Axial compressors seals

Because most axial compressors are in air service, most are equipped with labyrinth type end seals. There are no interstage seals in the machines with unshrouded stator blades. The balance piston seal, a labyrinth type, is the only internal seal. There is no reason that axials cannot use some of the other seals as described in Chapter 5, such as the controlled leakage or the mechanical contact type, if the gas being handled by the compressor needs a more positive seal. If there is any prob-... 

Figure 7.18. Heavy-duty centrifugal, axial, and reciprocating compressors, (a) Section of a three-stage compressor provided with steam-sealed packing boxes (DeLaval Steam Turbine Co.), (b) An axial compressor (Clark Brothers Co.), (c) Double-acting, two-stage reciprocating compressor with water-cooled jacket and intercooler (Ingersoll-Rand Co.).

Like centrifugal compressor, axial compressor needs shafr seal to reduce the gas leakage. It uses balance drum to reduce the axial hydraulic imbalance and thrust bearing for the remaining axial imbalance. Journal bearings are used for the radial hydraulic imbalance. 

The symptoms of surge are pulsating pressure, rapid flow reversals, a drop in motor current and a jump in turbine speed. Continuous, rapid flow reversals can cause severe damage to the compressor. In axial compressors the blades may touch, resulting in instant destruction. However, centrifugal compressors are more mgged, and only seal damage results [15]. 

Screw-Type This type of rotary compressor, as shown in Fig. 10-80, is capable of hancmng capacities up to about 4.248 X lO" m m (25,000 fF/min) at pressure ratios of 4 1 and higher. Relatively small-diameter rotors allow rotative speeds of several thousand rev/min. Unhke the straight-lobe rotary machine, it has male and female rotors whose rotation causes the axial progression of successive sealed cavities. These machines are staged with intercoolers when such an... 

Damage to the labyrinth requires replacement of the expander heat barrier or compressor shaft seal. A replacement design (Figure 5-6) uses a replaceable stainless-steel labyrinth mounted on the shaft. Because the seal is not tapered, axial movement of the shaft has little or no measurable effect on seal gas flowrates. Each labyrinth has an integral oil slinger incorporated into the design. Also, each rotating... 

In dry compressors, shaft end seals are generally one of five type.s. These are labyrinth, restrictive ring, mechanical contact, liquid film, and dry gas seal. The labyrinth type is the most simple but has the highest leakage. The labyrinth seal is generally ported at an axial point between the seals in order to use an eductor or ejector to control leakage and direct it to the suction or a suitable disposal area. Alternatively, a buffer gas is used to prevent the loss of process gas. Appendix D presents a calculation method for use with labyrinth seals. 

Although not universal, on most multistage compressors, the impellers are axially located by shaft sleeves. The sleeves form a part of the inter stage seal and are shrunk onto the shaft with a shrink level less than (Ik impeller. 

It is desirable to have additional axial-load control on the multistage compressor. A balance piston, also refeired to as the balance drum, can be located at the discharge end (see Figure 5-46). The balance piston consists of a rotating element that has a specified diameter and an extended rim for sealing. The area adjacent to the balance piston (opposite the last stage location) is vented, normally to suction pressure. The differential pressure across the balance piston acts on the balance piston area to develop a thrust force opposite that generated by the impellers. The pressure on the... 

Non-contact seals with defined narrow clearances, such as labyrinth seals in turbo-machines (Fig. 4.1-47 A), are less problematic owing to the relatively low differential pressures however, the fluid should not have an erosive effect. Differential pressures up to several hundred bar occur at the axial-thrust compensation pistons of centrifugal pumps and compressors, but the fluid expansion is distributed over the many labyrinth stages. 

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