Surge drum

Direct-expansions are more appropriate for smaller systems which should be compact, and where there are just one or few evaporators. Overfeed (recirculation) systems should be considered for aU applications where first cost for additional equipment (surge drums, low-pressure receivers, refrigerant pumps, and accessories) is lower than the savings for the evaporator surface. 

The performance of reciprocating pumps provides for ease of operation and control. Depending upon the type of piston action, the fluid may be subject to pulsations unless accumulator or surge drums are provided. 

Surge drums (vessels) usually operate about half full. Therefore, the wetted surface would be calculated at 50% of the total vessel surface, but higher if design is based on greater figure. 

A complete evaluation of the surge capacity and pulsation frequencies of the system (i.e., suction header and suction surge drum. Figure 13-1 A), compressor, discharge surge drum, and discharge header is necessary before reaching an... 

Figure 13-2. Gas surge drum inquiry specifications. (Used and adapted by permission Burgess-Manning, Subsidiary of Nitram Energy, inc.)...

Figure 13-7A. Surge drum internal details. Note The design indicated may not correspond to the internal details recommended by a professional computer analysis design. This diagram represents a concept suitable for some applications.

Figure 13-7B. Alternate surge drum internal details.

Generally, when placed close to the compressor cylinder, surge drums will minimize acoustic wave amplitudes, but they do not eliminate high-frequency acoustic response (Figures 13-11 and 13-12). 

Figure 13-11. Single compressor cylinder with surge drums.

Figure 13-12. Parallel compressor cylinders with surge drums.

Some situations bring into question the necessity of a surge drum in the system. This hecomes more evident in the low flow rate, high compression ratio units in which the drum is calculated to he only slighdy larger than the usual pipe size. In some of these cases, it has heen found satisfactory to enlarge the pipe size and eliminate the drum. Each system must he carefully evaluated as generalities cannot solve the variety of situations. 

Parallel Multicylinder Arrangement Using Common Surge Drum... 

Example 13-1. Surge Drums and Piping for Double-Acting, Parallel Cylinder, Compressor Installation... 

Size the discharge surge drum and associated piping for a single-acting, single-cylinder, motor-driven compressor with the following performance characteristics ... 

---