1493582

A Primer on Water TurbinesAuthor(s): Robert A. HowardSource: Bulletin of the Association for Preservation Technology, Vol. 8, No. 4 (1976), pp. 44-63Published by: Association for Preservation Technology International (APT)Stable URL: http://www.jstor.org/stable/1493582 .

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A PRIMER ON WATER TURBINES

by Robert A. Howard*

This article is intended to familiarize the reader with some mechanical concepts relative to the water turbine. It is written in generalized terms based on the writer's research and experience, and reflects observed practice in the Middle Atlantic region of the United States.

Man's application of technology should in no way be considered perfectly rational. Most turbine installations, for example, are somewhat modified over time, either for sound mechanical or economic reasons and/or because of some quirk on the part of the local operator.

In the 19th century the term waterwheel was applied to both what we call waterwheels and what we define as water turbines. To compound the confusion, both wheels and turbines are found oriented horizontally and vertically. In order to differentiate between wheels and turbines, anything with buckets or blades each in a single plane is a waterwheel, and anything with curved vanes is a water turbine.

Let us begin with Figure 1 and trace the water flow and define parts of the hydraulic system using a turbine.

In most systems the water enters the race (sometimes called the headrace) above or at the dam. This race or canal maintains the water level nearly at the dam level. The number of water turbines served by a race can vary from one to many. Generally, if several turbines are serviced, the race will narrow slightly after it passes the inlet for each. It is not economical to move more earth than needed when building a race; however, the race has to be sufficiently wide in every place to maintain the velocity of the water flowing through. Should the water flow too fast, a scouring action will occur and the walls of the race will erode away. Most races with which the writer is familiar are masonry walled being stone lined. Earthen trenches have also been observed. Often there will be control gates and trash racks at the inlet of the race and, occasionally, some sort of fixed or floating barrier will be provided to stop large floating logs.

To get water from the race to a turbine, a flume or penstock is employed. Occasionally a penstock will begin at the dam and no race will be present. Flumes may be open or enclosed, while a penstock is invariably a watertight pipe constructed of iron, steel, or wood. At the inlet end of

*Mr. Howard is Engineering Curator at The Hagley Museum, Greenville (Wilmington), Delaware.

A^F Vol. VIII No. 4 1976 Page 45



D RIVE

DETAILS

TAI L- RACE

TYPICAL SCHEME OF TURBINE

AR RANGEMENT

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Figure 2 Scroll case turbine at The Hagley Museum.

Courtesy of The Hagley Museum

AD[ Vol. VIII No. 4 1976 Page 46



the flume or penstock there is usually a control gate. This allows servicing of the waterway. In the case of gunpowder mills this gate is used to control the flow of water to the turbine so that the operator is some distance away from a mill in case of explosion. Most flumes and penstocks have a fine grating at the inlet point, also called a trash rack. This prevents debris from floating into the turbine.

Control Gates: Control gates are found in many arrangements. The principle of a gate barrier lifting to regulate the flow is nearly universal. The types of lift mechanisms observed by the author include a lever attached to the gate, several types of rack and gear mechanisms, a threaded rod with a large "nut" with handles, and worm gear to threaded rod drives. A "chain fall" attached to a gateway has also been observed in 20th century installations.

The water turbine can be one of many settings. The scroll case is an early type still being made. The case is designed to impart an angular momentum to the water. This type has its own pressure case which is bolted directly to the end of the flume or penstock. An example in operating condition can be found at Batsto Iron Works or in a static setting at The Hagley Museum (Figure 2).

In the open flume setting the end of the flume has a hole in the bottom which is plugged by the turbine (like the plug in the sink). In order for the water to escape it passes through the turbine, imparting its energy (see Figure 3).

Tub Turbine: A wooden tub is fixed to the end penstock. This tub has a hole in the bottom. The turbine rests between the penstock inlet and this hole. In the top of the tub are sealed joints (called packing glands) through which the turbine shaft is exited and through which a control rod passes. The Hagley Museum operates this type of turbine in the wheel mill restoration (Figure 4).

Other Pressure Cases: Instead of using a wooden tub, or an iron scroll case, some sort of pressure case is required when the level of water entering the turbine exceeds the height of the container in which the turbine sits. The pressure cases may be iron, concrete, or fabricated steel. The pictured example (Figure 5) is at The Hagley Museum and is at the bottom of a column of water 24 feet high.

Speed Control on the Turbine: Most processes operate best when the machinery is operating at a precalculated speed. For example, the stone on a grist mill revolves at a speed slightly in excess of one hundred revolutions per minute, while the wheels in a gunpowder mill revolve around the spindle at ten revolutions per minute. Hence, maintenance operating speed is critical, and if a new machine is turned on in a mill, as the bolter in a grist mill, then all the previously operating machinery will slow down. The turbine then has to be readjusted so that the flow of water is increased and the desired speed is re-established. Usually this is done by a gate arrangement on the turbine (Figure 6). There is a type of turbine -- the

ADr Vol. VIII No. 4 1976 Page 47



Open Flume

FIGURE 3

Vol. VIII No. 4 1976 Page 48 A^r



Figure 4 Tub setting for a turbine at The Hagley Museum.


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Kaplan type -- in which the blades of the runner are adjustable. These are found both with and without gates. The Kaplan turbines were invented in the 20th century and are not common in historical situations.

Governors: Some water turbines have feedback devices called governors (see Figure 7). These machines regulate the speed of the turbine (as much as the governors or steam engines regulate the speed of the engines) by controlling the flow of the water into the turbine. They automatically adjust the previously-discussed speed control. The topic "Governors" is treated in detail in Feedback Mechanisms in the Collections of the National Museum of History and Technology, by Otto Mayer. It is rare to find a governor in a small installation, but in hydroelectric plants and large installations governors are invariably present.

Draft Tube: The draft tube is a section of pipe below the turbine designed as a suction device. These vary in length from nonexistent to almost the total fall of the site, but not more than 20 feet. In some settings the turbine is set just below the level of the race and the tube is several feet long. Generally, installations with the draft tube are a bit more efficient than the ones without. There is a trade-off. When one gains by draft tubes, one in some measure loses by an effect called cavitation. This is a more rapid erosion of the vanes of the turbine caused by the bombardment of bubbles. Many 19th-century installations avoided cavitation by placing the turbine two feet below the level of the tailrace (see Figure 8).

Tailrace: The spent water flows out of the turbine and into the tailrace. Generally, where the tailrace intersects the river, there is a small deflection dam built into the river to allow the discharge to flow smoothly, and in some cases, to gain extra power by taking advantage of the continuing fall of the river (refer to Figure 1).

Turbines in General: Water turbines have several marked advantages over conventional waterwheels and a few drawbacks. Turbines are not as badly affected by ice as waterwheels. However, a phenomenon called "anchor ice" can raise problems. Not every installation which has freezing conditions has this problem. Since turbines sit under water, most ice, wooden debris and floating debris is not as much of a problem. Turbines generally require less maintenance than waterwheels, are easier to install, and are much easier to service.

Turbines by no means approach perfection. For example, a turbine will run very efficiently in only a small range of the possible flows (see Figure 9). The late Kaplan turbines were built with adjustable vanes to allow higher efficiency at several flows. Many small mills, in areas where water was scarce, converted back to waterwheels, since waterwheels are consistent in their efficiency throughout their operating range. Single- function mills where the power requirement was consistent, as cotton mills, merchant grist mills and machine works, were best served by the water turbine as were other mills where the amount of water available proved not to be a problem. Hence, in some cases inefficient utilization of the energy was more desirable than the maintenance of other power sources.

A^r Vol. VIII No. 4 1976 Page 50



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As the 20th century dawned, ancillary semi-diesel engines became popular and the problem of water turbine efficiency in small multipurpose mills was less important. Large mills had been using steam power to supplement waterpower as common practice since the second quarter of the 19th century. As an aside, the U. S. census indicates that steam passed water in popularity as a power source in the decade between 1860 and 1870.

Historically, the earliest turbines in the U. S. of which we are aware were installed in the early 1840's, and their popularity increased as the century passed. Many installations went from waterwheel to water turbine. For those studying such a building this presents several problems. First, the mill drive train will show signs of change. Waterwheels turn usually around six revolutions per minute. The median speed for small turbines is two hundred revolutions per minute. Hence, when looking at the mill, the transmission system and gearing has to be compatible with the power source.

Historians studying turbines will encounter the terms inward and outward discharge. The early turbines discharged the used water around the circum- ference of the runner while most later turbines discharged through the bottom. The illustration in Figure 6 is an inward discharge.

Turbines were cheaper and easier to install than waterwheels. In fact, it was common practice to install more than one turbine in small installations which served more than one function. For example, at the Black Rock Mill in Maryland one turbine powered the gristmill while a second one powered a sawmill. The writer does not believe these multiple turbines were all a manifestation of the efficiency/water problem, but more just a simpler way to gear up the machinery. [In the same Middle Atlantic region, all observed waterwheel installations for multipurpose small mills had a power takeoff from the gristmill machinery in whatever else was done (as sawmill, etc.)] The use of multiple wheels in small mills was not observed.

Having briefly discussed the salient parts of a turbine operation, the remainder of this article is devoted to restoration advice.

If one has an installation that was initially wheel-powered and subse- quently converted to turbine-powered, there has to be a decision as to which mode the restoration will follow. Waterwheels are by far more spectacular, and also more trouble. Wheel installation and operating costs are also higher. The writer likes working with turbines more than wheels as the technology for dealing successfully with them and obtaining the correct appearance of parts are both conveniently (almost) current. If the decision for turbine power is made, the following comments may prove useful.

Archaeology: The archaeology has two purposes. The first is to find out how the installation was assembled, and the second is to physically remove the debris in the way of reconstruction. The job is dirty, heavy work and can encounter undesirable inhabitants as poisonous snakes, spiders and the ever-present rat. Gristmills have rodent problems -- especially operative ones when grinding. With the archaeology there is a trade-off between retrieval of knowledge and allowing reusable parts to remain undisturbed.

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Figure 7 Governor of the Civil War period in original location at The Hagley Museum.





Beware of great timbers set and the surrounding wall being erected around them. If the timber has been continually wet, it will probably be in good shape. Removing it, on the other hand, could necessitate the rebuilding of a whole foundation. Archaeology in wet pits does not have to be concerned too much with the strata of fill. Although this is heresy, the simple truth is that all material exclusive of the original installation is scrap that dates in the last one hundred years or so. Since the pit will undoubtedly be wet and need pumps to keep water out, the strata will not be definable as every shovelful of mud will be immediately replaced by more mud.

On occasion the archaeology will find the original turbine in the pit. The effort in removing was usually greater than the scrap value and it survived because it was worthless. Turbines are basically cast iron. Heat and pounding have the tendency to crack castings. Removal of turbines should be done carefully unless one only wants to scrap it. Turbines are held in place by some form of bolts and brackets. These must go before the unit is lifted. Bolts and brackets are either wrought iron or steel. Since they will be too corroded to work conveniently, the bolts will have to be sheared (carefully). Getting the turbine out after it is loose is no problem if one is careful. Remember it will weigh from one-half ton to several tons, and the approximate weight needs to be known before choosing rigging. Lift straight up. This might well mean that a frame will have to be made for the job to hold the chain fall. Quite often old turbines can be rebuilt; there- fore it behooves the project manager to take special care in extracting an old unit.

In historic settings, the lower one goes the better the conditions of the setting because the lowest parts were constantly wet, and barring changes in river levels, probably remain wet. Since the original builders had the propensity of setting massive wooden beams and then building foundations around them, the reuse of sound original members can result in a great savings in money, time and aggravation. The wheel mill at Hagley reuses all original 1880-vintage timber 3 feet below the water line.

To test such surviving wooden beams, a Swedish increment boring tool is useful, since wood often seems fine on the outside but in the process of wetting and drying the center had rotted out.

If the original iron is intact and basically sound enough for reuse, be sure to check it again soon after start-up. Experience has shown that vibrations from running will shake the rusty scale loose, thereby reducing the dimensions and producing "slop" in the system. Since exact alignment of parts is essential to smooth operation and low maintenance costs, the above is very important. Upon completion, servicing becomes the new problem of the restoration.

Determining the condition of masonry work is fairly simple as rocks are visually obvious, and the mortar can be checked with a screwdriver. One can pretty much assume that repointing will be necessary. Cement installations should be inspected by a civil engineer.

A Fr Vol. VIII No. 4 1976 Page 55



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Selecting a Turbine: If replacement of the original turbine is necessary there are several factors to consider. One needs to know the head (nominally the difference in elevation between the top of water in headrace and top of water in the tailrace), the flow (usable cubic feet per second in power source), and the power requirement of one's mill. Turbines come in high-head and low-head varieties. This means that, if the difference between the water intake level and the tailrace is great (say, 100 feet), the turbine is a high-head turbine and has the curve of the vanes calculated to run efficiently with the great pressure. If the difference is minimal (10 feet or so), the turbine is a low-head turbine. Supposedly the turbines were originally supplied to each installation calculated for its head. The basic principle to know, however, is having a turbine the same size as the original, for the site will in no way assure efficient operation and the same power output. There are several variables to take into account.

REINSTALLATION -- SOME HINTS

Penstocks: If one has the responsibility of setting flume (penstocks) pipe, note that "level" pipe probably will incline downward at least 1/4 inch per foot. This allows for drainage during servicing. The lower one gets below the level of the race, the higher the internal pipe operating pressures. This means that pipe joints need to be carefully joined, sealed, or caulked and filled. The technology of wooden pipe, bell and spiked cast pipe, and fabricated sheet metal pipe varies considerably. At this writing all forms of pipe are still available, although large-diameter cast iron pipe is more difficult to obtain and quite costly.

Setting a Turbine: Modern industrial specifications for "setting" (or leveling) a turbine are t.005 inches per foot. If this can be achieved, do it. One can buy a machinist's level (ours is a Starrett) which will read to that tolerance. The more accurately the installation is initially set up, the less the maintenance problems in the future. Old buildings quite often settle and problems arise.

When settling occurs, there are two solutions. One can tear out the culprit and rebuild it, or one can shim it. All accurate settings have some shims. One deliberately builds the base a small fraction of an inch low and then shims up to true. This method is vastly superior to grinding excesses away. A settling problem will require careful examination to determine the best solution.

Generally a turbine will have two sets of bearings, the thrust and collar. The bottom set takes all the weight and is called the thrust bearing (see Figure 6). The shaft is held true by a series of adjustable blocks forming a collar bearing. These have historically been made of the wood lignum vitae. Lignum vitae is dense, oily and requires no lubrication beyond the water which flows through the turbine. Both the turbine case and the shaft have to be installed accurately. Do not set the case on askew and correct with the collar bearings.

ADr Vol. VIII No. 4 1976 Page 58



Figure 10 Generator floor under construction at the Hydroelectric Plant, Hagley Museum. This project places in service a Smith-Kaplan turbine (seen here being lowered into pressure case) and General Electric generator (originally made for the 1932 Winter Olympic Games in Lake Placid) on a site originally developed as a hydroelectric plant in the late 1890s. The plant is not a restoration. It will develop enough electric power to supply the needs of the Museum and will return in savings on the investment cost at a high rate. There is a Visitor's Room with explanatory panels and a viewing area for see- ing the generator floor. The foundations and exterior of the building visually duplicate the original plant. The machinery and switch gear meet modern standards. Waterpower is still the cleanest and cheapest practical source of energy available. Courtesy of The Hagley Museum

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Figure 11 Hydroelectric plant under construction. Generator to right partially obscured by

at the Hagley Museum. in center, oil pump to generator.

Generating floor left, governor


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If the turbine is set in a tub or pressure case, the driveshaft and control rod will protrude via a stuffing box (see sketch). These are not bearings; they are accurately aligned water seals.

Bearings, Couplings and Shafts: By the time turbines came into common usage, the form of the essentially modern bearing had evolved. The speeds of a turbine are considered "low speed" by modern standards. The bronze or babbit bearings are both correct (for mid-to-late 19th century). Roller and ball bearings are more usually found on 20th century installations. While modern roller bearings are found concealed in restorations, it is not necessary, and perhaps undesirable mechanically. Roller bearings will heat up if a roller breaks, which can cause a safety hazard as in the case of a gristmill with dust in the air. Of course, the modern bearings are not correct in older historical settings. As a general rule of thumb, go with the original technology. The writer has had experience with "improvements" which cause nothing but grief. The original, fabricated to the best attain- able accuracy, usually gives the best results.

Fortunately, most turbines are directly coupled to iron shafts geared with all-iron or one iron-and-mortise gear on another iron shaft. In some installations, wooden shafts still remain to power ancillary equipment, but this is usually light in terms of power requirements. Iron shafts and gears are simpler to work with than wood and infinitely more pleasant to maintain, and use easily available stock parts.

Start-up: The initial start-up period requires close supervision. Gears will "wear in" and will need adjustment; pieces will shake loose and need realignment; and pieces that are inherently weak will break. Schedule down- time soon after start-up for inspection. After running the installation there becomes a threefold maintenance problem. The first is lubrication, done at least daily, usually by the mill operator. Also, trash racks need daily inspection and cleaning when necessary, which varies seasonally. (At Hagley we have weekly inspections of the machinery by the maintenace staff, which results in occasional minor overhauls.) These include aligning gears, bearings, and tightening stuffing box seals. Major overhauls on turbines are uncommon but require major dismantling and machine shop work. At Hagley trash racks are cleaned as needed by the grounds crew.

Corrosion Problems: Most water turbines are cast iron. If the turbine is kept wet, the corrosion problem from rusting is virtually nonexistent. Wetting and drying will accelerate the rate of rusting; hence, the advantage to the installations which rest below the tailrace. The cavitation problem, where vapor bubbles bombard the runner and literally pop off the metal, is encountered with most draft tube turbines. The erosion problem is slow and, since most restorations operate in terms of demonstration instead of produc- tion, the erosion is a factor in long-range planning (like replacing tires on an automobile) and not a deterrent in doing a restoration.

A^r Vol. VIII No. 4 1976 Page 61



Maintenance Routine: Part of the planning for every restoration should be maintenance. Machines need lubricants, adjustment, and parts replaced. All of this is a factor usage. Beware of dirt getting in lubricants, as it will effectively convert grease to grinding compound. There is no economy in reusing the lubricant which works out of the fittings. The service policy at Hagley is to have the operator each day check lubricant levels, and replace low levels where accessible. As previously mentioned, the service department makes routine checks (as does the curator who put the mill together). The operator should be able to detect things going wrong by the change in sound of the machinery of vibrations. He should be trained to report the problems to the proper persons to make the necessary repairs. During all servicing except morning lubrication, two men should be present for safety. Mills were designed to increase man's strength and consequently present a hazard to a lone man.

Conclusion: Turbines allow mechanical restorations to function reliably at a very low cost for energy. The Hagley Museum, for example, has several, one of which was put into service three years ago with virtually no trouble. The institutional faith in this source of power is being demon- strated by the erection of a power plant (on the site of an 1893 power house) which will provide electricity for the entire property.

Turbine technology is an example of a technology which was perfected to a high level over a hundred years ago, and is a technology being utilized today with only a few improvements. Hence, when considering to attempt a turbine-powered restoration, one should be encouraged as the problems are not that great.

APPENDIX

Known Firms working with Water Turbines

James Leffel & Co. (manufacture and repair) 426 East Street Springfield, Ohio 45501

Barber Hydraulic Turbine, Ltd. (manufacture and repair) Box 340 Port Colburn, Ontario Canada L3K 5W1

Allis-Chalmers Corp. (large plants) Turbine Division 1126 S. 70th St. Milwaukee, Wisconsin 53201

Hydro International (civil contractor -- work with 1 Court Drive, Apt. C. Empire & Niagara) Wilmington, Delaware 19805




Harry J. McKay 68 Tennessee Ave. Port Colburn, Ontario Canada L3K 2R9

(erector only)

(repair and erecting) Empire Company General Delivery Woodland, Maine 04694

Niagara Water Wheels 706 E. Main St. Welland, Ontario Canada L3B 3Y4

Robert L. Johnson Whistles in the Woods Route 1, Box 265-A Rossville, Georgia 30741

Campbell Waterwheel Company 420 South 42nd Street Philadelphia, Pennsylvania 19104

(new/repair/design)

(will produce odd parts such as wooden gears)

(general services)

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