DIY Tesla Impulse Turbine

[Toymaker]

Yes, it is a common design of Engineering connection. Easy to assemble correctly, dismantle and re-assemble. I use Gas fittings - "Calor gas" used to use Butane at cylinder pressure - using 1/8in bore copper pipe and 1/8" BSP fittings. Now use LOW pressure butane or propane (via a regulator) to 1/4" BSP fittings... for caravans, etc. But I now use copper brake pipe for my steam as the "common" pipework, with 1/8" BSP fittings, or 5/16" x 32 M.E. to suit Model Engineering commercial fittings.
Pre-assemble olives onto pre-shaped pipes, using a fitting in a vice or similar, rather than using "the job" for the first tightening of the nut onto the olive. Then use the pipe assembly on the proper job.
K2

Thanks for the feedback K2. Your instructions closely match one of the how-to YouTube videos I've watched; the only addition to your instructions was to hand tighten the nut until snug, then turn the nut an additional 1/2 turn using a wrench, no more. I believe I may have initially over-tightened the nut, and the threads are now stripped from my attempts to stop the leaking. I've ordered replacement parts, but of course this means more waiting for those parts to arrive. :-(

 

[Steamchick]

You can add a single wrap of PTFE plumbers tape around an olive before assembling the joint. But I have never found that necessary if I pre-assemble olives onto the pipe. I have heard of some people apllying grease instead of PTFE TAPE. BUT I assemble dry and clean. Then you only need a nip to make a water -tight and pressure proof joint when you fit the pipe assembly to the job. Too much torque strips threads.
Take care. You don't want overstressed threads failing when you have pressure on the boiler.
K2

 

[Toymaker]

Problem solved,...no more leaks !!! After waiting 2 weeks for replacement parts, the new connections leaked almost as bad as the old ones; the difference being the new connections don't start leaking until a bit over 100 psi.

I had already decided that if the new connectors also leaked, I would move on to plan-B, which was to braze the 3mm copper tube to the brass fitting. This method makes diss-assembly and re-assembly a bit more difficult, but this method doesn't leak; I hydrostatically tested the fittings up to 450 psi with no problems.

 

[Steamchick]

Intended to be good for 6 bar NWP, = 12 bar hydro test without leak. I do use olives, but never see leaks. Possibly as I don't see >6bar...
K2

 

[Toymaker]

Intended to be good for 6 bar NWP, = 12 bar hydro test without leak. I do use olives, but never see leaks. Possibly as I don't see >6bar...
K2

The package of parts shown in post #339 was ordered from AliExpress, from China, and came with no instructions, no pressure ratings, not even a brand name. Both fittings began leaking at about 8 bar, so they didn't even make it to 12 bar without leaks.

12 bar max huh?,....Guess it's a good thing I brazed the tube to the fitting

 

[Steamchick]

I say "12bar" - because on the copper tube that is the highest test pressure I can speculate it will see. But there may be applications for these nuts and olives on thicker walled copper tube that see much higher hydraulic pressures.... I simply don't know. You bought stuff planned for car oil pressure systems - typically 80psi normal pressure, = 160psi "test" pressure. My experience is these fittings used for Butane at cylinder pressure - 15psi at 20 deg.C. - but must be capable of a couple of hundred psi for test.. I haven't got a reference document for that...
I do know however, that everything has an upper WORKING limit, much below where it fails. Maybe you should consult an Hydraulic component manufacturer to understand what is recommended for your pressure? Maybe Steel nuts to take the stresses of your higher pressure? - even steel pipework and brazed olives - or deformed/swaged steel ends such as used on Car Brake pipework? (That is a system you NEVER expect to fail at hydraulic pressures. - But I don't know what those pressures are...). >1500N force on the brake pedal (When a big strong guy is pressing in an emergency?) x the mechanical advantage of the lever, Plus the added SERVO generated load onto the piston of whatever area = pressure in the pipework.
I'm sure you can do the sums on your system - to be sure to be safe. - I GUESS that as this is on the water feed side, if a Pressure gauge fitting blew off during service, then the boiler would instantly discharge whatever steam was in the heater coil, then just melt-down, without any further drama? - The feed water being pumped out of an open tube would act as a quench to the outside of the boiler?
K2

 

[Toymaker]

I say "12bar" - because on the copper tube that is the highest test pressure I can speculate it will see. But there may be applications for these nuts and olives on thicker walled copper tube that see much higher hydraulic pressures.... I simply don't know. You bought stuff planned for car oil pressure systems - typically 80psi normal pressure, = 160psi "test" pressure. My experience is these fittings used for Butane at cylinder pressure - 15psi at 20 deg.C. - but must be capable of a couple of hundred psi for test.. I haven't got a reference document for that...
I do know however, that everything has an upper WORKING limit, much below where it fails. Maybe you should consult an Hydraulic component manufacturer to understand what is recommended for your pressure? Maybe Steel nuts to take the stresses of your higher pressure? - even steel pipework and brazed olives - or deformed/swaged steel ends such as used on Car Brake pipework? (That is a system you NEVER expect to fail at hydraulic pressures. - But I don't know what those pressures are...). >1500N force on the brake pedal (When a big strong guy is pressing in an emergency?) x the mechanical advantage of the lever, Plus the added SERVO generated load onto the piston of whatever area = pressure in the pipework.
I'm sure you can do the sums on your system - to be sure to be safe. - I GUESS that as this is on the water feed side, if a Pressure gauge fitting blew off during service, then the boiler would instantly discharge whatever steam was in the heater coil, then just melt-down, without any further drama? - The feed water being pumped out of an open tube would act as a quench to the outside of the boiler?
K2

The coper tube is 3mm (0.118") OD with a 0.053" ID, making the wall thickness a bit under 1mm, at 0.0325".
Using Barlow’s formula: P = 2*T*S/D and a copper yield strength of 11,000 psi, results in 6,059 psi,....which is 12 times my working pressure of 500 psi.

Now that I've brazed the copper tube to the brass fittings, thereby eliminating the flare-less connections, I believe the boiler tubes will fail before the newly installed 3mm pressure guage tube fails.

 

[Toymaker]

Today's Tesla Turbine test results. Big win as my epoxy resin spider (part of the coupler) held up. But only a tiny increase in power output; up to 47 watts from 36 previously. Sadly, my digital tachometer chose today to stop working, so I do not know turbine RPM. Per the gauges, steam flow rate into the turbine was about 0.7 LPM at about 20 psi.

I had to stop testing early because I started to smell burnt rubber which I suspect is coming from the throw-rugs I placed around the boiler as noise suppression.

 

[Steamchick]

Fun! What plan to check everything, before increasing the steam pressure and flow?
I find 20psi instantly becomes "wet" with expansion (A lot of condensation, not a lot of power), so I am sure higher steam temperatures (superheating) are needed to get turbines working properly. But then I have only a little experience of 1 Tesla turbine. (Lots of reciprocating engines though). So you are more expert, than I.
With a crude calculation, I have decided I need 3 times the superheater normally fitted to a Proprietary boiler. Loco users always appreciate a loco with large superheaters, more than one with less.
I guess your flash (tube) boiler should provide superheating in the final coils? What temperature of steam do you have at the point of entry to the turbine? (As the steam expands down the feed pipe some condenses to water becoming wet steam - I cannot see your feed-pipe - Is it well lagged to prevent excess heat loss and further condensation before the turbine?). I lag my stem pipes with Cotton string wound around the pipe, then painted with white paint. But on 2 boilers the superheating is so good it chars the cotton for a bit , leaving bare pipe. I must get some "proper" heat resistant string!
I suspect a lot of noise is coming from the boiler exhaust? An absorption silencer may be needed if noise is a problem. - That is 2 concentric tubes, with stainless wire wool between them and the inner one perforated. E.g.:

https://www.ebay.co.uk/itm/28374707...7779&msclkid=80f1e2f96318165516ba85a2936848c6
The Roar from your burner will mostly be white noise, so this is the most suitable silencer design for you, IMHO. (With NO restriction on the exhaust).
K2

 

[Steamchick]

Another thought - as you have a "HOT" exterior to the boiler... Wrap some crinkly aluminium foil around the boiler. Even a few layers making an "air trap" and "radiant heat reflector".
On one boiler, the surface temperature of the (conventional) boiler was measured at 135C, but when we placed a crinkly foil cover on the boiler the external temperature went to less than 50C on the non-contact thermometer, (warm to the touch) and the turbine increased speed a little, I guess with improved boiler temperature (2 or 3 degrees?) measured on the un-insulated boiler front.
Just ideas that may help, and become more significant as the pressure rises...
K2

 

[Toymaker]

Fun! What plan to check everything, before increasing the steam pressure and flow?

Since I stopped mid-way into my gradual power increase, I will start back at idle power and once again gradually increase burner-boiler power output, and the next time I can hopefully reach higher pressure into the Tesla turbine.

I guess your flash (tube) boiler should provide superheating in the final coils?

At least for now, I'm playing it safe and will limit steam pressure to 400 psi at to 231 C (448 F).

What temperature of steam do you have at the point of entry to the turbine?

Good question,...there's no easy way to measure steam temperature at that point. However, considering my feed line is only 1 meter long, I suspect minimal temperature drop between boiler out and turbine in.

(As the steam expands down the feed pipe some condenses to water becoming wet steam - I cannot see your feed-pipe - Is it well lagged to prevent excess heat loss and further condensation before the turbine?). I lag my stem pipes with Cotton string wound around the pipe, then painted with white paint. But on 2 boilers the superheating is so good it chars the cotton for a bit , leaving bare pipe. I must get some "proper" heat resistant string!
I suspect a lot of noise is coming from the boiler exhaust? An absorption silencer may be needed if noise is a problem. - That is 2 concentric tubes, with stainless wire wool between them and the inner one perforated. E.g.:

K2

The stainless steel braided tube in the photo below is the steam feed pipe. It's sold for use with steam and air at working pressures up to 1500 psi.

 

[Steamchick]

That's a fantastic bit of hose! But for a final installation I guess you'll fix everything together, so could easily insulate the steam connection then. The pressure drop of just a few psi of steam that is not superheated will cause condensation droplets. Also to push the steam along the pipe takes a few psi. Thus the outlet of the delivery Pipe is always a small pressure drop below the inlet. A Tesla turbine is pretty much immune to damage from droplets. Bladed turbines damage badly with water drops. Either way, super heating really helps get dry steam into the turbine, with more energy than wet steak of the same temperature. Your coil flash boiler naturally will give a degree of superheating. "How much" should be measured to understand how the system is performing. So can you arrange some temperature measurents? Even with a non- contact temperature of fitting on the pipework will hive you an idea.
I hope the boiler gives you lots of steam and lots of superheat. That mean's LOTS of power!
K2