316L Sanitary & Hygienic
Hygienic Valves for Dairy Processing: Pasteuriser, Separator and Aseptic Filling Duty
Dairy combines three difficult requirements: a thermally sensitive product that spoils quickly, a soil (milkstone) that is hard to remove once baked on, and in the case of UHT and aseptic filling, a sterility requirement that tolerates no compromise.
The temperature map of a dairy
| Process step | Typical temperature | Valve implication |
|---|---|---|
| Raw milk reception and cooling | 2–6 °C | Elastomers must stay resilient at low temperature |
| Preheating / regeneration | 60–75 °C | Standard EPDM; fouling begins here |
| HTST pasteurisation | 72 °C for 15 s (71.7 °C / 15 s in US regulation; 72–75 °C / 15–25 s elsewhere) | Flow-diversion valve must be fail-safe and position-monitored |
| Holding tube | Pasteurisation temperature, minimum residence time | No branches, no dead legs, sloped and drainable |
| UHT (direct steam injection or indirect) | 135–150 °C for 2–5 s | Valves rated for pressure and temperature; EPDM or PTFE composite at the limit |
| Aseptic filling | Ambient to 25 °C after cooling, sterile | Steam-barrier and aseptic valves with a validated SIP envelope |
| CIP | Caustic 70–80 °C, acid 60–70 °C | Full chemical and thermal compatibility required |
The flow-diversion valve is the critical one
In an HTST pasteuriser the flow-diversion valve (FDV) is the legal safety device: if the product leaves the holding tube below the set temperature, the valve must divert it back to the raw-milk balance tank. Requirements:
- Fail-safe action. On loss of air or power the valve must move to the divert position, not stay put.
- Position feedback. Two independent position switches, proved to the safety controller — the valve position is interlocked, not merely indicated.
- Speed and repeatability. Typically a stroke time of well under one second.
- Leakage integrity. The divert seat must hold, or unpasteurised milk can leak into pasteurised product.
- Cleanability. The FDV is a mixproof-style design with a leakage chamber vented to atmosphere; that chamber must be cleaned on every CIP cycle.
Milkstone and the CIP consequence
Milk soil is protein and fat that, once heated above about 60 °C, denatures and binds calcium phosphate into a hard deposit — milkstone. It will not dissolve in caustic alone, which is why dairy CIP is a two-stage alkaline-then-acid cycle: caustic removes fat and protein, and the acid stage removes the mineral scale. Valve selection follows from this: the wetted elastomers must survive daily exposure to 1–2% NaOH at 70–80 °C and 0.5–1% nitric or phosphoric acid at 60–70 °C. EPDM is the standard answer; PTFE/EPDM composite diaphragms are used where longer life is needed.
Recommended selections by duty
| Duty | Recommended valve | Seat / diaphragm | Notes |
|---|---|---|---|
| Raw and pasteurised milk routing | Mixproof double-seat, or hygienic diaphragm valve | EPDM | Drainable, position feedback required |
| HTST flow diversion | Mixproof flow-diversion valve | EPDM | Fail-safe to divert, dual position proof |
| UHT product after heating | Aseptic steam-barrier valve or diaphragm valve rated for the temperature | EPDM or PTFE/EPDM composite | Check the pressure/temperature curve at 140 °C |
| Aseptic filler infeed | Aseptic diaphragm valve with steam barrier | EPDM or platinum-cured silicone | SIP envelope must be validated |
| Cream, yoghurt, high-viscosity product | Hygienic butterfly or eccentric plug, full bore | EPDM or FKM | Low shear, low pressure drop, easy CIP |
| CIP supply and return | Hygienic ball or butterfly | EPDM or PTFE | Chemical compatibility drives the choice |
| Cheese vat and whey | 316L butterfly or diaphragm | EPDM | Whey is chloride-bearing — 316L, not 304 |
Material notes specific to dairy
- 316L, not 304. Whey, brine and cleaning chemicals carry chlorides that pit 304.
- Surface finish. Ra ≤ 0.8 µm on product contact; Ra ≤ 0.4 µm electropolished on UHT and aseptic lines, where fouling rate and cleanability both improve measurably.
- Connections. DIN 11851 and ISO 2853 are traditional in European dairies; Tri-Clamp is increasingly used on new build. Standardise and label transitions.
- Elastomer certification. FDA 21 CFR 177.2600, EC 1935/2004, and 3-A where applicable; request animal-derived-component-free statements if required by the customer.
Common failure modes to design out
- Fouling in the regeneration section raising pressure drop and reducing flow below the holding-tube requirement.
- Flow-diversion valve seats that leak, allowing raw product into the pasteurised side.
- Dead legs in the holding tube assembly — the holding tube must be sloped upward with no branches.
- Gasket extrusion from over-tightened clamps, creating a soil trap and a leak path.
- Inadequate CIP of the leakage chamber of mixproof valves.
Send your pasteurisation temperature, CIP chemistry and connection standard — we will return a schedule with diaphragm material and pressure/temperature ratings.
Frequently Asked Questions
Which valve is used as the flow diversion valve on a pasteuriser?
A mixproof or double-seat flow-diversion valve is used. It has two independent seats with a leakage chamber vented to atmosphere, must fail to the divert position on loss of air or power, and must provide two independent position feedback signals to the safety controller.
Why does dairy CIP need both caustic and acid stages?
Milk soil contains fat and protein plus calcium phosphate. Heating above about 60 degrees Celsius denatures the protein and binds the mineral into a hard deposit called milkstone. The alkaline stage removes fat and protein while the acid stage dissolves the mineral scale, so both are required.
What elastomer is used for dairy valves?
EPDM is the standard choice because it withstands hot caustic, hot acid and repeated steam or hot water sanitisation. A PTFE-faced EPDM composite diaphragm is used where longer service life or broader chemical resistance is needed.
Is 304 stainless acceptable for dairy equipment?
Not for product contact. Whey, cheese brine and cleaning chemicals contain chlorides that pit and crevice-corrode 304 stainless. 316L is the accepted minimum for dairy product contact surfaces.
What surface finish is required for dairy product contact?
Ra 0.8 micrometres or better is the usual requirement for hygienic dairy product contact. UHT and aseptic lines commonly specify electropolished surfaces at Ra 0.4 micrometres or better to reduce fouling rate and improve cleanability.
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.
Request a valve sizing quotedairy valveHTST pasteuriserUHTaseptic fillingmilkstone CIPhygienic 316L valve