The coverpicture (Lit. 23.4.1-13) of this chapter gives a summary of the manifold seal systems respectively sealing elements of an aeroengine. A selection, wich can be assigned the term `machine element', will be discussed in this chapter.

Following definitions of the different contact seals was choosen for this chapter. Under contact seals as machine elements are understood in this chapter exchangeable seals. Its sealing effect is based on the contact of sealing surfaces/faces. These features are certainly given form O rings. A relative movement at the sealing face usually is not foreseen. So they can be related the static seals, like exchangeable flange seals. Indeed, other seals like screw connections of pipe lines, membranes and bellows/boots can be definition conform, for a static sealing machine element. But its discussion would go beyond the scope of this chapter.

Contact sliding seals appear in form of journal bearings/sleeve bearings of the variable compressor vanes or as guidance of axial movable valves and actuator rods. Often lacks these the feature of exchageability for the whole element. Also these will not be discussed here. They are object of other chapters under different aspects like wear.

For sliding seals (chapter 23.4.2) like rotary shaft seals (radial seal ring, „Simmerring“ ©) and (axial) face seals the feature is the contact of the sealing surfaces, is only limited valid. During operation a bearing lubricant film (liquid, gas) develops between the sealing faces, which move with high speed relative to each other. This prevents the direct (dry) contact and is necessary for the function. Does it fail, it comes to overheating and destruction of the sliding faces and with this to the failure of the seal.

Brush seals are assigned to the contact seals. They can be exchanged like radial seals. During operation, a sealing gap with an air cushion develops at the hair tips. An own chapter (chapter 7.3) in volume 2 is dedicated brush seals.

As not contacting systems apply labyrinth seals (volume 2, chapter 7.2) or the sealing effect between the tip of a rotor blade and the casing (volume 2, chapter 7.1). Here it can come absolutely indeed to a short-time contact during bridging of the gap. However, this sealing effect is not used. Additionally these seals have at least in aeroengines mostly not the feature of exchangeability of a machine element.