Standard Unique Mixproof

The standard Unique Mixproof double seat valve is the broadest platform in the range. It supports up to 16 plug setups, four configuration levels (Basic, SeatClean, HighClean, UltraClean), and optional SpiralClean leakage-chamber flushing. Sizes run from DN 38 to DN 150 in ISO and DIN standards. The actuator is maintenance-free but repairable, and the modular design means plug assemblies, sealing elements, and body combinations can be configured independently. Product-wetted seals are available in EPDM, HNBR, NBR, and FPM to cover different chemical and thermal exposures.

Unique Mixproof CIP

The CIP variant is a lighter, purpose-built double block-and-bleed valve specifically for routing cleaning media. It can distribute pressurised CIP fluid toward the area requiring cleaning or direct it through the top of a tank-cleaning device. Based on the Unique Single Seat valve platform, the CIP variant is available in ISO sizes from DN 25 to DN 101.6 and DIN sizes from DN 25 to DN 100. It weighs between 8.3 kg and 25 kg depending on size and type. Where a process line needs dedicated cleaning-circuit isolation rather than full product-switching capability, the CIP valve reduces both weight and installed cost.

Unique Mixproof Process

The Process variant is described by Alfa Laval as a compact, cost-effective version of the premium Unique Mixproof. It is a double seat valve with seat lift, rated to the same 10 bar maximum product pressure and equipped with two independent plug seals forming an atmospheric leakage chamber. Sizes match the variety found across the range (ISO 25–101.6, DIN 25–100). The Process valve is designed to withstand pressure peaks and fits dairy, food, and beverage lines where fundamental hygienic double seat valve function is needed without the full option depth of the standard platform.

Unique Mixproof Tank Outlet

Tank Outlet valves mount directly on tank bottoms or walls at inlets and outlets, delivering full drainability and cleanability all the way up to the tank interior. Installation options include a standard tank flange or an optional stub flange, and Alfa Laval supplies dedicated welding jigs sized for each bore. Longstroke variants are available for sizes including DN 63.5 and DN 76.1. The modular platform carries the same actuator and plug-setup architecture as the standard Unique Mixproof, and the leakage detection pipe provides external visibility of any internal seal wear.

Unique Mixproof UltraPure

The UltraPure variant targets pharmaceutical, biotechnology, and other high-purity applications. It ships with the Alfa Laval Q-doc documentation package for full component traceability, uses EPDM elastomers conforming to FDA and USP Class VI requirements, and is available with surface finishes down to Ra 0.5 or Ra 0.4 EP. Sizing follows ASME BPE from 1½" to 4". Operating pressure is 10 bar; the temperature range extends to +125 °C for standard elastomers, with flush-housing sterilisation (SIP) rated to 140 °C for up to 40 minutes.

Dairy and food processing

In dairy plants, double seat valves sit at every junction in the valve matrix between reception, storage, pasteurisation, and filling. Two product streams often share the same physical pipe segment. During CIP, one line may carry caustic (1 kg NaOH per 100 l water for 1 % concentration) or acid (0.7 l 53 % HNO₃ per 100 l water for 0.5 % concentration) while the adjacent line still holds product. The double block-and-bleed principle ensures that any leakage exits through the atmospheric chamber rather than contaminating either stream. Recommended minimum CIP velocity is 1.5 m/s. For viscous products such as cream, yoghurt, or sauces, Alfa Laval recommends increasing the cleaning flow.

Tank outlet valves serve a specific role here. Mounted flush to the tank bottom, they eliminate dead legs and provide full drainability, which is a regulatory expectation in dairy. The welding jig supplied by Alfa Laval holds the flange true during pulsed-arc welding, and the conical valve seat must face downward (toward the pipeline) or upward (into the tank) depending on the specific Mounting instruction to maintain correct sealing geometry.

Beverage

Beverage facilities run many products through shared piping, cycling between flavoured waters, juices, soft drinks, and cleaning solutions. Each changeover demands that the previous product be fully flushed with no residual mixing. Double seat valves at every node in the matrix allow simultaneous CIP in one circuit while the adjacent circuit remains in production. Seat-lift durations during CIP should not exceed 10 seconds, and Alfa Laval recommends performing seat lift or seat push in the middle of each step of the CIP sequence.

Pharmaceutical and biotechnology

Pharmaceutical lines raise the specification bar. The Unique Mixproof UltraPure meets these requirements with ASME BPE sizing, FDA- and USP-Class-VI-compliant EPDM seals, and optional electropolished surface finishes. The Q-doc package delivers full traceability of every wetted component. Steam-in-place sterilisation at 140 °C for up to 40 minutes is supported. Where standard EPDM or HNBR elastomers are insufficient for specific chemical exposures, FPM seals are available across the wider Unique Mixproof platform.

Upstream and downstream positioning

In a typical process line, double seat valves sit between tanks, heat exchangers, homogenisers, and filling equipment. They control which stream reaches which destination. Upstream, process pumps deliver product at pressures up to 10 bar. Downstream, the valve routes fluid either to the next processing stage or to a CIP return circuit. Because internal leakage is externally visible through the leakage chamber outlet, operators can detect seal wear during normal operation without opening the valve.

The double block-and-bleed principle

A double seat valve contains two independent plug seals, an upper plug and a lower plug, each with its own seal ring. Between them sits a leakage chamber held at atmospheric pressure during every operating condition. If either seal develops a leak, product flows into this chamber and drains to an external outlet rather than crossing into the opposing product stream. This arrangement provides two barriers against cross-contamination, each independently verifiable.

The valve is normally closed. A pneumatic actuator, powered by compressed air typically in the 600–800 kPa (6–8 bar) range, lifts the plugs against spring force to open the main flow path. When air pressure is removed, the spring returns both plugs to the closed position. The actuator assembly contains a pre-loaded spring, and Alfa Laval marks every unit with a "DO NOT DISASSEMBLE" warning because the spring under load poses an injury risk if the housing is breached.

During CIP, each valve seat is lifted independently. The upper seat lift takes place during cleaning of the upper valve body; the lower seat push takes place during cleaning of the lower valve body. Air connections driven by the control system sequence these functions. They must never be pressurised simultaneously (specifically AC1 and AC3), because doing so would lift both plugs and create a direct flow path between the process and cleaning lines.

Seal architecture and materials

Product-wetted steel parts across the Unique Mixproof range are manufactured from 1.4404 (316L) stainless steel. Other steel parts use 1.4301 (304). Internal surfaces are polished to Ra < 0.8 µm (Ra < 32 µ-inch); external surfaces are semi-bright at Ra < 1.6 µm. The UltraPure variant offers optional finishes down to Ra 0.4 EP.

Elastomer selection depends on the product and cleaning chemistry. EPDM handles the broadest temperature window, rated from −5 °C to +140 °C on the CIP variant and −5 °C to +125 °C on the Process and standard variants. HNBR covers −5 °C to +125 °C. FPM is available for aggressive chemical environments. Actuator seals are NBR, and guide strips are PTFE. Seal ring sets and O-ring sets are available in 10-piece packs for maintenance stocking.

Selection factors

Choosing between variants and sizes involves several parameters:

Pressure. All variants share a maximum product pressure of 1000 kPa (10 bar) and handle full vacuum on the low end. Versions such as the Standard or Tank Outlet support SpiralClean at a recommended minimum pressure of 2 bar (29 psi). Holding pressure on the CIP variant's lower plug is 600 kPa (6 bar).

Temperature range. Elastomer grade sets the upper limit. Standard EPDM covers most dairy and beverage duties to +125 °C. Where brief temperature excursions occur during sterilisation, the CIP variant's EPDM rating extends to +140 °C. High-purity SIP cycles at 140 °C for 40 minutes are supported on the UltraPure.

Equipment size. ISO sizes from 25 mm to 101.6 mm and DIN sizes from DN 25 to DN 150 are available across the range. The UltraPure uses ASME BPE sizing from 1.5" to 4". Tank Outlet longstroke options are offered in models for 63.5 mm and 76.1 mm tubes.

Surface finish and traceability. Standard Ra < 0.8 µm internal polish satisfies most food and beverage applications. Pharma and biotech may require Ra 0.5 or Ra 0.4 EP plus the Q-doc documentation package for compliance.

Configuration depth. The standard Unique Mixproof supports up to 16 plug setups and four cleanability tiers (Basic, SeatClean, HighClean, UltraClean). The Process variant offers a simpler, lower-cost configuration for fundamental duties. The CIP variant is purpose-built for cleaning-circuit media routing.

Comparison with other valve types

Single seat valves close a flow path with one plug and one seal. They are simpler and less expensive, but they cannot provide mixproof separation. Where two process lines meet and must be isolated with a safely monitored drain between them, a single seat valve cannot substitute for a double seat valve. Furthermore, the double seat design allows for seat lift cleaning without stopping the process flow in the adjacent line.

Butterfly valves offer high flow capacity in a compact disc-style body. They suit bulk shut-off applications well but lack both the double physical barrier and the independent seat-lift cleaning functions. In hygienic valve matrices handling multiple products, butterfly valves are typically limited to utility or non-critical shut-off positions where contamination risks are absent.

Electronic control with ThinkTop

The Alfa Laval ThinkTop control and indication unit mounts directly on the actuator. It provides position feedback, solenoid control for seat-lift sequencing, and diagnostic data. When a ThinkTop is installed, 180 mm (7.1") must be added to the overall valve height (dimension B). The ThinkTop V-Series is available for the UltraPure variant, integrating valve monitoring into validated plant-level automation.

Maintenance and safety

Alfa Laval designs the actuator as a non-serviceable, sealed unit. The internal spring is under load at all times, and all actuator housings carry markings against disassembly. Bushing replacement on the actuator yoke is the primary field-serviceable actuator task, requiring a 27 mm (1 1/16") tubular box wrench and an aligning spindle (Alfa Laval part 9614198401) to centre the stem against spring offset. Torque for the bushing is 10 Nm (7 lb-ft), achievable by hand tightening.

Plug seals, O-rings, lip seals, and guide rings are routine replacement items. Alfa Laval specifies silicone-based grease from the service kit for plug seal rings and Molykote Longterm 2 Plus for actuator stem lubrication in specific variants. All product-wetted seals should be Alfa Laval genuine parts to maintain warranty. Protective devices must be visually inspected at least every 12 months.