If media with toxic, dangerous, aggressive, flammable or even carcinogenic substances are used in the plant, a bellows that is firmly welded to the stem and hermetically sealed to the outside is used for reasons of health and environmental safety. In the case of a conical execution with bellows, a wide variety of designs can be found in industry. On the one hand, the interchangeability of the plug independent of the bellows is important for the maintenance of the valve. On the other, the plug should be firmly attached to the bellows in order to avoid vibrations and damage during control. The fastening of the plug to the stem/bellows unit via a thread is a proven construction. In addition, the plug is secured to the stem via a pin.

If it should be necessary to replace the plug, e.g. due to wear, the hole for the pin in the new plug must line up with the hole in the existing stem. Usually, the customer receives an undrilled plug and must subsequently drill the hole in the workshop. Thanks to specially developed production jigs and precise CNC machining, Arca is now able to deliver the plug or the bellows/stem combination pre-drilled.