Mechanical Governors

Understanding The Mechanical Governor

Copyrighted 10-05-2005

Before you attempt to ‘tune’ a governor for acceptable performance, it is best to make sure you understand how it works. But first, it may be a good ideal to share why you will care about the governor and its accuracy.

The Lister 6/1 ST5 at our Easton Washington location  is a prime example. When I first set it up, it ran the 220 volt 60HZ AC well pump in irrigation mode, the pump ran all the time, and excess water was used to irrigate, a pressure tank was filled for cabin use, and a check valve assured that the water was held for that use. In this situation, the principle load was fixed, and it was easy to tune in the governor to maintain the frequency to exactly 60 hz.

As you will learn on the CD, I learned how to ruin a well pump with a generator (any generator), so I am careful to turn off the power to the pump before I stop the engine. The switch and the Generator are about 10 or more feet apart, when the load is removed, the lazy governor paid no attention to the extra RPMs as they rapidly increased, since there is no load, and I was there to manually shut down the engine, there is no problem, this is probably the typical Indian example.

But now, it is time to evolve the system; why burn the fuel when the irrigation water is not needed?

We will  add a pressure switch as is normal for a well pump, when the cut out pressure is reached the contacts are opened, and the pump load is dropped from the generator automatically. Now we have a need for a well tuned and well functioning Governor, if it is sluggish, the frequency and the voltage will rise, and the engine can go into over speed depending on just how poorly made, and poorly tuned the governor is. If the governor functions well, it will regulate the frequency and voltage well within the typical requirement, and do so without the need for electronics that all too often fail.

It is typical that Generators are set up to produce 61HZ at no load, and we allow the voltage and frequency to ‘droop’ into the sweet spot as a load is applied.  This gives us a little room for the governor to sense a speed change and to react. The Lister type Governor Design is up to the task, but tuning is often necessary.

End of Example, Back to the mechanics and how it works…

When we look at the vast majority of work engines, we discover that the speed control is a lever attached to a spring. This lever is often set up where we can lock it into position with a knob or indexed lever and ‘set’ the engine to run at a certain speed regardless of load.  On the other side of that spring is a linkage attached to the ‘injector fuel rack’; or in the case of a gas engine, ‘the throttle plate’.  Off this fuel rack lever, we see another linkage to the governor.

What we have is a spring pulling the fuel rack open from one side, and a mechanical governor that attempts to pull the fuel rack closed from the other. When the load is constant, the spring and governor reach equilibrium, and the speed remains constant. Increase the spring pressure, and the governor and spring will work to equalize and maintain a new and higher RPM, decrease the spring pressure, and the two will equalize at a lower RPM.

WE can change out springs for longer, shorter, stronger or weaker to tune the sensitivity and response of the governor to our liking.  Some Indian machines arrive with an extra spring, this allows the engine to be run and optimized for 600 RPM, or with the stronger spring, it may be run at 1000 RPMs, and tuned for an adequate response at that speed range. As I write this, you should note that governors are designed and tuned to run in a certain RPM range. If we take a Briggs and Stratton gas engine designed to run at 3600 RPMs, and expect it to run at 1800 RPMs and properly govern there, we’d probably be disappointed.

Some folks build generators around automotive engines, and don’t give the lack of a governor much thought, after market solutions are available, but you should do some research before hand to figure out what it will cost. Of course understanding how the simple device works will allow you to build your own, and you might have a good deal of fun doing so.

The governor will generate a pulling force in direct relation to the RPM of the engine, as it is usually coupled to the crank or cam shaft of the engine either by belt or gear train. Mechanical governors usually rely on weights and centrifugal force, as the speed increases, the weights move outwards and a mechanical linkage couples the position of these weights via a linkage back to the fuel or throttle rack.

When we set the governor up properly, it responds to changes in speed at the RPM we wish to maintain. As we place more load on the engine, the crank shaft slows, the flyweights on the governor slow, and the force they apply via the linkage to the fuel rack becomes less. This allows the adjustment ‘set’spring on the other side to open the fuel rack to overcome this added load, the extra fuel delivered brings the RPM back up, when this is done, the flyweights exert a greater force, and the governor returns the engine to the ‘set’ speed.

When a heavy load is removed from the engine, it will attempt to over speed, as the engine adds RPMs, the pulling force of the governor fly weight will close the fuel rack and again the ‘set’ speed or governed speed will be reached.

The response of a governor has a great deal to do with how it was designed, how well it was made, and how well it was tuned.  If we use the typical Indian Governor on the Lister Type 6/1 for an example, we can typically find a number of easily corrected problems that typically produce sluggish and non linear responses. India often uses these engines for irrigation pumps; in this case, accuracy is not nearly as important.

When we take the time to think about it, it all makes sense, but all too many of us have too much on our plate to fully analyze the simplicity of the governor, and understand it before we attempt to adjust it or improve its response or performance.

If we follow the movement of the fly weight, and all the linkages back to the throttle or fuel rack; we can easily spot troubles.

Listeroid Longevity discusses a good many of these things, but you can quickly see that binding linkage, un lubricated linkage posts, and parts that were not fully machined can be sources of trouble. A company called Prakash sent over a number of engines to North America with internal governor pieces not fully machined, this added to the non-linear response of the governor; easily corrected, but pulling the governor stumps some folks, and the steps for doing so were also discussed in LL.

I have found that the average governor in the Lister Type will not govern better than about 5 cycles from 60 HZ in a generator application. Replacing one small external part, usually improves frequency response to a cycle or two, and a half hour of tweaking can give even better results. There is a simple and inexpensive kit that will dramatically improve the average Lister type governor response and accuracy.

I receive quite a bit of email from folks wanting to use auto engines to run generators. One of the larger problems is providing speed regulation.  Here are a few links to learn from:

Remember there are electronic solutions as well.

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