VARIVENT® Mixproof Shut-off Valves

When the valve is closed (deactivated), there are always two seals between the separate pipelines. If a seal were to fail, any resulting leak can be safely directed through the leak outlet to the surrounding area without mixing with the product in the other pipe. This ensures that the media in the two pipes do not mix.

To meet the various requirements across different industries, applications, and processes, we offer mixproof shut-off valves in a variety of technical designs.

VARIVENT® double-seat valves with spray cleaning of the leakage chamber are often used in non-critical areas:

Breweries: cold storage areas, such as fermentation cellars
Dairies: prior to thermal processing, such as milk reception and raw milk storage

VARIVENT® long-stroke valves are used to transport products containing larger particles or viscous products, such as yogurt with fruit pieces.

• Certified, hygienic design
• Mechanical metal stop
• Flexibility thanks to the modular design
• Proven sealing geometry
• Mixproof separation
• Various valve designs are available
• Connection for spray cleaning of the leak chamber

The various models of the VARIVENT® double-seat valve make it possible to select valves that are optimally suited to the process.

The axially sealed valve types D and B result in a small switching leak each time the valve is switched, but they have a very long service life thanks to their axial seals.

The R-type radially sealed valve has the advantage of switching with virtually no switching leakage.

Valve types B and R are also equipped with a balancer in the lower valve body. This ensures that the valve remains securely closed even if a water hammer occurs in the lower pipeline.

Switching Leakage

In axially sealed double-seat valves, a situation arises for a brief moment during each switching operation in which the lower valve disc is neither in contact with the middle seal on the upper valve disc nor has reached the axial seating surface of the seat ring. Through the gap that forms, fluid enters the leakage chamber for this brief moment and flows out into the atmosphere. This is called switching leakage.

In radially sealed double-seat valves, no such gap occurs during the switching process. Switching leakage is therefore minimized, with the exception of any product residues that may become trapped on the metal surfaces.

If there is a water hammer in the lower pipeline, the force from the water hammer acts on the lower valve disc and may exceed the spring force of the actuator.

This creates a risk that the lower valve seat will be lifted off by the pressure in the pipeline.

In axially sealed double-seat valves, this would result in a connection to the atmosphere, which would cause leakage (see leakage during switching). The connection to the atmosphere would also cause a sudden drop in the overpressure in the pipeline. This would cause the actuator spring to close the valve again.

To prevent the lower valve seat from lifting during a pressure surge in the lower pipeline, valves are equipped with a lower balancer. With its downward-facing balancing surface, the balancer compensates for the pressure forces acting on the valve disc and prevents the lower valve disc from moving upward up to a certain overpressure.

Radially sealed double-seat valves are always equipped with this lower balancer to prevent the lower valve disc from opening.

Type D, D_/V, B, R. Please refer to the catalog for more information.

Technical Data of the Standard Version