.

The polypropylene hose that I will have coming from the regulator (regulator connected to two (2) tanks) what diameter should it be? 

The galvanized steel pipe, connectors and everything, the person selling me the kiln recommends is 1/2''. Is this acceptable?

Do you recommend  a ball valve or a needle valve to control flow while firing as per my particular setup?

The INSBLOK-19 is considerably more expensive here than Ceramic KAOWOOL. Since it is an octagon, the boards that they sell here are: 1.5'' x 12'' x 36''. It would take many boards to get it done. I have change the plan a bit because of economy for the additional outside insulation, to wrap the outside of IFB 2.5'' - 3'' with a roll of KAOWOOL and then put the stainless steel jacket on the outside, (learned this is a viable technique on this forum and on potters.org) without compressing the fiber too much (learned on this forum that that takes away from the insulating properties of the fiber) . Do i have to rigidize it with sodium silicate before (saw that online)? they do not sell rigidizer here, or can I put a bit of refractory cement over the ceramic fiber in order to protect it before I put the steel jacket on top? That is my plan for the moment. I will be firing in this open terrace, there is a narrow wall perpendicular in the middle of terrace, that will shield me form wind, but is is very windy up here, hence my thinking of the need to have this outside extra insulation after the bricks and before the stainless steel jacket. 

I feel I have bombarded you with questions, do not want to overwhelm, but just want to get this right and invest in a smart / safe way and take advantage that I have a family member in the states to bring the stuff over. Thank you for helping me determine what it is I need to buy (list) from amazon or where you suggest in order to be able to get this small kiln to cone 5 - 6 max. 

Sincerely,

Gus

 

 

Edited by Gusf
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@Gusf  Assuming it’s just super inconvenient to regulate this down to inches for local operation then I would plan on low PSI operation and resize the orifice so the burner operates to its design output, then pick a gauge that has decent divisions so you have meaningful operating pressures to log. Tapping the gauge and guessing it moved a few tenths is not really good. . You can always drill the orifice bigger if needed so no worries there

I am working right now (Full day of work) and will address everything later tonight, just wanted to give you an answer before you imported a two stage regulator. Operating on a few PSI requires your piping is reasonably safe and well done and you have the proper orifice. I will need to work through a best orifice table and give you my suggested range and size …….. and answer your questions completely from above later.

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Posted (edited)

@Bill KielbThank you so much. Importing it is no problem at all.

I would actually would prefer to import the 2stage regulator and whatever else I need rather than mess with the burners,  But if you believe it would be better for me to switch to high pressure system (as high pressure regulators are local) and / or order different orifices for these burners  (slowly understanding) would do that and work with a smaller psi gauge, would do that. I have found a gauge in amazon that is 0-3 psi..

 I want to read the pressure and control the flow in WC a per your explanation. or whatever is most efficient. Also the efficiency of the burners, if I need to have a different orifice also. If I need to import the gauge and that will help me be precise with the firing and my learning curve. Just want to know exactly the gauge and 2 step regulator, and anything else that I will need to fire correctly this small propane kiln with the two tanks connected. Also the gauges here that are mostly found in PSI I mean are for water pumps for buldings and the likes, 0-100psi , 0-250psi way way too much. I want to have a nice kiln that I can fire to cone 5-6 if I want to, learn how to gas fire efficiently from greenware to bisque to glaze, etc.. reduction, oxidation, learn how to work the damper, pressure, learn how the kiln breaths, firing logs, pyrometer and have a nice setup while not depending on electricity.  I am investing in myself and make things easier for me moving forward. I am a visual artist and an educator and will be using it for sculptures, etc.. 

These are the regulators that you typically find here. Pages from local hardware stores.

They look and feel really cheap. But I don't know that is just my feeling. 

https://ferremix.com.do/products?utf8=✓&keywords=regulador

https://ochoa.com.do/buscar?departamento=0&param=regulador&page=1

'Alta Presion' means 'High Pressure'

Thank you so much and will await your reply.

Edited by Gusf
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On 7/7/2021 at 11:27 AM, Gusf said:

When you say "dial down" you mean, get the burners, their flame under control instead of having a too big of flame, is this correct? is it related to efficient combustion?

A little fair pretext here- these are my observations and opinions if you will, based on combustion knowledge over the past 30+ years with combustion products of many types and of course kiln operation for 10+ years.  I will try and give you my reasoning along the way but the designer of this kiln was successful with this being down draft. There may be minor errors in pressure to operate etc... but overall it has proven success and simple pressure errors are easy to correct without changing the design. Turning this into an updraft may present its own significant challenges which I will elaborate on later ........ and maybe someone will elaborate here on their experience  as well, so you can get the best insight from several sources.

OK having said that, Yes, I meant more precise control .... and is it related to more efficient combustion the answer is generally yes but the reasons are more complex than just the burner is better, instead often the control of the draft is more manageable which has a large effect on the efficiency of the burner, but more later if we have room.

On 7/7/2021 at 11:27 AM, Gusf said:

Yes, is my thinking correct that I should be able to start with only one (1) burner?

Yes, these small kilns have a habit of heating too quickly so often folks candle or just heat overnight with just pilots to dry out anything still with wet glaze and slowly heat to several hundred degrees. One burner would likely be more than enough to heat nice and slowly and if you go the low pressure route you will be able to lower the output much more precisely than the medium pressure. I am compelled to warn, the downside to not having a pilot is it needs to be fully supervised so heating slowly with burners on very low flame presents risk if not fully supervised. As the author noted his pilot design was not entirely successful which is due in part to the lack of a pilot style burner. Premade and approved pilot safety configurations are in my opinion worth even more than just being able to candle, but it is a nice side benefit. OK enough on that assuming you are going to build this and fully supervise each firing.

Baso makes a nice easy safety system solution for these by the way - how about that for cool! I believe these can be piped horizontally along with the individual shutoff to save space. Now pilot protection and the ability to isolate without trapping gas! 

image.png.c3a15fcac357169ae224c297a69ab630.png

 

On 7/7/2021 at 11:27 AM, Gusf said:

How do I know I will not exceed this? On the Axner website: https://www.axner.com/mr-750venturiburner.aspx for the burner it says that "The BTU values listed above can be increased with increases in pressure, however this burner may be subject to less efficiencies at pressures greater than 10 psi.  The BTU they have listed at 10psi is 171,910 but It is rated at 77,400 BTUs operating on propane at 11" WC. Confused still. 

The published range for this burner is 17,000 BTUH to 78,440 BTUH which if we look at the chart puts it in the 3" - 2PSI (55.44 inches). This is consistent as generally traditional low pressure burners operate in the 20,000 - 40,000 BTUH range.   At the low end its reasonable to assume that the 3 inch pressure provides enough velocity to effectively entrain primary air to be reasonably mixed and efficient. Below 3" its performance likely falls off and as it approaches the published maximum it likely falls off as well so likely designed to operate best in the  3 inch to 11 inch range which is consistent with many low pressure burners. The data from Gaco on these burners is conflicting and their published output is deceiving as the natural gas at 7 inches probably has a #28 orifice and the LP has the #50 but - they are decent popular burners and ........ working backwards from a standard electric kiln equivalent btu, we would expect to need maybe 50,000 - 60,000 Btuh which puts these in the low pressure range for a downdraft configuration and in the typical published operating range of these burners.  Additionally the authors published operating pressures are between 0 and 2 PSI with difficulties in draft, speed, tapping the gauge etc.... so in my opinion I feel we have reasonably verified the proper sizing using low pressure.

 

On 7/7/2021 at 11:27 AM, Gusf said:

Just to be sure, what regulator do you recommend for my setup?

Easiest answer here is if you can do so buy a high and low pressure. The high mounted on the tank and the low mounted near the burners. This allows you the freedom to not worry a whole bunch about pipe sizing although regardless my suggestion would be 3/8" or better flexible as short as reasonable. Its customary not to exceed six feet. 100,000 Btuh plus  low pressure regulators generally come with 3/8" connectors for a reason so a single - two stage regulator - 3/8" minimum. For the two regulator setup 10' probably gets you 300,000 Plus btuh with 3/8".  Common would be tank regulator reduces tank pressure to 10 PSI and Low reduces it frem 10 PSI to 11" WC.

 

On 7/7/2021 at 11:27 AM, Gusf said:

The galvanized steel pipe, connectors and everything, the person selling me the kiln recommends is 1/2''. Is this acceptable?

Do you recommend  a ball valve or a needle valve to control flow while firing as per my particular setup?

1/2" seems more than fine, plenty of capacity especially parallel.  Ball valves at 11" act pretty smoothly so many gas kilns no longer use needle valves.

 

On 7/7/2021 at 11:27 AM, Gusf said:

Does the regulator need a gauge also in case I need to UP the pressure?

and then the what gauge? 

If the first stage regulator output is 10 PSi then you could get a suitable gauge. Although by the time this reaches less than 10 PSI your tank is probably near empty. A gauge on the high pressure side could read as high as 350 PSI so usually not an economical or practical add.  More economical and somewhat practical might be the LP fill gauges that mount on the tank just to give you an idea of remaing LP. They are very temperature dependent though and not the greatest in accuracy but before the start of a firing they would give you an idea of how much you have in the tank and as the tank cools during use you can estimate as well. This might be more productive than a high pressure gauge and these are very inexpensive on Amazon

 142414395_Screenshot2021-07-07223207.jpg.c243ac91e3f435c0fb02a028e50bae1a.jpg

On 7/7/2021 at 11:27 AM, Gusf said:

 I have change the plan a bit because of economy for the additional outside insulation, to wrap the outside of IFB 2.5'' - 3'' with a roll of KAOWOOL and then put the stainless steel jacket on the outside,

This idea seems fine to me - not sure why any rigidiser would be needed as long as you can retain it and not compress it too much.

I should stop now as this is getting very long - and it is just my opinion so hopefully others will weigh in. If you find this helps DM me with any additional questions.

 

Edited by Bill Kielb
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