Food grade is not a sticker on the box. It is a chain of decisions that starts with the material of the wetted parts and ends with how the valve is cleaned. Too many lines are specified as "stainless, food grade" and then fail at the seal, or at the body, or in the corner of the bore where product sits and never comes out. This guide sets out what to specify, what to ask a supplier for, and where each valve type actually holds up.

A valve can only be called food grade when three things line up:

A 316 stainless body with a non-certified seal is not a food grade valve. A certified seal in an aluminium body is not either. Specify all three or specify none.

The important detail is that in a pinch valve the medium never touches the body at all. It stays inside the rubber sleeve. That is why an aluminium pinch valve body can still be used on a hygienic line — as long as the sleeve itself is food grade. On a butterfly or ball valve the medium does touch the body, so there the body material is the decision, and it has to be stainless.

One honest caveat: if your medium contains chloride, salt or aggressive cleaning chemicals, say so at quotation stage. The grade has to be reviewed against the actual medium rather than assumed from the word "food".

The body gets all the attention; the seal does all the damage. A pinhole in a food contact seat, or an elastomer that has not been certified, can contaminate a batch — and it will not show up in a pressure test.

We supply two sleeve compounds for pinch valves, and we state plainly which is which:

If a supplier offers you a pinch valve sleeve in whatever elastomer the order happens to need, ask for the material of the sleeve that will actually be fitted and where it was moulded. Our position is deliberately narrow: two compounds, specified honestly.

On butterfly valves the equivalent decision is the seat. Our inflatable seated butterfly valve uses an EPDM seat that is inflated only at the moment of closing, which protects the sealing surface while the valve is open and reduces the torque needed to seat it.

The straight-through bore and the absence of any rotating part make it the easiest geometry to flush. The sleeve is the wear item and the food contact part, and it can be removed and replaced without replacing the valve body. For powder dosing, silo discharge and food-grade conveying lines this is usually the first thing to look at. Our VF series air-operated pinch valve covers DN40 to DN300 in flanged aluminium bodies; the GJ641X manual pinch valve covers handwheel duty on the same principle.

Compact between flanges and light, which matters on tanker and silo equipment. The disc sits in the flow path, so the seat is doing the food contact work. Suitable where the medium is dry powder or gas rather than a washdown-prone slurry line.

Here the body material decides the answer. Our KFQ ball diverter valve is stainless, as are the KFB and KFZ types — those are the ones to specify on a hygienic line. The VAB flap diverter valve is aluminium, which makes it the right choice for abrasive powder duty but not for food contact service.

Food lines are judged as much on cleaning as on metallurgy. Three questions decide the answer:

If you are comparing geometries for a washdown duty, our side-by-side write-up on pinch valve versus butterfly valve covers the pressure drop and wear differences that follow from that geometry.

Before you accept a valve, put these in writing:

We publish our conformity documentation on the CE page, and the full valve range is on our product list. Our broader approach to powder and bulk solids duty is set out in the powder and bulk solids valve guide.

Valves are warranted for twelve months on the valve body. Wear parts — sleeves, seats and sealing rings — are excluded, because their life is set by the medium, the cycle count and the cleaning regime rather than by the manufacture of the valve. On a hygienic line that is not a disadvantage; it simply means you plan for a sleeve change instead of discovering one during a production run.

If you tell us the product, the temperature, the pressure and how the line is cleaned, we will tell you which valve and which sleeve we would fit — and if the right answer is a material we do not normally ship, we will say that too. Write to zjxnjx@126.com.

ZHEJIANG XINGNENG MACHINERY CO., LTD. manufactures pinch valves, diverter valves, iris valves and inflatable seated butterfly valves for powder, bulk solids and slurry duty.