Instrument connections can also be provided with welding special bosses directly onto the pipe during installation. 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.
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. The plug is first removed and all parts that could contaminate the sample are sterilized 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, after which the needle of a hypodermic syringe is inserted through the bung into the product, and a sample is withdrawn.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. 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 sterilization 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 sterilization.
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. 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 drain without any possibility of one medium being mixed with the other. This is a common problem faced when engineering dairy plants. Dairy products and cleaning solutions flow in separate lines, and have to be kept separate. Figure 6.
Piping and Pipeline Calculations Manual
Zoom Fig. There are many places in a piping system where it must be possible to stop the flow or divert it to another line. These functions are performed by valves. Seat valves, manually or pneumatically controlled, or butterfly valves, are used for this purpose. The valve body has a seat for the closing plug at the end of the stem. The plug is lifted from and lowered onto the seat by the stem, which is moved by a crank or a pneumatic actuator Figure 6.
The seat valve is also available in a change-over version. This valve has three to five ports.
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When the plug is lowered, the liquid flows from inlet 2 to outlet 1, and when the plug is lifted to the upper seat, the flow is directed through outlet 3, according to the drawings to the right in Figure 6. This type of valve can have up to five ports.
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The number is determined by the process requirements. There is also another type of seat valve, where the valve plug closes in the opposite way compared to a standard valve. This valve type can be used to eliminate pressure shocks in the product lines.
This type of valve can be either in change-over or shut-off version.
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Various remote-controlled actuator alternatives are available. For example, the valve can be opened by compressed air and closed with a spring, or vice versa. It can also be both opened and closed by compressed air Figure 6.
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Actuators for an intermediate plug position and for two-stage opening and closing are also available. The valve control unit Figure 6. The top unit includes indication unit, activation stem, sensor system and solenoid valves to control and supervise all kinds of pneumatic processing valves. It receives signals from a PLC to control the valve and it sends feedback signals to the PLC to indicate when the valve is in a certain position.
The top unit can easily be set by remote control and indicate seat lift of mixproof valves and it includes a maintenance programme to indicate when plug seals of a single seat is worn out. The modern top units can be used for digital as well as bus communication systems.
A solenoid valve is fitted in the top unit. An electric signal triggers the solenoid valve and allows compressed air to enter the actuator. The valve then opens or closes as required.
On the way, the compressed air passes through a filter to free it from oil and other foreign matter that might affect proper operation of the valve. The air supply is cut off when the solenoid is de-energized and the air in the product valve is then evacuated through an exhaust port in the solenoid valve. Manual shut-off seat valve and pneumatically operated change-over seat valve. The operating mechanism is interchangeable between shut-off and change-over seat valves. The butterfly valve Figure 6. 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 very small, resulting in very low pressure drop and no turbulence. It is also good for high viscosities and, being a straight-through valve, it can be fitted in straight pipes. 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. The butterfly valve is fitted with a handle, usually for two positions — open and closed. This type of valve is not really suitable as a control valve, but can be used for coarse control with a special handle for infinite positions.
The disc is easy to turn until it touches the seal ring. Then it needs more power to compress the rubber. A normal, spring powered actuator is strongest in the beginning, when less power is required, and weaker at the end, when more power is required. It is therefore an advantage to use actuators which are designed so that they provide the correct power at the right time. Another type of the butterfly valve is the flange valve, shown in Figure 6. 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 as an ordinary butterfly valve.
During operation, it is clamped between the flanges with screws. For servicing, the screws are loosened. The valve part can then be pulled out for easy servicing. Mixproof valves Figure 6. A double-seated valve has two independent plug seals separating two liquids, forming a leakage chamber between them under atmospheric pressure during every working condition. In case of rare accidental leaking of product, this will flow into the leakage chamber and be discharged through the leakage detection pipe. When the valve is open, the leakage chamber is closed.
The product can then flow from one line to the other. During 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 tank outlet valve is compact and the valve body can be turned in any angle to fit the piping. A valve can be fitted with various types of position indication Figure 6.
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.
Using the new guide system, the pipe only comes in contact with a low-friction, molded HDPE insert that allows it to easily slide with minimal stress or wear during each thermal-expansion cycle. The pipe never touches any metal bracket, which could potentially cause wear on the piping because of sharp edges.
The pipe-guide inserts are designed to have a 3mm gap around the OD of the pipe, which allows unrestricted movement of the pipe in the axial direction. It also lets engineers design for lower accelerations and forces caused by seismic or water-hammer events. This website requires certain cookies to work and uses other cookies to help you have the best experience.
BUILDING BLOCKS OF DAIRY PROCESSING