Most butterfly valves in powder service eventually leak. Not because they are badly made, but because of how they close: a rigid disc with a seal on its edge has to slide into contact with the seat on every cycle, and an abrasive powder between the two surfaces acts like grinding paste. The inflatable seated butterfly valve solves this by changing the closing motion entirely.

A conventional butterfly valve achieves shut-off by rotating the disc until its peripheral seal presses against the body seat. The last few degrees of travel involve sliding contact under load. In clean liquid service that is acceptable. In a powder line, particles trapped between seal and seat score the elastomer, and the damage compounds with every cycle until the valve weeps product.

In an inflatable seated butterfly valve the seal is a flexible ring mounted on the disc periphery, and it is charged with compressed air to achieve shut-off. The disc rotates to the closed position with its seal deflated and therefore clear of the body. Only then is air admitted behind the seal, expanding it outwards into contact with the seat.

Because contact is made and broken radially rather than by sliding, there is essentially no abrasive wear on the sealing surfaces.

The key insight is that the seal never travels across the seat. It moves perpendicular to it. Powder that finds its way between the two surfaces is simply pushed aside as the seal expands, and the expanding action also helps to sweep the seat clean. This is the reason an inflatable seated valve keeps sealing after cycle counts that would have destroyed a conventional butterfly seat.

Sealing force comes from the air pressure behind the seal, so the valve can be made to seal firmly against a range of line pressures simply by setting the seal air pressure. That independence from the actuator is a real advantage in large sizes, where conventional designs need substantial torque to achieve the same tightness.

See the inflatable seated butterfly valve PZD for the product page, or the inflatable seated butterfly valve range for sizes and options.

The valve needs a compressed air supply for both the actuator and the seal. Confirm the available pressure and the air quality — the seal cavity is a small volume but it must be reliably fed. Where air is unavailable, a conventional or pinch valve design is the practical alternative.

Install with the seal air connection accessible, and keep a spare seal on the shelf. Seal replacement is a defined maintenance task rather than a workshop job on most sizes. As with all of our valves, the body carries a 12-month warranty; the seal is an elastomer wear part and is excluded.

Read the pneumatic conveying valves overview for how this valve fits into a dense-phase system, or contact us to size one for your line.