Losing my mind trying to find safety valve for monotube

[rhambus]

Hey all,

Long time lurker, first time poster. I am in the process of building a monotube flash steam boiler, hopefully to drive a small kart-type of car. (I am aiming for 1hp). I am in the process of pressure testing the various pieces and it is going fine, but I am having real trouble trying to figure out what kind of safety valve I need on the steam side of the coil. Basically, what I have is a vertical coil of copper tubing, with a jet of natural gas blowing up it. Water goes in the bottom as water, goes out the top as steam. I am shooting for 100 psi working pressure, and I'd obviously like to get a safety release valve or 2. I figured that I would get a 125 psi and a 150 psi. However, the steam safety valves I can find out there for that pressure steam are mostly huge and expensive. Is that the only option? There are lots of those 1/4 inch type spring valves for air compressors out there, and of course water heater valves at low pressure, but the steam ones are few and far between. What are people out there using for steam safety valves? Can I just use the air compressor type ones? Some people also suggest that I don't even need one since I just have a copper coil, and maybe that's true (I did build it this way so it would be safer than a boiler with standing water in it) but I'd rather be safe than sorry. I'd really appreciate any advice!

 

[goldstar31]

I'm sort of surprised that you have been deafened by a thundering silence

My thoughts on 'what I know' are that domestic pressure cookers have a fusible link to melt.
Again, domestic 'night storage heaters and direct acting electrical heaters have fusible links to blow when a safe temperature is exceeded.

Wandering Off-I also recall a situation with testing diving air cylinders--- blah, blah but perhaps someone else will comment one way or another


Norm

 

[vederstein]

There's a guy on Youtube (Lynxsteam) who published a monotube boiler build. He didn't blow himself up. Perhaps his build will be of some assistance. I made a smaller version of his design and it works ok. I did purchase a rated relief valve of McMaster Carr for mine, but it's no longer available.

Perhaps something from China or Ebay?

 

[BWMSBLDR1]

The book "Flash Steam" by Rayman, while old, has a wealth of information and should be still available. Also wasn't there a discussion here on making modern safety valves in scale sizes? Bill in Boulder CO USA

 

[goldstar31]

Obviously, we Limey B------s have done it all in Model Engineer.

With fading memory etc, I recall someone actually building a flash steam buggy.

Probably somebody will have details.

Norm

 

[rhambus]

Thanks, I just bought the flash steam book.

Is there any reason the air compressor type valves, or even hot water pressure valves, would not work on steam? I am worried about pressure only, not temperature, as the temperature can immediately be dropped by my just cutting off the gas. I would put the valve in a place where it would not spray scalding steam any anything, of course, maybe with the help of some kind of diverter. The thread on making your own safety valves appeared to be replicating that type of valve anyway.

 

[fcheslop]

Have a word with George aka Ooyya on the Model Boat Mayhem forum he has built a few flash steam plants and an rc model boat that runs at over 40mph, He also did a good thread on the RC forums Steam Boat section
You only generate pressure on the dead cycle of the engine
Im sure there is a gentleman whos name escapes me on this forum that has built a 120+mph tethered hydro plane
The temperatures reached on a flash steamer would probably burn out a standard valve as my version of Pices2 used a nitrided inlet valve and it would burn out quickly.
Personally I never had the need for a safety valve as you are not storing pressure simply generating it and using it but youre application maybe different also the burner and water pump stop once the engine has stopped
I gave up at 70mph just got sick of burning my fingers and the exhaust setting fire to the workshop. The coil was stainless steel and the three burners burned a pint of paraffin in about 6 minutes .Bob Kirtley has some good utube videos and he was the record holder for a few years as well as the designer of Pices2
cheers

 

[vederstein]

Double redundancy is often a valid type of safety control. If you have two pressure sensors in wired series each controlling a gas separate valve, again plumbed in series, then both devices must be in working order for gas (fire) to be applied to your coils. So if one control system fails, the entire system stops, heat (fire) is stopped, and then the pressure decreases due to a loss of energy.

Used in conjunction with a melting fuse as suggested above can be argued as being safe. On my boiler I put my pressure sensors on the water (lower, not upper steam) side where the temperatures are much much lower and then I didn't need to worry about a pressure sensor that needs to handle 350+ degrees. Farhenheit.

Just a suggestion.

...Ved.

 

[marvin hedberg]

https://www.homemodelenginemachinist.com//threads/making-safety-valves.19161/

 

[lohring]

The record setting flash steam boilers don't have safety valves. Because such a small amount of water is in the boiler, a burst tube is a minor event. The Lynx boiler is described in this post. It is a lower pressure boiler than the model flash steam boilers. See Windy's posts on his record setting hydros here.

Lohring Miller

 

[peter2uat]

ask "doubleboost" from England - his youtube channel is https://www.youtube.com/user/doubleboost/videos - he quite regularly works on an Sentinel DG8 - a beast of machine with a real BIG flash boiler - ask him for advice, he shows his email in every clip he posts, so can be contacted quite easily. And he is quite a helpful kind of person too.

 

[rhambus]

Thank you so much, folks, for all this advice! I think, as a good start, I will at least add a valve on the cold water side of the boiler tube - it can't hurt, and might help. Wish I had thought of that myself. Brilliant! Thanks vederstein.

For fun, here's a pic of the boiler as of a couple of weeks ago. The copper coil is inside the metal housing. Sorry if the pic or link does not work.

 

[vederstein]

One more thing Rhambus,

You will need a timer on your circuit to prevent short cycling of the fire and water. When I first built mine, I didn't have a timer and the valve went apeshit when it was time to fill. on/off/on/off etc. because the level sensor was "on the bubble". My fire control was similar, but not quite as bad.

I have my boiler under an arduino control. I have a five second timer off-delay for the water fill and a five second on-delay for the fire control. The Arduino also controls the boiler feed pump. If C programming isn't in your wheelhouse, then a simple on and off delay timer would do the job. You can even wire up a 505 chip to a power transistor to create the timer. FYI: An on-delay timer close the circuit XXX time after the contacta are closed. An off-delay timer will open the circuit XXX time after the contacts are opened.

(Yeah, I know that all these use electricity, but I wanted the boiler to run without much human interaction. A 12V battery lasts quite a long time).

...Ved.

 

[rhambus]

Thank you! I am still figuring all this stuff out. I actually have the ambition of hooking up an alternator to the motor once I get it going, so hopefully plenty of 12V will not be a problem. In fact, I am going back and forth on the idea of basically making this a steam-based hybrid, where I would run the system at a constant speed to run an alternator, which would charge a battery, and then I would just use electric motors off of that. I'd rather do it in a more old-fashioned way if I can, but frankly the hybrid idea is probably more practical. Though I admit practical in this case is a bit of an overstatement.

 

[Charles Lamont]

Sentinel DG8 - a beast of machine with a real BIG flash boiler

Sentinel waggons do not have flash boilers. See Sentinel boiler on english Wikipedia.

 

[fcheslop]

Not sure .Was the Doble E series cars flash steam or am I thinking about the Huges modified Doble car
I know they made such a good condenser that no exhaust steam was emitted and it and it could travel 1500 miles to a tank of water compared to a Stanley that managed about 50
cheers

 

[vederstein]

The Doble was a monotube boiler. I may be wrong, but a monotube and a flash steam boiler are not exactly the same thing although one may be a subset of another.

...Ved.

 

[fcheslop]

Thanks, not sure what the difference is but they could lick along
cheers

 

[rhambus]

Hey all,

Thanks for the help here. I got some real time to work on this thing over the Christmas holidays and it is starting to actually get into shape. Picture attached. I have converted a Homelite string trimmer engine to run on a bash valve and it's working fine on 60+ psi of air. Pretty loud, though, with the bashing.

I got a pressure relief valve from Amazon that's adjustable from 75-150 psi (though you have to figure it out, no manual for adjustments) and I set it so it's blowing off at 120 psi. It actually doesn't blow, it just lets enough out to get it back down to pressure, which is nice. You can see it towards the top right of the boiler. The coil is inside that sheet metal housing behind all the piping, and I set it up to counterflow, which I hadn't remembered to do before.

I also leak tested this thing and it holds air everywhere except at the copper union joints between the plumbing and the boiler coil. I need to figure out how to get them to stop leaking. (I have wrenched them down as hard as I can.) Someone suggested plumbing grease, but that seems... unwise in a high temperature application. I will probably try using that #5 pipe thread compound on the mating surfaces, I guess? If anyone has suggestions, I am all ears!

Is there a better way to do removable joints like this than unions? With all the bends, normal threads just are too hard to deal with. I guess I could get a flare tool and flare them? What do you folks do?

BTW, the water pump is a 12V electrical RV hot water pump set to maintain 100 psi. In an earlier test of the boiler in barely assembled mode, it worked fine, pulsing on and off. That's why I have that copper pressure vessel looking thing there - my thinking is that the air pressure in there will help keep the water pressure constant. The steam came out of the coil smoothly despite the pulsing water when I did it a while back, so I think it worked.