Compressor sliding vane

Generally, a longer element life can be expected if the air is compressed by a reciprocating compressor. Sliding vane and rotary screw compressors have a high oil carryover so that a shorter element life can be expected. In a rotary screw compressor, the bulk of the aerosol droplets measure between 0.1 and 0.5 pm. It is therefore advisable to fit a sub-micrometre filter if oil is to be separated from the compressed air effectively. The internal oil separator is intended to minimize oil carryover into the air stream. In the event of separator failure, large quantities of oil will be released, causing, in some cases, immediate failure of the filter element. 

The sliding-vane compressor uses a single rotating element (see Figure 1-8). The rotor is mounted eccentric to the center of the cylinder portion of the casing and is slotted and fitted with vanes. The vanes are free to... 

Figure 1-8. Cross section of a sliding vane compressor. Courtesy ofA-C Compressor Corporation)...

The sliding-vane compressor is widely used as a vacuum pump as well as a compressor, with the largest volume approximately 6,000 cfm. The lower end of the volume range is 50 cfm. A single-stage compressor with atmospheric inlet pressure is limited to a 50 psi discharge pressure. In booster service, the smaller units can be used to approximately 400 psi. 

The sliding vane compressor consists of a single rotor mounted eccentrically in a cylinder slightly larger than the rotor. The rotor has a series of radial slots that hold a set of vanes. The vanes are free to move radially within the rotor slots. They maintain contact with the cylinder wall by centrifugal force generated as the rotor turns. 

Most of the drivers used with the sliding vane compressor are electric motors. Variable speed operation is possible within the limits of vane speed requirements. The vanes must travel fast enough to seal against the cylinder wall but not so fast that they cause excessive wear. For the smaller units, under 100 hp, V-belts are widely used. Direct connection to a motor, however, is possible for most compressors and is used through out the size range. 

The sliding vane compressors and vacuum pumps have internal sliding vanes mounted longitudinally on an eccentric rotor in the body casing, Figures 12-114 and 12-115. 

Figure 12-114. Cross-section of sliding-vane rotary compressor. (Used by permission Fuller Bulk Handling.).

Figure 12-115. Coupling drive end of Ro-Flo Sliding-Vane compressor showing vanes in rotor or shaft slots and bearing and shaft seal. (Used by permission Bui. CCB-0072-2. A C Compressor Corporation.)...

In much the same manner as pumps, compressors are classified as one of two general classes positive displacement or dynamic (see Figure 3-68) [23]. These two general classes of compressors are the same as that for pumps. The positive displacement class of compressors is an intermittent flow device, which is usually a reciprocating piston compressor or a rotary compressor (e.g., sliding vane, screws, etc.). The dynamic class of compressor is a continuous flow device, which is usually an axial-flow or centrifugal compressor (or mix of the two). 

Another important positive displacement compressor is the rotary compressor. This type of compressor is usually of rather simple construction, having no valves and being lightweight. These compressors are constructed to handle volumetric flowrates up to around 2,000 actual cfm and pressure ratios up to around 15 (see Figure 3-69). Rotary compressors are available in a variety of designs. The most widely used rotary compressors are sliding vane, rotary screw, rotary lobe, and liquid-piston. 

There is no clearance in a rotary compressor. However, there is leakage of air within the internal seal system and around the vanes. Thus, the typical volumetric efficiency for the sliding vane compression is of the order of 0.82 to 0.90. The heavier the gas, the greater the volumetric efficiency. The higher the pressure ratio through the stage, the lower the volumetric efficiency. 

Rotary compressors are classified into three general groups sliding vane, helical lobe, and liquid-seal ring. 

The fundamental design considerations of a sliding-vane compressor are the rotor assembly, cylinder housing, and the lubrication system. 

For installations which might be very sensitive to accumulations of oil, a two-stage oil separator can be fitted. The second stage cools the gas to just above condensing temperature, and up to 99.7% of the entrained oil can be removed. Even so, a small quantity will be carried over. Sliding vane and screw compressors mayhave extra oil injected into the casing to assist with sealing, and this must be separated out and re-cooled. 

For higher pressures, rotary compressors of the sliding vane type will give delivery pressures up to 1 MN/m2. In a compressor of this type, as illustrated in Figure 8.35, the compression ratio is achieved by eccentric mounting of the rotor which is slotted to take sliding vanes which sub-divide the crescent-shaped space between the rotor and... 

Figure 8.35. The sliding vane rolary compressor and vacuum pump...

Sliding vane, rotary blowers and compressors 346 --------- vacuum pumps 365... 

Rotary compressors are generally classified as of the straight-lobe type, screw type, sliding-vane type, and liquid-piston type. 

Figure 7.19. Some rotary positive displacement compressors, (a) A two-lobe blower, (b) Performance of a two-lobe blower (Rools-Connersville Co.), (c) A screw pump with one power and two idle rotors (Kristal and Annett, 1940). (d) Performance of 3.5" screw pump handling oils at 1150 rpm against 325 psig (Kristal and Annett, 1940). (e) Principle of the liquid ring seal compressor (Nash Engineering Co.). (0 A sliding vane blower (Beaeh-Russ Co.).

The sliding vane compressor can deliver pressures of 50 psig or... 

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