Stationary Engine List

By Staff
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We started this thread last issue, presenting Part 1 of our
discussion on governing speed and what it means when running a
hit-and-miss. As we noted then, we had far too much material to use
in a single issue, so here, as promised, is Part 2 of our
discussion on governing speed.

Suppose you have an Alamo that is rated at, say, 650 rpm with a
potential of producing 7 HP. If you reduce the governed speed to
360 rpm then the horsepower output potential is accordingly
reduced. One thing to keep in mind is that the horsepower is not
being generated simply by maintaining the governed speed. If the
engine is not loaded, and is a hit-and-miss, it will fire, coast a
while, then fire again, all the while trying to maintain the
governed speed. In a throttle-governed engine the throttle will be
closed a bit to keep the speed down to the governed speed. With
either kind of engine, running at speeds lower than their maximum
rated speed will result in reduced potential horsepower output.

Just for grins, sometime you might belt your Alamo up to a
little 1 or 2 HP Briggs and set your Alamo exhaust valve open so it
doesn’t get compression. If the little Briggs can turn your
Alamo at its rated speed of 650 or so rpm, you’ll see how
little horsepower is needed for overcoming engine friction. I
suspect a 2 HP Briggs would do the job of spinning the engine. If
so, and the maker rated the engine at 7 HP, that means the engine
is capable of producing a potential 7 HP on the output pulley,
overcoming the approximate 2 HP internal friction loss. Simply put,
the engine isn’t producing the rated horsepower until you let
the clutch out. Then, if the load is equivalent to the rated
horsepower, and the engine can maintain the rated rpm, it is.

I found the following information in my 1912 IHC engine
operators guide. According to it, the ‘Make-and-Break’ type
is used almost entirely for engines running below 500 rpm. The
guide says: ‘The governor is designed to hold the speed of an
engine uniform. It either regulates the amount of mixture for each
charge – as in the case of the throttling-governor – or it acts so
as to permit an impulse only when power is required, as in the case
of the ‘hit-and-miss’ type governor.’

Am I right when I say for a constant speed you need a
throttle-governed engine and the amount of ‘hits’ of a
hit-and-miss engine depends on the horse power needed at that
moment?

I would think that for something like a sawmill you would want a
constant speed, but for something like a corn sheller or mill you
would want to use a hit-and-miss that you can run all day long if
need be on less gas.

What about engines where the manufacturer raised horsepower
ratings simply by setting the governed speed higher? With such an
engine, would running it on the previously rated max load cause
damage?

Many engine manufacturers (e.g., Hercules, Witte) claimed that
their engines were purposely underrated in horsepower. Thus, the
‘upping’ in horsepower by simply increasing the speed by 25
or 50 rpms did not hurt the engine in any way. To run the older
engine at 25 or 50 rpms faster, or the newer ones at 25 or 50 rpms
slower, would not appear to hurt the engine in any way.

It may be running at a constant speed, but it is being load
governed as opposed to mechanically governed. I finally found a
reference to what I was trying to explain in an international
correspondence school book with a copyright date of 1907. It is
titled Care and Management of Stationary Engines. I quote
section two here:

‘In determining the size of an engine for a given amount of
work, it should be borne in mind that an engine that is called upon
to run at its full capacity during the greater part of the time is
actually overtaxed. Working an engine to this extent will result in
rapid wearing of the piston and cylinder and consequent loss of
power and economy due to leakage. When doing the maximum amount of
work possible in a plant, the engine, if governed by the regulation
of the number of impulses, should cut off at least once in four or
five charging strokes. This will benefit the cylinder through the
admission of charges of cool air at more or less regular
intervals.’

Here are my thoughts: First why would anyone want to run an
antique that you are trying to preserve with a heavy load that will
wear it out? Second, it is probably not a good idea to load any old
engine much more than 50 percent of it’s rated horsepower and
probably not much more than 80 percent on brand new engines.

I really have wondered about this for some time now, since I use
my 7 HP Alamo to run my cane mill and it is firing under load as
long as I am keeping the feedbox full of cane. It does latch up at
times when the box isn’t full, so it might just run for five
minutes solid, with a few misses in between. The mill I am using
requires a 6 HP gasoline engine or 4 HP steam engine. It usually
takes an hour and a half to make enough juice for one batch.

From what I am hearing this engine shouldn’t be run in this
manner even though I am using a machine that is rated below the
horsepower of the engine. One more excuse to get a larger engine! I
didn’t think I was overworking the engine because I have never
boiled the water in it. I use the engine because it is a great way
to use of one of my hobbies to assist in another, syrup making. If
you go to shows with steam engines, you will probably notice they
give them a pretty good workout, and most of those engines are
older than our gas engines.

To summarize, then, so as to make sure I’ve read ALL the
words correctly, whatever the governing system used it is a bad
idea to constantly run an engine above 75 to 80 percent of its
maximum power output for several reasons:

1) You are operating on the droop of the efficiency curve and
therefore below peak fuel efficiency.

2) The engine will be running hot and also probably near the
extremes of lubrication. Also perhaps worth noting that most
hit-and-miss engines predate NiMoNiC steels and valve warping was
common.

3) It’s noisy (and in the interest of preservation mostly
unnecessary).

I’d add that a hit-and-miss governor is not the most precise
governing system (its cyclic variation can be in excess of 20
percent), and I would expect it to latch every time some time
before maximum power output is reached. Also, some manufacturers
were very conservative in ratings and their machines could be – and
were – run for long periods at rated power. Ruston and Petter
(pre-war) being two good examples.

Okay, I can’t stand it any longer and am compelled to open
my mouth (or keyboard). The original premise was that it was
harmful to run a hit-and-miss engine under such a load that it
fires every time. Because no one has made any compelling arguments
regarding exactly WHAT harm would be done to the engine, I must
take the position that it does NO harm to an engine to run it at
it’s rated horsepower.

Certainly, an engine will endure more wear when run under a
heavy load, but this is evident, and would hardly be considered
‘damaging’ by any stretch of the imagination.

A cylinder and piston on a hot running engine wear considerably
less than on a cold running engine. The rate of wear climbs
dramatically as temperature decreases. We’ve all seen the
effects a cold running engine has on spark plugs; all that carbon
buildup is an indicator of inefficient combustion. Those are two
good reasons to run an engine hot.

Lubrication is a non-issue if you set your oilers to the
manufacturer’s specs.

When the work to be performed is a given, then the only other
option to using a small engine that ‘hits’ every time is
using a larger engine. The larger engine will have greater losses
due to internal friction, the losses due to the inherent
inefficiency of combustion will be greater in the larger engine,
thermal losses will be greater, and the larger engine just plain
costs more. Economically, it’s better to get the correct sized
engine to perform a given task.

An engine SHOULD be able to run at its rated horsepower. An
engine that cannot be run at full power for an extended period is
either poorly designed, or in need of repair.

Basically true, BUT, is the rated horsepower the true maximum
output of the engine? Full power that the engine can develop may
well be above the rating at which the manufacturer intended the
engine to operate continuously. If you put ‘full RATED
power’ into that second statement above, no one can reasonably
argue against it.

I rather suspect that most of these old engines will in fact run
wide open for a long time without incident, but it was often
recommended not to do so.

Engine enthusiast Helen French lives in Leicester, England. You
can join the Stationary Engine List on the Internet at:
www.atis.net Contact Helen French via e-mail at:
Helen@insulate.co.uk

‘Lubrication is a non-issue if you set your oilers to the
manufacturer’s specs.’

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