07.06.13 - 1001TheoryEquipmentAuxiliaries (1)Without cocks or valves, chemical or petrochemical plants would not be able tooperate. In addition to pipes for transporting liquids and gases, auxiliaries areneeded to be able to shut off or regulate this transport. The category ofauxiliaries includes all equipment on and in pipes and vessels: valves, cocks,filters, meters and sight glasses, among other things.As knowledge of cocks and valves (auxiliaries) is of great importance, we havedevoted three lessons to the subject. This is the first of the three: this lessonexamines the valves with 90 operation. The objective of these lessons is toprovide a good insight into the possibilities, properties and impossibilities in theuse of the various types of valves. Enhancing this insight has the followingadvantages:-ability to make a better choice when purchasing new valves;-ability to judge whether the valve supplied meets the requirements;-better ability to assess the condition of a valve in operation.This lesson does not aim to provide instructions for repair. What will bediscussed is the ability to assess whether the valve meets the requirements.After studying these lessons, you will also be able to judge whether the choiceof a valve is the optimum one for the service concerned.Contents of the lesson1Shut off devices2Hand-operated valves3Ball valves4Plug valves5Butterfly valvesThe copyrightin thismaterialisvested in Shell Global Solutions International B.V., The Hague, The Netherlands and Shell NetherlandsRaffinaderijB.V.Allrightsreserved.Neitherthewholeoranypartofthisdocumentmaybereproduced,storedinanyretrievalsystemortransmittedinanyformbyanymeans(electronic,mechanical, reprographic, recording or otherwise) without the prior written consent of the copyright owner.Theory / 07.06.13 - 1002Lesson1Shut off devicesThere is a wide range of shut off devices, allowing many requirements to bemet. In these lessons, however, we will limit ourselves to the most importanttypes and categories.Shut off devices can be divided into:-open and shut valves (manual, pneumatic, hydraulic or electrical operation);-control valves;-safety valves;-one-way valves.The right choice of shut off device depends, among other things, on thefollowing factors:-density;-temperature;-rust particles;-crystals.It is not possible to draw up a standard guide for the selection of the right shutoff device; practical experience and information provided by manufacturers arevery important.2Hand-operated valvesManualvalves have three main functions in fluid flow systems:-starting and stopping the flow;-regulating the flow quantity;-different flow paths.Open and shut valves for starting and stopping the flow are also often used forcontrol of the flow quantities and vice versa, whereas valves for directing theflowto different pipes are designed for that purpose only.In manually operated shut off devices, we can distinguish three groups:-Valve with 90 turn:ball valve;plug valve;butterfly valve.-Valve with rising spindle:gate valve;piston valve;diaphragm valve.- main functionsTheory / 07.06.13 - 1003-Valve with arising-rotating spindle:globe valve;diaphragm valve.Valves with 90 turnAnother name for these devices is rotating open and shut valves. This means thatthis type of valve is operated by rotating the sealing element a quarter turn (90)around an axis perpendicular to the direction of flow.The shut off devices with 90 turn can be divided into three groups:-ball valves;-plug valves;-butterfly valves.This lesson describes these three groups. The rising spindle valve and the valveswith a spindle that is both rising and rotating will be discussed in the nextlesson.Question 1What does 90turn mean?3Ball valvesThe ball valve is a valve with 90 turn, in which the sealing element is a ballprovided with a round hole. This ball always remains in contact with the seat.In the design of ball valves, different variations are possible with respect to:-ball design;-ball type;-body type;-seal rings;-valve bore;-mounting space.3.1Ball designBall valve with floating ball and reduced boreIn ball valves with 'floating' ball and reduced bore (see figure 1), the seal ring isin PTFE. The pressure of the medium presses the ball against the seat. If thepressure difference is too small, the ball is pressed into the seat with insufficientforce, which leads to leakage. If the pressure difference becomes too large,however, the surface pressure on the seat becomes too large, causing the seat toyield. In other words, this design is suitable only for use within a certainpressure range.- ball valves- plug valves- butterfly valvesTheory / 07.06.13 - 1004Rem.In closed position, the ball can move towards the downstream seat since theball can move relative to the spindle (float).5603-100-001-PFigure 1Valve with 'floating' ball against 'downstream' seal ringBall valve with floating ball with full boreThis type of valve can be recognised by a flange in the body (both split body andtop entry, see section 3.3). It should be pointed out that in many cases, split bodyis not allowed, and it is never allowed with the centre line of the ball and stem(the spindle) through the plane of the flange.Ball valves with bearing-mounted balls (trunnion supported)This is a type of ball valve in which the ball is supported by bearings in thebody. The top and bottom of the ball are fitted with fixed trunnions. Due to this,the forces acting on the ball are absorbed by the bearings rather than the seats.This results in a lower actuating torque. By means of a spring packet, the seatsare pressed in position against the ball. This ensures a constant and adequate sealat all times, even with extremely low and high pressures. Whether or not tomount the ball on bearings will depend on diameter and pressure.3.2Ball typeIn principle, we can distinguish two types of ball: the solid ball and the hollowball.Theory / 07.06.13 - 1005Solid ballThe solid ball (see figure 2) is in most cases made from a perforated rod. Thetop of the ball has been provided with a recess, on which the spindle acts. Thesolid ball has a straight bore, ensuring uniform flow. As a result, no residualflow will remain behind in the ball. Particularly in the case of larger dimensions,the weight is a disadvantage.5603-100-002-P/Figure 2Solid ballFigure 3Hollow ballHollow ballFor diameters over 6", hollow balls (see figure 3) are often used.The advantages relative to the solid ball are:-less weight and therefore lower cost;-reduction of the surface pressure on the seal rings.One disadvantage to be noted is the fact that the cavity in the ball is hard toflush. In other words, a 100 % clean valve can never be guaranteed. To enableflushing to be as efficient as possible, it is done in the open position.Ball valves are designed in such a way that they have a so-called 'dead' space(cavity). This is the part of the body around the ball and between the seal rings.During opening or closing, the bore opening is disengaged from the seal rings.As a result, the 'dead' space is filled with medium. Due to the temperature, thepressure in the 'dead' space increases, which may lead to damage to the sealingmechanism.An unacceptably high pressure must be avoided. To this end, the ball is providedwith a pressure balance hole under or opposite the spindle (see figure 4). Inclosed position, pressure balancing can take place by means of providing a hole(cavity relief hole) in the ball (see figure 5). Although this balances the pressure,the valve will be suitable for only one direction of flow in this case. A better, butmore complicated solution consists in fitting a spring packet on the seal rings,which balances the pressure.- cavity- pressure balanceholes- cavity relief holeTheory / 07.06.13 - 10065603-100-004-PFigure 4Ball valve with "pressure balance hole"Figure 5Ball valve with 'cavity relief hole'3.3Type of casingThe following casing designs are possible:One-piece body (see figure 6)In contrast with the split body ball valve, this type does not have any flangeconnection(s), which reduces the risk of leakage. The body is therefore in onepart, usually with a reduced bore.Split body (see figure 7)Here, the two body halves are joined by means of flanges.This type is generally used when a full bore is required. A disadvantage is theincreased risk of leakage in comparison with the one-piece body.Sandwich (see figure 8)In this type, the body consists of three components. In multi-part bodies, thecentral part, which contains all working components, can be removed as awhole, while the two connecting ends remain in position. This is practical whenthe valve is welded into the pipe. This also enables the use of exchangeableconnecting ends.5603-100-006-PFigure 6Ball valve; one-piece bodyFigure 7Ball valve; split bodyTheory / 07.06.13 - 1007The three types discussed above (all of them 'side entry', i.e. the shut offmechanism is inserted into the valve from the side) are provided with an 'anti-blow-out' spindle design. This is a protection device which ensures the spindle isnot blown out by the pressure of the medium if the top part is loosened. Thisprecautionary measure is necessary in valves not fitted with a bonnet. The resultis that in removing the gland, the spindle is forced out.'Top-entry' (see figure 9)The body of this ball valve forms one unit and does not have any screwedinsert(s). The sealing components are mounted 'from the top', and the whole unitis subsequently locked by a removable cover. In this type too, an 'anti-blow-out'spindle design can be fitted. This type also allows 'in line' repairs. This meansthat maintenance can be carried out without removing the valve. A disadvantageis the increased risk of leakage of the cover gasket.5603-100-008-PFigure 8Ball valve; sandwichFigure 9Ball valve; 'top-entry'Finally, we should point out for all types that in case of corrosive media (such asH2SO4and HCl) the surfaces in contact with these media can be lined withPTFE (such as Teflon) (lined ball valves), including the ball and the spindle.3.4SeatsThe seats can be made in synthetic or metal.Synthetic seat (soft seated seal ring)The synthetic seal ring is usually made in PTFE (Teflon). The advantages ofsynthetic seal rings are:-price;-if the ball is not perfectly round, this is compensated for by the soft seat;-optimum sealing;-low coefficient of friction.The disadvantages are:-limited temperature range;-unsuitable for dirty media;-not form-retaining, particularly at high temperatures and pressures;-low resistance to abrasive effects.- side entry- anti-blow-out- seatsTheory / 07.06.13 - 1008Metal seal rings (metal to metal seal ring)Due to the increasingly demanding design requirements (due to the highertemperatures and pressures and the occurrence of dirt), the use of metal sealrings is increasing. The seat and the ball are provided with a hard coating (suchas 'stellite').The advantages of metal seal rings are:-wide temperature range;-high allowable surface pressure;-high wear resistance;-practically identical coefficients of expansion of seat and ball;-fire-safe and form-retaining.The disadvantages are:-extremely accurate manufacturing required, making it expensive;-no optimum seal;-high coefficient of friction.3.5Medium boreIn principle, two types can be distinguished with respect to valve opening toflow: full bore and reduced bore.The valve bore is the opening the medium flows through if the valve is fullyopened.If the valve bore is the same diameter as that of the pipe it is connected to, wespeak of full bore.If the valve bore is smaller than the diameter of the pipe, however, the valve willform a constriction in the pipe. We then speak of a reduced bore. Particularly incase of viscous liquids and when there is an increased risk of clogging, it isnecessary to use a valve with a full bore.Valves with a reduced bore have more pipe resistance than valves with a fullbore, so in case of a reduced bore, the pressure loss will be greater.3.6Mounting distanceWith respect to mounting distance, we distinguish a short pattern and a longpattern. In the petrochemical industry, the following standard ball valves areused: 'short pattern' and 'long pattern' ball valves, both with a floating ball andsynthetic seats; the 'short pattern' ball valve having a reduced bore and the 'longpattern' ball valve having a full bore.3.7Advantages and disadvantages of ball valves compared withplug valves, butterfly valves and spindle valvesAdvantages of ball valves-rapid switching (90 turn, which also applies to plug and butterfly valves).-low flow resistance;-easy to automate by installing an actuator;-good availability.- full bore- reduced bore- short pattern- long patternTheory / 07.06.13 - 1009Disadvantages of ball valves-sensitive to fouling (particularly the hard parts);-sensitive to incorrect mounting of the actuator (spindle leakage);-the 'dead' space, in which medium and possibly dirt remains behind;-if a full bore is required, a split body must be used, making the valve moresensitive to pipe stress.In the case of synthetic deal rings, the following applies:-limited temperature range;-sensitive to improper use in case of:incomplete opening or closing;regulating.Question 2Which three types of ball designs are there?Question 3What are 'lined ball valves'?4Plug valvesThe plug valve (see figure 10) (where is fig.10) is also known as cock or plugcock. In this type, flow is regulated by means of rotating the plug. A bigadvantage compared with the ball valves is the fact that the plug valves do nothave any 'dead' space. The valve is switched from fully opened to fully closedby turning the operating lever a quarter turn. The passage in the valve is straight.The bore of the pipe is round, but the passage of the plug is not. This shapetransition results in a pressure drop.An important characteristic of this valve is the ease with which it can beconverted to a so-called 'multiple path' design. By this we mean a 3- or 4-wayplug valve. In 3-way plug valves, the plug has an L- or T-shaped passage. The 4-way design is provided with two L-shaped passages (see figure 11). In addition,there is a distinction between passage overlap and passage interruption inswitching. In case of an overlap, at a given moment all passages are open,whereas in case of an interruption, all passages are closed first, before the nextpassage is opened. These designs can simplify the configuration of the pipes andalso reduce the number of valves required at the plant.- 'multiple-path'designTheory / 07.06.13 - 100101.PFA diaphragm2.PTFE inner bush3.Raised sealing ribs4.ANSI (ASA) or DIN flange designs5.Tapering plug6.Adjustment7.Adjusting plate8.Retaining circlip5603-100-090-HFigure 10Plug valvePlug valves can be subdivided into three groups:-unbalanced (grease lubricated) plug valves;-balanced (grease lubricated) plug valves;-plug valves with PTFE seats.4.1Unbalanced (grease-lubricated) plug valvesThese plug valves are provided with conical plugs with lubrication grooves. Thespindle forms one whole with the plug, due to which the spindle packing will actas a bearing. In unbalanced plug valves, the plug will tend to get stuck relativelyrapidly due to changes in pressure and temperature. As a result, forces aregenerated which press the plug into the seat. These forces are:-the force due to the plug's own weight;-the force due to the medium pressure;-the force due to adjusting the bonnet.Theory / 07.06.13 - 100115603-100-011-PFigure 11Schematic diagram of plug valves with multiple portsIn this grease lubricated type, an insoluble lubricant is injected under pressureand forms a thin coating between the plug and the body. The lubricant isinjected via the spindle, by means of a grease gun or a lubrication screw. Thelubricant flows through a check valve and then reaches the seat via narrowgrooves in the seat and the body.The lubricant, which is injected via a grease nipple, has the following functions:-sealing in the direction of flow;-lubrication of the plug in the seat;-maintenance of the moving surfaces;-pumping the plug loose from the seat if it gets stuck.When the valve is in the closed position, the plug is forced into the low pressureside due to the pressure of the medium. Due to the fact that the spindle formsone whole with the plug, the spindle packing will act as a bearing. Anotherdisadvantage is that the plug gets stuck fairly rapidly as a result of changes inpressure and temperature, fouling and low switching frequencies. The advantageis the simple design. This type of plug valve is used for low pressures.4.2Balanced (grease-lubricated) plug valvesTo compensate for the disadvantages of an unbalanced plug valve, a plug valvewith floating balanced plug has been developed. During operation, there aredifferent forces acting on the plug (see figure 12). This difference between theforces is created by the difference in surface areas the pressure acts on. Theseforces ensure the plug is forced into the seat. The forces in questions are:-the force due to the pressure of the medium;-the force due to adjusting the bonnet.Theory / 07.06.13 - 10012a. unbalanced plugb. balanced plug5603-100-012-PFigure 12Pressure distribution of plugsIn a balanced design, a number of features are provided to balance the plug:-pressure balancing holes at the top and bottom of the plug;-balancing spring (on the side of the smallest diameter of the plug);-'loose' plug design (i.e. free from the spindle).The pressure balancing holes ensure a uniform pressure on all sides of the plug.The adjusting screw at the bottom ensures a correct position of the plug in thebody.The balancing spring compensates for the difference in surface area of the topand bottom of the plug and the force with which the plug is forced in the seat. Inaddition, the plug remains in the correct position in the body, in spite of changesin pressure and temperature.The loose plug design prevents the spindle packing from functioning as abearing. In this design, the plug is not forced into the seat and the plug isprovided with a PTFE coating to keep friction and moment of torque low. Adisadvantage is the complicated design. This type is also suitable for highpressure applications.4.3Plug valves with PTFE seatThe introduction of the plug valve with synthetic inner sleeve ('PTFE sleeved')provided a big advantage. This synthetic inner sleeve is mounted between theplug and the body and takes over the function of the lubricant. The material ofthe inner sleeve is a synthetic material with a low coefficient of friction (such asPTFE).- balancing springTheory / 07.06.13 - 10013Plug valves with a synthetic inner sleeve ensure smooth operation withimproved sealing and, as a result of the self lubricating effect of the syntheticinner sleeve, require less maintenance than grease lubricated plug valves. Theself lubricating effect of the inner sleeve consequently makes the plug valvehighly suitable for applications in which grease lubricated plug valves areunacceptable. A disadvantage is the maximum operating temperature of 200 C(unloaded).Finally, it should be pointed out that the choice of lubricant depends on themedium, the temperature and the operating pressure.4.4Advantages and disadvantages of plug valves compared withball valves, butterfly valves and spindle valvesAdvantages-one-piece body;-straight passage;-'in line' repairs possible;-rapid switching;-absence of 'dead' space (compared with ball valves);-easy to automate by installing an actuator.Disadvantages-sensitive to fouling:the dirt adheres to the lubricant; with PTFE sleeve: damage to the plug and the inner sleeve, leading toleakage.-maintenance-sensitive:seals on lubricant;regular lubrication necessary;lubricant in the product.-high moment of torque in metal-to-metal seals;-metal seating surfaces are hard to regrind;-high flow resistance (due to passage transition);-no universal lubricant;-high purchase cost;-maximum operating temperature is determined by lubricant.Question 4What is meant by passage overlap?5Butterfly valvesA circular disc rotates around a diametrical axis. A 90 movement opens orcloses the valve in a fast and simple manner. A butterfly valve usually is lightand compact and has relatively few components. The type of butterfly valvedepends on:-type of valve;-valve geometry;-type of body;-seal rings.Theory / 07.06.13 - 100145.1Valve typeThere are three types of butterfly valve:-wafer type;-lug type;-flange type.Wafer typeIf the application allows it, this is the preferred type of butterfly valve (seefigure 13). The reason is the relatively low cost, the light weight and the shortmounting valves. This type is wedged between two flanges. A big disadvantage,however, is the fact that the flange bolts must absorb all the tensile stressescaused by system stretch. In addition, these bolts must provide the compressionof the two packing surfaces. As a result, there is an increased risk of leakage dueto bolt relaxation. Moreover, this type cannot be spaded (blind flange). Also,because of the close clearance of the valve, even minor sagging in the pipe issufficient to damage the valve disc.5603-100-013-PFigure 13Butterfly valve; wafer type (without flanges)Lug typeThe difference between the wafer type and the lug type is that the latter has cast-on lugs with tapped holes which are attached to the pipe flange by means of tapbolts (see figure 14). This type is used if the entire system must be 'fire safe'(including the bolts). With the wafer type, this is not the case. Anotheradvantage in comparison with the wafer type is that the lug type is bettercentred. In addition, this type has the following advantages in common with thewafer type: lightweight and short mounting distance. This type cannot be spadedeither.Flange type.This type of butterfly valve differs from the other types in that it is fitted with aflange on both sides of the body. This increases the (see remarks), avoidingproblems with dismantling, even if the valve is not entirely closed. Anotheradvantage is the fact that this type can spaded. The mounting distance is notstandardised.- preferredbutterfly valve- 'fire safe'- can be spadedTheory / 07.06.13 - 100155603-100-014-PFigure 14Butterfly valve; lug type5.2Valve geometryThe different valve designs are:Concentric valve (see figure 15)A concentric or symmetric valve is insensitive to the direction of flow.Concentric valves are generally used in 'rubber lined' butterfly valves and inbutterfly valves in low pressure (gas) flows. This type requires the seat to beadapted to the valve geometry at the location of the spindle passage. The sealingcurve is interrupted by the valve disc as a result of symmetry. There is apermanent contact between the seat and the valve spindle. The advantage incomparison with eccentric valves is the fact that due to the concentric position,the thin valve disc requires only minor thickening for the purpose of the valvespindles at the top and bottom. Consequently, the pressure drop is reduced.Symmetric valve discApplication*Rubber coated butterfly valves*Flue gas ducts or air ducts (air conditioning system)Disadvantage*Valve spindle penetrates the sealingsurface. No metal-to-metal sealpossible between valve disc and seatAdvantage*Simple design5603-100-050-PFigure 15Concentric (symmetric) butterfly valveTheory / 07.06.13 - 10016Single eccentric valve (see figure 16)Here, the spindle is positioned 'adjacent to' the valve, in such a way that a roundand uninterrupted sealing surface of both valve and seat is obtained. Adisadvantage is that there is a permanent contact between the valve disc and theseat, making the valve sensitive to vibrations. A consequence is that the seat onthe valve disc and the body is damaged. Another disadvantage is the fact thatoperation depends on the direction of flow.1st eccentricityValve spindle adjacent to valve discAdvantage*Metal-to-metal seal possibleDisadvantage*Valve disc remains in contact withseat.Consequence: local wear at place ofcontactUsed rarely5603-100-060-P/Figure 16Single eccentric butterfly valveDouble-eccentric valve (see figure 17)To compensate for the permanent contact between the valve disc and the seat, asecond eccentricity was introduced. Here, the sealing surface is located a smalldistance in front of the axis of rotation. The centre line of the valve spindle hasbee placed adjacent to the centre line in the longitudinal direction of the valve.This second eccentricity ensures the valve rotates in or out of the seat onlyduring opening and closing, resulting in minimum seat wear. A disadvantage isthe unequal valve surface areas with respect to the spindle, which results in apreferential direction of flow. This type is the one most frequently used as thereis no permanent contact between the seat and the valve disc.Triple-eccentric valve (see figure 18)The final type we will describe here is the triple-eccentric valve, in which theseal is obtained by pressing the valve against the seat. The angle of contact is ca.5 degrees. This valve can be compared with the operation of the gate in a gatevalve. The seat has the shape of a slanted cone section and a slightly ellipsoidperiphery. Consequently, the valve is pressed against the seat and is not rotated.The disadvantage is that any dirt is not moved from the seat by the valve. Inaddition, this type is quite complicated and its purchase price is high. Finally, itshould be pointed out that the degree of leak-tightness of the passage isdetermined by the torque with which the valve disc is pressed against the seat.Theory / 07.06.13 - 100172nd EccentricityAdvantage*Metal-to-metal seal possible*Valve disc in open position not incontact with seal ringDisadvantage*Preferential sealing directionAttention required in mounting indischarge of pumps5603-100-070-pFigure 17Double eccentric butterfly valve3rd EccentricityAdvantage*Metal-to-metal seal possible*Valve disc in open position incontactwith seal ring*Sealing torque*High temperature seats possible* Disadvantage*Preferential sealing direction*More expensive design5603-100-080-pFigure 18Triple eccentric butterfly valve5.3Body typeTwo types can be distinguished: a one-piece body and a split body.One-piece bodyThis body forms one unit, with a spindle passage at the top and secured at thebottom, enabling the valve to be bearing mounted.Split bodySplit body butterfly valves are usually PTFE lined or rubber lined. Theadvantage of this type of body is the simplicity of replacing the PTFE or rubberseat. Just as in the one-piece body, in split body butterfly valves, bearingmounting is possible.Theory / 07.06.13 - 100185.4Seal ringsThe seal rings can be divided into two groups:-synthetic seal rings;-metal seal rings.Synthetic seal ring (see figure 19a)Often the design consists of two components: the seal ring and the support ring.The seal ring is primarily made of PTFE, whereas the material of the supportring is a resilient elastomer.Metal seal ring (see figure 19b)Here, the seat design consists of one single component. The metal seal ring ismechanically locked in the body by means of a so-called 'T-lock'.5603-100-018-pFigure 19Seals in butterfly valvesThe seal ring has a smaller radius and diameter than the corresponding valvesurface area, causing it to be stretched when the butterfly valve is closed. Thepressure is concentrated on the vertices of the sealing ring, achieving anexcellent seal. With increasing pressure, the seal improves due to this pressurepenetrating the 'T-lock'.5.5Advantages and disadvantages of butterfly valve comparedwith ball valves, plug valves and spindle valvesAdvantages of butterfly valves-no 'dead' space;-rapid switching;-easy to automate;-good availability;-relatively low purchase price;-short (see remarks);-less sensitive to fouling than other types of valve with '90 turn'.- elastomer- 'T lock'Theory / 07.06.13 - 10019Disadvantages of butterfly valves-can be used from 3 inches due to the large volume of the valve (high flowresistance);-some makes have a preferential direction of flow because of a lower torque;-wafer type and lug type butterfly valve are sensitive to incorrect use anddisassembly (valve half open);-if the valve is blocked (in the open position), the pipe must be disassembled.Question 5Which three types of butterfly valves are there?Question 6What is the advantage of a concentric valve compared with an eccentric one?Theory / 07.06.13 - 10020SummaryValvescan be divided into: open and shut valves, control valves, safety valvesand one-way valves.The three main functions of hand-operated valves are: starting and stopping theflow, regulating the flow quantity and providing multiple pipe connectionsValves with 90 turn can be divided into: ball valves, plug valves and butterflyvalves.Ball valvesBall valves can have the following ball design: 'floating ball' with reduced bore,'floating' ball with full bore, and thirdly bearing mounted balls.The balls can be solid or hollow and can be provided with a pressure balancehole or a cavity relief hole. The body can be of the one-piece, split or sandwichtype or it can be a top entry design.The sealing rings can be made in synthetic material or metal.Plug valvesPlug valves have no 'dead space'. They are highly suitable for 'multiple path'designs.Plug valves can be divided into groups: unbalanced types, balanced types andtypes with a synthetic seat.A balanced plug has pressure balance holes, a balancing spring on the smallestside and the plug has a flexible connection to the spindle.Butterfly valvesA butterfly valve has a disc which rotates in the passage. Rotating disc types canbe divided into wafer type, lug type or flange type.The following valve geometries can be distinguished: concentric valve, single-eccentric valve, double-eccentric valve and triple-eccentric valve.The body type can be distinguished into one-piece or split.The sealing ring can be made in synthetic material or metal.Theory / 07.06.13 - 10021TestExercisesDo not send in your answers for correction1.Which three groups of hand-operated valves are there?2.Which three groups of valves with 90 turn are there?3.What is the purpose of an 'anti-blow-out' spindle design?4.Which body designs are there in the case of ball valves?5.Into which groups can plug valves be divided?6.Give the advantages and disadvantages of plug valves with a synthetic seat.Answers to the questions in the lesson1.Rotate a quarter turn to open or close (in contrast with the spindle valves).2.a.Floating ball with reduced bore.b.Floating ball with full bore.c.Bearing mounted ball.3.Ball valves with coating against corrosive media.4.During switching, all ports are open for a moment; there is no fully closedintermediate position.5.Wafer type, lug type and flange type.6.Insensitive to direction of flow and the valve disc can remain thin, resultingin smaller pressure drop.Answers to the exercises1.a.With 90 turn.b.With rising spindle.c.With rising and rotating spindle.2.a.Ball valves.b.Plug valves.c.Butterfly valves.3.For the protection of 'side entry' valves to prevent the spindle from beingblown out during disassembly.Theory / 07.06.13 - 100224.a.One-piece body.b.Split body.c.Sandwich body.5.a.Unbalanced plug valves.b.Balanced plug valves.c.Plug valves with PTFE seat.6.Advantages:a.smooth operation.b.improved seal.c.less maintenance.Disadvantage: operating temperature limited to a maximum of 200 CProblems and assignmentsAnswer and send in for correction1.Which are the main functions of valves?2.What is the function of a pressure balance hole in a ball valve?3.Which types of sealing ring are there for ball valves and give thedisadvantages.4.Which are the functions of the lubricant in a plug valve?5.How can we prevent a plug from getting stuck?6.Give the advantages and disadvantages of the wafer type butterfly valve.