Table of Contents
23.4 Contact seals
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.