06.08 Pipes, Valves and Fittings

8/12/2019 06.08 Pipes, Valves and Fittings

1/8

Dairy Processing Handbook/Chapter 6.8 165

The pipe systemThe product flows between the components of the plant in the pipe system.

A dairy also has conduit systems for other media such as water, steam,cleaning solutions, coolant and compressed air. A waste-water system tothe drain is also necessary. All these systems are basically built up in thesame way. The difference is in the materials used, the design of thecomponents 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, copperand aluminium. Plastic is used for water and air lines, and ceramic fordrainage and sewage pipes.

The following section deals only with the product line and itscomponents. The pipe systems for service media are described in thesection 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 supports

Pipes, valves and

fittings

For hygiene reasons, all product-wetted parts of dairy equipmentare made of stainless steel. Two main grades are used, AISI 304and AISI 316. The latter grade is often called acidproof steel.Corresponding (not exactly equivalent) specifications forEuropean steel grades are:

USA AISI 304 AISI 316 AISI 316LEurope EN 1.4301 EN 1.4401 EN 1.4404

ConnectionsPermanent joints are welded (Figure 6.8.1). Where disconnection isrequired, the pipe connection is in the form of a threaded union with a maleend and a retained nut with a joint ring in between, or a clamped union witha joint ring (Figure 6.8.2).

The union permits disconnection without disturbing other pipework. Thistype 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 forpermanent welding.

1 Tees2 Reducers

3 Bends

1

2 3

*) IDF = International Dairy Federation

ISO = International Standardisation Organisation


2/8

Dairy Processing Handbook/Chapter 6.8166

Nut SMS

IDF/ISO

DIN

BS

Clamp

Male part

Joint ring

Liner

Fig. 6.8.3 Sampling cock.

Fig. 6.8.5 Plug for aseptic sampling.

Fig. 6.8.2 Dairy unions ofdifferent standards.

unions. In the latter case, the fitting can be ordered with nut or male ends orwith clamp fittings.

All unions must be tightened firmly to prevent liquid from leaking out orair from being sucked into the system and causing problems in downstreamparts of the process.

Special pipe fittingsSight glasses are fitted in the line where a visual check of the product isrequired.

Bends with instrument connections are used for fitting instruments likethermometers and gauges. The sensor should be directed against the flowto make readings as accurate as possible. The connection boss can alsobe used for a sampling cock. Instrument connections can also be providedwith welding special bosses directly onto the pipe during installation.

Sampling devicesSampling devices need to be installed at strategic points in the plant tocollect product samples for analysis. For quality control, such asdetermining 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 beused. 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 sampleare sterilised (typically a wad moistened in a chlorine solution just beforesampling), after which the needle of a hypodermic syringe is insertedthrough the bung into the product, and a sample is withdrawn.

The aseptic sampling valve (Figure 6.8.5) consists of three parts, a valvebody, a valve head and a membrane. The rubber membrane is placed onthe stem of the valve head and works as a stretchable plug. The asepticsampling 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 pass.Using 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 samplingvalve to avoid reinfection.

Valves

Mixproof valve systemsThere are many junctions in a piping system where product normally flowsfrom one line to the other, but which must sometimes be closed off so thattwo different media can flow through the two lines without being mixed.

Fig. 6.8.4 Sampling cock for

bacteriological analysis.


3/8


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 directed

through outlet 3, according to the drawings to theright in Figure 6.8.8.

Fig. 6.8.7 Manual shut-off seat valveand pneumatically operated change-

over seat valve. The operating mecha-

nism is interchangeable between shut-off and change-over seat valves.

Fig. 6.8.8Shut-off and change-over valves with the plug in different positions and

the corresponding flow chart symbols.

1

2

3A

B

D

C

4

Fig. 6.8.6Sanitary mixproof valve systems.1 Swing bend for manual change between different lines.2 Three shut-off valves can perform the same function.

3 One shut-off valve and one change-over valve can do the same job.4 One mixproof valve is enough for securing and switching the flow.

1

2

3


4/8


This type of valve can have up to five ports. The number is determinedby the process requirements.

There is also another type of seat valve, where the valve plug closesagainst the flow to eliminate pressure chocks in the product lines. This typeof valve can be either in change-over or shut-off version.

Various remote-controlled actuator alternatives are available. Forexample, the valve can be opened by compressed air and closed with aspring, or vice versa. It can also be both opened and closed bycompressed air (Figure 6.8.9).

Actuators for an intermediate plug position and for two-stage openingand closing are also available.

The valve control unit (Figure 6.8.10) is fitted on the top of the valveactuator. The top unit includes indication unit, activation stem, sensorsystem and solenoid valves to control and supervise all kinds of pneumaticprocessing valves. It receives signals from a PLC to control the valve and itsends feedback signals to the PLC to indicate when the valve is in a certainposition.

The top unit can easily be set by remote control and indicate seat lift ofmixproof valves and it includes a maintenance program to indicate whenplug seals of a single seat is worn out.

The modern top units can be used for digital as well as buscommunication systems. More basic top units can be used only in digitalsystems for simple control and indication of open/closed valve positions.

A solenoid valve is fitted in the top unit. An electric signal triggers thesolenoid valve and allows compressed air to enter the actuator. The valvethen opens or closes as required. On the way, the compressed air passesthrough a filter to free it from oil and other foreign matter that might affectproper operation of the valve. The air supply is cut off when the solenoid isde-energized and the air in the product valve is then evacuated through anexhaust port in the solenoid valve.

Butterfly valvesThe butterfly valve (Figure 6.8.11) is a shut-off valve. Two valves must be

used to obtain a change-over function.Butterfly valves are often used for sensitive products, such as yoghurt

and other cultured milk products, as the restriction through the valve is verysmall, resulting in very low pressure drop and no turbulence. It is also goodfor high viscosities and, being a straight-through valve, it can be fitted instraight pipes.

The valve usually consists of two identical halves with a seal ringclamped between them. A streamlined disc is fitted in the centre of thevalve. It is usually supported by bushes to prevent the stem from seizingagainst the valve bodies.

With the disc in the open position, the valve offers very low flowresistance. In the closed position, the disc seals against the seal ring.

Fig. 6.8.12 Principle of the air driven

actuator for butterfly valves.

Fig. 6.8.11Manually controlled butterfly valve in open position (left) and in closed

position (right).

Fig. 6.8.9 Examples of pneumaticallyoperated actuators.

1 Valve opened by spring. Closedwith compressed air.

2 Valve closed by spring. Opened withcompressed air.

Fig. 6.8.10The valve plug position

indicator and control unit is fitted on topof the actuator.

2 1


5/8


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 control

An 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, but

it 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 valvesMixproof valves (Figure 6.8.15) can be either double- or single-seated, butwhen discussing mixproof valves, it is generally the double-seat type (Figure6.8.14) that is referred to.

A double-seated valve has two independant plug seals separating twoliquids, forming a leakage chamber between them under atmospheric

pressure during every working condition. In case of rare accidental leakingof product, this will flow into the leakage chamber and be dischargedthrough the leakage detection pipe.

When the valve is open, the leakage chamber is closed. The product canthen flow from one line to the other.

Fig. 6.8.13Pneumatically operated

butterfly sandwich valve design forsimplified maintenance.

Fig. 6.8.15 Three types of mixproof valves.1 Double-seat valve with seat-lift cleaning2 Single-seat valve with external cleaning and leakage indication

3 Tank outlet valve

Fig. 6.8.14Double-seat mixproof valve

with balanced plug and built-in seat lift1 Actuator2 Upper port

3 Upper plug4 Leakage chamber

5 Leakage detection pipe6 Lower port

7 Lower plug with balancer

1 2 3

1

6

4

7

5

3

2


6/8


Flow

direction

During cleaning one (upper or lower) of the plugs lift so that seat andplug are cleaned. The cleaning liquid is discharged through the leakagechamber. 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 levelaccording to the needs in the specific process. There is virtually no spillageof product when operating the valve.

It is also possible to have a double-seated tank outlet valve. This isdesigned for mixproof tank outlet operation when cleaning of the line rightup to the bottom of the tank is required.The independent seat lift of the lower plug provides easy cleaning withoutthe need of external cleaning. The lower plug is insensitive to high pressureand water hammer in the line.

The tank outlet valve is compact and the valve body can be turned inany angle to fit the piping.

Position indication and control

Position indication onlyA 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 switchesare microswitches, inductive proximity switches or Hall elements. Theswitches are used for feedback signals to the control system.

When only switches are fitted to the valves, it is necessary to have onesolenoid valve for each valve in a solenoid-valve cabinet. A solenoid valvesupplies compressed air to the product valve when it receives a signal andreleases the air pressure when the signal disappears.

This system (1) requires one electric cable and one air hose for eachvalve.

The combined unit (2) is a basic top unit, which is fitted on the top of thevalve actuator. It includes activation stem, sensor system and solenoid

valves. One air hose can supply many valves but one electric cable pervalve is still required.

The ultimate controlThis is done with a top unit shown in Figure 6.8.10, which is speciallydesigned 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 andcommunicate with a large number of valves. The top unit can beprogrammed centrally and the installation costs are low.

The unit includes many functions, such as remote setting, control andindication 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 valvesA check valve (Figure 6.8.17) is fitted when it is necessary to prevent theproduct from flowing in the wrong direction. The valve is kept open by theliquid flow in the correct direction. If the flow stops, the valve plug is forcedagainst its seat by the spring. The valve then closes against reversal of theflow.

Control valvesShut-off and change-over valves have distinct positions, open or closed. In

Fig. 6.8.16Valve position indicationsystems.

1 Indication only2 Indication with top unit

3 Indication and control system

Fig. 6.8.17Check valve

V1 V2 V3

1

2

3 V1V2 V3

V1

V2 V3


7/8


1 2 3

Flow direction

the regulating valve, the passage can be changed gradually. The controlvalve is used for accurate control of flows and pressures at various points inthe system.

Apressure 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 reduced

Fig. 6.8.18Pressure relief valve. Fig. 6.8.19 Manual control valvewith variable-flow plug.

Flow

direction

Fig. 6.8.20 Pneumatic control valve with

variable-flow plug.

Fig. 6.8.22 Function of the constant-pressure valve when regulating the pressure before the valve.1 Equilibrium air/product.2 Product pressure drops, the valve closes and the product pressure increases to the preset value.

3 Product pressureincreases, the valve opens, and the product pressure drops to the preset value.

Fig. 6.8.21Constant-pressure valve.


8/8


Fig. 6.8.25Examples of standard pipesupports.

product pressure results in a greater force on the diaphragm from the airpressure, which remains constant. The valve plug then moves downwardswith the diaphragm, the flow is reduced and the product pressure increasedto the pre-set value.

An increased product pressure results in a force on the diaphragm that isgreater than the downward force from the compressed air. The valve plugthen moves upwards, increasing the passage for the product. The flow willthen increase until the product pressure has dropped to the pre-set value.This valve is available in two versions for constant pressure before or afterthe valve.

The valve cannot control the product pressure if the available air pressureis lower than the required product pressure. In such cases, a booster canbe fitted to the top of the valve. In this way, the valve can be used forproduct pressures up to about twice the available air pressure.

Valves for constant inlet pressure are often used after separators andpasteurisers. Those for constant outlet pressure are used before fillingmachines.

Valve systems

Valves are arranged in clusters to minimise dead ends and make it possibleto 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 safelycleaned while the product is flowing in others.

Pipe supportsPipes usually run about 2 3 metres above the dairy floor. All componentsmust be easily accessible for inspection and maintenance. The lines shouldslope 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 cancollect.

Pipes must be firmly supported. On the other hand the pipes should notbe 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.

There must always be a freedrain opening betweenproduct and CIP flows andbetween different products.

Produ

ctout

Producttoor

fromtanks

Produ

ctin

Produ

ctout

Producttoor

fromtanks

Produ

ctin

Fig. 6.8.23Constant-pressure modulat-ing valve with a booster for control of

products with a higher pressure than the

available air pressure.

Documents

06.08 Pipes, Valves and Fittings