Rev Counter

[bushbuck]

Morning All

Another two questions (maybe silly ones!!!)
How do you monitor the speed of the engine? Do you install a rev counter somehow and if so, how?
What is the exact purpose of an economizer?

Regards
Gavin

[DetroiTug]

Hi Gavin,

On checking the RPM, the most common way I've seen is an infrared Tachometer. Just draw a Sharpie line on the flywheel, point the unit at it and it displays the RPM. The RC guys use these and they are available at Hobby Shops. I used a mechanical tach that goes on the end of the crank. I bench ran the engine and can sorta tell by the sound how fast it's turning.

The economizer is typically a coil of tubing in the smokehood that the feedwater is ran through to preheat it before it enters the boiler. It's a good use of otherwise hot gases that are vented away. An economizer will greatly increase the efficiency of a steamplant. Another method to preheat feedwater is to use a heat exchanger on the engines' exhaust, these work pretty well, but the economizer works much better. I have both and wound up totally bypassing the exhaust heater. It's important that this coil be on the exhaust side, as it is not removing heat from an interfering with the boilers' steam generation process.

Another type of coil you'll see refereed to is the "Superheater". It's purpose is to superheat the steamline from the boiler to the engine. It's typically just a U-coil of stainless tubing in the firebox. It raises the temperature of the steam in the line and also since temperature and pressure are constant - raises the pressure. This is an engine performance enhancement and as most of those do, it introduces some undesirable side effects. Special heavier weight engine oils must be used and it also considerably raises the temperature of the engine. I've read accounts of where too much superheating was used and it cooked the paint off the engine - too hot. Also the throttle should be before the superheater. The high heat can destroy the teflon seats and packing of most valves.

-Ron

[bushbuck]

Thanks for the answers Ron

I visited an old gent on Tuesday that builds steam locomotives. He showed me a super heater that basically consists of an inlet and outlet tube in a big chunk if copper rod. The rod lies in the smoke box of the loco. Similar principle to what you have just explained?

I am assuming that you do not have a permanent rev counter installed in your tug?

Regards
Gavin

[fredrosse]

Revolutions Per Minute = RPM Meter = Tachometer, the best easy way to do this is with a bycycle speedometer. A small magnet attached to a flywheel signals every revolution, they come wired or wireless. Buy one for 10-15 USD, and set it so that the kM/hr indication is indicating some multiple of RPM. For example, if your engine runs to 400 RPM, set up the bicyle speedometer to indicate 40.0 kM/hr at that Engine RPM. Now you have a very accurate tachometer that will read from 0 - 99.9 kM/hr, corresponding to 0 - 999 RPM.

These electronic speedometers need to have a user input of the size bicycle tire that is being monitored for speed. You want to find a bycycle wheel diameter that will be turning 400RPM when it is traveling at 40kM/hr. That comes out to a wheel diameter of 530 mm, or 20.88 inches.

The math is fairly simple, at 40 kM/hr = 40,000 Meters per hour / 60 minutes pre hour = 666.666 Meters per minute. The wheel we are looking for turns 400 revolutions per minute, so at 40 kM/hr, it will traverse 666.666/400 = 1.666 Meters per revolution. Some bike speedometers require input of this single revolution distance, in mm, and that is 1666 mm per revolution. Other speedometers need input of wheel diameter, which is the distance divided by PI (3.14), in this case 1666/3.14 = 530mm diameter, or 530/25.4 = 20.88 inches diameter.

For my sidewheeler, engine RPM is less than 100, so I want the bike speedometer to show 50 MPH when the engine is turning 50 RPM. Same calculation @50 MPH, 50 x 5280 / 60 = 4400 feet per minute. at 50 RPM, each revolution would cover 4400 feet / 50 revolutions = 88 feet per revolution, so I would need to input a 28 feet wheel diameter = 336 inches (I wonder if the device would take this). Alternately I could choose the kM/hr display, giving 50RPM = 50 kM/hr, with an input of 16666mm per revolution, or 5304 mm ( 209 inch dia) wheel diameter (I wonder if the device would take this).

[farmerden]

There's no such thing as a silly question! If you don't know ask! I have a rev counter on my boat-after about a million revs I quit counting! I have a portable tach which counts a reflective mark on the flywheel. My max RPM is 410.Again stuff you might want to know but it really never changes.I can learn more about the engine by listening to it.Also I can run my boat alone but it's so much nicer to have someone steering ,then I can play Chief Engineer! Den

[Lopez Mike]

Some of the bike tachs use the circumference of the wheel in mm. The correct number for them is 2682.
Mike

[fredrosse]

If your speedometer is set to display kilometers per hour, the circumference entry would be 1,666 mm (65.6 inches) per wheel revolution. If your speedometer is set to display miles per hour, the circumference entry would be 2,682 mm (105.5 inches) per wheel revolution.

Either way you get the display to indicate RPM where the LCD display of 99.9 would correspond to 999 RPM of the actual machine.

[Lopez Mike]

A sad commentary on my local world view that I never considered displaying the readings in metric.

Some day the U.S. will start making things easier but I suspect not in my life time.

Mike

[fredrosse]

You may remember that in 1976 all of the USA was going to change to the Metric System. It was law, everything would be in Metric, sales were to be Metric, with English measures to be repeated in parentheses afte the Metric measure for a year, then only Metric throughout the USA. But it was a law that almost nobody (in the USA) paid attention to.

I have been getting MECHANICAL ENGINEERING magazine, from the late 1970's to the present, back then they started to publish only in Metric, but the Metric never really caught on, and now, at least in the power industry, we universally use the English weights and measures for US built plants.

I agree Mike, Metric in the USA, probably not in my lifetime.

[farmerden]

Metric Please don't go there! In Canada it's the law! and we still build houses in feet and inches but not commercial buildings A sheet of plywood is still 4ftby8ft the speed is in km but I still think mph I just can't [won't] change!!! Den
PS And then there's PSI !! My pick-up is in Kilopascals -I guess I've got good oil pressure -But I really don't know. Well nothing is rattling so that's a good sign!!