Valve Engineering.
How the mechanisms work. Weir geometry, the diaphragm seal, bonnet compression, pinch closure, and the drain angle that decides whether any of it stays clean.
Two mechanisms cover almost all hygienic flow control. A diaphragm pressed onto a weir, or a pinch head closing tubing from outside. Everything else on this page follows from which of those two you need.
Two mechanisms, one question
The question that decides the valve is not size or material. It is whether the flow path is a consumable.
| Diaphragm | Pinch | |
|---|---|---|
| Closing member | Elastomer or PTFE diaphragm onto a machined weir | Pinch head collapsing the tube from outside |
| Wetted path | 316L body plus the diaphragm | Tubing only |
| Consumable | The diaphragm | The whole flow path |
| Changeover | Clean and validate in place | Replace the tubing |
| Suits | Multi-use lines, CIP and SIP | Single use, frequent product change |
If the line is cleaned and reused, a diaphragm valve is almost always right. If it is a single-use assembly that gets discarded between batches, a pinch valve removes the cleaning step, and cleaning is usually the expensive part.
The weir is the sealing surface
Cut a hygienic diaphragm valve in half and a raised ridge runs across the bore. That is the weir. Flow passes over it; to shut the valve a diaphragm is pressed onto its crown until the two meet across the full width.
Everything follows from that. The closing member is also the barrier between product and mechanism, so there is no stem in the wetted volume, no packing to leak, and no rotating shaft seal to wear.
Where the sealing ridge lives is a real design fork. It can be molded into the diaphragm, which is the more common approach and puts the sealing geometry in the part that wears. Or it can be machined into the body in the same operation as the bore, from the same piece of bar, so a ridge in 316L holds its profile as diaphragms come and go. Aquasyn bodies take the second route, and ASME BPE Part SD is where to look for the surface and geometry requirements either way.
How diaphragm valves work takes the mechanism apart properly.
What the bonnet has to survive
Three failure modes dominate, and none of them is about pressure.
- Over-compression. Tighten the bolts too far and the diaphragm is crushed rather than seated. It seals, then takes a set, then fails early.
- Bolt loosening. A valve running steam then cold buffer expands and contracts every cycle. Ordinary bolted joints work loose and the valve weeps.
- Uneven compression at the drain angle. The one people miss. Every diaphragm valve is mounted at an angle, so the bonnet is not square to gravity and leans. One edge of the diaphragm is compressed harder than the other, and wears out while the opposite edge never sealed properly.
That third one is the argument for Tork-Tite. Even compression across a diaphragm that is deliberately not level is the whole problem.
Drainability is an installation property
A valve only self-drains if the body is rotated so the bore falls continuously to the outlet, and the angle that achieves it depends on nominal size. It is not intuitive: smaller bores need a steeper angle, because surface tension holds proportionally more liquid.
| Size | Angle |
|---|---|
| ¼″ | 41° |
| ⅜″ | 30° |
| ½″ | 25° |
| ¾″ | 18° |
| 1″ | 30° |
| 1½″ | 25° |
| 2″ | 23° |
Sterile access and GMP port bodies exist in twenty rotations for a reason, and the rotation is not a preference. Mount one the wrong way round and liquid pools in a corner that never drains. It is the single most common reason a correctly specified part fails a drainability check, and it is why the configurator shows the drawing for every orientation rather than just the code.
Where pinch valves belong
A pinch valve compresses flexible tubing until the bore collapses on itself. Nothing in the valve is wetted, so replacing the tubing replaces the entire flow path with no cleaning and no cleaning validation. That moves the compliance question off the valve and onto the tubing, where USP Class VI status and ISO 10993 evaluation come from the tubing vendor rather than the valve maker.
ARTēVA® uses a reusable 316L encapsulated pinch head rated well past 10,000 cycles, on silicone or TPE from ⅛″ to 1″ inside diameter, unbraided as the standard specification.
A braid exists to stop a tube collapsing under pressure, which is exactly what a pinch valve needs it to do. So reinforcement and pinch closure pull against each other, and that tension is real.
It does not make braided tubing impossible. Whether a tube closes reliably turns on its construction rather than on the label, so the answer is to test the actual tubing rather than rule out the category. Double-braid is the case that has given us trouble.
How pinch valves work covers tubing selection, which is the whole decision.
How the valve gets operated
| Code | Operator | Up to |
|---|---|---|
| 16 | Standard manual bonnet | 4″ |
| 17 | Sealed manual bonnet, keeps liquid out | 4″ |
| 18 | Pneumatic, normally open | 2½″ |
| 19 | Pneumatic, normally closed | 2½″ |
| 21 | Submersible bonnet, vented so cleaning solution flows through | 2″ |
| 78 | eMaxion™ electric | 4″ |
Pneumatic stops at 2½″. Above that the actuator needed to close a diaphragm onto the weir is a two-person lift, so 3″ and 4″ bodies are manual, submersible or electric. Historical records contain 3″ and 4″ pneumatic part numbers; they are not current.
Watch 17 against 21. A sealed bonnet keeps liquid out of the mechanism. A submersible bonnet is deliberately vented so wash-down solution flows through it. Opposite designs, adjacent codes.
Sizing against flow
Cv is the figure most often asked for and the one to treat with the most care. Published values cover ½″ to 2″ only, carry a ±10% tolerance, and the original test conditions were not recorded. Use them to size, not as a guaranteed performance limit. The full table is on the flow control page.
Two-way bodies run ⅛″ to 4″. A ⅛″ bore cannot be polished, so no Ra grade applies to it.
Put it against a real specification
The configurator applies these rules live. It only offers combinations that can be built, and it sends the decode straight to engineering.
Open the configurator →