Nicholson Fixed Pressure Air Cell Ring The Nicholson External Link Bellows Air Cell Ring is a simple fixed pressure design. Pressure for all arms is manually adjusted at one of six standard air fittings located around the ring. Pressure is adjusted with the ring stopped and access to the filling point is through a large access door on the back of the ring cartridge. The Air Cell Ring is very economical and easy to maintain. Portable installations that require minimum air consumption are great applications for this ring. The Air Cell Ring is also suggested for situations where log diameter is fairly constant and where very high speeds are required.