Crossheads, compressor

Compressors up to around 75 kW (100 hp) usually have a single center-throw crank, as illustrated in Fig. 10-83. In larger sizes compressors are commonly of duplex construction with cranks on each end of the shaft (see Fig. 10-87). Some large synchronous motor-driven units are of four-corner construction i.e., they are of doubleduplex construction with two connecting rods from each of the two crank throws (see Fig. 10-88). Steam-driven compressors have one or more steam cylinders connected directly by piston rod or tie rods to the gas-cyhnder piston or crosshead. 

COMPRESSOR WILL NOT START 1. Power supply failure. 2. Switchgear or starting panel. 3. Low oil pressure shut down switch. 4. Controi panel. NOISE IN CYLINDER 1. Loose piston. 2. Piston hitting outer head or frame end of cylinder. 3. Loose crosshead lock nut. 

The compressor frame, shown in Figure I i -2, is a heavy, rugged casting containing all the rotating parts and on which the cylinders and crossheads are mounted. Ail frames are rated by the compressor manu-... 

In addition to the gas load, the rod and cros.shead pin bushing is subject to the inertia forces created by the acceleration and deceleration of the compressor reciprocating mass. The inertia load is a direct function of crank radius, the reciprocating weight, and speed squared. The total load imposed on the crosshead pin and bushing is the sum of the gas load and the inertia load and is referred to as the combined rod load. ... 

Due to the basic design of the compressor, its rotating and reciprocating masses produce inertia forces and moments tha cannot be completely eliminated and must be absorbed by the foundation. The manufacturer has the ability to minimize the magnitude of these forces and moments by adding counterweights to the crossheads but cannot totally eliminate them. 

Figure 3-72. Double-acting (crosshead-type) reciprocating piston compressor [4],...

The compressors most commonly used for compressing gases have a crosshead to which the connecting rod and piston rod are connected. This provides a straight-line motion for the piston rod and... 

Piston rod runout and crosshead design. A imique procedure is used by this manufacturer to verify the piston rod alignment of horizontal compressors and to reduce the rod runout to a minimtun. The system allows the rod nmout to be minimized by adjusting the piston rod in relation to the piston by means of a patented eccentric device for the connection of piston and piston rod. It does not need any dismantling of the driving mechanism. This solution is superior to the method recommended in API 618, which advocates crossheads incorporating shimmed shoes. See Fig. C-71. 

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