Double seat valve
Double seat valves are used for the mix-proof shut-off of "hostile" media at pipe crossing points. Typical areas of application are the brewery, beverage, milk processing and food industries as well as the pharmaceutical, healthcare, biotechnology and fine chemical industries.
Function of the valve
Valves for hygienic applications are usually equipped with an air-spring actuator. The actuator piston rod is connected to the valve disk. A stroke movement of the valve is generated by applying air under the piston surface. When the air admission is deactivated, the valve is closed by the spring force of the actuator.
When the valve is closed (rest position) there are always two seals between the separate pipes. If a seal should be defective, the resulting leakage can flow out of the leakage outlet into the periphery without mixing with the product in the second pipeline. This ensures that there is no mixing between the media in two pipelines.
Application examples
In order to be able to meet the different requirements in different branches of industry, areas of application and processes, there are different mix-proof shut-off valves for different requirements (e.g. axially sealing, radial sealing, pressure shock-proof, piggable). Double seat valves with spray cleaning of the leakage area are often used in non-critical areas:
- Breweries: cold area, e.g. B. fermentation cellar
- Dairies: Before the thermal treatment, e.g. B. Milk acceptance, raw milk tank farm, etc.
In order to clean the seals in the leakage chamber without leaving any residues, valves with seat lifting are used for highly viscous media or media with a high sugar content.
Shift leakage
With axially sealing double seat valves, each switching process results in a short point in time at which neither the lower valve disk is in contact with the center seal of the upper valve disk nor has reached the axial seating surface of the seat ring. During this brief moment, liquid penetrates the leakage space through the gap and flows off to the atmosphere. This is known as switching leakage.
In the case of radially sealing double seat valves, this gap does not arise during the switching process, which means that switching leakage is reduced to a minimum (any product residues adhering to the metal surfaces).
Pressure surge protection
If a pressure surge occurs in the lower pipeline, the force of the pressure surge acts on the lower valve disc and could exceed the locking force of the drive spring. This results in the risk that the lower valve disk will be lifted by the increased pressure in the pipeline.
In the case of axially sealing double seat valves, this would result in a connection to the atmosphere, which would lead to leakage (see switching leakage). The connection to the atmosphere also causes the overpressure in the pipeline to be abruptly reduced, after which the actuator spring closes the valve again.
Valves with a lower balancer are available to prevent the lower valve disk from lifting during a pressure surge in the lower pipeline. The balancer balances the effective direction of the pressure with a downward-facing compensation surface and prevents movement of the lower valve disk up to a certain overpressure.
Radially sealing double seat valves are always equipped with this lower balancer to prevent the lower valve disk from opening.
Cleaning the leakage space
Spray cleaning
A cleaning connection to be connected at the level of the lantern can be used to supply cleaning fluid externally to the leakage space in order to clean this space by means of an integrated spray nozzle. The cleaning fluid then drains into the periphery without pressure through the leakage outlet. Since cleaning takes place when the valve is closed, the sealing surfaces that are in contact are not detected during cleaning. In this way, the leakage space can be cleaned independently of the pipe cleaning. In addition, intermediate flushing can be carried out before or after the valve is switched.
Periphery
In order to be able to use the spray cleaning via the external connection in the lantern, feed valves are required in the periphery, which supply the cleaning connection of the double seat valve with cleaning medium at the intended time. For this purpose, feed valves of smaller nominal widths are used on the pipeline carrying the cleaning fluid. Each feed valve usually supplies several cleaning connections of double seat valves. It is important to ensure that all connected double seat valves are adequately supplied with cleaning fluid during cleaning. As a guide, no more than six double seat valves should be supplied from one feed valve.
Cleaning by lifting the seat
Double seat valves, which are equipped with a lift drive, allow an individual lifting of a single valve disc during the respective pipe cleaning. The cleaning medium flows past the seal of the lifted valve disk, cleans the leakage space and then flows off without pressure through the leakage outlet into the periphery. In this way, all surfaces in contact with the product, including the surfaces of the valve disk seals, can be cleaned. With axially sealing double seat valves, it is possible to lift the upper valve disk upwards, provided there is cleaning liquid in the upper pipeline.
If there is cleaning fluid in the lower pipeline, it is possible to lift the lower valve disk upwards with axially sealing double seat valves.
See also
Individual evidence
- ↑ Bernd Thier: Industrial valves: components of pipeline technology. 5th edition, Vulkan Verlag, Essen, 1997, p. 512
- ↑ Wolfgang Kunze: Technology brewers and maltsters. 11th edition, VLB Berlin, 2016, ISBN 978-3-921690-81-9 , p. 458
- ↑ Bernd Thier: Industrial valves: components of pipeline technology. 5th edition, Vulkan Verlag, Essen, 1997, p. 516
- ↑ Bernd Thier: Industrial valves: components of pipeline technology. 5th edition, Vulkan Verlag, Essen, 1997, p. 513
- ↑ Bernd Thier: Industrial valves: components of pipeline technology. 5th edition, Vulkan Verlag, Essen, 1997, p. 513
- ↑ Bernd Thier: Industrial valves: components of pipeline technology. 5th edition, Vulkan Verlag, Essen, 1997, p. 512
- ↑ Bernd Thier: Industrial valves: components of pipeline technology. 5th edition, Vulkan Verlag, Essen, 1997, p. 513