Wcf steam seals 7 and 8

c

TVA

Operations Continuing Training

Tennessee Valley Authority

TVA

Widow’s Creek Units’ 7 & 8 Gland Steam Seal Systems

2 Widow’s Creek Units’ 7 & 8 Gland Steam Seal Systems

Table of Contents Units’ 7 & 8

TABLE OF CONTENTS ...................................................................................................................................................................................... LIST OF FIGURES ..............................................................................................................................................................................................3 STUDENT OBJECTIVES ..................................................................................................................................................................................4

Description of Rotor Glands...............................................................................................................................................

Steam Seal System Overview .................................................................................................................................................................5 General Description of Unit 7 Steam Seals ....................................................................................................................................5

7

Description Shaft Seal Packing’s.................................................................................................................................... Description of the Shaft Sealing System.........................................................................................................................8

. Description of Unit 7 Steam Seal Regulator...............................................................................................................

..9

General Description of Unit 8 Steam Seals................................................................................................................. 10

Description of Unit Attemperation................................................................................................................................ .15

Description of Cooling for the Intermediate Pressure Rotor Unit 8.................................................................. 16

Unit 7 Seal Oil Print............................................................................................................................................................171

Unit 8 Seal Oil Print............................................................................................................................................................8

Description of Gland Seal Exhauster............................................................................................................................ 19.20

Abnormal Operations of Steam Seal Systems............................................................................................................22 Procedures ..........................................................................................................................................................................................................

I‐10.045.201 U7 Loss of Steam Seals on Unit 7 Main Turbines .................................................................. I‐10.045.201 U8 Loss of Steam Seals on Unit 8 Main Turbines ..................................................................

WCF‐AOWCF‐AO

Summary ........................................................................................................................

.................................................................................. 25


List of Figures Figure 1 Turbine rotor gland ....................................................................................................................................7

Figure 2 Pressure distribution for a single shaft .............................................................................................7

Figure 3 Pressure distribution for multiple shafts .........................................................................................8

Figure 4 Labyrinth Seal Diagram ............................................................................................................................9

Figure 5 Part list of the steam seal regulator ................................................................................................. 12

Figure 6 Diagram of unit 7 steam seal regulator .......................................................................................... 13

Figure 7 Color diagram of unit 7 steam seal regulator ............................................................................. 14 Figure 8 Unit 8 steam seal regulator .................................................................................................................. 15

Figure 9 Unit 8 attemperator valve .................................................................................................................... 16

Figure 10 Unit 8 rotor cooling valve ..................................................................................................................... 17

Figure 11 Unit 7 colorized steam seal print ...................................................................................................... 18

Figure 12 Unit 8 colorized steam seal print ...................................................................................................... 19

Figure 13 Unit 7 steam seal exhauster ................................................................................................................. 20

Figure 14 Unit 7 gland steam desuperheater ................................................................................................... 21

Figure 15 Unit 7 gland steam condenser vent drain ...................................................................................... 21

Figure 16 Unit 8 gland steam condenser exhauster drain .......................................................................... 21

Figure 17 Unit 7 steam seal regulator manual bypass .................................................................................. 22

Figure 18 Unit 7 steam seal manual dump valve ............................................................................................ 23

Figure 19 Unit 8 steam seal regulator bypass valve ...................................................................................... 23

Unit 8 steam seal dump valve ............................................................................................................. 23 Figure 20


Student Objectives

1. Explain the purpose of steam seals. ..............................................................................................................................

2. Explain the sources of steam seals for Unit 7 and Unit 8........................................................................................

3. Explain operation of steam seal regulators on Unit 7 and Unit 8. ....................................................................

4. Explain the construction of shaft labyrinth seals. ................................................................................................... 5. Explain the function of the gland steam condenser. ..............................................................................................

6. Explain the operation of Attemperation and identify the location of the water supply associated with gland steam seals on Unit 8. ....................................................................................................................................... 7. Explain operation and location of the controls of the steam seal systems on Unit 7 and Unit 8. ........ 8. Give the temperature and pressures of the steam used in the steam seal systems on unit 7 and 8. .

9. Explain the actions required upon the loss of steam seals on the turbine for unit 7 and unit 8. ........


System Overview

1. Purpose of Steam Seals

seal system is to seal the turbine steam spaces gainst steam leakage to the atmosphere, or air ingress into casings operating at l

The purpose of the steam athan atmospheric pressure.

ess

ENERAL DESCRIPTION of Unit 7G

lies sealing steam at low loads and during start-p to the steam seal system. The steam is taken near the main stop valve and routed to

efore the steam is supplied to the turbine seals, it must be reduced to a useable ressure for the steam seals, normally less than 5 psig. Reducing the steam pressure is

o

l load. t lower loads, when a vacuum can exist throughout some stages of the turbine, they

m

the steam seal header leak off annulus there is a vent annulus which is aintained at a slight vacuum (3-5 in H O) by a steam packing exhauster. This takes

e

The main steam system normally supputhe steam seal feed valve from which it is introduced into the steam seal header and into the turbine seals. Sealing steam is also used for smaller turbines such as the boiler feed pump turbine. It is supplied to these auxiliaries in a similar manner as to the mainturbine. Bpcommonly accomplished through an air operated pressure controller or regulator assembly which is designed to automatically regulate the pressure within design specifications regardless of the load on the turbine. A typical regulator includes twvalves; the steam seal feed valve, and the steam seal packing unloading valve. Pressure packing’s are those that normally seal against a positive pressure at fulAhave to provide a seal against air leakage into the turbine. The pressure packing’s havea leak off to the steam seal header which is regulated between 2.5 and 4.5 psig by automatic feed and unloading valves. Steam must be fed into the packing through this leak off line at lower loads. At higher loads, when the stage pressures build up, steaflows from the packing into the annulus leak off. Pressure packing’s may also have oneor more intermediate leak offs which discharge steam to higher pressure extraction points. Beyondm 2steam leaking from the leak off annulus and air pulled in from the atmosphere. Thsteam packing exhauster consists of a shell and tube heat exchanger to condense thesteam, and a motor driven blower to handle the air and hold a slight vacuum on the system. It is normally supplied with water from the condensate system.


acuum packing’s are those which always seal against a vacuum, therefore, steam g’s

t light loads, the steam seal feed valve supplies steam from the main steam line or in

o prevent or minimize steam leakage around the shaft of a turbine a gland or shaft he

the t

easing the vacuum, a the

here are four principal types of steam turbine glands: (1) metallic-packed or stuffing )

etallic labyrinth glands are designed to force the steam to follow a long winding path

re ts

am over the

Vmust be supplied to them at all loads. The vent annulus arrangement on these packinis the same as it is on pressure packing’s. Asome cases from an auxiliary steam source, to the steam seal header. At higher loads, when more steam is leaking from the pressure packing’s than is required by the vacuumpacking’s, the steam seal unloading valve discharges the excess through the steam seal diverting valve to the #8 heater extraction line Tpacking is provided. In a pressure-staged or a velocity-and-pressure-staged turbine tpressure on one side of a diaphragm is less than the pressure on the other side. Consequently there is a tendency for the steam to leak past the diaphragm along periphery of the shaft. To minimize the steam leakage at these locations, a gland musbe used. When a turbine is operated condensing, the steam pressure within the turbine casing at the exhaust end is less than atmospheric pressure. Therefore, to prevent air from leaking into the turbine and decrgland must be provided around the shaft where it passes through the exhaust end of turbine. Tbox glands, (2) metallic labyrinth gland, (3) the centrifugal water-packed gland, and (4the carbon packed gland. Mthrough the gland. In passing through each constriction in the path, the steam is subjected to a throttling action with a consequent reduction in pressure. Thus thereduction in pressure and the frictional resistance that are occasioned in passing through the labyrinth passage permit only a small amount of steam to escape. Theare two types of metallic labyrinth glands: (1) the double labyrinth gland, which consisof annular rings on the rotating element which fit into annular grooves in the stationary element, and (2) the single labyrinth gland which consists of a number of stationary annular saw-toothed projections that are closely fitted to the smooth shaft. The double labyrinth glands are generally used (1) to prevent leakage of stebalance pistons in a reaction turbine, and (2) to prevent steam or air leakage around the shaft at the exhaust end of an impulse turbine.


otor Glands

tain a umber of seal strips

r at

nd (Figure 5-327)

ressure (HP and IP) equals zone "X" pressure, a reversal in

ow increases and the gland becomes self-

R The glands connwhich encircle the rotothe ends of each outercylinder, clearing the rotor surface just enough to prevent contact during operation. On starting the turbine aat low loadsthe pressure at the HP, EP, and LP exhaust is below atmospheric pressure. Sealing steam is

supplied to chamber "X", leaking past the seals into the turbine on one side, and into chamber "Y" through a connection to the gland steam condenser. When the exhaust zone pflow occurs across the inner seal ring. As exhaust zone pressure increases, flsealing (Figure 5-328). At this point, steam is discharged from zone "X" to the LP glands. At high loads, spillover is used.

Figure 327


Figure 328

GENERAL ELECTRIC TURBINE SYSTEMS SHAFT SEALING SYSTEM The purpose of the shaft sealing system is to control steam pressure in the shaft packing’s at the ends of the turbine casings, thereby sealing the ends of the rotor shaft under all operating conditions between startup and full load. At startup, the system seals the turbine casing so that vacuum may be established, and after startup, sealing is maintained so that air will not leak into the sub-atmospheric section of the machine. Further, the system prevents excess steam in the high-pressure section of the machine from blowing out into the turbine room, or into the bearing housings to contaminate lubricating oil. At startup, sealing is achieved by introducing steam between the intermediate packing rings, and venting it between outer packing rings to a sub-atmospheric point such as a vacuum pump or condenser. After startup, the steam flow out of the packing of the high-pressure end of the turbine is sufficient to provide sealing steam for the low-pressure end of the turbine. The excess steam from the high-pressure packing, over that required for sealing the low-pressure end is dumped to a low-pressure point in the turbine or the condenser. This control of steam flows is maintained by a hydraulically operated steam seal regulator which accurately holds the steam seal manifold pressure by either admission or dumping. The operation of the steam seal regulator is described in detail later in this section.


haft Seal Packing’s

etallic Labyrinth Type

he shaft packing’s are located at points where the shaft passes through the turbine e

ESCRIPTION steam throttling device consisting of stationary and rotating teeth

ce

in the turbine rotor,

ter

l or r and

. e ring

hich

S M Tcasings and their object is to limit the flow of steam through the openings in the turbincasings and to seal these openings against the leakage of steam into the station or air into the turbine. DThe packing is aarranged concentrically with small radial clearances, thus presenting a high resistanto the flow of steam and greatly reducing the amount of leakage. The rotating element consists of step recesses machined directly

while the stationary elements are segment rings provided with teeth. The packing rings are basically of two types: (1) For low temperature service [below 750°F (398.8°C)] the ring segments are made of BTH leaded bronze with teeth machined integral in the material; (2) for high temperature service [above 750°F (398.8°C)] the ring segments are steel. The ring segments are machined with proper butt clearance so as to provide complete circumferential protection afthe segments have expanded due to operating temperatures. Longitudinally, the packing teeth are assembled in the packing grooves machined in the turbine rotor so that no rubbing will occur in the axial direction during transient load conditions. The packing segments are spring backed. These springs are made of Inconel–X material and are of sufficient strength to hold the segments in place against shoulders machined in the turbine shel

a packing casing so as to maintain a minimum running clearance between the rotothe packing teeth. The segmental spring–back construction is to provide additional clearance in case the rotor should become distorted due to some operating conditionThe ring will spring back at each revolution and thus prevent serious damage to thor heavy rubbing on the shaft, thereby reducing the possibility of local heating wmight reach a degree sufficient to damage the shaft.


U7 Steam Seal Regulator ISOBAR TYPE WITH OVERHEAD STEAM VALVES

The steam seal regulator, schematically represented in Fig. 3 is a fluid-

restored pressure regulator with zero steady-state regulation. It is, therefore, called a constant pressure or isobar regulator. It will maintain the same preselected steam pressure in the packing header regardless of the load of the steam turbine.

FUNCTIONAL DESCRIPTION

The steam-seal regulator consists of two major assemblies; these are the control mechanism and the steam valves. The control mechanism is oper-ated by hydraulic oil from the turbine oil system and is controlled by the steam packing leak off and seal (SPL) header pressure. IL actuates the two steam valves in sequence so that sufficient steam is admitted to or bled from the packing header as to maintain a predetermined pressure in the latter.

The packing pressure is transmitted from the SPL header to the pressure sensing element (2) by means of the water pot system (1). The water pot (la) is connected to the SPL header by means of the riser pipe (lb) which can be shut off by the valve (1c). It is connected to the pressure connection (1d) on the control mechanism by means of the pipe (le). During operation the water pot contains condensate up to the mouth of the riser pipe (1b) whereby the pipe (le) and the pressure sensing element (2) are always filled with water to protect the bellows (2b). Condensation of steam will keep the water pot filled to the proper level.

The pressure sensing element (2) is enclosed in the housing (2a) and consists of the outer bellows (2b), the plate (2c), the inner bellows (2d) and the bellows rod (2e). The bellows assembly is spring biased by the spring (2f) which can be adjusted by means of the spring plug (2g). The upper end of the bellows rod is connected to the lever (2h) by means of a self-aligning link (2i).

The servo-motor (3) which provides the necessary force to operate the steam valves consists of the oil inlet (3a), the pilot valve (3b) and the piston (3c). The oil flow to the pilot valve can be restricted by the needle valve (3d). The pilot valve is actuated by the lever (211) across another self-aligning link (3e). The piston actuates the output rod (3f) which has two functions:


1. It operates the unloader valve (6b) which is directly connected to the piston rod (3f) and the high-pressure admission valve (6c) by means of the linkage (4).

2. It operates the restoring mechanism (5).

The steam valve assembly (6) contains, in a common valve casing (6a), the unloader valve (6b) and the high-pressure admission valve (6c). The unloader valve is built as a seatless valve which can slide up into the discharge bore (6d) beyond the position where it is closed, in order to permit the servo-motor to open the high-pressure admission valve by means of the linkage (4) .

The high-pressure admission valve is of the tapered type in order to obtain fine control of the high-pressure steam flow. It is actuated by the walking beam (4a) and it is spring closed against steam pressure by the spring (4b). A fork and guide tube arrangement (4c) prevents the valve stem from turning in order to allow the coupling (4d) to take misalignment of the spring rod (4e) and the steam of the valve (6c) when the valve casing (6a) becomes hot.

The restoring mechanism (5) actuated by the piston rod (3f) by means of the link (5a) consists of the lever (513), the roller fulcrum (5c), the dashpot piston (5d) biased by spring (5e), the expansion bellows assembly (5f), the connection (5g) to the between-bellows chamber (2k) of the pressure-sensitive element (2) and the controlled bleed line (5h) which contains the restoring needle valve (5i). The dashpot system is continuously replenished with oil through the leak off line (5k) and any excess oil is drained through the drain line (5m). The suction relief valve (5n) in the dashpot piston (5d) serves to permit rapid action for closing the unloader valve and opening the high-pressure admission valve when the turbine load is decreased rapidly. In case of rapid load increase, the roller fulcrum (5c) will lift away from its guide, having a similar effect as the suction relief valve.

A locking device (7) is provided to permit blocking of the regulator in a position where valves (6b and 6c) are both closed. This has been done in order to permit inactivating the regulator in case of malfunction.



OPERATION

The steam requirements of the packing system depend on the load of the turbine. At low load there is no or little steam leaking out of the high-pressure packing’s of the turbine and, therefore, steam must be admitted to the SPL header in order to supply, particularly, the low-pressure packing’s with sufficient steam. At high loads the steam flow from the high-pressure packing’s is in excess of the flow absorbed by the low-pressure packing’s and, therefore, steam must be bled from the SPL header to some lower pressure extraction.

Assuming that the system is in operation at a certain steam flow to the packing and a change in load, say a decrease, tends to lower the SPL header pressure, the spring (2g) will pull the bellows rod (2e) down, which will lower the pilot valve

(3b). This will cause oil to be admitted to the chamber below the piston (3c) and oil will be drained from the chamber above the piston, whereby the piston will travel upward. This will reduce the steam flow bled from the system by valve (6b) or increase

the flow admitted to the system by valve (6c) depending upon what the load of the unit was. This action counteracts the initial pressure change, tending to restore the set pressure. At the same time the linkage (5a, 5b) has raised the piston (5d) creating a slightly negative pressure in the line (5g) which will pull the bellows rod (2e) backup and restore the on-port position of the pilot valve (3b) which will stop the motion of the piston (3c).

Meanwhile the negative pressure in the chamber (5g) decreases slowly by oil flowing into (5g) across the needle valve (5i). This will allow the pilot valve to be lowered slightly and displace the piston until the SPL header pressure has come back to exactly the same value as before the disturbance and the negative pressure in the dashpot chamber has completely subsided.

If the disturbance takes place in the other direction, all actions will take place in the opposite direction.



GENERAL DESCRIPTION of Unit 8 There is a common gland steam system for the main turbine and the two BFTs. It is possible, however, to separate one or both of the BFTs from the main system. The system has the following objects: a) To prevent the ingress of air along the glands into the LP turbine casings. b) To prevent the escape of steam along the glands. In order to fulfill the requirements mentioned above the following 4 systems are provided:

a) The vapor suction system 241 in which a pressure of approx. 13.9 PSIA is maintained. The steam extracted from this system is condensed in gland steam condenser 255. The air drawn off escapes to atmosphere through ventilators 256.

b) The sealing system 242 in which a pressure of approx. 14.94 PSIA is maintained by controller 6202.

During standstill, no load and low load operation the losses from this system into the turbine and into the suction system 241 exceed the steam quantity entering it from the HP turbine parts such as HP casing, control valves, etc. The desired pressure can only by maintained by the supply of steam.

Two steam admission valves 6301 and 6302 are provided for operating conditions with low steam pressures. During start up of the turbine both valves are open. With increasing pressure in the live steam line, first the admission valve 6302 will close and later on valve 6301 will follow. During normal turbine operation only valve 6301 is regulating.

In case of too high pressure in system 242 - with closed steam admission valves - an exhaust valve 6305 will leak off the excess steam into the #8 extraction line. In detail: In case of too low gland steam pressure the pressure transmitter 6201 transmits a low input signal to pressure controller 6202. Exhaust valve 6305 remains closed. The steam admission valve 6301 will be opened to let steam from the live steam line into system 6102 until the gland steam pressure coincides with the set-point pressure. With increasing load, the steam pressure within the turbine increases and forces more steam out through the

seals into system 242. The output signal from controller 6202 increases, first closing valve 6301 and subsequently opening exhaust valve 6305 - if necessary - to leak off the excess into the #8 heater extraction.


temperation

AtTemperature controller 6207, water injection valve 6310 and desuperheater 6718 are provided for cooling the gland steam to the HP-, IP- and BFT-cylinder glands the control valves 26/1, 5 and the main stop valves 58/1 the set-point of this temperature controller is approx. 660 F.

Temperature controllers 6208/09, water injection valves 6311/12 and desuperheaters 6719/20 are provided for cooling the gland steam to the LP-cylinder glands. The set-points of the temperature controllers are approx. 3350F.

An alarm is given by the double contact thermostatic switches 6511-13 in case of too high or too low temperatures. Filter 6713 prevents blocking of spray nozzles 6715-17.

c) A Relief system. At high pressure points a relief system is added. This prevents unnecessary large quantities of steam entering system 242 and a recuperation of part of thermal losses. The control valves 26/1-4 of the main turbine are relieved to the HP exhaust also the control valves, 26/1 and 26/5, on the high pressure steam side to the BFTs. The relief system for the HP turbine glands is connected to extraction A4 and for the BFTs to the exhaust line A6.

The stop valves 58 and 60 have no spindle leakage in both end positions and they are provided only with connections to the sealing and to the suction systems. Intercept valves 28 are fully open above 70 MW and then have no spindle leakage.


•

d) Cooling System for

The IPT rotor is cooled by

ater discharging to the condenser through this line with consequent danger of the

Intermediate Pressure Rotor.

steam taken from the cold side of the re-heater. Valve 269 is connected to the control system 35. It closes with decreasing load, being fully closed at approx. no-load. On generator tripping the valve prevents the rehe

turbine over speeding.



Steam Packing Exhauster

For Steam Sealed Shaft Packing’s

Steam packing exhausters are used to pull a low vacuum in the packing annuli nearest to the atmosphere. This prevents the escape of steam to the atmosphere in the region adjacent to the oil deflectors and consequently prevents water from collecting in the oil due to steam packing leakage. Air and steam are carried to the exhauster where the steam is condensed and the air is blown to the atmosphere. The condensed steam is returned to the

condensate system through a loop seal. The steam packing exhauster consists of a shell and tube-type surface condenser, air removal equipment, and associated piping and valve arrangement as shown in Figure1. Two full size motor driven fans are supplied, each sufficient to handle the full air load.



A water loop seal on the outlet of the blower prevents condensate from running back to the blower from the vent piping. The loop seal on the drain side of the blower prevents air from being pulled into the system.

Bypass piping around the condensed permissive under a flow of cooling water a removal of the condensate is what to prepare, if necessary, without shut down the system. The water loop seal at the bottom of the

condenser acts as a tell- tale to show a clogged drain or broken condenser tube. In either case, the loop will discharge a steady flow of water.

The desuperheater is not normally used during system operation but only when the condenser is taken out of service. At such times, the desuperheating water spray is lined up to cool the steam and air mixture, thereby protecting the blower bearings against overheating.

Unit 8 uses a casing drain at the bottom of the blower to prevent water from pooling in the bottom and being picked up by the blower blades.


AOperations bnormal

There are times when steams seals cannot be supplied by normal means. For unit 7 this is done by the us s is normally an air operated valve copa

control room. In order to do this the main root valve located riverside of the main steam stop valves must be checked open. After checking tosteam seals could not be established we will proceed to the manual bypass valve. Make sure you have good communication with the unit opeswitch must be placed in manual. This equalizes the Next rotate the hand wheel until the outer sleeve portoperating shaft. Once you have these to ports aligned take the pin usually lying near the valve packing and insert into the ports. Now as youto open the bypass valve and admit steam to the s n for the operator to tell you when you have enough steam seal pressure.

e of the manual bypass valve. Thi

ntrolled by the steam seal sub nel on “C” bench board in the

ensure this wasn’t the reason

rator. The auto manual control pressure on the diaphragm valve. lines up with the port in the

turn the hand wheel you will begin ystem. Liste


As the unit load comes up so does steam pressure and flow. This causes a corresponding rise in steam seal pressure. If the steam seal regulator is still malfunctioning it will be the responsibility of the AUO to decrease the steam seal pressure to a desired value. This must be performed by using the manual steam seal dump valve. This valve is operated in the same way as the manual bypass valve. Place the controller in manual

insert the pin through the ports. Manipulate the hand wheel to dump the extra pressure to the #8 heater extraction.

For unit 8 if the regulators are not operating properWe can manually manipulate the regulating valvesother regulating valve in the plant so we won’t belabor that point. Another option is to manipulate the bypass valve around the regulators Again proper communication with the unit operatorpressurize the seals. Also as load increases we need to be aware that changes must be made to the steam seal system as it increases.

and rotate the hand wheel to align the ports. Once the ports are aligned

ly then we have a couple of options. themselves. This is done like any

to supply steam seals to the system. is imperative so that we do not over


Another common problem on Unit 7 duringregulator bypass is used to establish steam seals as stated earlier. It’s very easy to get busy with legitimate

roble

heater extraction. The #8 heater has a dual extracturbine to help in flow. They are labeled LP Turbine

startup the steam seal

p ms and forget the position of this valve. The steam seal regulator will still try to maintain 4LBS on the supply header. In order to do this the steam seal dump valve to the #8

tion one from each side of the LP Section A and B Seal Steam

Temperature High. When the steam seal bypass valve is left open then the extra steam will be dumped to the #8 heater extraction and cause a rise in the extraction temperature. This is an unwanted condition since you are raising the temperature in the extraction to a point where it will affect the proper operation of the heater. Noise fromthe steam seal regulator can be a tool we use to monitor this condition, when operated properly the steam seals should not have a roar associated with them.


There’s an additional aide that’s been added to Unit 8 boiler feed pump system which as on Unit 7 is essentially a part of the main turbine’s system. A regulator has been added to assist Gland Seal Exhauster under heavy loads to maintain a negative pressure on the exhaust annulus. This regulator will open whenever the pressure get’s to atmospheric and opens to the B condenser to help maintain the flow of steam through the seals.

Summary: The steam seal system is one of the most important systems in the safe and efficient operation of our units. For the most part it goes unnoticed unless there’s a problem with the system. Proper care should be taken not to exceed the recommended pressure for each of the units since it will affect operation. Too high a pressure can cause vibration problems as well as bearing temperature issues. High pressure can also be a cause of water entrainment in our lube oil systems.

Wcf steam seals 7 and 8

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