Mechanical Seal Installation

echanical Seal Installation
Here's what to do when manufacturer's instructions aren't available.
-----nstallation of mechanical seals is a
seemingly simple topic that actually 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 considered in any mechanical seal installation 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 procedures provided in this article, while
applicable to most situations, are not
meant to be all-inclusive.
PUMP CONDITION
To limit the scope of this discussion, 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 preferred choice. Any time the manufacturer'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. However, this simple task can become confusing 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.
44
APRIL1996
BY-at
I
_
COMPONENT SEALS
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.
Here are a few tips for installing
the stationary hardface into the
gland:
If a seal drawing is not available,
use the following steps to determine
Line B (Figure 2):
1. For O-ring type seats lubricate
the O-ring with a product-compatible
grease to ease the pressure of installation. (Dow Corning 111 Valve
Lubricant and Sealant works well.)
This is especially true for silicon carbide 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.
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 chambedbackplate 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 operate 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.
Single Spring
Bellows
Half the Spring Length
*In non-hazardous services a set of 1/85/32" for bellows less than Q',3/16 for
seals above 5 .
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
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ANSI PUMP
MANUFACTURERS
For more information from the
following ANSI Pump Manufacturers, 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
294
ITT A-C Pump ..............................
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
......252
A.R. Wilfley & Sons ......
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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 complete assemblies are produced. A given 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.
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 problem. 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 acceptable.
Figure 2B
With multi-spring seals, or especially bellows seals, this deviation
from the recommended working
length could lead to premature failure. In light hydrocarbon and flashing services, working length can
become even more critical due to the
importance of correct face loading,
which prevents flashing and dry running 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.
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 manufacturers 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 correctly. This can be done by connecting 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 opposite the in and out ports on the outboard end of the pump. Since the
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 disassembly. 1
For seals with grafoil secondary
seals:
4. Crush grafoil rings with bolts
provided.
5. Tighten sleeve collar set
screws to the shaft.
6. Remove centering tabs or
spacers. (Retain for pumpdisassemblY.1
I
OTHER CONSIDERATIONS
Secondary Seals - Gaskets, orings, 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 cautionary 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-
PUMPS AND SYSTEMS MAGAZINE
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Working Length
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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 specify it at the time of order. Errors in
these situations are even more common 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 Edition 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 industry realize that this is often impossible. In situations where compromise
is a must, enlarge the tubing to 314"
I
'Figure4
46
APRIL1996
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 fitter the reason for reduced runs and
gradual bends can increase buy-in on
an installation. Pipe fitters may view
as shoddy craftsmanship the arrangements that yield solid pump
performance, but the benefits of performance 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 themselves. 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 convection 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 pressures 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 condensate enters the gland, it most likely vaporizes to steam. In hot
installations, though, the condensate
rapidly flashes to steam, which is a
safety concern for operations personnel 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, limited 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 following is a list of things I have seen most
frequently go wrong during seal
installations.
Secondary Seals - Many conscientious mechanics have had difficulty 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 damages 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 hydrocarbon 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 exception to this is split case pumps, especially 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 surface for the gland gasket may often
not be flat. In addition, the case gasket on the pump is a part of the sealing surface for the gland gasket. On
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 problems 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 wallet 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 installation appears to be quite simple, a variety of factors can contribute to failure.
Paying attention to details will increase
the probability of a successful installation, And, if their benefits are recognized, proven procedures will become
routine for the mechanics. W
Removing
Stationary Inserts
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
1. Seal & Survive, Seal School
Handbook, EG&G Sealol, 1991
2. Dura Seal Manual, Ninth Edition, Durametallic Corporation, 1993
One technique to remove stationary 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”
P.O. Box 68172, Indianapolis, IN 46268-0172
Telephone (317) 293-2930, FAX (317) 297-7028
Circle Number 236
Circle Number 237
Reducing Noise In API
Process Pumps
Tests and observations point to geometry change
as solution.
By Leon K. Stanmore
In offshore drilling operations,
API process pumps sometimes have
e pump assemto a concrete
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
vibration had
pumps were
field and set
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
48
APRIL1996
pumps
are
base is made of welded
steel, and there is no
grout to provide damping or rigidity. End suction, top discharge
pumps have been used successfully in this situation since 1956. However, top suction designs were added
later, and few pumps with the bellmouth 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, generated intermittent bursts of broadband 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 character. 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 (splitter).
The pressure and flow pulsation
may be periodic or broadband in frequency and excite either the piping
or the pump into mechanical vibration. Mechanical vibrations can then
radiate acoustic noise into the environment.
Pump pulsating sources are
classified as:
discrete frequency components produced by the pump
impeller
broadband turbulent energy
resulting from areas of high velocities
impact noise consisting of
intermittent bursts of broadband
noise caused by cavitation, flashing, 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 a n obstruction.
Secondary flow patterns that
can produce pressure fluctuations
in centrifugal pumps include stall,
recirculation (secondary flow), circulation, 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 examined for dimensional compliance,
casting quality, machining, balancing 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
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