Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length.

[Xtian29]

I have been looking for some way of having a mechanically driven water pump that is adjustable for flow, so I can use your control system but not have the need for powerful batteries.

I have just seen a pump in the book by K N Harris .... "Model stationary and marine steam engines" "second edition" fitted to a paddlewheel engine that may just fit the bill. It is on page 73, and further detailed on page 76. It could have it's stroke controlled via a servo.

http://www.fastonline.org/CD3WD_40/JF/424/19-423.pdf

It has a tiny air accumulator in the system to take out the hydraulic pulses that may exist in such things and it seems very compact, but my main interest is in the fact that I could prime the system mechanically or electrically,get the engine working and then switch over to  the engine driven pump.

[flashtwo]

Hi,


No news on the publication date as yet.

My software is designed for a flow from a mechanical pump if I ever fit one. The engine speed would be used to calculated the feed from the mechanical pump and, as the mechanical pump's output increased, the electric pump would slow down or even stop automatically and vice-versa.

I still think an electric pump is very useful for starting and also caters for when the engine is required to accelerate and decelerate or even stop mid-lake under radio control. I suppose if your boat is manned you will be able to have additional controls like pump bypass.

Whats a micro-Oldham?

The motor bearing failure was actually at the non-drive end near the commutator. The pump has a ball-bearing block that absorbs all the trans-axial force of the ram so that the motor and its gearbox are just affected by the rotative forces. If you go back to the original post of this thread, you will see photos of the pumps.

Regarding matching the pump size to the engine size can be a bit of an experiment. I did note that the effective flow of my pumps under pressure, was about 86% of that expected from the calculations suppossibly caused by the valves not seating immediately and passing. Based on my experience, I'm getting 500RPM at 20psi with the D10 with a flow of about 75cc/min (using the 86% correction mentioned above) - this could be a good starting point.

Currently I don't require both pumps to run to achieve the 500RPM objective. If the pump battery is low in volts and the main pump can't maintain the flow, the second pump will come in automatically to compensate, but this is only if I've forgotten to charge the batteries.

On an earlier software version the computer actually logged the total number of strokes per pump per run and per season, with the intention of some "preventive" maintainance in replacing the ram "o"-ring and ball valves and, like you suggest, running the pumps evenly - this was getting a bit daft I thought. From an industry point of view though, one thing you don't want is your standby bit of plant to wear out the same time as the main plant. I've known some instances when some plant has only logged 20% running time and then had an overhaul, principly because you haven't the resources to overhaul every item at the same time. Different for aircraft I suppose!

Regarding the pipes being used. The flared pipes would be easier than using the pipe nipples and silver soldering them on. Beware that even this small pump of mine can deliver 300psi or more!


The drawings that I have done myself won't scan very well since the lines are very fine.

I have however produced a set of typed sequential instructions that I use in the workshop, since I have built a number of the pumps for experimenting with. I'm afraid the measurements are in metric and imperial, since the metal stock is in imperial and the workshop lathe and milling machine are in metric. The instructions are three pages long and may be more suitable as a personal message than in the open forum.

With this type of pump it is very easy to get air trapped inside so causing the pump to fail. To get around this problem stainless steel blanks are fitted just above the ball valves to take up the volume that the air would have used. The blanks can also be machined to limit the lift of the ball valves. The ball valves make a seal directly with the brass body without the need of "o"-rings.

The batteries are oversized for the job they do. I could use much smaller ones for a days steaming, but the larger batteries are also used as ballast.

Ian

[Xtian29]

Hi Ian,

The drive couplings you have on your pumps are called "Oldham" couplings, unless I am mistaken, and you have made rather small and neat ones compared to the ones I can see are commercially available at RS. hence "micro Oldham"

I would gladly receive sequential instructions in a PM  It keeps me away from the telly....

[Xtian29]

I was wondering if there is any update on the magazine article?

At the moment, I am tarting about with the peristaltic pumps I have designed and built for my brewery, and their performance leads me to wonder if they could be used as boiler feed pumps?

The tube I use in my brewery pumps is 15mm ID 3 mm wall soft silicone, and it would be a good idea to test what sort of pressures can be developed if the tube size is drastically reduced to say 1 or 2 mm ID, using the stuff that is used as model aircraft fuel line. The limit will be the burst pressure of the tube....

 I would not be at all surprised if the pressure these simple pumps can produce is quite high, and given that there are no pistons to lubricate, or valves to get blocked, and they are self priming, it may be worth investigating, but if they were indeed a viable option , surely someone would have done it by now!! Has anyone seen mention anywhere of such tests?

While building the brewery and making beer remains the highest priority, I will try to do some testing on a little pump sometime soon to see what pressure they will pump to!

Rog.

[Xtian29]

It seems the magazine article will be in the February edition of engineering in miniature magazine. The Jan edition is out now, so start looking in a few weeks.

[derekwarner_decoy]

This will be interesting Silverbrewer & it is good to see you have your priorities sorted  

I tinkered with a minature peristaltic pumps 20 years ago....the burst pressure of the DUBRO silicone hose was never an issue....BUT keeing the tube attached to the pump ferrules was......

Even with DUBRO hose clamps........@ 15>20 PSI the slippery silicone tubing displaced it self off the ferrule....attempeted brass ferrules with sharper serations & they simply cut the tube ....

Keep us posted as the concept is great .....Derek

[Xtian29]

It looks like the magazine article will be in the February edition of Engineering in miniature. The Jan. edition is out now, so mid Jan I suppose before it hits the shelves. I've ordered mine!!

[flashtwo]

Hi,

"Vital Byte" and "Vital Thrust" will be exhibited at the annual London Model Engineering Exhibtion 20th to the 22nd January, Ally Pally. They will be on Stand S, "A Team Boatyard" alongside the 14ft HMS Daring and other large "items".

Looking forward to having a good old chin-wag.

Ian.

[flashtwo]

Hi Mayhemers,

I've been investigating a problem that developed towards the end of September last year, but didn't have time to sort out.

Under hard steaming conditions with the gas valve fully open, Vital Byte was issuing flames from the top of the stack and the performance was deteriorating.

It was obvious that there was not enough combustion air to burn off all the fuel in within the boiler and I found that the stainless steel mesh scroll (see 2nd June 2011 posting) had developed deposits caused by combustion within its structure. Blowing through the mesh indicated a lot of flow resistance. I've replaced the scoll with a single layer mesh fixed across the top of the burner "bowl" and the combustion has much improved and you don't get that incomplete combustion smell either.

Today, I've been running under cold conditions of 5degC ambient and, despite using liquid fuel from the gas cylinder, found the performance was not up to scratch. With a 5degC cold full gas cylinder I found the gas pressure was at 2bar, but heating a full cylinder in warm water at 25degC the gas pressure went up to 4 bar and the performance was much better. Because the gas cylinder is inverted, the gas doesn't evaporate in the cylinder and hence the cylinder maintains its warmth much longer.

Roll on summer!

Ian.

[ooyah/2]

Ian,
I experienced the same problem early on in my flash steam project.
I wanted to burn L.P.G  originally so I set up a roaring type burner and a copper gas tank with the burner firing into an A.A. Rayman design boiler.
The burner had a .025" jet and brass vaporiser coil on the end.
Before setting it up with the boiler I tested it just as a burner on the bench, heated the coil with a plumbers blow lamp, as I was burning liquid, coil getting a bit red, opened the liquid valve and away the burner went.
Great I thought it's burning well, after a few minutes all hell broke loose as the liquid came shooting out of the burner like a flame thrower and set the inside of the garage door on fire, quickly shut down the valve and  it was fortunate that it was a flash fire so no damage done, C.O. 2 extinguisher now installed at bench.

When installed in the test boiler it worked well but was inclined to flame and then would go into the cycle of cooling and losing pressure due to the size of the jet and the amount of liquid being drawn from the tank, heating the tank with a gentle application of the plumbers blow lamp increased the flame strength.
The burner seamed to work better when firing into the boiler space, possibly get more air sucked in, with the occasional flame out from the boiler exhaust.

Eventually I deduced that to get the power from the L.P.G. I would need a massive tank to supply the burner and stop it freezing, went on to paraffin.

Where does all this lead to your problem.
The out side temp of the tank is one, looking at your burner , is the tube too thick to allow it to glow hot and vaporize the liquid?
I found that the outside shell works better at .025" thk.

Do you still have so much tubing in your coil which could be preventing combustion ?
I found that the more space around the coil and the coils spaced about 1/4" apart was about correct, but then my aim was for power that your coil can't produce.

No doubt you will solve the problem when it gets a bit warmer.

Here is a pic of the experimental burner and A.A.Rayman boiler, burner is now fired by pressurized paraffin, this was an early experiment before my final  
triple burner.

Hope this helps.

[flashtwo]

Hi Mayhemers,

I know one shouldn't advertise, but "Vital Byte" has left me a personal message (something about a certain magazine article I assume):-

Ian

[flashtwo]

Hi Mayhemers,

I’ve investigated the reduced performance a bit more and have noted that, with the gas control valve fully open, the burner noise was much less than expected and the outlet pipe from the gas control valve was frosting up badly. This indicated a partial blockage in the gas valve causing a throttling effect which made the assembly act like a refrigerator.

Sure enough, on dismantling the valve it was blocked. I cleaned it out and normal service was resumed.

At the London Model Engineering Exhibition last weekend, where “Vital Byte” was on display, I discussed this problem with a couple of visitors. One chap had had a similar problem with his gas fired steam loco and found that a waxy substance from the gas cylinder had caused the blockage. He had fitted a “coffee paper” filter (the cigarette filter he tried caused problems with its fibres)  and this stopped the valves blocking. With the gas cylinder inverted perhaps this encourages deposits to be expelled from the cylinder.

Another good tip from the same guy (16mm gauge loco enthusiast) was regarding the burner mesh. He is using a nichrome mesh instead of stainless, since it degrades far less with the heat. He makes his own mesh from wire using a pin board.

Another visitor had built his own manned steam canoe incorporating a monotube boiler. He thought my system was a bit complicated, but I did remind him that I wasn’t onboard to adjust things unlike himself.

Anyway, there was lots of interest in “Vital Byte” with very much welcomed advice from visitors and other exhibitors alike.

My favourite exhibit was Jack Snary’s (and expert grandson) “Royal Spithead Review” with it hundreds of miniature ships detailing naval history from Ancient Egyptian times up to the present.

For the next part of the project, I will be rebuilding the timing linkages on the D10 engine, since they are very worn and sloppy.

Ian

[TurboTyne]

Hi Ian

I've just read your excellent article in EiM. I think it is very interesting and I look forward to the next part. The trouble you take to explain the principles of computerised control to the wider audience reminds me how much I have learnt since I last pestered you with questions - which was over a year ago now. Before I saw your blog about Vital Byte I had not heard of PIC devices at all. Your advice was not wasted because, since then I've learnt a lot about PIC programming. So far I have constructed a gas burner and a needle-type gas valve operated by a stepper motor which is controlled by a PIC. This PIC receives instructions from the master temperature monitoring PIC via the I2C bus. The latter master PIC also sends data to a display PIC and to a serial EEPROM which can be removed and (I hope) have it's data read into a PC via a cheap USB-I2C interface that I've bought. So I am getting near to having a temperature controlled gas valve - but a lot more work will be needed before I know if all this effort will give a workable boiler control system.  It's been great fun learning all this - thankyou for showing me the light.

Regards,  Mike

[flashtwo]

Hi Mike,

I think its great that you've made such progress - I shall be asking for your advice very soon, especially about I2C.

How do the stepper motors compare with the ordinary radio control servos - do you have to set a mechanical starting point of reference, or have they developed since I last used them many years ago?

Have you used anything like picAXE boards?

Will you be using your burner with a conventional boiler or a monotube?

Thanks you your EiM comment - any feedback will be appreicated.

Ian.

[TurboTyne]

Hi Ian

Always happy to chat but I doubt I could add much to your knowledge.
I have never used (or even seen) a radio control servo. My lack of familiarity with them is one reason I chose to go down the route I have. My hobby activities have been in model engineering etc and I felt inclined to have a go at making a valve from scratch. Also, I've long wanted to have a go at trying to use a stepper motor - for something or other, mainly so I'd properly understand how they function. This was undoubtedly not the most efficient way forward to make a boiler control system and for that I should have followed more closely what you have done with servos etc. My efforts have taken much time and the valve is not exactly compact. The stepper (taken from an old ink-jet printer) does, as you say, lack any points of reference. I've attached a couple of photos which show the arrangement  I came up with. Movement is by a screw which drives a block attached to a lever. The 40 tpi thread and the 5:1 lever combine to give a very fine adjustment of the valve rod such that about 10 turns, each with 48 steps, are needed to fully open the valve. The limits to movement of the screw-block are by the optical sensors - the black blocks with a central slot. As I'm sure you recognise, the thin metal sheet attached to the screw-block goes into the gap in the sensor and blocks the light beam. I am new to all this and was amazed at the accuracy of these particular devices. I estimate the electrical output goes from full on to full off with just 2 or 3 thou movement of the block. Of course the sensors connect to pins on the PIC (16F818). The programme includes a few lines of code which ensure that, when the direction of the motor is reversed, a few extra steps to the movement are inserted so as to take up the slack in the mechanism.

No, I did not use the picAXE items - I just ordered PIC chips from Farnell. Another thing thats amazed me is the amount of free stuff they provide. I use their free MP LAB IDE programme for all my programming in conjunction with a Pickit3 programmer.
 
RE: the boiler. I shall initially be messing about with a monotube boiler coil that I actually wound over 40 years ago - but never used. I had dreams of making a flash-steam hydroplane, but now I am aiming for something more sedate - but definitely monotube.

Mike

[Xtian29]

The second and final part of the article is in the March issue of Engineering in miniature, and is on the shelves now.....Don't miss it!

[flashtwo]

Hi Mike,

Thanks for sharing the gas valve photos. I've just replaced my gas valve servo (£7 type) with a more expensive all metal gear and spline type (£!), because the plastic spline of the original servo was getting chewed up with the clamping grub screws.

I used to set the closed position mechanically by loosening the grub screws and rotating the gas valve shaft. Now I can set it accurately by setting  values on the display screen, which nominally set the fully open position to 1000us (PWM) and fully shut to 2000us. If the gas valve hasn’t fully shut then I can increase the 2000us value to say 2100us and the servo travels a bit more to shut the valve – the controller remembers this position even when powered off.

I’ve been carrying out some pump flow tests today, since I thought the “A” pump wasn’t performing well. I replaced the steam pipe between the boiler outlet manifold and the engine with one containing a flow control valve with the outlet going to a laboratory 500ml measuring cylinder.

I measured the pump flow over a three minute period with and without constrained flow  - the constrained flow made the pump work against a pressure of about 50 to 200kPa (7 to 30psi).

I found that the displayed flows (“A” &”B” pumps) were reading about 7% lower than that recorded by the measuring cylinder. This can be corrected by amending the pump capacity in the controller.

I’ve recently rebuilt the timing linkages of the D10 engine, since the wear on the original quadrants was making accurate timing impossible. New quadrant bronze castings were obtained  from Stuarts. This time I made a jig to fit on the milling machine’s rotary table, which enabled me to mill the quadrants to the exact radius without resorting to tiresome filing. I also found that I had limited the travel of one of the quadrants when I had originally built the engine 4 years ago – I repinned the linkage to the correct position.

I also tightened up the eccentric straps to reduced the slack.

With both the above overhauls completed, the valve timing setting was greatly improved.

With the above sorted out, I gave Vital Byte a run in the test pool with very good results.

From a low last July of 380RPM (max) with flames leaping out of the stack and very hot boiler casing  -  to a performance today of 590 - 620RPM (peaking at 710RPM) with no flames leaping out the stack – in fact I could place my hand over the stack, on the stack and on the casing without it being unduly hot, indicating a very efficient boiler.

The flaming problem, as discussed in earlier posts, was caused by the mesh in the burner bowl corroding up and limiting the airflow into the boiler.

Ian.

[flashtwo]

Hi Mayhemers,

Here’s a series of photographs show the latest development of “Vital Byte”.

The first couple show the jig made for milling the timing quadrants (octants?) more accurately and quicker than by filing. The dimensions ensure that the exact radius is kept around the piece and a 4mm end miller cuts the correct dimensions.

In the other photographs the new compact water filled gas heat exchanger is shown with the reconstructed burner and the vertical boiler.

From the burner photograph you can see that the liquid fuel enters a the union furthest away, does 3 ½ turns around the burner in 1/8th copper pipe and gas exits at the tee-piece where some is tapped off back to the three pilot lights spread around the burner, which also heats the liquid fuel evaporation coils.

Above the burner is some 1.8mm pitch stainless mesh, which is surviving better than the scroll of mesh originally in the burner bowl. The mesh ensures that the flame doesn’t propagate to the nozzle.

In the previous setup, the exit gas pipe lay in an open trough of water to cool the gas before it entered the servo gas valve, which had an “o”-ring seal and a lead soft seat, both of which I didn’t want to overheat.

The gas exiting the gas valve, when heavily throttled, can come out freezing, so that pipe was put through the same trough to warm up before going to the burner nozzle.

The trough had to be filled with water before running the boat, so a replacement design was installed, which was connected to the incoming feed water from the lake. This design would automatically fill when the boat was floated with the vertical silicon tube indicating that it was full.

With this arrangement, the problems of cold weather operation are eliminated with no gas evaporation taking place in the upside-down cylinder and also all the fuel is used from the cylinder. One has to be aware of any fuel residues blocking the gas valve, so I allow a full flow blast of gas through the valve before reshutting the valve, and allowing the gas to disperse before igniting the pilot lights.

Looking forward to Wickers, and special thanks to the Wickstead Model Boat Club and Martin for all their efforts.

Ian.

[flashtwo]

Hi Mayhemers,

Subsequent to the feed pump tests, I've made some additions to the Display menu (see photograph) and software.

I can now update the pumps' capacity in mm^3 to give a more accurate display, and can also swop over which is the Master Pump without having to swop the ESC and shaft pickup connectors on the interface board.

From the menu I can choose whether the "A" or "B" pump will the Master with the other acting as Stand-by.

"Vital Byte" is getting ready for Wickers - hopefully with a fresh coat of paint!

Ian

[essex2visuvesi]

We must all bow down before the almighty B pump!



It is written that it shall be master






Sorry slow afternoon in the office 

[flashtwo]

Well the "Almighty B pump" wasn't to be bowed down to!

The non-return valves needed to be re-seated, since they were letting by (see "simple feed flow indicator" thread).

Over the last year I have had problems with the gas control valve blocking up causing a much reduced performance of the boiler. I had been lead to believe that using the gas cylinders upside down would allow waxy deposits from the cylinder to pass through the system and eventually blocking the valve. Well, I've dismantled the valve several times and poked a fine wire through to open up the valve and, although I couldn't see any waxy deposit, the valve did clear.

After only one or two runs the valve would block again. This time I opened up an empty gas cylinder to find the "fabled" waxy deposit only to discover the inside of the cylinder was totally clean with not a hint of the "wax".

The actual valve seat is made of lead with a small needle size hole. This soft valve seat, I suspected, had been deformed, over time, by the valve plug and being repeatably partially closed again after I had cleared it with a fine wire. This time I drilled out the hole to 1mm dia. and so far the blockage has not re-occurred and the performance is the best for ages. I think the recently fitted high torque servo may have contributed  to this deformation of the seat.

Another reduction in performance was caused by a sliver of silver solder that had travelled down the gas pipe to the nozzle causing throttling and frosting up at the nozzle. If ever you see frosting up it seems to indicate a partial blockage.

The gas cooler arrangement has been changed with the feed flow being drawn through the cooler as the gas was getting too hot at the valve. I think I will have to reduce the length of the evaporator pipe around the burner as it is heating the gas too much.

Ian

[flashtwo]

Hi Mayhemers,

Having solved a few things that were restricting the power output (engine timing and fuel gas obstructions), I've been experimenting with some of the control system settings.

From previous posts and the magazine article, you may know that the steam temperature desired value is offset by the feed demand, i.e. the higher the feed demand the higher the target steam temperature.

Well today I've run the plant with both pumps running at full speed (170cc/min indicated), with a steam temperature at 145degC (controlled!) and achieved a remarkable 720RPM running (not peak) and steam pressure at 300kPa (45psi). You can imagine that, with the 5 inch prop, the water was quite turbulent especially slamming into astern then ahead.

Normally I've been running with a single pump and getting 530 or so RPM with a gas consumption of about 4.5grams/min, which would be more than adequate for the model boat. I think 720RPM would be showing off! Perhaps the boiler is now oversized at 250sq.inches for the engine.

By the way, are there any questions from those who have read the magazine article (its gone rather quiet)?

Ian

[HS93]

the Post has been going on for some time so is there any chance of a run down of what the system now does in the finished state as I think from day one it has changed so much and it would be nice to know what is possable with steam in the modern world, thanks forthe informative Post.

Peter

[flashtwo]

Here is a breakdown of the current situation:-

Engine: Stuart D10 double cylinder, double acting, ¾” bore by ¾” stroke, driving the
             Propshop’s 5 inch prop designed for the D10.

Boiler: Vertical Monotube, 50foot of 3/16 inch copper brake pipe wound in three
             layers.
Boiler dimensions: diameter 108mm, Height 270mm plus 190mm stack.

Electric pumps (2 off): Feed rate 85cc/min each. Filtered Pond water is used.

Fuel: Butane/Propane in liquid form with evaporator on burner.
         The heated gas is attemperated by a cooler fed with incoming feed water.

Burner: Jet 0.7mm dia., mixing tube ¾” dia., 100mm long, Stainless bowl 1¼ “ dia. with 1.2mm pitch mesh to prevent flashback to the jet..

Fuel consumption 4.5g/min at 530RPM.

Currently achieving 720RPM at 170cc/min feed and 45psi, 145degC steam conditions.

The exhaust steam is directed to an oil separator / feed heater (dia.50mm, height 225mm plus 108mm high vent pipe). The oil free water is dumped overboard.

Control system:
PIC based microcontrollers monitoring the feed pumps’ strokes per minute, steam temperature and pressure and the gas cylinder pressure.

The demanded feed flow is set at the radio transmitter and the controller, via ESCs, ensures that the pumps maintain the flow independent of the boiler pressure.

The steam temperature has a manual setting that is amended by the demanded feed flow, such that, as the feed is increased, the desired temperature is raised, which in turn causes an increased firing rate via a servo gas valve, raising more steam and an increase in speed
–   put simply more water in, more steam out and the faster the boat goes.

The controller has a start up mode such that the boiler is warmed up at a optimum rate to the boiling point without over firing and causing excessively high temperatures. Being a monotube boiler, it takes only a few minutes to raise pressure.

There are a few safety features: high temperature shutdown of the gas valve, high pressure shutdown of the gas valve and pumps, pump failure detection and standby pump cut-in. The boat automatically restarts itself if any of the above occurs.

Current problem: the stainless steel burner mesh crumbles away after about 5 hours running and is to be replaced by a ni-chrome mesh once I’ve woven it!

Was it worth it? The initial objective was to build a simple cheap boiler that didn’t require insurance or annual testing. Well the boiler is certainly cheap at £60 (£20 copper brake pipe, £20 toilet brush holder boiler casing, £10 brass stack, £10 sundries) perhaps a tenth of the price of a conventional boiler. Certainly it is very simple to make with only two silver soldered connections, plus one joining the two 25 ft lengths of copper. Not being a pressure vessel it is exempt from the test and insurance requirements.

At the project start, the best method of controlling the monotube boiler was a matter of debate and using a programmable system enabled many ideas to be explored without massive amounts of rebuilding mechanical and/or electronic controls. One thing you don’t have to worry about is the boiler water level!

So we have a boiler that is cheap, quick to start and runs as long as the fuel lasts (100minutes or more).

The controller hardware bits came to about £70 and took around a week to solder together, although it is transferable between models or even a full size boat.

The software is a totally a different kettle of fish, with thousands of lines of code, but, since completed, can be downloaded to the raw controller in minutes.

It took 2 years of experimenting (including pump and boat construction) to arrive at a practical solution with “Vital Byte” having it maiden voyage at Wicksteed in May 2009.

Where to now? I’ve got Selway Fisher plans of a 30ft steam launch and I’m just scaling them for the 5 inch prop; that determines that I build a 75inch launch to install the existing system in.

Now that I’ve broken the back of the problem, it would nice to know that other enthusiasts will take up the challenge and build a similar (perhaps better) monotube boiler system.


Ian

 

[dreadnought72]

Ian, I'm very impressed with the set-up - but could you explain more about this line (maybe it lost something in your post):

There are a few safety features: high temperature shutdown of the gas valve, high pressure shutdown of the gas valve and pumps, pump failure detection and standby pump cut-in. The boat automatically restarts itself if any of the above occurs.

Is that the right thing to do? If a fault is detected, do you want it to restart with the fault not fixed?

Andy

[flashtwo]

Sorry for the confusion Andy,

During development and use, I adjust the response of the control loops so that they respond either sluggishly or lively to changes in feed flow command. If the controls are too lively then, on occasions, the steam temperature can get out of control and the system shuts down to protect the engine. The boat then sits on the pond and waits for things to cool down before it restarts itself and I can bring it back to shore. If it keeps happening, I then "detune" the temperature control loop to ensure only gradual temperature changes.

Actually discussing this has usefully reminded me (and duly entered in the boat's log) to put back the function of setting both pumps to full speed in case the gas valve jams in the open position; I commented it out of the software last week when I was doing some experimenting - a fateful mistake!

It was very amusing, when "Vital Byte" was steaming down at the Dover Model Boat Club's pond and it did shut down due to high temperature. The lads there were very keen to send out their electric tugs on a rescue mission, but I told them that the boat was in "auto-recovery" mode and would return (fingers crossed), which it did to their amazement (and mine!).

The high steam pressure shut down (which has never occurred) is there in case the prop fouls up with debris and stops turning.

I suppose the priority is to return to shore.

Thanks for your compliments and interest.

Ian.

[flashtwo]

Here are couple of photographs showing the crumbling stainless steel burner mesh and the weaving loom for making a ni-chrome mesh.

The weaving loom has two brass guides each with 60x 0.5mm grooves at 1.2mm pitch, mounted in a steel frame. I did consider drilling 120 0.5mm holes in a brass plate, but then thought the better of it.

The warp is wound around the guides. The two "tangs" are for mounting firmly in a vice as the weft is woven through the warp.

Once the ni-chrome is woven, it will be placed on a former and bent into a slightly domed shape in order to slide into the burner cup.

I can see this is going to try my patience!

Ian.

[boneash]

I did consider drilling 120 0.5mm holes in a brass plate, but then thought the better of it.

Oh come on now a milling machine, you have, and a Pic, 3 motors and a CAD package......

or  a xyz package off Ebay.....

[flashtwo]

ouch!

I don't want to wear out the milling machine, you might want to use it one day!

[Mad_Mike]

I dont know much bout steam but would these work?

http://www.ebay.co.uk/itm/PIPE-BOWL-GAUZE-SCREEN-METAL-RIMMED-STEEL-5-X-20MM-/170751019951?pt=UK_Collectables_Tobacciana_Smoking_LE&hash=item27c18dcbaf

[HS93]

how about  Bruce steam models they do some stainless steel for spark arestors will that work

Peter

Peter

[flashtwo]

Hi,

Thanks Mike for that suggestion - never knew they existed. My burner bowl is about 32mm diameter, so I'll have to make my own. I'm now thinking of a use for the pipe bowl filters.

Peter -  the stainless steel ones work fine until they oxidise due to the burner flame sitting just above it, especially at low gas flows. The ni-chrome wire, which is normally used for electric fires, should not oxidise and last much longer - I'll keep you posted with its performance.

In the mean time, I've found a new method of weaving called the "Scotty" method that enables you to finish before you've started - many an enterprise use it apparently, even up to warp speed 9! (yawn!)

Ian

[flashtwo]

Hi Mayhemers,

Now that I'm using both pumps to achieve "ramming" speeds (700RPM), the previous control philosophy to having one pump purely as the standby has changed somewhat.

I've made some software changes so that, if either pump stops reciprocating or there is a high steam temperature trip (possibly caused by a feed pump problem), the Feed demand is automatically halved. This ensures that the boiler feed requirement can be handled by one pump.

Another change is to now allow 10 seconds for the pumps to re-establish flow, after a trip, before the gas valve starts to open.

The steam temperature target, which is a function of the feed demand, has been further refined by allowing the equation parameters (offset and slope) to be set at the display and command unit whilst the boiler is running. (For the mathematical it is the old "y = mx + c" equation and I can now adjust m and c whilst running). This will allow fine tuning to take place.

....and not a soldering iron in sight!


Ian

[flashtwo]

Just to give Mayhemers a flavour of what is going on, here is a small part of the code that has just been modified for the new method of running with two pumps (without the use of the soldering iron!...)


TEST_A_RUNNING   
      BTFSC   C_FLAGS_6,1   ; (BTFSC) Times up! Is the "A" Pump running?
      GOTO   ENB_GAS_VALVE   ; Yes, the "A" Pump is running, therefore enable the gas valve to open.

      BSF   C_FLAGS_1,7   ; The "A" Pump is not running, therefore set the "B" Pump as Control Master.
      BSF   C_FLAGS_1,3   ; Set because one of the pumps is unavailable and the target T4_DV must be lowered.
      BSF   C_FLAGS_3,0   ; Set the "A" pump failed flag.

      MOVLW   D'100'      ; Set the pump established counter to 10seconds (100d) to allow the pump to start turning.
      MOVWF   PUMP_COUNT
      GOTO   DIS_GAS_VV              ; Disable gas valve from opening.

Ian

[steamboatmodel]

Ian 30 years ago I mite have understood it better, but I can sort of follow it through. When I my round tuit I am going to have to sit down and do more than glance at embedded C.
Regards,
Gerald.