Double-seat Valves Mixproof Shut-off Valves with Seat Lifting VARIVENT®

VARIVENT® double-seat valves are used for mixproof shut-off of incompatible products at the pipe junctions.


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.

Application Examples

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.

Special Features

  • Certified, hygienic configuration
  • Metallic stop
  • Flexibility because of the modular principle
  • Proven seal geometry
  • Mixproof separation
  • Different valve configurations available
  • Separate lifting actuator for lifting both valve discs
  • Optional spray cleaning connection for cleaning the leakage chamber

Variety of Types

The different variants of the VARIVENT® double-seat valve make it possible to select valves that are optimally adapted to the process.  The axial sealing valve types D and B entail a small switching leakage during each switching procedure, but they notably have a very long service life with the axial seals.  The radial sealing valve type R, on the other hand, offers the advantage of switching nearly without any switching leakage.  Valve types B and R are additionally characterized by a balancer in the lower valve housing. This enables the valve to reliably remain in the closed position even if there are water hammers in the lower pipeline.

Double-seat valvesLong-stroke double-seat valves
DN 25 – DN 150DN 65 – DN 150
OD 1" – OD 6"OD 3" – OD 4"
IPS 2" – IPS 6"IPS 2" – IPS 4"
The structure of the VARIVENT® modular system means that many optional versions are available for adapting the valve optimally to the process. Please refer to the options section in the catalog for information about these.
Valve Selection Scheme: Mixproof Shut-off Valves with Seat Lifting
Axial Sealing (Switching Leakages)Modular SystemDouble-seat Valve,
Type D_L, D_C
Axial Sealing (Switching Leakages)With Water Hammer SafetyDouble-seat Valve with Balancer, Type B_L, B_C
Radial SealingWith Water Hammer SafetyRadial Sealing Double-seat Valve, Type R_L, R_C
Axial Sealing (Switching Leakages)Viscous Products or Products with large ParticlesDouble-seat Long-stroke Valve, Type D_L/V, D_C/V
Product Range, piggableRadial SealingPigging Pipe
Piggable Double-seat Valve Upside Down,
Type L_HL, L_HC
Product Range, piggableRadial SealingPigging Pipe BottomPiggable Double-seat Valve Upright, Type L_SL, L_SC
According to PMO RegulationsRadial SealingWith Allowance for Seat Lifting24/7 PMO Valve 2.0,
Type M/2.0

Switching leakage

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).

Water hammer safety

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. 


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Types D_L, D_C B_L, B_C, R_L, R_C, D_L/V, D_C/V

Please refer to the catalog for more information.

Technical Data of the Standard Version
D_L, D_C & D_L/V, D_C/V (Longstroke)
B_L, B_C
R_L, R_C
Material in contact with the product1.4404 / AISI 316 L
Material not in contact with the product1.4301 / AISI 304
Seal material in contact with the productEPDM, FKM, HNBR
Ambient temperature0 to 45 °C
Air supply pressure6 bar (87 psi)
Product pressure5 bar (73 psi)5 bar (73 psi)5 bar (73 psi)7 bar (101 psi)
Water hammer safetyup to 25 bar30 bar up to
DN 50, OD 2",
IPS 2"
50 bar from
DN 65, OD 2 ½", IPS 3"
Surface in contact with the productDN, OD
Ra ≤ 0.8 μm
IPS Ra ≤ 1.2 µm
Ra ≤ 0.8 μm
IPSRa ≤ 1.2 µm
Ra ≤ 0.8 μm
IPS Ra ≤ 1.2 µm
Ra ≤ 0.8 μm   

External housing surfaceMatte blasted
Control and feedback systemConnection 0 (without control top)
Actuator typePneumatic actuator air / spring
Connection fittingsWelding end
IdentificationAdhesive ID tag
Valve seat versionClamped or welded seat ringClamped or welded seat ringClamped or welded seat ringWelded seat ring
CertificatesEHEDG, A3, CEA3, CEEHEDG, A3, CEA3, CE


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