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Dipl.-Ing. Erhard Stork, ARI-Armaturen Albert Richter GmbH & Co. KG, D-33756 Schlo Holte-StukenbrockTel.: +49 5207/994-0, Fax: +49 5207/994-297, E-Mail: [email protected], Internet:: http://www.ari-armaturen.com

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Valves for Steam Facilities

1. Introduction

2. Valve constructions

3. Steam and the demands it makes on valves

4. Design solutions

4.1. Seat/plug area4.2. Stem guide

4.3. Connections

5. Valve executions

5.1. Stop valves5.2. Control valves5.3. Pressure reducers5.4. Safety valves5.5. Steam traps5.6. Strainers/water separators5.7. Distributors/collectors5.8. Other valves

6. Selection and sizing

6.1. Finding the right type6.2. Defining sizes6.3. Important information for correct product selection

7. Installation, operation and maintenance

8. Summary

9. References

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1. Introduction

Because steam has good heat transfer properties, installations that use steam as theenergy carrier are widespread in power stations, plant manufacturing, the chemicaland petrochemical industries and the manufacturing industry. In addition to the main

components such as boilers, heat exchangers and pipes, the valves for isolation,control, safety and steam trapping the medium are also highly important. Some, suchas regulating valves and steam traps are indispensable for standard service, others,such as safety valves, are only needed in an emergency. Stop valves, for example,are needed for manual operation, compensation procedures, inspections andmaintenance work. As well as high temperatures, the steam medium puts specificdemands on the valves, as in a later physical state, it is almost always foundsimultaneously as condensate and as liquid.

2. Valve constructions

There are various styles of valve that can actively affect flow and the one describedhere is based on the valve principle. Figure 1 shows this in diagrammatic form. Amovable closing component, developed as a plug or a disc, is mounted in a housing.This prevents the medium applied to the inlet from exiting. Intermediate positionslead to throttling or control, thus affecting the flow. The plug can be operatedmanually, via actuators driven by a separate power supply or by the medium itself. Agreat variety of valve styles are derived from this basic type and these are describedbelow.

Figure 1: Basic valve type

3. Steam and the demands it makes on valves

In vapour facilities, steam almost always exists simultaneously in two physical states,"gaseous" and "liquid", as the maximum insulating strength of all installationcomponents is limited and condensate constantly forms on the cooler inner walls ofthe components and the pipes. When hot steam meets greater collections ofcondensate, there is sudden evaporation. The changes in volume associated with

this sometimes cause violent water hammers and thus powerful pressure surges thatcan far exceed the operating pressure. Water hammers also occur if vapour bubbles

Closing component

Body

OutletInlet

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are absorbed in the condensate, which is cooler in comparison with the vapour, sothat condensation causes the bubbles to implode all of a sudden. With valves, thereis then the risk of interior damage or even total operational failure, seals canmalfunction and in the worst-case scenario, rupture the valve body.

Another pressure situation that puts great stress on the valves is evaporation of theboiling hot condensate. If this is diverted from the vapour system and the pressurereduces, the severity of evaporation increases, the greater the pressure differenceand the higher the temperature of the incoming condensate. As this drop in pressurechiefly takes place in the narrowest cross-section of the valves, the stress is also atthe maximum there. The risk of washout and material abrasion is then apparent if thecomponents are not designed accordingly.

The condensate is not pure water. If the boiler water is not adequately conditioned,this may result in residual acids, salts and bases. If air and therefore oxygen gets intothe vapour facility, for example, when it is not being used, there are highly aggressive

chemical reactions with the ferrous products of the installation components, such asthe pipes and the valves. The associated material abrasion of all the installationcomponent surfaces that come into contact with the media causes particles of rust toform that then pollute the entire installation. Larger particles are carried along in themedia flow and cause wear on the valve guides and seals. At points where the flow isdiverted, there is erosion and washout. The finer particles turn into corrosion sludgethat builds up and leads to blockages in the finer channels and gauging holes.

4. Design solutions

4.1. Seat/plug area

The plug (or disc) as the closing element, stops the medium applied to the inlet(steam/condensate) from getting to the outlet, by pressing on the seat. As well as this"main task", in many cases the plug/seat unit also has a second important function tofulfil, that of throttling the flow. Whereas during isolation, the requirements are mainlyconcentrated on a permanently good seal, during throttling, the stability of the plugmovement and the flow characteristic come to the fore. The seat/plug area is alsoexposed to the greatest stresses in the valve, as this is where the flow is at its fastestbecause of the minute cross-section of the flow. The associated flow forces workingon the plug must be safely intercepted. The saturated steam still mostly contains

condensation droplets or these reform on the cooler walls and at these high flowrates, lead to erosion. Plugs and seats damaged in this way then cannot close tightly,with dirt accumulation and deposits also working to the greatest detriment with regardto leakage.

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In vapour facilities, because of the high temperatures, the most commonly found typeof valves are those with a metallic plug/seat seal in the "flat seat" (Figure 2) and"marginal seat" (Figure 3) types.

Figure 2: Flat seat Figure 3: Marginal seat

Flat seats are used to isolate and are less suitable for regulating and throttling

functions, as when there is little change in the travel, the flow increases very rapidlyshortly after the valve starts to open. If valves with flat seats are operated rarely,deposits and encrustations can lead to the valve no longer being able to close tightly.The minimum width of the seat with the plane-parallel bearing makes it more difficultfor this accumulation of dirt to be removed, even if great force is applied. Theassociated risk of pressure point formation and thus damage to the facings meansthat it is no longer possible for the valve to close without leakage.

Marginal seats with their conical seating are better for flow and more suitable forthrottling and regulating functions. Dirt accumulation in the area of the seal, whichoccurs after longer periods of operation with few or even no closing actions(encrustation/deposits), can be removed so well with this type of seating that aleakproof closure is obtained.

The valve seat shown in Figure 4 has been in use over a long period of time and thedeposits on the seat are clear to see. The narrow sealing edge of the marginal seat iseasily recognised as the light line.

Figure 4: Marginal valve seat with deposits

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To further increase the service life, it is usual to harden the plug, as this receives thegreatest exposure to the particles carried along by the flow. This is further improvedby armouring or stelliting the seat and the plug. This procedure is frequently used inthe regulating valve area.

4.2. Stem guide

The second important function of the valves, ensuring that there is a leakproof sealkeeping the medium in, is given by the body components, the seals and the stemguide. Here the latter makes the most stringent demands on the design andconstruction of the valves. The body and the accompanying seals are staticcomponents, movement does not occur at the seals. The stem guide, on the otherhand is subjected to dynamic stresses caused by the movement of the stem, whichcan be axial, radial or a combination of the two. Manual stop valves are usually notoperated very often, regulating valves, on the other hand are used anything fromfrequently to constantly.

As far as the stem seal is concerned, there are three different designs for use insteam and condensate applications:

- gland packing- V-ring unit- stainless steel bellow seal

Gland packing, the oldest type of seal for valve stems is shown in Figure 5. Thepacking material made of pure graphite is pretensioned using packing fixtures anddistributes the resultant pressure on all sides, thus sealing the gap between the stem

and the upper part of the body (the bonnet) towards the outside world. Leakagescaused by the easing of the packing pressure can be combated by retightening,which automatically involves a certain amount of maintenance expenditure. If there istoo much pretensioning, this can also cause a great deal of friction at the stem, whichinhibits its movement. If these forces become too great, it is no longer possible tooperate a manual valve or the function of the regulating valves is restricted.

Figure 5: Figure 6:

Gland packing V-ring unit stem seal

The V-ring stem seal shown in Figure 6, provides an improvement with regard tomaintenance, as the PTFE V-ring units are permanently pretensioned by means of

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springs, thus ensuring a constant seal. The frictional forces are also defined by thisand are not dependent on the manual force applied by the particular fitter. Onedisadvantage is the limited temperature of max. 220C. This is why it is necessary toknow the operating parameters exactly and application is restricted mainly to thecontrol valve sector.

The bellow seal shown in Figure 7 provides a permanently leakproof andmaintenance-free stem seal, even at high temperatures. The material mostcommonly used for the bellow seal is austenitic stainless steel 1.4541 or 1.4571,which also shows adequate corrosion resistance even with an aggressivecondensate. The sealing does not cause any additional frictional forces and whenused in manually operated or power-operated valves, the rigidity of the spring-constant makes the forces negligible. With valves that work automatically, withoutauxiliary power, such as pressure reducers and safety valves, rigidity is already takeninto account in the design and remains constant throughout the life of the valve.Depending on its design, the bellow seal simultaneously protects the stem guide from

the medium and prevents wear from dirt particles.

Figure 7: Bellow stem seal Figure 8: Flange connection

4.3. Connections

The valve is connected to the pipe in the steam and condensate area by means of aflange or it is directly welded on. The valve connections must be developedaccordingly, Figure 8 shows the flange connection and Figure 9 the welded end.

Flange connections have the advantage of being easier to dismantle when it isnecessary to replace a valve. The weak point is the seal, which may fail, as a resultof changes in temperature, for example. The sudden blowing of a seal alsorepresents an increased risk potential thanks to the high temperatures present in thesteam and condensate. This problem does not occur if the valve is welded directly tothe pipe and this is also a more cost-effective solution, as it does away with

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Figure 9: Welded end Figure 10: Shoed end

the need for two welded flanges including fitting for each valve, with the need tocreate weld seams in both cases. But should this need to be removed, higherexpenditure is involved. As the material of the valve is normally different to that of thepipe, welding the valve to the pipe puts greater demands on execution (weldingtechnique, post-treatment, such as annealing, etc.). For this reason, valves areavailable with shoed ends in the material of the pipe (Figure 10). Thus the highlydemanding (different materials) welding operation is moved from the building site tothe valve factory. On site at the plant, the same materials are welded together andexpenditure is sometimes far less.

5. Valve executions

5.1. Stop valves

Should flows of steam and condensate need to be isolated, the "ARI-FABA

frEnergien" type (Figure 11) is particularly suitable, thanks to the combination of

Figure 11: Stop valve"ARI-FABA fr Energien" [1]

Hand wheel

Bonnet

Stem

Gland packing

Bellows seal

Plug

Seat

Body

OutletInlet

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special design solutions. Depending on the nominal diameter, the body of the valvecan also be made of the ductile materials spheroidal graphite iron GGG 40.3 or caststeel 1.0619+N (>DN 50). The plug sealing to the edge of the seat is made by amarginal seat, with the plug being hardened to improve the resistance to wear. Thestem guide is double-sealed, once by a stainless steel bellow seal that

simultaneously protects the guide from dirt and secondly, through a secondarysealing gland packing, which, should the bellow seal become damaged, takes overthe sealing function for the transitional period until the valve is replaced. Theenclosure of the threaded stem in the handwheel area stops dirt getting onto thethread, which would make it run sluggishly. On the other hand, a bare, greasedthread would greatly consolidate the local dirt and there is usually no cleaning beforethe next operation. With this design, the handwheel is also "non-rising" and thus,even at different settings, always remains at the same height relative to the valvebody. The extra-fine thread stem produces a better force ratio with the advantages ofbeing smooth running and having greater plug pressure acting on the seat.

5.2. Control valves

Vapour facilities are seldom only operated at full load, usually it must be possible toset all the operating states between 0 and 100% for the individual areas of the entireinstallation independently of one another at any time. This is achieved by throttlingthe vapour flow by means of control valves. Figure 12 shows the valve that is

particularly suited to this task, the "ARI-STEVI 470" valve, that is

Figure 12:

Control valve "ARI-STEVI470" [1]

Actuator

Yoke

Stem

Stem guide

V-ring unit

Mounting bonnet

Plug

Seat

Body

OutletIntlet

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operated by an electric actuator. The marginal seat plug has a parabolic contour,which makes it possible to regulate even the smallest flow rates precisely andaccurately. The seat is screwed and because of the vast number of differentdiameters, as well as the usual nominal diameter selection, there is also a finegraduation in the flow output and thus the option of accurate sizing. The plug stem

guide allows precise regulation and the hardened bush makes this executionparticularly resistant to wear. The valve shown has a V-ring unit seal for the stemguide. If the temperature of the medium is higher than the permitted level, anexecution with a stainless steel bellow seal is also available. Further details are givenin [1].

5.3. Pressure reducers

In contrast to control valves, pressure reducers operate without auxiliary power andare driven solely by the medium. Their function is reducing a high pressure (upstreampressure) to a lower pressure (downstream pressure). At the same time, the

downstream pressure is automatically kept constant during changes in the flow rateor fluctuations of the admission pressure. A pressure reducer of the "ARI-PREDU"type, as shown in Figure 13, is particularly suited to meet the demands of the steammedium. A marginal seat is screwed into the transitional body. The plug has a smallparabolic lug, that keeps the regulating process safe from vibration at the lowest flowrates. In the same way as with the control valve, a spindle guide with a hardenedbush is also available here. This pressure reducer has two stainless steel bellowseals. The lower one serves to seal the spindle against the outside world. The upperone is the compensating bellow seal, whose function is to equalise the forces at theplug. To do this, the admission pressure goes through a hole in the plug in theinterior space to the outside of the bellow seal. The inside of the bellow seal is

connected to the downstream pressure side via openings. As the effective surface ofthe bellow seal is the same size as the seating, the differential forces arecompensated for and fluctuations in the admission pressure have very little effect.

Figure 13: Pressure reducer"ARI-PREDU" [1]

Seat

Body

Plug

Compensating bellow

Spring

Bellows seal

Actuator

Water seal pot

Downstreampressure

Upstream pressure

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The pressure reducer is driven by a diaphragm actuator. The downstream pressureto be regulated gets to the actuator diaphragm via the water seal pot and the controlline with a hydraulic seal (protection against high temperatures) and is converted to apressure that acts in the opposite direction to the spring pressure. The pre-tensioningof the spring can be adjusted in such a way that at the desired downstream pressure,

both forces are counterbalanced. If the vapour flow then changes, this leads to anadjustment of the plug until equilibrium is restored. Further details, design tips and

data on the "PREDU" can be found in [1] and [2].

5.4. Safety valves

Safety valves are necessary to protect the components of vapour facilities, such assteam boilers, deaeraters and installation areas after the pressure reducers frominadmissibly high pressure. Figure 14 shows the type suitable for this, the "ARI-SAFE" type, that has an angle body.

Figure 14:Safety valve "ARI-SAFE" [1]

The disc (plug) isolates the pressurised medium applied to the inlet from the usuallyatmospheric pressure prevalent at the outlet. The pre-tensioned spring in the springbonnet transfers the pressure to the disc via the spindle. The pretensioning of thespring can be varied with the adjusting screw, thus altering the set pressure. Thehardened plug is flexibly mounted and an even set pressure is ensured even if it hasbeen idle for a long time, thanks to the sensitive flat seat lapping. As the safety valveis usually always closed, the seating surface is covered by the disc to protect itagainst deposits. At high steam temperatures, the open spring bonnet prevents toomuch heating, as if the temperature of the spring is too high, this simultaneously leadto a lessening of force and a reduction in the set pressure. When used in deaerators

and in the condensate area, on the other hand, an enclosed execution is required.The drainage opening closed with a screw can be used if steam trapping via the

Lifting device

Adjusting screw

Spring

Bonnet

Plug

Seat

Drain plug

Body

Outlet

Inlet

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exhaust line is insufficient. For further details and information on safety valves, see[1, 3].

5.5. Steam traps

Steam traps are valves that automatically divert the condensate in vapour systems,but which retain the vapour. With the "ARI-CONA"product line, you have availablean extensive range for a great variety of applications. The distinction is made herebetween two groups: firstly there are the traps that continuously carry away all the

accruing condensate without delay, like the "CONA S"shown in Figure 15, thatworks on the float principle. As soon as any liquid flows into the cover, the ball floats,the valve opens and the condensate can flow away. The vapour arising from thesteam trap is then retained.

Figure 15: Float steam trap Figure 16: Bimetallic steam trap

"CONAS" [1] "CONAB [1]

On the other hand, the second group functions at a specific undercooling of the

condensate, an example of which is shown in the bimetallically driven "CONA B"inFigure 16. The metallically packaged controller opens below the saturated steamtemperature, to ensure that only condensate is removed. The buildup of condensatethat this produces is sometimes also intentional, if the heat of the condensate is to beused. The temperature at which the valve opens can be varied according to thechoice made from the controllers available. Additional types that also remove the

condensate below the saturated steam temperature and thus delay condensateremoval, are the enclosed diaphragm "CONA M" trap and the thermodynamic

"CONA TD" trap.

With all the traps shown here (apart from the CONATD), the starting dewateringand deaerating function, that is to say the immediate removal of large amounts ofcondensate when drying out the installation, is integrated. Below the operatingtemperature, the valve is fully open, it is only when this temperature is reached thatthe trap works in its designated function. As steam trapping as a whole is anextremely complex area and there are a vast number of products variants available,

we refer you to the additional information at this point [1, 4, 5].

Body

Controller Hood

Body

Controller

CoverInlet

Outlet

OutletInlet

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5.6. Strainers/water separators

In its two physical states, the medium of steam is in practice only rarely free ofimpurities and accumulated dirt. Strainers (Figure 17) with interior screens are idealfor filtering out coarse matter, such as welding residue and particles of rust. Screens

are available in various mesh sizes. When making the selection, you have to find acompromise between good separation and a permissible maintenance interval / lossof pressure. At high steam speeds, droplets of condensate can cause erosion andmaterial abrasion.

Figure 17: Strainer [1] Figure 18: Water separator

Fine matter in the vapour can be separated together with these condensate dropletsby means of water separators (Figure 18). These comprise a housing with aninternal, spiral-shaped sheet, which uses centrifugal forces to separate the dropletsand the contaminants. The condensate must be diverted via a steam trap at the lowerdryer connection. To protect the seats and the plugs against damage and to minimisewear, strainers and if possible a water separator should always be arranged beforethe control valves and the pressure reducers.

5.7. Distributors/collectors

To supply the individual consumers in vapour facilities, the pipes are normallydistributed from a central main to the individual lines. The reverse is true for thecondensate, this occurs locally in the individual lines at the consumers and has to bebrought together again centrally by means of collecting mains. This used to meancomplicated welded structures consisting of lengths of pipe, dished boiler ends,connecting sleeves and stop valves. The variable modular design of the compact

distributor "ARI-CODI" (Figure 19) with integrated stop valves vastly reduces thisexpenditure. The functioning parts of the valves can be replaced without having toremove the entire distributor from the pipe. The individual valves have a stainlesssteel bellow seal to seal the stem and have available a safety return seal which, if thebellow seal is damaged and the valve is fully open, provides a temporary seal until it

is possible to effect replacements. For more information on the compact distributor,see [1, 6].

Body

Cover

Screen

OutletInlet

OutletInlet

Spiral plate

Trap connection

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Figure 19: Compact distributor "ARI-CODI" [1]

5.8. Other valves

In addition to the valves described here, there are other types of valves that areuseful and in special cases essential for the efficient and trouble-free operation ofvapour facilities. These include venting valves (vacuum breakers), flow indicators,condensate operating temperature limiters, automatic starting dewatering machinesand return temperature limiters. These valves are described in more detail in [1, 5].

6. Selection and sizing

6.1. Finding the right type of valve

If the required type of valve is not stipulated when product selection begins, a roughselection has to be made on the basis of your knowledge of the plant and theparameters. The following points should be of assistance for this:

- The requisite function (e.g. isolation, control, safety, steam trap)- Combining different functions in one valve

- Permissible limits/tolerances (e.g. control performance, loss of pressure)- The medium (steam only, condensate only, etc.)- The demands made on steam quality (e.g. pure steam for sterilisation)- Fitting position- Type of connection (e.g. flange, welded end)- Remote maintenance/diagnostic options

These two examples should make things clearer: If a higher pressure is to bereduced to a lower one, the simplest option is simply static throttling, for example, byusing a manual valve, where the required lower pressure is set once. At a steady flowand constant admission pressure, this option is certainly adequate. If the conditions

are not constant, then a pressure reducer driven by the intrinsic medium can beused, which will automatically adjust to the various operating states. However,

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because they regulate proportionally, there is a certain deviation with pressurereducers. Although if there are stringent demands for control accuracy, control valvesmust be used, which meet these requirements in conjunction with appropriateelectronic or pneumatic controllers. A further example is the selection of steam traps.Knowledge of the plant is necessary for this, for example, is immediate trapping

required before the regulating valves. On the other hand, a defined buildup ofcondensate is desirable with steam-heated devices, to take advantage of the heat ofthe condensate.

6.2. Defining sizes

The size of the chosen valve is determined by the flow rate of the steam or thecondensate for which it is intended. If the selected valve is too small, it provides toomuch resistance, which could cause subsequent consumers to be undersupplied orcould allow too much condensate to build up. But there can also be problems withvalves that are too big, as well as the associated higher costs. If the selected

regulating valves are too big, the control properties worsen in line with the degree ofoversizing. For example, if a control valve with a linear flow characteristic is chosentwice as big as the maximum required, this achieves the full flow required at approx.50% of the travel distance. This means that the positioning accuracy and thus theaccuracy of control, is worse.

Safety valves that are oversized tend to vibrate and can hammer. These associatedmechanical stresses do not only affect the seat and the plug and thus the quality ofthe seal. In extreme cases this can also result in the valve actually breaking.

Complete and correct valve sizing requires knowledge of the operating parameters,

such as the pressures, the temperatures and the flow rates. Various sizing aids areavailable to the user, such as tables, charts and calculation slides. The computer

sizing program "ARI-VASI" is a fast, reliable and accurate option for sizemeasurement. As well as pure sizing, it is also possible to select the valves andspecify the precise type and manage it to suit the project.

The calculation formulae necessary for sizing are stipulated mainly by a vast numberof specified standards and regulations, as well as the pertinent technicaldocumentation. For example, [8] is applicable to stop valves and control valves and[9, 10, and 11] apply to safety valves. They apply to the situation where the steammedium remains in the same physical state and there is no phase change. Withsteam trapping, on the other hand, there is usually evaporation, as the boiling hot oronly just below saturated steam temperature condensate loses pressure over thetrap. There are not yet generally valid, protected regulations defined by the specifiedstandards for this partial evaporation. The charts available for steam traps aretherefore based on measurements.

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6.3. Important information for correct product selection

In addition to simply calculating the sizes of the valves, there are also additional

points to take into account for correct selection and determination. The choice ofmaterial also involves correctly determining the nominal pressure level subject to thetemperature, to apply to all the valve types. For example, Table 1 shows the followingtemperature/pressure assignment for flanges made of cast steel 1.0619+N:

Table 1: Pressure/temperature classification for flanges made of cast steel1.01619+N (DIN EN 1092-1)

The type of stem seal, e.g. bellow seal or V-ring unit, must also be stipulated. Withcontrol valves, once you have selected the valve, there are various options availablefor choosing the method of actuation, but this is not covered by this essay.

7. Installation, operation and maintenance

For a steam valve to function properly, not only must the correct valve be chosen andthe size be right, it must also be fitted correctly. The list below reflects the mostimportant possible errors, although others can be found in the relevant operating andinstallation instructions:

- The shipping braces and protective caps on the inlet and outlet have not beenremoved

- Attention has not been paid to the direction of flow and the mounting position- The pipe is not properly supported, the forces and the torque fall on the valve- The flange seals are not fitted centrally and are constricting the media flow path

Commissioning is also described in the operating instructions, possible errors hereinclude:

- Installation not rinsed before valve is used for the first time

- Strainer not subsequently cleaned- Hydraulic seal for pressure reducers not filled- Any test gags fitted for the safety valves have not been removed- The blow-off line for safety valves is not connected

Maintenance includes cleaning the strainers and regularly "desludging" thecondensate collector supports. Leaky gland packing on the stem guides should betightened, if possible. Safety valves must be vented from time to time, to test thatthey work. However, this should not be done too often, as this will wear the sensitivelapping on the facings, as it is not possible to have strainers before the safety valves.

max. perm. pressures in bar at temperature

20C 100C 150C 200C 250C 300C 350C 400C 450C

PN 25 25 bar 23.3bar 21.7 bar 19.4 bar 17.8 bar 16.1 bar 15 bar 14.4 bar 13.9 bar

PN 40 40 bar 37.3 bar 34.7 bar 30.2 bar 28.4 bar 25.8 bar 24 bar 23.1 bar 22.2 bar

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8. Summary

Vapour facilities make particular demands on the valves, as the medium of steam

occurs in the two physical states of steam and condensate. The most important valvetypes among the great variety of variants that are required to operate these plantsare described, design details are explained in more detail and the advantages anddisadvantages of use with this special medium are shown. Following selection andsizing some actual possible errors that may arise through incorrect installation andcommissioning are presented.

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9. References

[1] ARI-Armaturen: Manufacturers Catalogue 2003 edition[2] Stork, E.: Dampfdruck-Reduzierstation fr die Prozess- und Anlagentechnik.

Industrial Valves Magazine Issue 2/2000

[3] Stork, E.: Das Edelstahl-Sicherheitsventil als Hauptkomponente zurDruckabsicherung von Anlagen mit korrosiven Medien. Industrial ValvesMagazine Issue 4/1996

[4] Dr. Urbanek, H.; Bhm, L.: Eine neue Generation thermischerBimetallkondensatableiter. Industrial Valves Magazine Issue 2/1996

[5] ARI-Armaturen: Condensate management advisor (in progress)[6] Dr. Urbanek, H.; Wei, W.: Neues Sammel- und Verteilsystem fr

Wrmetrgermedien. Industrial Valves Magazine Issue 3/2002

[7] ARI-Armaturen: Computer valve sizing program ARI-VASI[8] DIN EN 60534: Stop valves for process control[9] TRD 421: Safety valves for overpressure prevention - safety valves -

for steam boilers[10] DIN EN 12952-10: Water tube boiler the demands made on

safety devices to prevent excess pressure[11] DIN EN 12953-8: Large waterspace boilers the demands made on

safety valves for overpressure prevention

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