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Resonant circuit

Posted by frustrated 
Resonant circuit
October 02, 2018 11:25AM
This is just because I like to toss a weird one out there, every so often....

I was trying to figure out a way to accurately gauge water level in a monotube boiler and the following idea popped up. I almost instantly tossed it out but figured "what the hey".

Suppose we position a straight leg of tube inside of a pair of electrical coils positioned a ways along the tube. One coil is hooked to an oscillator and the other to a detector. The oscillator sets up a magnetic field in the coil which causes the tube to vibrate and the other coil detects the vibration. As the water level rises, the amount of vibration should diminish due to the dampening effect of the increased water mass....

An alternative method would be the two coils closely spaced together and there is a feedback loop tossed into a circuit designed to drive the tube to a resonant frequency. The frequency should vary depending on the amount of water in the tube....

Told ya it's weird.

Re: Resonant circuit
October 02, 2018 10:26PM
Resonant frequency will vary with temperature.
The electric coils would need to survive high temperature.

Seems to me it would be easier to use a weigh scale.
Re: Resonant circuit
October 03, 2018 11:38AM

I say oscillate the whole boiler for the purpose of “shaking loose” any steam bubbles that might be clinging to the inside surfaces to get a better heat exchange. My poorly balanced gas-to-steam converted engine kinda does this on the go kart anywaysmiling smiley. I agree with Scott that the temps would be an issue with what you suggest....perhaps a computerized controller that factors in temperature readings to keep the frequency at a set rate, and/or compensate for it at the receiver end? Personally, I prefer an old school approach, mechanical solution for water level control. To quote Art Gardiner from the last SACA bulletin “I am a mechanical engineer, thus I do not believe in electrons”. Weighing would work great in a stationary system...but in a moving vehicle I believe it might be difficult to get an accurate reading, considering the impact of g forces and all.

I am currently working on an auxiliary engine (weed-wacker bash valve) driven feed pump that gets it’s steam feed from a strategic point in the monotube tubing or drum that once water reaches that point in the circuit...it floods the engine (hydro-locks) and stops the pumping. It has a spring return that slowly bleeds the water out of the cylinder past the piston rings (or separate orifice) until the bash valve is lifted again and it resumes pumping. The engine and pump are already fabricated and working separately, just need to couple them together and test with the boiler. I will create a separate post on this project in the near future....unless it is an utter failure, then this will probably be the last you will hear about it.

Re: Resonant circuit
October 04, 2018 06:13PM
Actually Ken,
You are on to something. And Jamison just put the icing on the cake.

Observing Bill's go-cart, I believe his mono-tube gets good stimulation from the vibration being right on top of the IC converted, bump valve engine. This stimulation, my opinion again, is significant to his operation. This vibration is the input. Measure input and output at the coil and feedback into the relief regulator or by-pass, what ever your preference. Sort of kills two birds with one stone.

I hope this thread doesn't show up on one of those S@x Toy Sites winking smiley

Any way...good thoughts.

Kind regards,
Re: Resonant circuit
October 04, 2018 09:32PM
Hi Rick,

My idea was to make the coils such that they and the tubing would not be in physical contact. This would reduce heat transfer. Actually, it's pretty much necessary if you are trying to induce motion and then measure the motion … think of a coil mike and a speaker. If necessary, cooling could be applied to the coils. There's probably better ways to do this but I was looking for an electrical signal that wasn't produced by conduction. On the other hand, I have a purely mechanical method that might be more capable overall.

Re: Resonant circuit
October 05, 2018 08:50AM
There are many ways to do this electrically. Capacitive coupling and inductive coupling. Also common in industry is ultrasonic sensing of fluid and flow in tubing. Capacitive sensing is easy in theory but it suffers from drift that will require more complicated programming to compensate for.

It gets harder when you aren't looking for a solid water level. Capacitive sensing can tell you if there's a mix of water and steam far better than resistive sensing. Ultrasonic would be the best, but that's going to be hard due to the temperatures. You might try sending an ultrasonic pulse into the coil through a long rod to keep the heat away and analyzing the return echoes.

I would start with setting up a capacitance sensing circuit hooked up to a spark plug style probe. If you experiment with that you may be able to get it to detect the amount of water vs steam in a spot. Arduino has a library for capacitive sensing.
Re: Resonant circuit
November 15, 2018 10:20AM
I experimented some years ago, but didn't actually make it. (ended up using modified spark plugs) Just an idea I had. A neodymium magnet inside a stainless tube. The stainless is low enough in magnetic conductivity that some of the flux makes it to the outside which can be picked up by sensor. It was enough to carry a steel wire ring up the pipe. Mount magnet in a float that will slide inside the pipe and read water level from outside. But the problem is that magnets loose their force if too hot, so a high temperature magnet would be necessary, if one can be found that will retain sufficient flux at the required temperature. There might be issues to work out with it, like steam flow passing the float trying to lift it. Not a problem where it's a side pipe not passing steam.
Re: Resonant circuit
November 15, 2018 12:59PM

I have experimented with using permanent magnets inside a nonferrous tube to externally actuate a switch or valve for water level control. It worked great...with everything at atmospheric pressure. The biggest hurdle I came across, besides the temperature issue, is getting a magnet to float in boiler pressure. A typical float will have atmospheric pressure on the inside and would quickly implode at boiler pressures. Anything strong enough to handle the pressure would usually be too heavy to float. Ken Helmick suggested using a counter balance, but in a moving vehicle it would be problematic. I’m sure there is a way to pull it off...but I gave up trying. Using spark plugs or water level probes is easy and reliable enough to do the same thing. Personally, I like the challenge of not using any electrical systems at all....everything 100% mechanical. I recently experimented with using a 3/4” copper tube, capped at both ends, inside a 1” seamless stainless steel pipe that would internally open and close a valve based on water level. The problem with that was the aforementioned buoyancy issue. Even the thin walled 3/4” copper tubing that I used (1’ long) sinks like an anchor in water. Perhaps using a standard copper float with a small amount of water sealed inside could work....the water would turn to steam at boiler temps and would be an internal counter force to the boiler pressure.

Re: Resonant circuit
November 15, 2018 05:10PM
I used a commercial water level control on my 35 foot boat. It was part of the water column.
In the water column was a stainless steel float with a 3/16 SS rod up into a SS nipple. On top of the rod was a ferrous ring. Outside the stainless nipple and mounted to it was a set of magnet switches that would pull into the side of the nipple as the ferrous disk inside the nipple would alien with the switch. I had booth high and low water level control that actuated a solenoid valve for the feed water bypass to the boiler. It worked perfect all the time I had the boat.
Re: Resonant circuit
December 12, 2018 11:19AM
Just to add another option to think about. I would try one of the heat sensor's that require no physical contact but just uses an infrared receiver. A few of these placed correctly could be used to find a temperature gradient. From that you could get a closer idea of where the actual water is. Constant readings could be averaged to take into account vibration. Not a KISS design (Keep it Simple ****) but just my 2 cents .
Re: Resonant circuit
December 13, 2018 04:29PM
I decided I’m going to use the Stanley “water automatic” principal for water level control. It’s a relatively simple device that uses a brass pipe in which one end is connected to a valve actuator and the other end is fixed. It Is installed horizontally on the outside of the boiler, connected to the drum (at both ends) at the height of the desired water level. It uses the expansion of the brass pipe to close a valve when the water level is low and the pipe is subjected to the higher temperature steam. This is a simple, proven and relatively easy to fabricate device. The original Stanley design used the valve to close a bypass from the feed water pump outlet going to the water tank. I plan on using it to automate my one valve, one pump recirculating system on the go kart.


Here is a picture of the Stanley version and the 12” long, 3/8” NPT schedule 80 brass pipe nipple I’m going to use for my version:

Edited 1 time(s). Last edit at 12/14/2018 10:47AM by Arch-Tone.

Re: Resonant circuit
December 14, 2018 10:57AM
.....I also found this little liquid level switch that is rated for 300 PSI and 200 deg C (392 deg F), if I decide to go electric. It’s made out of stainless steel and uses a 1/8” NPT mounting / wire conduit.


Re: Resonant circuit
December 14, 2018 01:44PM
Hi Jamison. One old time trick for a hollow boiler float was to seal some water in the float. The water would vaporize and, since the float is at saturation temperature, the internal and external pressures balance.
Re: Resonant circuit
December 14, 2018 01:59PM
I keep reading about the pressure difference between internal and external of a float; what difference would it make to bouyancy? A spherical shaped surface can withstand enormous surface pressure when equally applied. Which law of physics am I ignoring? smiling smiley

Re: Resonant circuit
December 14, 2018 05:34PM
Haaaaa smiling smiley about the physic's talk about specific gravity

I don't use a float level with my design, I have been doing some experimenting with my feedpump lately, and have been posting on another site (yes I own it) .

By this Wednesday I will get my master links and 1 additional sprocket, Im making adjustments to engine driven feed pump gear ratio.

since the float is at saturation temperature, the internal and external pressures balance.

This prevents the float from being crushed, the more interesting question is will the air in the float counter act the same as steam at 212f

My uncle did some stuff with hot air balloons, we were talking about a helium in a large balloon, I said well a tank of helium wont float in the air like that...

Edited 3 time(s). Last edit at 12/14/2018 06:46PM by Jeremy Holmes.
Re: Resonant circuit
December 14, 2018 08:33PM
Hi Jeremy,

If the float has no water in it, the air won't counter the boiler pressure since steam volume rises something like, I dunno, 1400 times when it vaporizes …. air doesn't expand anything like the same amount for the same temperature rise. With water in the float, the air WILL expand a bit and contribute to pressure rise, but this just means that less water can evaporate because saturation temperature is unchanged. Your big problem is not having enough water in the float so that it is all vaporized before reaching saturation pressure....but given that expansion ratio we'd be talking about only adding a miniscule amount of water. As I think about it, you'd probably want to do some math and add just a tiny bit more water than is needed to maintain equilibrium at peak pressure. The lower the water mass, the quicker its temperature matches that outside the float.

Re: Resonant circuit
December 14, 2018 08:44PM
I'm going to deffer to this quote
A spherical shaped surface can withstand enormous surface pressure when equally applied

Yes water does expand 1600 to 1. As a flash steamer I know that by heart. But there are some problems,

check this link [flashsteam.com]

Looking for some honest criticism

Edited 1 time(s). Last edit at 12/14/2018 09:05PM by Jeremy Holmes.
Re: Resonant circuit
December 14, 2018 10:27PM
I'm probably just heading further down the road of confusion, but I'm not understanding why there has to be equal pressure. Coarse analogy, but let's look at the submarine, it's internal pressure is obviously not equal to external pressure, or it's design would be futile, they are safe because the interior is kept at atmospheric, made possible by the design shape of the vessel. A properly constructed spherical or other capable shape can withstand thousands of pounds of force. Another place to look is the boiler tube, much stronger in compression of force equally applied, although one could be collapsed easily with a pair of pliers. .


Edited 1 time(s). Last edit at 12/14/2018 10:35PM by IronChief.
Re: Resonant circuit
December 14, 2018 10:32PM
Wow I have been archiving the forum and have found some pretty neat stuff

Re: Resonant circuit
December 14, 2018 10:35PM
Hi Jamison,

I'd go with the expansion tube setup. Remember that the "thermal expansion" is "differential expansion", of course. With a Stanley expansion-tube 'Feedwater Automatic", the brass expansion tube's expansion/lengthening with heat due to water level drop is _relative_ to the temp of the 2 steel rods on either side of the tube. The 2 steel "reference rods" run at a general under-hood temp of about 150F, while the brass expansion tube between them can go up to saturated steam temp when boiler water level drops and saturated steam from boiler fills them. Check your steam tables book/website for your pressure/temp, but the old standard book, Keenan and Keyes, gives 467F at 500 psia.

So if the boiler water level dropped entirely below the expansion-tube level in a system with a Stanley-style "Feedwater Automatic", then the expansion tube would fill with 500psi steam at 500 psig, and the expansion tube would expand/lengthen a lot more than the 150F "reference rods". flanking it. That difference in expansion is what drives the control mechanism. In Abner Doble's boiler control system, a steel tube's expansion/contraction was compared to quartz rods inside the tube, which had nearly-zero thermal expansion.

i suspect that the ultimate steam car propulsion system would use a copper or brass tube, with the very highest thermal expansion, "referencing" against quartz or Pyrex/borosilicate rods of the very lowest thermal expansion.

Thermal expansion of metal figures are easily located on the Internet, and in the old engineering books. The math is not difficult. If you hit a wall, e-mail or PM me. ashenfern@webtv.net

Re: Resonant circuit
December 14, 2018 10:48PM

I agree that was a good design, simple, no electricity, no high volume of moving parts. I liken it to the veritable old thermostat used by virtually every engine manufacturer, simple, cheap, effective and reliable.

I calculated it once, the thermal expansion of brass over the length of that tube by temperature difference, and there isn't a lot of movement to work with, so the valve must be precise. Ofeldt had a nice design for this also, I think it had a cam at the point of actuation that multiplied motion..


Re: Resonant circuit
December 14, 2018 10:59PM
I remember Jim Crank mentioned a quartz rod in place of the brass rod.

I have the flyer from the 2017 summer meet, about double history, Jim's Book. We should all be reading that right now. I not about to unfold my tent to get the flyer. But hows that going? I would pay 350 dollars for it.
Re: Resonant circuit
December 15, 2018 12:35AM
Hi Ron and Jeremy,

Oh yeah, I did the numbers on that and figured something like 1/16th inch relative expansion/travel for an 18" brass tube between 500psi boiler and 150F steel reference rods flanking it. Somebody will probably now run the numbers and say, no, not 0.0625", actually 0.06245", you're totally wrong Peter, we're going to ignore everything you say from now on because of that gross error, obviously you have no idea what you're talking about.

Anyway, the small motion was compensated for by building the Feedwater Automatic with very fine adjustment. And by all reports, once properly adjusted, it runs fine for many years, even decades.

Thanks for posting the Ofeldt Feed-Water Automatic drawing, Ron. This worked as well as the Stanley device, but with a very short expansion tube and a step-up leverage to convert the shorter expansion/travel into longer valve travel. The only issue there is wear/play in the step-up mechanism, but it is do-able. Maybe needs more adjustment over time for that wear.

Which gives me the opportunity to mention an article I saw 10-15 years ago in the British steam car magazine about an Ofeldt-like feedwater controller which the author of the article [speak up if you are reading this] built and tested. He was surprised to find that the controller closed the feedwater bypass valve in something like one second, or less, after the boiler level dropped below the level of the expansion tube. He had been expecting it to take a very long time, based on comments he had read about these kinds of controllers only being suitable for cars with huge boilers with large steam/water reserves. Instead it ended up giving "almost instant' response time.

I mentioned that on this or some other Forum many years ago, and got replies from a number of Stanley drivers about how amazingly fast their noisy pumps would "sound off" [meaning, water being fed] after some quick tiny change in boiler water level. They had no illusions about their Stanleys' Feedwater Automatic controllers being slow to respond.

It's just a good, simple feed-water controller for water-level boilers.

Anybody prejudiced against such a feedwater controller on the grounds that the Stanley brothers used it, and that everything the Brothers used was outdated worthless junk, therefore this too must have been junk ["guilt by association"?], should perhaps consider that the Stanley Brothers did not invent or originate the expansion-tube boiler feedwater control. I have seen patent papers and advertisements for a number of nearly identical devices dated many years before it was made a standard feature on Stanley cars. It was very standard and widely-used tech long before the illustrious/accomplished and [therefore?] sometimes controversial FE & FO adopted it.

As a flagrantly off-topic aside, I have just worked out all the basics of the remote-operated cable-op ball valves for my steam car. When I get it built and operational, I will post blueprints. Many possible uses throughout the control system of a modernized/automated steam car. Next comes vast amounts of tedious/dreary blueprinting. Cue "The Volga Boatmen".



Edited 3 time(s). Last edit at 12/15/2018 06:21AM by Peter Brow.
Re: Resonant circuit
December 15, 2018 01:08AM
OK, that version, with Kharitonov & the Red Army Choir, ended up sounding a bit glorious, in a Soviet kind of way. Then again, my dreary/tedious design work might some day end up contributing to the glory of the American Homeland. The USSA automotive equivalent of Mr. Kalashnikov's famously durable rifle ["throw a handful of sand into the receiver and it still works fine"] would not be a bad thing. Kind of a Stanley Brothers/Henry Ford approach; as simple as possible, yet reliable under the worst conditions.

Edited 2 time(s). Last edit at 12/17/2018 01:27AM by Peter Brow.
Re: Resonant circuit
December 15, 2018 01:26AM
Right on Jeremy; where is Jim Crank's long-awaited Doble book at, anyway?

I offer my sincere very best wishes to everyone working to make this book available to everyone interested. There is great interest in this book among the light-steam/steam car community.

To quote Larry The Cable Guy, "git 'er done!" smiling smiley


Edited 5 time(s). Last edit at 12/21/2018 05:45AM by Peter Brow.
Re: Resonant circuit
December 15, 2018 08:49AM
Quote: "I did the numbers on that and figured something like 1/16th inch relative expansion/travel for an 18" brass tube between 500psi boiler and 150F steel reference rods flanking it. Somebody will probably now run the numbers and say, no, not 0.0625", actually 0.06245", you're totally wrong Peter, we're going to ignore everything you say from now on because of that gross error, obviously you have no idea what you're talking about."

The difference is only the temperature of the water vs steam temperature and it is not a great deal to work with. I think what is probably happening here to a larger extent is that when boiler water is present in the tube, the temperature is close to constant, however when steam is present it condenses quickly due to the ambient air over the tube, it's not so much the steam temperature, but the steams inability to maintain constant temperature due to rapid condensation - temperature drop - contraction of the tube length.

Re: Resonant circuit
December 15, 2018 11:09AM
Hi Ron,

You want to equalize pressure so that the float isn't squashed like a grape.

Re: Resonant circuit
December 15, 2018 05:28PM

Thanks, I was sort of confused about what you folks were suggesting.

Getting back to the Stanley and Ofeldt thermal tube controls. Keep something in mind while designing, a dead ended steam line can be at ambient regardless of the boiler temperature. I found this out on the Tugboat, I put this nice old 12" Crosby steam gauge on the back wall of the wheelhouse, piping it up the warnings came in about making sure the gauge was "fitted with a siphon", a loop of pipe below the gauge to isolate the sensitive bourdon tube within from boiler temperature - it was not needed. That line although piped directly to the boiler stays ice cold. At somewhere along that line headed to the gauge, the steam is fully condensed.


Re: Resonant circuit
December 15, 2018 06:58PM
Scott F I was mentioning to archive posts and I have no luck with the current search feature... I there any way you can add a Mod to google search the site, I did this on my forum fieldlines.com and it really works great.
Re: Resonant circuit
December 15, 2018 07:14PM
The story on the book is complicated... suffice it to say that Jim Anderson is paying to get it printed and he now owns all of Jim Crank's research material, which is available for study at Tom Kimmel's shop. I just received a draft printing of a section of the book, it looks excellent,so I have to believe it is coming. I know Jim A would love to have had it printed quite a bit of time ago, the problem is with the editor.

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