S PECIAL - FEATURE

Oil lubrication eradicated, on paradise island The Department of Hawaiian Homes wanted to eliminate oil contamination while overhauling a deep well pump used as a primary potable water source for the island of Molokai. Bearing failures are often experienced when systems of tbis depth are convert- ed to water lubricution because of tbe difliculty of maintaining lubrication duringpump startup. Roscoe Moss tells bow these problems were avoided by switching from bronze to graphite metal alloy bearings that withstand run-dry conditions. The result has been four years of trouble-flee operation.

Molokai is the fifth largest island in the Hawaiian archipelag: 260 square miles in area, 38 miles long, and ten miles wide at its widest pointThe popula- tion is estimated at 7000 residents, half of whom

Molokai is the fifth largest island in the Hawaiian archipelag: 260 square miles in area, 38 miles long, and ten miles wide at its widest pointThe popula- tion is estimated at 7000 residents, half of whom

One of the wells on which oil-lubricated bronze bearings One of the wells on which oil-lubricated bronze bearings were replaced by graphite-metal alloy. were replaced by graphite-metal alloy.

1: ive in or near the principal town of Kaunakakai. Nearly 40% are of Hawaiian descent, thus the nick- name,“The Most Hawaiian Island.“The Department of Hawaiian Homes (DHH) operates the water sup- ply system on the island including the Kualapuu Wells, one of the primary sources of potable water on the island.

By Bill Moore, president, & Norman Messenger, mechanical engineer, Roscoe Moss Hawaii, Inc. Kapolei, Hawaii

New pumps needed

In 1994, the DHH requested bids for two new line- shaft pumping units for these wells. Well no. 1 pump required a complete unit including motor and discharge head assembly while the existing 300 hp motor and discharge head assembly for well no. 2 pump was in good condition and could be reused.The existing pumps used enclosed line- shafts and oil-lubricated bronze bushings through- out. Each pump was 1000 ft long with the water level approximately 950 ft below the mounting ele- vation. Bearings were lubricated by dripping a lightweight turbine oil into the top of the enclosing tube from a solenoid oiler, which stops oil flow when the pump is not operating.The oil descended by gravity from bearing to bearing and escaped into the well through drain ports just above the top impeller that were sealed against leakage.

This approach provides excellent lubrication but is rapidly becoming obsolete due to water quality and environmental concerns.As with most recent water supply projects, the DHH specified in this case that the stuffing box assembly be con- verted from oil to water lubrication in order to eliminate oil contamination of the water sup@y. The use of food-grade lubricants was ruled out here because the water provided by these wells would be very expensive to replace, even for short periods of time.

Considering the alternatives

Another option would have been to use a sub- mersible pump. Submersible pumps have been

0262 1762/99/$ - see front matter 0 1999 Elsevier Science Ltd. All rights reserved.

PECIAL FEATURE

used in a number of deep-set pump applications with success in recent years but they are quite expensive both from an initial purchase and from an operations standpoint. In addition, the life expectancy of a submersible pump on this appli- cation would be only about five yearshs a result, Roscoe Moss engineers, working with DHH’s con- sulting engineer, Clifford Jamile, investigated the water-lubricated bearing approach.

An open lineshaft running in cutlass rubber bearings can be lubricated and cooled by intro- ducing a considerable quantities of water through a port in the discharge head for a period of 10 to 15 minutes prior to energizing the pump. However, frequent failures have been seen in water lubricated open lineshafts with rubber bearing construction in deep-set applications of 600 ft and higher. Water is a good lubricant, but the loss of water during the prelubrication period just prior to pump start-up will cause cutlass rub- ber bearings to fail in a matter of seconds once the motor is energized. Bearing failures require expensive maintenance that force the pump to go out of service for up to a week.This means that the bearings must be continually infused with water during the startup and shutdown phases. In deep-set applications, air rushing up the shaft during the startup phase atomizes the water stream in the upper portion of the well, prevent- ing proper lubrication. In addition, adequate lubri- cating water may not be available in certain situa- tions such as during a storm or breakdown.

Another approach is to substitute water for oil in a standard enclosed lineshaft using threaded bronze tube connectors and bearings.This type of system is used extensively in short-coupled water supply applications, however, it typically fails quickly in deep-set applications above 600 ft for the same reasons that open lineshaft systems fail. In an effort to avoid these problems, a scheme has been developed in which water is introduced at various levels in the welLThis approach provides more consistent lubrication but is quite expensive and still subject to failure during an interruption of the water supply.

0 Graphite-metal bearings

In an effort to solve this problem, Roscoe Moss engineers evaluated a wide range of run-dry bear- ing materials.Their tests included trials of several alternative synthetic nylon bearing materials. Some improvements were seen over bronze and rubber materials but the new materials still did not exhibit the ability to consistently withstand the demanding run-dry conditions of the applica- tion.Then, an engineer heard about graphite-metal alloys that take advantage of the special proper- ties of graphite. A graphite structure can be com- pared to a deck of cards with individual layers able to easily slide off the deck.This phenomenon

Bearing failures could knock the pump out for up to a week.

gives the material a self-lubricating ability that is matched by no other material. External lubricants are simply not necessary.The graphite matrix can be filled with a variety of impregnants to enhance chemical, mechanical and tribological properties.

Roscoe Moss engineers identified a graphite- alloy material that had already been successfully used in several deep-set well applications, Graphalloy@ graphite-metal alloy from Graphite Metallizing Corporation, Yonkers, New York. This unique self-lubricating bearing material requires no grease or oil, survives run-dry conditions and

Fitted with the graphite-metal alloy bearings, the pumps are more tolerant of upset conditions.

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S PECIAL - FEATZTRE

Boosters 1 and 2 with altitude valves in the foreground.

eliminates galling and seizing in a hot and dry con- ditions.The material works at higher temperatures up to 1000°F (525°C) where oil-based lubricants burn off or oxidize and plastics fail. It maintains its integrity even when submerged in hostile liquids such as acids, alkalis, hydrocarbons, black liquor and liquid gases.The material provides a constant, low coefficient of friction rather than just a sur- face layer, helping to protect against catastrophic failure. Lubrication is maintained even during lin- ear motion; lubricant is not drawn out and dust is not pulled in.

m Proposal and design

The proposal that Roscoe Moss submitted to the Department of Hawaiian Homelands stated that “the additional expenditure for the graphite bear- ings will provide, for the end user, a value that far

Boosters 1 and 2 looking East.

exceeds the bearing insert cost by extending the life of the machine, providing a positive method of lubricating the lineshaft with or without water flush as described in the specifications.” The department accepted the company’s proposal.

Well pump no. 1 used a Layne and Bowler lORKEH-22 stage bowl assembly with 8 inch columns, 3 inch enclosing tube and lll/lh inch shaft diameter. This pump was rated for 600 gpm with a field head of 1080 ft.Well pump no. 2 used a Layne and Bowler 11 DWH-19 stage bowl assem- bly with 8 inch columns, 4 inch enclosing tube and 1 15/16 shaft diameter.This pump used the exist- ing 300 horsepower motor.This pump was rated for 800 gpm with a field head of 1080 ft.

Bearing implementation

Installing the Graphalloy bearings required only minimal modifications to the existing enclosure. Roscoe Moss engineers provided their dimension- al constraints to Graphite Metallizing who designed the new bearings which are fitted in SAE 660 bronze tube connectors located at five foot intervals throughout the length of the lineshaft. Every other tube connector contains a full bear- ing and the other connectors contain a half bear- ing. The existing 415 stainless steel lineshaft did not require modification.

The smaller 200 horsepower pump for well no. 1 was the first to be completed and installed. This unit was started in September of 1995 and was run 24 hours per day until the second pump was installed.The larger pump for well no. 2 was delivered and installed in May of 1996 with a final walk-through inspection in June. Since that time, only one of the two pumps has been run at any given time due to power restrictions on the island.The smaller 200 horsepower pump is run during peak hours and the larger 300 horsepower pump during off-peak hours.

This installation has delivered trouble-free ser- vice since installation. A standard lubrication sys- tem was provided, however, in emergency situa- tions, operators restart the pump without any lubrication. The success of this application has led to the installation of Graphalloy bearings in several other open and enclosed lineshaft applica- tions in Hawaii by Roscoe Moss.These include an enclosed lineshaft water flush system owned by the Hawaiian Electric Company, an enclosed line- shaft potable water supply owned by the Maui Board of Water Supply and an open lineshaft potable water system owned by the Hawaii Department of Water Supply. Each of these sys- tems has provided the same trouble-free service as the original installation in Molokai. n

Contact: Graphite Metallizing Corp., 1050 Nepperhan Ave., PO Box 110, Yonkers, NY 10702, USA. Tel: +l 914 966 6400; Fax: +l 914 968 8468.

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