horsepower

[johnp]

So, According to the P.L.A.N. method my 2.25"x 3" has 3hp at 125psi. If i make a new cylinder with a 3" bore i will have 5hp. The feed pump is crosshead driven, how much power should i subtract for friction and pump drive?

[fredrosse]

Friction is in the vicinity of 10-20% of indicated horsepower. The feed pump consumes only 2 or 3% of the engine's output, if the packings are not too tight. The 3 horsepower you quoted is with full steam admission for the full stroke, probably some earlier cutoff will be prudent, so 2-2.5 horsepower is what you can expect.

[Lopez Mike]

Not that hard to measure the brake horse power. Especially at these levels. You just need a way to clamp a wood block to your flywheel and measure the torque and at the same time measure the rpm.

Of course, if you are condensing, you will need to provide a heat sump. A bucket of water would do for short runs.

For now, just enjoy the fruits of your considerable work.

[fredrosse]

The device Mike mentions to measure engine torque is called a "Prony Brake". Most modern dynamometers have lots of electronic stuff, but the old time Prony Brake actually can work very well. They were used throughout the late 1800s and well into the 20th century. When I was in engineering school, we actually used Prony Brakes to test engines, and that was in the 1960's

The attached drawing is for an actual Prony Brake that was used to measure the output of the Unflow Engine that ran my Domestic Heat-Power Module. That engine made 4.64 horsepower at 1040 RPM back in 1980. This brake would be about right for our steam launch engines, a few horsepower at several hundred RPM.

As you probably know, the Power to Speed function for displacement boats running a or below "Hull Speed" allows getting 80% speed with only 50% power, so if your horsepower numbers are off by quite a large amount, the boat still moves thru the water OK.