McKenzie’s Boiler Blog

Boiler Horsepower

The term Horsepower is attributed to James Watt, the inventor of the steam engine (and the term “Watt” as a unit of power) as a way to help sell his engines. Watt knew he had to have a way to communicate the power of his steam engines and the best way was to equate it the most common form of power at the time - the horse which his engines would replace.

He noted that horses were typically used in grinding mills where they would walk in a 24 foot diameter circle (75.4 feet circumference).  He estimated that the typical horse pulled with the equivalent force of 180 pounds and further observed that the horse would make 144 trips around the circle in an hour or 2.4 laps per minute. This means that the horse traveled at a speed of 180.96 feet per minute. Rounding up to 181 feet per minute and multiplying that by 180 pounds of force he arrived at 32,580 ft-lbs./minute which was rounded up to 33,000 ft-lbs./minute or 1 Horsepower.

Boiler Horsepower was calculated in a much different manner. Prior to 1876 Boiler Horsepower was based upon the heating area of a boiler with every 10 square foot of heating surface equaling 1 boiler horsepower. This would mean that a boiler with 200 square feet of heating surface would be rated at 20 boiler horsepower. Not a very exact way to measure the output of a boiler to say the least, especially given the different designs and efficiencies of boilers available.

All this changed at the 1876 Centennial Exhibition held in Philadelphia, PA. There judges decided to use “developed horsepower” which they defined as the ability to turn 30 pounds of 100 degree  F feedwater per hour into steam at 70 psi. In 1884, ASME defined Boiler Horsepower as the amount of power required to convert 34.5 pounds of water per hour from feedwater at 212 degree F to dry, saturated steam at the same temperature. Today 1 boiler horsepower is equal to 33,475 Btu/Hour which is the amount of energy required to evaporate 34.5 pounds of water at 212 degree F in one hour.

blowerwheel.pdf

THREE WAYS TO FIND THE CORRECT KEWANEE BLOWER WHEEL
One of the most common requests made of our parts department is the identification, pricing and availability of Kewanee Blower Wheels. Since Kewanee has been out of business for quite some time, finding these wheels can be a bit of a challenge. There are three ways to find the correct blower wheel.

1. The best way to identify exactly what blower wheel is needed is through the original part number. With this key piece of information there is no doubt what wheel is needed. But, as we have often seen, these numbers, along with most of the boiler documentation, is long gone.
2. The second method is to trace back through the Sales Order Number. This number is located on the front nameplate of the boiler and is a six digit number. By referring to the Sales Order number often times we can determine what was originally supplied through old records. Prior to 1965, Sales Order Numbers were in the 900,000 series. These records are harder to find and we would guess that if your Kewanee Boiler is older than 1965, we will need to use another method to pin point your blower wheel.
3. The third option to locating the correct blower wheel is to physically measure the existing wheel and fill out a Blower Wheel Dimension sheet. This allows us to compare what you have against what is available. We have included a copy of this sheet below.

blowerwheel.pdf

Ask all Kewanee Boiler Questions here.  If you are looking for parts, please provide the SO# or the Sales Order Number of your boiler.

TESTING THE LOW WATER CUT-OFF

As mentioned in a previous post, one of the most important safety controls on a boiler is the Low Water Cut-off of which there are two on a boiler. Both the primary and the auxiliary LWCO need to be tested on a regular basis to keep your boiler operating in a safe manner.

Here is a procedure our service techs use to check Low water cut-off’s -

1. Blow down the water column and observe that the water level in the sight glass returns quickly.
2. Confirm that the shunt switches are working properly.
3.  Place the boiler control in manual and set the firing rate at a minimum.
4.  Observe the water level in the sight glass.
5.  Close the feedwater valve to the boiler in order to generate a slow drain condition.
6. Confirm that the feedwater pump re-circulation line is in place and operational, so that the pump will not dead head.
7. While the boiler is operating, observe the water in the sight glass noting where the first LWCO shuts the boiler off. Make sure the water level does not leave the sight glass.
8. Open the feedwater valve to the boiler in order to establish a normal operating condition.
9. Again, observe the water level in the sight glass.
10. Override the first LWCO, take note of the water level in the sight glass, and operate until the second LWCO shuts the boiler off. Remember; do not let the water level leave the sight glass. 
11. Open the feedwater valve to the boiler in order to establish a normal operating condition.
12. Reset the second LWCO.

We also replace the low water cut-off gaskets as part of our standard maintenance procedure. In fact we include these with many of our gasket kits that we provide for boilers. 

We found a great site* that had some rather interesting photos of some boiler explosions and their results. None of them are pretty sights, as you can see from this photograph from a 1919 explosion in Mobile, Alabama, but, they do remind us to be careful with our boilers and that means proper maintenance.

According to the National Board of Boiler and Pressure Vessel Inspectors, low water conditions are the cause for 50% of all boiler related accidents. Low water within a boiler means water that falls below a pre-set level recommended by the manufacturer for safe operation. This can result in catastrophic boiler explosions.

Perhaps one of the most important controls found on your boiler is the low water cut-off (LWCO). This device can either use a float or probes to sense the water level within the boiler. When the water level drops below a pre-set level, the LWCO will cause a switch to activate which, in turn, will cause the automatic fuel valves to close. No fuel - no flame - no opportunity for over pressurizing the boiler.

We will take a closer look at LWCOs in future posts. Also, if you have any interesting photos of boiler occurrences (the polite word for explosion) please send them to us along with, what you believe to be, the cause of the failure.

*  Wisconsin Boiler Inspector’s  Association
http://thewbia.com/index_files/Page2120.htm

Boiler Questions

Please ask your boiler questions here or contact us with any questions or comments you may have. If you don’t agree with our answers or advice, by all means, let us know!

Over the years, we have answered many questions related to boiler operation, maintenance and design sent to us via email.  Issues covered have included water quality, proper blowdown procedures, combustion settings and many more. Some of these questions and answers can be found at the following link –

http://www.mckenziecorp.com/boiler_questions.htm

We had also developed a boiler tips page to assist boiler owners in some of the more common questions and topics we are often asked about. These can be found on our boiler tips page located at the following link –

http://www.mckenziecorp.com/boiler_tips.htm

We offer these links to you so that you may get a better idea of how we can lend assistance. We don’t have all the answers, but will do our best to get them for you.

DON’T FORGET TO GIVE US THE BOILER MANUFACTURER.

http://www.mckenziecorp.com

Some would say that boilers, boiler room equipment, boiler parts and service are all very boring subjects but, we take issue with that. Just look around and you will find steam boilers and hot water boilers operating in most of the places you visit. They are used to heat office buildings, schools and hospitals. They provide steam for processes like steel production, the food industry and chemical plants.

For some, this is transparent technology; they don’t see it so they don’t really think about it. But just wait until the boiler goes out on a cold winter day or a factory goes off line because the steam boiler can not deliver. Then the importance of the boiler becomes very real, not transparent at all.

Our goal with this Boiler Blog is to discuss boilers in their entirety. We want questions and comments. We want to refer to your sites and your recommended links. So, please, join the discussion.