When the valve is closed (non-actuated position), there are always two seals between the separated pipelines. If one seal is defective, the resulting leakage will be directed through the leakage outlet into the periphery, without mixing with the product in the second pipeline.
This method enables that there is no mixing between the products from two pipelines.
To accommodate the different requirements of various industries, applications and processes, we have a variety of mixproof shut-off valves in our portfolio. The selection scheme on pages provides an overview of all the options.
VARIVENT® long-stroke valves are used for manufacturing products with relatively large particles or for viscous products, such as strawberry yoghurt.
In axial sealing double-seat valves, with every switching procedure there is a short time during which the lower valve disc is neither in contact with the middle seal of the upper valve disc, nor has it reached the axial seat surface of the seat ring. During this brief moment liquid can percolate through the resulting gap into the leakage chamber and flow out into the atmosphere. This is referred to as the switching leakage.
In radial sealing double-seat valves, this gap does not occur during the switching procedure, which means the switching leakage is reduced to a minimum (possibility of product residues adhering to the metallic surfaces).
If there is a water hammer in the lower pipeline, the force of the water hammer acts on the lower valve disc and could exceed the locking force of the actuator spring.
This gives rise to the danger of the lower valve disc being lifted by the pressure in the pipeline.
In axial sealing double-seat valves, this would result in a connection to the atmosphere, leading to a leak (see switching leakage). The connection to the atmosphere would also cause a sudden reduction in the excess pressure in the pipeline. Then the actuator spring would close the valve again.
Valves with a lower balancer are available to prevent the lower valve disc from lifting during a water hammer in the lower pipeline. With its downward-facing compensation surface, the balancer adjusts out the operating direction of the pressure and prevents movement of the lower valve disc up to a particular excess pressure.
Radial sealing double-seat valves are always equipped with this lower balancer to prevent the opening movement of the lower valve disc.
Both valve disks of the valve type MX from GEA are equipped with balancers. The valve is thus pressure-resistant in the closed valve position in both the upper and lower pipelines and enables switching when the product is enclosed.