Piston Valve 3 HP Marine Steam engine Twin Cylinder - Super Smooth Runner - Air Test
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- Опубліковано 8 лют 2025
- This fine piece of hardware came from the collection of A.E. Burr and before that it was in the collection of Peter Renzetti. I am honored to be it's custodian for this moment in time.
What a beautiful engine! Looks like it could do some serious work.
Definitely!
Bonjour Gil,
Beautiful engine perfectly built, indeed, my only concern would be its power, I think 3 HP is too much, but I don't know how to measure it.
Amicalement, Raphaël
Given the bore and stroke are similar to the Stuart Swan and Tiny Power W, and are both 3 hp, it is reasonable that this would also be 3 hp.
@@reddrryder Bonjour Gil,
I fully trust you and imagine this beautiful steam machine in a scale 1 launch... A dream...
Amicalement, Raphaël
Horse power labels with steam engines can be rather finicky, as horse power is just torque multiplied by RPM, and the max torque will vary on how much pressure the boiler can produce, and since steam engines are usually operated as direct drive engines, their working RPM range can be anything from 0 to several hundred.
For example, the 20HP rating on a Stanley steam car comes from what the boiler can supply continuously, however when the boiler is at full pressure the engine itself can deliver much more power than that, but the steam consumption will outpace what the boiler can produce, causing pressure, and thus power, to drop until it hits equilibrium with the boiler's steam generation rate at that 20HP mark.
So even though a Stanley is labeled at 20HP, in actuality if you were to give it full throttle when it's running at near its top speed (about 90mph) the engine will, briefly, be producing more like 120HP with the full 500PSI of boiler pressure behind it.
This from only a small twin cylinder engine with a 4" bore and 5" stroke. Most steam engines have lower horse power labels because they are usually operated with lower pressure boilers, and at lower RPMs.
@@DAKOTA56777 Bonjour,
Thank you for the clarification, especially with the example of the Stanley which actually has more than 20 hp in appearance.
Amicalement, Raphaël
@@rhavrane You're welcome, but I did make a little error on the Stanley, the place that lists the horse power has it at 30mph and 420RPM on the engine, not at the 90mph mark. To be fair, the HP at 90mph probably isn't much higher since to achieve that speed without emptying the boiler of all its steam the engine's cutoff (when the valve closes and stops admission of steam during the power stroke) would need to be greatly reduced.
However if you want to run your own calculations, the equation for Indicated Horse Power (IHP) is actually fairly simple. Just note that IHP doesn't factor in losses from friction, heat, parasitic systems (think of pumps built onto the engine), and other inefficiencies, so it tends to read higher than the actually obtainable HP.
The equation is IHP = (PLANK)/33,000, where:
P=Mean Effective Pressure (average pressure during the power stroke basically) in PSI. This is generally the hardest to factor because it varies a lot based on valve cutoff, but if you know the cutoff you just subtract the percentage and average the start and end. So if the engine is running in full cutoff, which is, say, 85% then you remove 15% of the starting (boiler) pressure to end up with your end pressure. For example, if you have a boiler at 100psi, then 85% of that will be 85psi, for an average pressure of 92.5psi.
L=Length of stroke in feet.
A=Area of piston in inches, equation for a normal round piston is πr^2, where r is radius, so half of bore diameter, and π is pi, or 3.14 depending on how precise you want to be.
N=RPM multiplied by number of power strokes per revolution (2 for a double acting steam engine).
K=Number of cylinders (Note this only works with simple expansion engines, as compounds and triples have different cylinder sizes and pressures so they can't just be multiplied).
For example, since the Tiny Power W was mentioned, we'll use it. The W has a bore of 2inches, and a stroke of 2.25inches, and is listed at reaching its 3HP with 100PSI of pressure.
So, P=92.5psi (I assumed full cutoff), L=(2.25/12), A=(π1^2), N=450*2 (They don't list the RPM, so I just plugged in numbers until I reached ~3IHP, since I didn't feel like doing algebra.), K=2.
92.5*0.1875*π*900*2=98,077.
98,077/33,000=2.97IHP.
450RPM seems high to me, but then again, it is a small engine, and it's what they had to use to get 3HP from only 100psi.
Now for dealing with compounds and triple expansion engines, you would have to do the PLANK for each individual cylinder then add them up, however I've noticed that, a very rough estimate can be done by halving the horse power of the higher pressure cylinder in sequence. So if you do the PLANK for the high pressure cylinder and get, say 10HP, then you can assume the low pressure will get 5HP, for 15HP total, and if it's a triple, just half the number again, for 2.5HP, or 17.5HP total. (Basically, if a compound, multiply by 1.5, if a triple, multiply by 1.75).
Again this is a very rough estimate as the exact efficiency of multiple expansion engines varies a lot based on both boiler pressure and steam temperature, but as a very crude estimate it works okay enough.
It's a marvelous engine! What's the gear ratio between the crankshaft and the feedwater pump? It almost looked 2:1 but then noticed it was slightly off
maybe 2.5/1
It is a very nice engine. How many psi do you need to produce 3 hp. Have a nice evening 🇧🇻
100 PSI delivers 3 hp for a Stuart Swan. This of similar dimensions ought to be about the same.
@@reddrryder thanks a lot. I want to build a 5 cyl radial engine for my generator.
Do you have it still including the Stuart turner swan or cygnet steam engine I'm needing one of these for a 14ft boat
I still have this one, a Swan,and a Cygnet
@@reddrryder ok do you want to sell it