Rotary moulding

A method of rotary moulding with a rotary mould, said method comprising the steps of

• inserting a plug valve as a valving insert into an opening of the rotary mould and into a mould space, at least substantially sealing the mould space from ambient air, controlling air inflow into the rotary mould from unducted ambient air, and controlling fluid outflow from the mould space, the plug valve having a passageway,
• providing flow of gas into the mould through the plug valve when a pressure differential from outside the mould and inside the mould favors an inflow of air into the rotary mould, and
• providing an outflow of gas from the rotary mould through the plug valve only when there is a pressure differential where a pressure inside the mould is above a specified limit with respect to a pressure outside the mould so that
• (A) in use, the passageway of the plug valve is opened by resiliently opening at least in part a closed end of the passageway responsive to a pressure differential, ambient air to mould space, above a first threshold pressure to allow, as in a one way valve, an ambient air inflow, and
• (B) in use, the passageway is opened by failure at least in part of the closed end of the passageway by deformation or parting, or both, to allow an outflow of air or gas responsive to a pressure differential, mould space to ambient air, above a second threshold pressure higher than the first threshold pressure.