Sealing basics (2)

10.2.1 Centrifugal Parking Seal Figure 10-10 shows a typical centrifugal parking seal structure that is sealed by the centrifugal action of the backing blade during pump operation. Parking, driven by the spring force, the pump shaft to the left slip and the sleeve taped to prevent leakage. Centrifugal start off after rejection, the Department of the Ministry of pulling his shoulder pull the shaft to the left, the sleeve and packing seal off, the sealing surface is not subject to wear and tear. 10.2.2 Pressure-regulated parking seal and screw seal combination of pressure-regulated seal, parking, the screw can move on the shaft, driven by the spring force is the step end face and the housing end face compression and seal. In operation, two reverse spirals cause the viscous fluid in the gap to form a pressure peak at the end face, acting on the stepped end face of the screw shaft to disengage it from the housing end face. Parking with slide valve, sealed. When the differential pressure cylinder pressure relief, the leaf spring sliding valve and shoulder tight to achieve parking seal. 10.3 Fully Sealed Seal 10.3.1 Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Sealed Fully enclosed seal There is no general dynamic seal existing friction, wear, lubrication and fluid flow through the sealing surface that is leaked, is a special type of seal. Hermetically sealed, hermetically sealed, contain radioactive and rare valuables, as well as in its experiments and production, have important uses. 11, floating ring seal floating ring seal referred to as the floating ring seal for centrifugal compressors, hydrogen-cooled gas turbine generators, centrifugal pumps and other shaft seals. In medium and high pressure centrifugal compressor seal options available are: mechanical seal, labyrinth seal and packing seal. However, due to the gas cooling and lubrication conditions than the liquid, so the packing seal only small, low speed use, and the mechanical seal at a peripheral speed greater than 40m / s temperature is higher than 200 ℃ after the hard to adapt, only the labyrinth seal and the ring seal is The two most commonly used methods. Floating ring seal has the following advantages: 1) The sealing structure is simple, only a few simple ring, pin, spring and other parts. Multi-layer floating ring only these combinations of simple parts, mechanical seal parts less. 2) The machine is not sensitive to the operating conditions, a stable sealing performance. 3) The seal does not produce wear and tear, reliable sealing, easy maintenance, easy maintenance. 4) due to the sealing material is metal, solid high temperature. 5) Floating ring can be used in parallel, composed of multi-layer floating ring, which can effectively seal the high pressure of 10mpa. 6) It can be used in high speed rotary fluid machine with 10000 ~ 20000r / min, especially for gas compressor, its permissible speed is up to 100m / s, which is unmatched by other seals. 7) As long as the use of corrosion-resistant metal or lined corrosion-resistant non-metallic materials (such as graphite) as a floating ring, can be used for strong corrosive media seal. 8) Because the seal gap is a liquid film, so the frictional power is very small, the machine has a higher efficiency. The shortcomings of the floating ring seal: seal manufacturing requirements of high precision, the ring of different concentricity and the end of the non-perpendicularity and surface roughness of the sealing performance has a significant impact. In addition, this seal can not be sealed on the liquid leakproof. Although the gas can be sealed, but requires a complex and expensive automated oil supply system. 11.1 Floating Ring Sealing Mechanism Floating ring seal belongs to flow resistance non-contact dynamic seal, which is based on the fluid resistance effect within the seal gap to achieve the purpose of blocking leakage. Because there is a gap, to avoid the friction of the solid, suitable for high-speed situations, you can block the liquid, but also sealing gas, but the larger amount of leakage, in some cases must be configured more complex seal aids. 11.2 Floating ring Floating ring seals are available in a wide variety of configurations, including wide and narrow rings, smooth rings and split rings, liquid films, and dry floating rings. 11.2.1 wide ring and narrow ring Wide ring width relative to its diameter, the ratio l / d = 0.4 ~ 0.6. The characteristic of this ring is that the hydrodynamic force acting on this ring during operation is larger than that of the narrow ring, and the attachment to the center is not needed. Under a certain pressure difference and leakage amount, the number of the rings can be smaller than that of the narrow ring, so that the structure of the sealing device can be simplified and the assembling, disassembling and overhauling are facilitated. The disadvantage of wide rings is that there will be a large pressure difference on both sides of the ring, so that the pressure acting on the end face of the ring is also larger, and the friction on the face to be overcome during the free float is larger, that is, it is difficult to float. Narrow ring width relative to its smaller diameter, the ratio l / d = 0.1 ~ 0.2. Narrow ring and shaft gap smaller, work, the gap formed in the fluid power smaller, so its ability to automatically concentric poor, mostly with rubber o-ring to help the center. Due to the adoption of this kind of auxiliary measures, the eccentricity is smaller and the parking time is less, so that although the ring is narrow, the amount of leakage is not large. Narrow ring can also o-ring positioning, but instead use the spring. The ring is pressed against the end face of the spacer ring by the spring force. When the pressure of the sealing liquid is reduced, the ring can still maintain its centering position. Since the pressure difference acting on each narrow ring is smaller than that of the wide ring, the pressure exerted by the ring on the end face of the isolating ring is also small, that is, the narrow ring floats easily.