06.08 Pipes, valves and fittings

The pipe systemsame way. The difference is in the materials used, the design of the components and the sizes of the pipes.All components in contact with the product are made of stainless steel.Various materials are used in the other systems, e.g. cast iron, steel, copper and aluminium. Plastic is used for water and air lines, and ceramic for drainage and sewage pipes.The following section deals only with the product line and its components. The pipe systems for service media are described in the section dealing with utility installations.The following types of fittings are included in the product pipe system:•Straight pipes, bends, tees, reducers and unions•Special fittings such as sight glasses, instrument bends, etc.•Valves for stopping and directing the flow•Valves for pressure and flow control•Pipe supportsPipes, valves and fittingsConnectionsPermanent joints are welded (Figure 6.8.1). Where disconnection is required, the pipe connection is in the form of a threaded union with a male end and a retained nut with a joint ring in between, or a clamped union with a joint ring (Figure 6.8.2).The union permits disconnection without disturbing other pipework. This type of joint is therefore used to connect process equipment, instruments,etc. that need to be removed for cleaning, repair or replacement.Different countries have different union standards. These can be SMS (Swedish Dairy Standard) also used internationally, DIN (German), BS (British), IDF/ISO* and ISO clamps (widely used in the USA).Bends, tees and similar fittings are available for welding, and with welded Fig. 6.8.1 Some examples of fittings for permanent welding.1Tees 2Reducers 3Bends *)IDF =International Dairy FederationISO =International Standardisation OrganisationFig. 6.8.2 Dairy unions of different standards.unions. In the latter case, the fitting can be ordered with nut or male ends or with clamp fittings.All unions must be tightened firmly to prevent liquid from leaking out or air from being sucked into the system and causing problems in downstream parts of the process.Special pipe fittings Sight glasses are fitted in the line where a visual check of the product is required.Bends with instrument connections are used for fitting instruments like thermometers and gauges. The sensor should be directed against the flow to make readings as accurate as possible. The connection boss can also be used for a sampling cock. Instrument connections can also be provided with welding special bosses directly onto the pipe during installation.Sampling devices Sampling devices need to be installed at strategic points in the plant to collect product samples for analysis. For quality control, such as determining the fat content of milk and the pH value of cultured products,the samples can be collected from a sampling cock (Figure 6.8.3).For hygienic quality tests, the sampling method must preclude any risk of contamination from outside the pipe. A sampling plug can therefore be used. This plug, shown in Figure 6.8.4, has a rubber bung at the bottom.The plug is first removed and all parts that could contaminate the sample are sterilised (typically a wad moistened in a chlorine solution just before sampling), after which the needle of a hypodermic syringe is inserted through the bung into the product, and a sample is withdrawn.The aseptic sampling valve (Figure 6.8.5) consists of three parts, a valve body, a valve head and a membrane. The rubber membrane is placed on the stem of the valve head and works as a stretchable plug. The aseptic sampling valve is designed for sterilisation before and after each sampling.The manual valve is opened by rotating a handle or by activating a lever.The stem and the membrane are then retracted, allowing liquid to ing the reverse procedure the built-in spring closes the valve and keeps the channel between the hose pieces open for sterilisation.Samples of aseptic products – heat treated at such a high temperature that they are sterile – are always collected through an aseptic sampling valve to avoid reinfection.Valves Mixproof valve systems There are many junctions in a piping system where product normally flows from one line to the other, but which must sometimes be closed off so that two different media can flow through the two lines without being mixed.When the lines are isolated from each other, any leakage must go to drainwithout any possibility of one medium being mixed with the other.This is a common problem faced when engineering dairy plants. Dairyproducts and cleaning solutions flow in separate lines, and have to be keptseparate. Figure 6.8.6 shows four different solutions to the same task.Shut-off and change-over valvesThere are many places in a piping system where it must be possible to stopthe flow or divert it to another line. These functions are performed by valves.Seat valves, manually or pneumatically controlled, or butterfly valves, areused for this purpose.Seat valvesThe valve body has a seat for the closing plug at the end of the stem. Theplug is lifted from and lowered onto the seat by the stem, which is movedby a crank or a pneumatic actuator (Figure 6.8.7).The seat valve is also available in a change-over version. This valve hasthree to five ports. When the plug is lowered, the liquid flows from inlet 2 tooutlet 1, and when the plug is lifted to the upper seat, the flow is directedthrough outlet 3, according to the drawings to theright in Figure 6.8.8.Fig. 6.8.7 Manual shut-off seat valve and pneumatically operated change-over seat valve. The operating mecha-nism is interchangeable between shut-off and change-over seat valves.Fig. 6.8.8 Shut-off and change-over valves with the plug in different positions andthe corresponding flow chart symbols.Fig. 6.8.6 Sanitary mixproof valve systems.1Swing bend for manual change between different lines.2Three shut-off valves can perform the same function.3One shut-off valve and one change-over valve can do the same job.4One mixproof valve is enough for securing and switching the flow.The valve usually consists of two identical halves with a seal ring clamped between them. A streamlined disc is fitted in the centre of the valve. It is usually supported by bushes to prevent the stem from seizing against the valve bodies.With the disc in the open position, the valve offers very low flow resistance. In the closed position, the disc seals against the seal ring.Fig. 6.8.12 Principle of the air drivenactuator for butterfly valves.position (right).Fig. 6.8.10 The valve plug positionindicator and control unit is fitted on topof the actuator.Manual controlThe butterfly valve is fitted with a handle, usually for two positions – openand closed.This type of valve is not really suitable as a control valve, but can be usedfor coarse control with a special handle for infinite positions.Automatic controlAn air actuator (Figure 6.8.12) is used for automatic control of the butterflyvalve. The function can be:•Spring closing/air opening (Normally closed, NC)•Air closing/spring opening (Normally open, NO)•Air opening and closing (A/A)The disc is easy to turn until it touches the seal ring. Then it needs morepower to compress the rubber. A normal, spring powered actuator isstrongest in the beginning, when less power is required, and weaker at theend, when more power is required. It is therefore an advantage to useactuators which are designed so that they provide the correct power at theright time.Another type of the butterfly valve is the “sandwich” valve, shown inFigure 6.8.13. It is the same type of butterfly valve as described above, butit is fitted between two flanges welded to the line. Its function is the same asan ordinary butterfly valve. During operation, it is clamped between theflanges with screws. For servicing, the screws are loosened. The valve partcan then be pulled out for easy servicing.Mixproof valves6.8.14) that is referred to.through the leakage detection pipe.butterfly “sandwich” valve design for simplified maintenance.Fig. 6.8.15 Three types of mixproof valves.1Double-seat valve with seat-lift cleaning2Single-seat valve with external cleaning and leakage indication3Tank outlet valve2Upper port 3Upper plug 4Leakage chamber 5Leakage detection pipe 6Lower port 7Lower plug with balancerDuring cleaning one (upper or lower) of the plugs lift so that seat and plug are cleaned. The cleaning liquid is discharged through the leakage chamber. External cleaning of upper and lower plugs and leakage chamber,as well as aseptic-like operation are also possible.The valve can be cleaned and water hammer protected to any level according to the needs in the specific process. There is virtually no spillage of product when operating the valve.It is also possible to have a double-seated tank outlet valve. This is designed for mixproof tank outlet operation when cleaning of the line right up to the bottom of the tank is required.The independent seat lift of the lower plug provides easy cleaning without the need of external cleaning. The lower plug is insensitive to high pressure and water hammer in the line.The tank outlet valve is compact and the valve body can be turned in any angle to fit the piping.Position indication and control Position indication only A valve can be fitted with various types of position indication (Figure 6.8.16),depending on the control system of the plant. Different types of switches are microswitches, inductive proximity switches or Hall elements. The switches are used for feedback signals to the control system.When only switches are fitted to the valves, it is necessary to have one solenoid valve for each valve in a solenoid-valve cabinet. A solenoid valve supplies compressed air to the product valve when it receives a signal and releases the air pressure when the signal disappears.This system (1) requires one electric cable and one air hose for each valve.The combined unit (2) is a basic top unit, which is fitted on the top of the valve actuator. It includes activation stem, sensor system and solenoid valves. One air hose can supply many valves but one electric cable per valve is still required.The ultimate control This is done with a top unit shown in Figure 6.8.10, which is specially designed for computer control. The top unit includes indication unit,activation stem, sensor system and solenoid valves.This top unit can be used for digital and bus communication systems,allowing only one air hose and one electrical cable to control and communicate with a large number of valves. The top unit can be programmed centrally and the installation costs are low.The unit includes many functions, such as remote setting, control and indication of seat lift on mixproof valves, maintenance program for single seat valves, control and indication on position of valve plug, etc.Check and control valves Check valves A check valve (Figure 6.8.17) is fitted when it is necessary to prevent the product from flowing in the wrong direction. The valve is kept open by the liquid flow in the correct direction. If the flow stops, the valve plug is forced against its seat by the spring. The valve then closes against reversal of the flow.Control valves Shut-off and change-over valves have distinct positions, open or closed. In Fig. 6.8.16 Valve position indicationsystems.1Indication only2Indication with top unit3Indication and control systemFig. 6.8.17 Check valve12the regulating valve, the passage can be changed gradually. The controlvalve is used for accurate control of flows and pressures at various points inthe system.A pressure relief valve (Figure 6.8.18) maintains the pressure in thesystem. If the pressure is low, the spring holds the plug against the seat.When the pressure has reached a certain value, the force on the plugovercomes the spring force and the valve opens. The opening pressure canbe set to the required level by adjusting the spring tension.Manual control valve with variable-flow plug (Figure 6.8.19).This valvehas a stem with a specially shaped plug. When the regulating handle isturned, the plug moves up or down, varying the passage and thereby theflow rate or the pressure. A scale on the valve indicates the setting.The pneumatic control valve with variable-flow plug (Figure 6.8.20)works similarly to the previously described valve. The plug-and-seatarrangement is similar to that of the manual valve. The flow is graduallythrottled when the plug is lowered towards the seat.This type of valve is used for automatic control of pressures, flows andlevels in processes. A transmitter is fitted in the process line andcontinuously transmits the measured value to a controller. This controllerthen adjusts the setting of the valve so that the pre-set value is maintained.A valve often used is the constant-pressure valve (Figure 6.8.21).Compressed air is supplied through a reducing valve to the space above adiaphragm. The air pressure is adjusted by the reducing valve until theproduct pressure gauge shows the required pressure. The pre-set pressureis then maintained regardless of changes in the operating conditions. Figure6.8.22 describes the function of the constant-pressure valve.The valve reacts rapidly to changes in the product pressure. A reducedFig. 6.8.18 Pressure relief valve.Fig. 6.8.19 Manual control valvewith variable-flow plug.Fig. 6.8.20 Pneumatic control valve withvariable-flow plug.Fig. 6.8.22 Function of the constant-pressure valve when regulating the pressure before the valve.1Equilibrium air/product.2Product pressure drops, the valve closes and the product pressure increases to the preset value.3Product pressure increases, the valve opens, and the product pressure drops to the preset value.Fig. 6.8.21 Constant-pressure valve.Fig. 6.8.25 Examples of standard pipesupports.product pressure results in a greater force on the diaphragm from the air pressure, which remains constant. The valve plug then moves downwards with the diaphragm, the flow is reduced and the product pressure increased to the pre-set value.An increased product pressure results in a force on the diaphragm that is greater than the downward force from the compressed air. The valve plug then moves upwards, increasing the passage for the product. The flow will then increase until the product pressure has dropped to the pre-set value.This valve is available in two versions for constant pressure before or after the valve.The valve cannot control the product pressure if the available air pressure is lower than the required product pressure. In such cases, a booster can be fitted to the top of the valve. In this way, the valve can be used for product pressures up to about twice the available air pressure.Valves for constant inlet pressure are often used after separators and pasteurisers. Those for constant outlet pressure are used before fillingmachines.Valves are arranged in clusters to minimise dead ends and make it possible to distribute the product between different parts or blocks within the dairy.Valves are also used to isolate individual lines so that one line can be safely cleaned while the product is flowing in others.Pipe supportsPipes usually run about 2 – 3 metres above the dairy floor. All components must be easily accessible for inspection and maintenance. The lines should slope slightly (1:200 – 1:1000) to be self-draining. There should be nopockets at any point along the line where the product or cleaning fluid can collect.Pipes must be firmly supported. On the other hand the pipes should not be so restrained that movement is prevented. The pipes will expandconsiderably, when the product temperatures are high and during cleaning.The resulting increase in length and torsional forces in bends and equipment must be absorbed. This, plus the fact that the variouscomponents make the pipe system very heavy, place great demands onaccuracy and on the experience of the system designer.Fig. 6.8.24 Valve arrangement in a tank garden for independent routing of products and cleaning solutions to and from the tanks.Fig. 6.8.23 Constant-pressure modulat-ing valve with a booster for control ofproducts with a higher pressure than theavailable air pressure.。