Compressors spacing

A normal refrigerator has many sources of ignition within it— the thermostat, interior light, the hght switch on the door, the defrost heater, the defrost control switch, the compressor unit, and the air circulation fan. Most of these are located within the space being maintained cool, but self-defrosting units contain an internal drain that can permit the internal vapors to flow into the compressor space below the usable space. 

Space needs to be provided for the auxiliaries, including the lube oil and seal systems, lube oil cooler, intercoolers, and pulsation dampeners. A control panel or console is usually provided as part of the local console. This panel contains instmments that provide the necessary information for start-up and shutdown, and should also include warning and trouble lights. Access must be provided for motor repair and ultimate replacement needs to be considered. If a steam turbine is used, a surface condenser is probably required with a vacuum system to increase the efficiency. AH these additional systems need to be considered in the layout and spacing. In addition, room for pulsation dampeners required between stages has to be included. Aftercoolers may also be required with knockout dmms. Reference 8 describes the requirements of compressor layouts and provides many useful piping hints. 

Figure 4-15. Axial compressor with fixed stator blades, double-casing design, and forged monoblock rotor. Particularly suitable for compressing nitrous gases. There are no dead spaces provoking buildup of ammonium nitrate salt.

Theoretical work or compressor head is the heart and substance of compressor design. Some basic form of understanding must be devel oped even if involvement with compressors is less than that of design of the machine itself. Proper applications cannot be made if this understanding is absent. The following theoretical evaluations will be abbreviated as much as possible to reduce the length and still present the philosophy. For the reader with the ambition and desire, the presentation will be an outline to which the reader can fill in the spaces. 

The balance chamber leakoff line, while recommended to be held within the confines of the compressor casing may well turn out to require some user piping. There are some situations where the desire for keeping open space around the compressor for maintenance may require compromise on the part of the user. The balance of the connections on the axial are for lube oil and other auxiliary equipment not different from that found on other compressors. 

I or biualkr compressors, where the speed is relatively high and space is limited, a solid rotor construction is used. This is similar to the disc type of construction, except that the discs are an integral part of the rotor Blade attachment slots are cut into the rotor, similar to the slots cut into the discs. Rotor blades are rarely, if ever, shrouded. 

For the slower speed compressors, an evaluation must be made concerning the use of direct-connected motors that are more expensive, or the use of a less expensive 1,800 rpm or a 1,200 rpm motor with a speed-reducing gear. As before, the evaluation must include all factors, such as installation and the extra space, as well as some factor for additional maintenance. 

Screw compressors are rotary positive displacement machines. Two helical rotors are rotated by a senes of timing gears as shown in Figure 10-8 so that gas trapped in the space between them is transported from the suction to the discharge piping. In low-pressure air service, non-lubri-cated screw compressors can deliver a clean, oil-free air. In hydrocarbon service most screw compressors require that liquid be injected to help provide a seal. After-coolers and separators are required to separate the seal oil and recirculate it to suction. 

This case uses the large cloud, as in Cases 2 and 3, but the ignition point is moved to the center of the space under the compressor building (IGN3). 

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