316L Sanitary & Hygienic
CIP/SIP Valve Design for Food and Beverage: Dead Legs, Velocity and Cleanability
Clean-in-place fails for three reasons: the cleaning solution never reaches the surface, it reaches it with too little velocity, or it reaches it for too short a time. Valve selection controls the first of those, and strongly influences the second.
The cleaning window
A typical food and beverage CIP cycle runs caustic (1–2% NaOH at 60–80 °C, 10–20 min), an intermediate rinse, acid (0.5–1% nitric or phosphoric acid at 50–70 °C, 5–15 min) and a final rinse, followed by sanitisation with hot water at ≥ 85 °C or chemical. Every valve in the circuit must tolerate the full chemical and temperature envelope — for the elastomers, the gaskets and the surface finish.
Valve types in a hygienic CIP circuit
| Type | Role | Key design features |
|---|---|---|
| Hygienic diaphragm valve | Product-contact shut-off, take-off points | Drainable weir body; diaphragm isolates the bonnet; EPDM or PTFE/EPDM composite |
| Hygienic butterfly valve | Large-diameter isolation, tank outlet | Seat that seals against the disc without a pocket; often with a steam barrier on aseptic duty |
| Mixproof / double-seat valve | Simultaneous product and CIP routing without cross-contamination | Two independent seats with a leakage chamber vented to atmosphere; the chamber is cleaned between sequences |
| Double-seat tank bottom valve | Tank outlet with CIP of the seat area | Upper and lower seats with a cleanable leakage chamber |
| Aseptic / steam-barrier valve | Product sterility after SIP | Steam or condensate barrier between the product and the outside world |
| Hygienic ball valve (full bore) | Utilities, CIP supply and return | Cavity-filled design for cleanability |
The three hard rules
2. Turbulent cleaning flow. Maintain at least 1.5 m/s in the largest pipe in the circuit, and check the Reynolds number: Re = (ρ × v × D) / µ should exceed 10 000, and ideally above 30 000 for reliable soil removal. This is why CIP return lines are sized from flow rate, not from pressure drop.
3. Everything drains. A horizontal line must slope at least 1:100 (about 10 mm per metre). Valves must be orientated so the body drains; a diaphragm valve installed upside down holds liquid.
Specifying for cleanability
| Feature | Requirement | Why |
|---|---|---|
| Product-contact surface finish | Ra ≤ 0.8 µm, mechanically polished; Ra ≤ 0.4 µm electropolished for aseptic | Soil is removed by shear only if the surface features are smaller than the boundary layer |
| Internal geometry | No crevices, no threads in the product path, self-draining | A crevice is a permanent contamination reservoir |
| Elastomers | EPDM or FKM compliant with FDA 21 CFR 177.2600, EC 1935/2004; USP Class VI for aseptic | Chemical and temperature compatibility plus regulatory compliance |
| Connections | Tri-Clamp (ISO 2852) or aseptic union; bore-matched gasket | Flush joint, no crevice, easy to inspect |
| Certification | 3-A, EHEDG Type EL Class I Aseptic where required | Independent demonstration of cleanability, drainability and sterilizability |
Mixproof valves: what to check
A mixproof valve lets product flow on one side and CIP on the other at the same time, with a leakage chamber between two seats that is vented to atmosphere. If either seat leaks, the fluid goes to atmosphere through a visible drain rather than into the other side. Points to specify:
- The leakage chamber must be cleaned on every cycle — usually by a defined CIP sequence through the chamber ports.
- Seat lifting must be controlled and monitored; the valve should not fully lift both seats at once unless the design permits it.
- Confirm the failure mode: on air loss the valve should go to the normally closed position with the leakage chamber open to atmosphere.
- Position feedback to the PLC is mandatory — an unconfirmed valve position is a food-safety incident waiting to happen.
Validating the clean
- Visual / borescope — the cheapest and most underrated check; do it at commissioning.
- ATP bioluminescence — a result in seconds; use it as a screening tool, not a release criterion.
- Protein or carbohydrate swabs on defined worst-case locations (valve seats, gasket faces, sight glasses).
- Rinse water analysis — conductivity for caustic/acid carryover, TOC for organics.
- Microbiological — for aseptic lines, a media fill or a defined incubation test.
KOSA's 316L hygienic valves for food and beverage are supplied with FDA and EC 1935/2004 elastomer certification, Ra reports and full traceability.
Frequently Asked Questions
What flow velocity is needed for effective CIP?
A minimum of 1.5 metres per second is the usual design target in the largest pipe in the circuit, with a Reynolds number above 10 000 and ideally above 30 000. Turbulent flow is what removes soil by shear; low-velocity flow merely recirculates the cleaning solution over the surface.
What is a mixproof valve?
A mixproof or double-seat valve has two independent seats with a leakage chamber between them that is vented to atmosphere. It allows product and cleaning fluid to be routed simultaneously without any possibility of cross-contamination, because any seat leak is discharged visibly to atmosphere rather than into the other fluid.
What is the maximum acceptable dead leg?
The widely applied target is a length-to-diameter ratio of 2 or less, measured from the inner wall of the main pipe to the point of closure. Some standards permit specific exceptions, but shorter is always better and zero-dead-leg designs are preferred at points of use.
Which standards apply to hygienic valve cleanability?
3-A Sanitary Standards and EHEDG are the principal references. EHEDG Type EL Class I Aseptic certification demonstrates that a valve is cleanable, drainable and sterilizable in place, while 3-A provides material and design criteria widely used in dairy and food processing in North America.
Do hygienic valves need to be drainable?
Yes. A valve body that retains liquid after draining creates a stagnant volume where microorganisms can grow between production runs. Hygienic diaphragm and butterfly valves must be installed at the correct orientation and slope so the body drains completely.
Send us the process data — fluid, inlet pressure, differential pressure, temperature, required flow and pipe size — and our engineers will return a sized selection with Cv calculation, leakage class and material recommendation, plus documentation packs for FAT / IQ-OQ.
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