Steam Thruster?

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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marinesteam
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Re: Steam Thruster?

Post by marinesteam » Tue Mar 13, 2018 6:24 pm

Cyberbadger, Hopefully you will read this in the spirit intended and not with any ill will.

Mike had posted a reasonable response to the post re: baloni cuts. The only safety related item in his post was not to reduce the outlet diameter of the exhaust. A perfectly reasonable thing to mention since mentioned in every safety valve installation manual are items regarding the valve outlet backpressure or the limit of any backpressure created by the outlet piping & design. He did say " You probably know this"

A very quick Google found this from the Spirax/Sarco website: I have bolded the most important sentences.
Reaction forces when discharging

In open systems, careful consideration must be given to the effects of the reaction forces generated in the discharge system when the valve lifts. In these systems, there will be significant resultant force acting in the opposite direction to that of discharge. It is important to prevent excessive loads being imposed on the valve or the inlet connection by these reaction forces, as they can cause damage to the inlet pipework. The magnitude of the reaction forces can be calculated using the formula in Equation 9.5.2:​

equation 9.5.2 gcm72.jpg
fig 9.5.7.jpg

The reaction forces are typically small for safety valves with a nominal diameter of less than 75 mm, but safety valves larger than this usually have mounting flanges for a reaction bar on the body to allow the valve to be secured.

These reaction forces are typically negligible in closed systems, and they can therefore be ignored.

Regardless of the magnitude of the reaction forces, the safety valve itself should never be relied upon to support the discharge pipework itself and a support should be provided to resist the weight of the discharge pipework. This support should be located as close as possible to the centreline of the vent pipe (see Figure 9.5.7).

Figures 9.5.8 and 9.5.9 show typical safety valve installations for both open and closed systems.
A statement was made with a basic misunderstanding (that the reason industry moved away from that design also applies in our circumstances). A little research would have shown this to be the case. Maybe if a question was made like: "Does angling the end of the discharge tube lower the noise, it's was done in industry but they moved away because of the force created. Is this an issue in our sized steam plants?" you might have received some more useful answers.

I like a spirited conversation as it gets the thought process going but it is the internet, any question will be answered and many answered that weren't asked. You surely can't be surprised if you ask a "how many angels can fit on the head of a pin" type of question that the response might be that maybe angels don't even exist.

Cheers

Ken
Last edited by marinesteam on Tue Mar 13, 2018 6:51 pm, edited 1 time in total.
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Lopez Mike
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Re: Steam Thruster?

Post by Lopez Mike » Tue Mar 13, 2018 6:39 pm

An interesting observation: My safety valve has a side exhaust as do many. To avoid shooting hot water right in people's faces I installed a 90 degree elbow so that the blast came out vertically. But the racket was still close to nervous people (My main enjoyment is taking mobs of people for rides!) so I added an 18" length of 1" copper pipe so that the commotion was up further away. On my first test of this addition, the pipe, which was just resting in the female end of the pipe elbow, took off! The friction of the steam passing through it exceeded it's weight. Who knew?

I promptly silver soldered it in place.

I am mildly humbled (I don't humble much more than that) by the observation that my exhaust extension is, indeed, only supported by the safety valve. This will be remedied!
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Re: Steam Thruster?

Post by marinesteam » Tue Mar 13, 2018 6:59 pm

Mike,


There was a recent video showing a pipe blow off when the safety popped, I thought it was just a poor braze job but maybe not so much that as a lack of accounting for the forces involved. (wasn't yours was it? :-) Does show that you need (as you found out) to fasten these things well.

http://www.spiraxsarco.com/Resources/Pa ... ation.aspx

The guidelines look to be more for stationary installations (in buildings) where the pipework would be more weighty. I would not worry so much about supporting a short discharge bythe valve though a stack length discharge pipe probably should be attached to the stack anyway. I have seen installations where there is an elbow to direct the discharge up a larger pipe attached to the stack, but not actually joined to allow for quick stack removal

Cheers

Ken
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Re: Steam Thruster?

Post by cyberbadger » Tue Mar 13, 2018 7:23 pm

Rephrase the question.

I have a 1" NPT Pipe that is going from the drain of my boiler to under water right now as a drain/blowdown.

I intend to put a 90 elbow so that it will face either toward port or toward starboard from the almost exact center of the hull. (The boiler itself was exactly positioned in the center)

Can any sort of a nozzel that one could make I could simply make on a lathe or mill be made to give a higher thrust then just that 1" pipe? Assume Boiler MAWP of 200PSI.

Something like this discussion:
https://physics.stackexchange.com/quest ... e-geometry

-CB
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Re: Steam Thruster?

Post by DetroiTug » Tue Mar 13, 2018 8:28 pm

Quote: "Can any sort of a nozzel that one could make I could simply make on a lathe or mill be made to give a higher thrust then just that 1" pipe?"

This has already been answered earlier in this thread, but you're essentially suggesting the same principle as an ejector. My experience with an ejector, the water they push has very low velocity in relation to the steam pressure/velocity used.

Here's why.

Steam is only a gas above 212°F at atmospheric pressure, any temperature below that, it loses it's volume by a factor of 1600 - it's no longer a gas, it condenses. Any force requires an equal and opposite reaction, when one is immediately disappearing in a few milliseconds, there is not going to be much reaction against anything opposing it. That is why suggested using the blow-downs, as the boiler water will not condense and would actually provide some force. Now if you can find a 250° lake... :)

-Ron
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Re: Steam Thruster?

Post by cyberbadger » Tue Mar 13, 2018 8:54 pm

DetroiTug wrote:Now if you can find a 250° lake... :)

-Ron
Well I was wondering if coating the pipe in a solid refractory(hell maybe even a tough plastic) to add insulation. That way the water will quickly heat the pipe and not immediately loose all the heat before the ~350F water exits...

-CB
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Re: Steam Thruster?

Post by marinesteam » Tue Mar 13, 2018 9:37 pm

I think this is going to be impossible due to the steam condensation factor that Ron mentions.

If anything, research "entrainment nozzle" or "air amplifier". There are ones that work with air but don't know what effect a more viscous medium will have

example:
http://www.exair.com/index.php/products ... ts/aj.html
or
http://www.exair.com/index.php/products ... /htal.html

You might have better luck with a steam driven turbine, running a small prop.

Don't let us stop you, build something and tell us how it works out.

Cheers

Ken
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Re: Steam Thruster?

Post by DetroiTug » Wed Mar 14, 2018 12:01 am

I remember a mythbusters episode where they tried to power a very small speedboat with compressed gas, a Co2 cylinder at a few thousand psi connected to a submerged pipe at the transom, it was a failure. It did provide a small amount of thrust for a very short distance. That is without the steam condensing at the interface issue

-Ron
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Re: Steam Thruster?

Post by cyberbadger » Wed Mar 14, 2018 12:08 am

DetroiTug wrote: it was a failure. It did provide a small amount of thrust for a very short distance. That is without the steam condensing at the interface issue
The thing is a small amount of thrust for a very short distance is sufficient to be a success how I'm looking at things.

So just a 1" pipe elbow(for the angle) is the best choice to maximize the thrust? No restriction or special geometry?

-CB
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Re: Steam Thruster?

Post by Lionel Connell » Wed Mar 14, 2018 12:36 am

I stand corrected, red flag does ring a bell now that you mention it.
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