echanical Seal Installation Here's what to do when manufacturer's instructions aren't available.

BY ta- ------

I_

nstallation of mechanical seals is a seemingly simple topic that actu- ally involves many issues, each of which must be addressed to

insure success. To some readers, some of these considerations may seem a bit overwhelming; to others they may seem petty. All of these points, however, should be consid- ered in any mechanical seal installa- tion and many of them should be a part of a written procedure for plant mechanics. Others will become a part of the repair process without specific written or oral instructions. However, implementation of OSHA CFR 1910 - Mechanical Integrity - should include a written procedure pertinent to your facility. The proce- dures provided in this article, while applicable to most situations, are not meant to be all-inclusive.

PUMP CONDITION To limit the scope of this discus-

sion, we will assume that the bearing frame of the pump has been repaired properly and that all runouts are within 0.002" at the seal area. Before installing the seal, the condition of the pump shaft must be noted. If the shaft has a hook sleeve, the surface of the gasket seats should be free of any nicks or burrs. If the seal has a sleeve with an O-ring, the shaft should be free of pits or scratches where the ring seats.

BASIC INSTALLATION PROCEDURES The general rule of thumb is,

"Install per the manufacturer's instructions" or "Install per the seal drawing." Obviously this is the pre- ferred choice. Any time the manufac- turer's drawing is available, the mechanic should use it to set the tension on the seal, and follow the printed installation instructions accompanying the drawing. Howev- er, this simple task can become con- fusing if a drawing is not available. Table 1 gives a guide for sctting seals in such a case. Note that the table is not exact and should be used with caution in hazardous services.

Single Spring Bellows

Half the Spring Length

*In non-hazardous services a set of 1/8- 5/32" for bellows less than Q', 3/16 for seals above 5 .

COMPONENT SEALS

Here are a few tips for installing the stationary hardface into the gland:

1. For O-ring type seats lubricate the O-ring with a product-compatible grease to ease the pressure of instal- lation. (Dow Corning 111 Valve Lubricant and Sealant works well.) This is especially true for silicon car- bide seats, which are brittle. (See hint on removing silicon carbide hardfaces from glands.)

2. For seats with grafoil, chamfer the gland to prevent the square edge from damaging the grafoil. This can be done with tool steel. The process does not require a lathe.

The following steps should be taken in installing component seals when the seal drawing is available (Figure 1):

1. Scribe a mark on the shaft or shaft sleeve that lines up with the face of the stuffing box (Line A). Be certain to have all gaskets on the seal chamber/backplate installed before determining this location.

2. Scribe a second mark on the shaft (Line B) for the seal-setting dimension determined from the seal drawing.

3. Place the gland on the shaft

Figure 1

close to the bearing frame, taking care not to bump the stationary seat.

4. Place the gland gasket on the shaft.

5. Install the rotary unit using Line B as the reference for the set point and tighten the set screws evenly.

6. Complete the pump assembly and tighten gland bolts evenly.

If a seal drawing is not available, use the following steps to determine Line B (Figure 2):

1. Determine the seal working length. (This number is often stamped on the rotary unit.)

a. Measure the free length of the rotary unit.

b. Using Table 1, determine the working length by subtracting the seal set from the free length.

2. Scribe a mark on the shaft or shaft sleeve that lines up with the face of the stuffing box (Line A on Figure 2a and 2b). Be certain to have all gaskets on the seal chambedback- plate installed before determining this location.

3. Determine the location of the stationary seat. The seat will either protrude into the seal chamber, as in Figure Za, or be recessed in the gland (Figure 2b).

4. Referring to Figures 2a and 2b, scribe a line (Line C) on the shaft where the stationary face will oper- ate with the gland bolted in place. This is dimension 'x' on the drawing.

a. If the hardface protrudes into the seal chamber, measure from Line A into the seal chamber and scribe Line C.

b. If the hardface is recessed in the gland, measure from Line A away from the seal chamber and scribe Line C.

5. Measure into the stuffing box from Line C the working length of the seal and scribe Line B.

6. Install the rotary unit, using Line B as the reference for the set point, and tighten the set screws evenly.

44 APRIL1996 PUMPS AND SYSTEMS MAGAZINE

ANSI PUMP MANUFACTURERS For more information from the

following ANSI Pump Manufactur- ers, circle the corresponding number on the Reader Service Card.

Manufacturer Circle Number

ABS ...................................................... 275 American Turbine Pump ........................ 276 Ansimag.. ................................. .277

.............................. ..278

................................ 279 A.W. Chesterton ......................... .281 R.S. Corcoran ........................ Crane Chempump ................................ 283 Crane Deming ...................................... 280 Dean Pump Division, Metpro Corp. The Duriron Company .......................... 285 Endura Division of Liquiflo Corp. .......... 286 Environamics ........................................ 287 Floway Pumps ...................................... 288 Fybroc Division, Metpro Corp. ........ 289 Gorman Rupp Company ........................ 290 Goulds Pumps ...................................... 292 Griswold Pumps .................................... 291 Ingersoll-Dresser Pumps ...................... 293 ITT A-C Pump .............................. 294 ITT Marlow ............................................ 295 lwaki Walchem ............................ 250 Johnston Pumps .......... Klaus Union .................. KSB ...................................................... 298 LaBour Pumps ...................................... 299 Magnatex Pumps .................................. 300 Paco Pumps .............................. 301 Patterson Pumps .................................. 302 Peerless Pumps .................................... 303 Shanley Pump & Equipment Smart Turner ........................................ 305 Sulzer Bingham Pumps ........ Sundstrand Fluid Handling .................... 307 Vanton Pump & Equipment ............ 308 Warren Pumps ...................................... 309 WDM .................................................... 251 A.R. Wilfley & Sons ...... ...... 252

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PUMPS AND SYSTEMS MAGAZINE APRIL1996 43

7. Complete pump assembly and tighten gland bolts evenly.

CARTRIDGE SEALS The set of the seal on cartridge

seals is inherent in the design and established at the factory as com- plete assemblies are produced. A giv- en assembly will contain center tabs or spacer washers that must be removed after the seal assembly is bolted in position and the sleeve is locked to the shaft. The following are typical installation instructions:

1. Install the seal assembly on the shaft.

2. Assemble pump backplate and impeller. In the case of open or semi-open impellers, make impeller clearance adjustments at this time.

3. Slide seal assembly into the stuffing box and tighten gland bolts.

For seals with O-ring secondary seals:

4. Tighten sleeve collar set screws to the shaft.

5. Remove centering tabs or spacers. (Retain for pump disassem- bly. 1

For seals with grafoil secondary seals:

4. Crush grafoil rings with bolts

5. Tighten sleeve collar set

6. Remove centering tabs or

provided.

screws to the shaft.

spacers. (Retain for pumpdisassem- blY. 1

I OTHER CONSIDERATIONS Secondary Seals - Gaskets, o-

rings, or grafoil are all secondary seals for shaft sleeves. The following are questions to ask when installing these: Is the seal material the right material? Is the sealing surface in good condition? Am I installing it over threads? Installation over threads is a common occurrence on vertical pumps. One simple caution- ary approach is to wrap the shaft with masking tape and then slide the seal over the shaft. This minimizes the chance of the threads (especially square groove threads) cutting the o-

ring during installation. Note that masking tape is about 0.005” thick. If the outside diameter of threads is close to the inside diameter of the seal or sleeve, this technique will not work.

Pump Types - Pumps with open face impellers usually have the clearance from the volute adjusted in the field. If the seal is a component design, this can be a significant prob- lem. Consider that the mechanic measures the working length of the seal, either spring or bellows, in the shop and installs the seal gland. After he installs the bearing frame in the field, he will need to determine the distance the impeller is away from the volute. Depending on shaft variability, he may need to adjust this distance .032” or more. With a single spring seal application, this variability is more than likely accept- able.

With multi-spring seals, or espe- cially bellows seals, this deviation from the recommended working length could lead to premature fail- ure. In light hydrocarbon and flash- ing services, working length can become even more critical due to the importance of correct face loading, which prevents flashing and dry run- ning of seal faces. One solution to this problem is to use cartridge seals in these services. In this case the impeller adjustment is made prior to tightening the seal gland bolts.

B Lina,,JK A

Working Length

Figure 2A

I+- tine B t i n e - q . r l z ~

f Worklng Length

Figure 2B

Another remedy is to remove thc volute with the bearing frame wher the pump is overhauled. In this wal the distance between the impellei and the volute could then be sei without the seal. The pump could be disassembled and the seal installed.

Gland Piping - This item may seem obvious but is often overlooked - CLEAN the piping! This simple task can prevent orifices from gettint plugged and, with dual seals, can prevent contaminants from entering new barrierlbuffer fluid in the seal pots. Unfortunately, seal manufac- turers can mislabel the gland ports. This is especially true of seals that were built prior to API 682, which standardized porting terminology. Care should be taken to insure that the flush port and the in and out ports on dual seals are labeled cor- rectly. This can be done by connect- ing low pressure shop air to the seal or by referring to the seal drawing.

Split Case Pumps With Dual Seals - These pumps use two seals to prevent leakage at the ends of the shaft. Dual seals incorporating pumping rings or cutwaters to assist in the circulation of the barrier fluid are direction- dependent, In other words, the in and out ports on the coupling end of the pump are oppo- site the in and out ports on the out- board end of the pump. Since the

PUMPS AND SYSTEMS MAGAZINE APRIL1996 45

Figure 3 glands usually are shipped with ports stamped, they may need to be restamped both for the ports and for designating the end of the pump on which each of the seals is to be installed. This can be done by the vendor if the person ordering the seal takes the time and care to speci- fy it at the time of order. Errors in these situations are even more com- mon if pipe fitters and not pump mechanics are used to pipe the seal to the seal pots.

An item to note concerning gland piping is that the Eighth Edi- tion of API 610 allows for stainless steel tubing in hydrocarbon services. This is a change. Previously, only pipe was allowed in hydrocarbon service.

Seal Pot Piping - The general recommendation of seal vendors is to keep the piping to the seal pots to a maximum of five linear feet. Unfortunately, those of us in indus- try realize that this is often impossi- ble. In situations where compromise is a must, enlarge the tubing to 314"

I 'Figure4

to minimize pressure drop. On dual seals with pumping rings, one seal supplier recommends installing a larger supply line to the seal than the return to the seal pot. Typically, this will mean a 518"- 314" supply line will be used with a 1/2" return line.

Also, many pipe fitters are trained to install what I call "pretty tubing." Although 90° bends are nice to look at, they usually increase the linear footage of the pipe system and will increase the pressure drop. These 90" bends also increase the chance of there being low spots in the piping. Explaining to the pipe fit- ter the reason for reduced runs and gradual bends can increase buy-in on an installation. Pipe fitters may view as shoddy craftsmanship the ar- rangements that yield solid pump performance, but the benefits of per- formance over beauty are clear to most people.

Seal Pots - Seal pots purchased from the seal vendors are built to insure proper installation; however, many pots are built by users them- selves. The most common problem I have encountered with these is that the return line to the seal pot is above the liquid level in the pot. This scenario prevents proper circulation of the barrier fluid. In applications without pumping rings, thermal con- vection does not exist, eliminating cooling - a situation that can easily cause premature inner or outer seal failure.

Steam Quench - Steam quench pressure recommendations vary among seal manufacturers, but the range is often 2-4 psi. One problem often encountered at these low pres- sures is that it is not a steam quench at all but more like a condensate quench. In cooler services this may not be a problem because as the con- densate enters the gland, it most like- ly vaporizes to steam. In hot installations, though, the condensate rapidly flashes to steam, which is a safety concern for operations person- nel inspecting the equipment. Also, it can be damaging to the seal faces and shaft.

'Ityo techniques can be used to minimize this problem. One is to pipe the steam as seen in Figure 3. This setup allows the condensate to drain to the sewer while the steam

enters the seal. Many seal vendors believe that no steam is better than wet steam. The other method, limit- ed to hot services, is to run the quench line along the flush line (if an API Plan 11 is used). This keeps the steam from condensing as it enters the gland, and it slightly cools the flush. A setup like this has another advantage. In hot oil services it will keep the flush line warm while the pump is idle, thus preventing the oil from setting up in the line.

WHAT GOES WRONG? Although I have addressed some

of these issues previously, the follow- ing is a list of things I have seen most frequently go wrong during seal installations.

Secondary Seals - Many consci- entious mechanics have had difficul- ty with grafoil rings. Let's face it, they are tough to handle without damaging them. A good practice is to ask the seal vendor to supply an extra ring or set of rings with each new or rebuilt seal. Although this may seem excessive, it can help a mechanic at 2 a.m. when he dam- ages one. The sleeve gasket on hook sleeves often is the only source of VOC emissions on a pump. If the environmental department for your company has written-up a seal for repair due to VOC emissions, take the time to ask an inspector from that department to go out to the pump and sniff it with you present. Understanding where the leak is can prevent a lot of wasted time and effort. On old pumps in light hydro- carbon services, the leak will often be entirely under the sleeve.

Gland Gaskets - A two dollar part on a $4,000 seal can cause a mechanic an entire day of work if care is not taken. Take the time to insure that the gaskets of the right size and material are being installed. Installation is not difficult if the right parts are available. The lone excep- tion to this is split case pumps, espe- cially older ones. Seldom is the bottom half of a split case pump removed from the field and brought to the shop. Because of this the sur- face for the gland gasket may often not be flat. In addition, the case gas- ket on the pump is a part of the seal- ing surface for the gland gasket. On

46 APRIL1996 PUMPS AND SYSTEMS MAGAZINE

~

split case pumps with a paper style gasket, tabs should be left protruding at the gland sealing surface until the case is bolted tight. After the case is bolted tight and the pump is free to rotate, these tabs can be cut with a razor blade flush with the gland face, Also, in low pressure conditions a product compatible sealant can be used in conjunction with the gland gasket to help fill any voids. If prob- lems persist, other gasket materials, such as flexible graphite, may more readily conform to surface defects.

Piping - As stated, piping to the seal is often installed incorrectly. Getting the pump mechanic involved in the piping can help eliminate this problem since he typically has access to seal drawings. Also, he may have access to pump drawings, as in the case of Sundyne pumps where no gland exists and the piping must be installed to numbered ports that are identified only in the manufacturers instruction manual.

Bellows Working Length - Each seal manufacturer has its own working length dimension for bel-

lows, based on the size of the seal. I strongly recommend a chart or wal- let size card be made available to mechanics to assist them in installing the bellows with the proper working length. Beware of bellows with grafoil rings for the secondary seal. Each manufacturer references the seal from a different point, a fact that can cause great confusion.

Although mechanical seal installa- tion appears to be quite simple, a vari- ety of factors can contribute to failure. Paying attention to details will increase the probability of a successful installa- tion, And, if their benefits are recog- nized, proven procedures will become routine for the mechanics. W

Removing Stationary Inserts

One technique to remove sta- tionary inserts is to drill and tap for a small- diameter bolt behind the seat through the gland. See Figure 4. This allows the mechanic to push out the

R5000 Pumps “The High Temperature Process Pump People”

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seat slowly, minimizing the risk of fracturing seats, especially silicon carbide.

The author would like to thank Art Quirk of EG&G Sealol for his help in preparing this article.

Eddie Mechelay is Mechanical Supervisor at Total Petroleum’s Denver Refinery. He is a member of the Pumps and Systems User Advisory Team and a frequent contributor to the magazine.

BIBLIOGRAPHY

Handbook, EG&G Sealol, 1991 1. Seal & Survive, Seal School

2. Dura Seal Manual, Ninth Edi- tion, Durametallic Corporation, 1993

Circle Number 236 Circle Number 237

Richard L. Allen Principal Pump Specialist Fluor Daniel

Jeff N. Bryan Rotating Equipment Specialist Suncor Inc.

John Buck Machinery Technology Coordinator Chevron U.S.A. Products Company

Rick Enlow Rotating Equipment Specialist Mobil Oil Corporation

Eric M. Gillis Maintenance Engineer Merichem Company

Gary E. Glidden Foreman and Crew Leader Houston Lighting & Power Compan)

Ron Hoffman Supervisor, Maintenance Dept. City of Fort Collins Wastewater Treatment Plant

David A. Johns Senior Mechanical Equipment Engineer Shell Oil

Vern Maddox Reliability Engineering Superintendent Quantum Chemical Company

Eddie Mechelay Mechanical Supervisor Colorado Refining Company

Antonio Perez Senior Maintenance Engineer Union Carbide

Luis E Rizo Reliability Engineering Manager GE Silicones

Dewey W. Stump Senior Technical Specialist Duke Power Company

Reducing Noise In API Process Pumps Tests and observations point as solution. By Leon K. Stanmore

to geometry change

In offshore drilling operations, API process pumps sometimes have

e pump assem- to a concrete

vibration had

pumps were field and set

pumps are

base is made of welded steel, and there is no

grout to provide damping or rigidi- ty. End suction, top discharge pumps have been used successful- ly in this situation since 1956. How- ever, top suction designs were added later, and few pumps with the bell- mouth design were built and tested.

The pumps in question, tested at duty conditions of Q = 2 150 gpm, H = 314 ft and N = 1770 rpm, gener- ated intermittent bursts of broad- band noise. Reviews of test logs did not indicate any unusual pump behavior.

PROBLEM DISCUSSION When pressure fluctuations are

produced by liquid motion, the sources are fluid dynamic in char- acter. Fluid dynamic sources include turbulence, flow separation, cavita-

tion, water hammer, flashing and impeller interaction with the case at the water or inlet guide vane (split- ter).

The pressure and flow pulsation may be periodic or broadband in fre- quency and excite either the piping or the pump into mechanical vibra- tion. Mechanical vibrations can then radiate acoustic noise into the envi- ronment.

Pump pulsating sources are classified as:

discrete frequency compo- nents produced by the pump impeller

broadband turbulent energy resulting from areas of high veloci- ties

impact noise consisting of intermittent bursts of broadband noise caused by cavitation, flash- ing, water shearing action, water hammer and pockets of entrapped air at the suction inlet near the impeller

flow-induced pulsation caused by periodic vortex formation when the pump fluid passes an obstruc- tion.

Secondary flow patterns that can produce pressure fluctuations in centrifugal pumps include stall, recirculation (secondary flow), cir- culation, leakage, cavitation and wake (vortices) at inlet guide vane (splitter).

PROCEDURES One of the pumps was opened

and examined for any possible restrictions that could trap air. The pump case and impeller were exam- ined for dimensional compliance, casting quality, machining, balanc- ing and cavitation or mechanical damage.

During the investigation it was discovered that the suction flow splitter had square edges instead of radii facing and trailing the flow. This would create a disturbed flow

48 APRIL1996 PUMPS AND SYSTEMS MAGAZINE