Crossheads

Simplex Double-Acting Pumps These pumps may be direc t-acting (i.e., direct-connected to a steam cyhnder) or power-driven (through a crank and flywheel from the crosshead of a steam engine). 

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. 

FRAME KNOCKS 1. Loose crosshead pin, pin caps or crosshead shoes. 2. Loose/worn main, crankpin or crosshead bearings. 3. Low oil pressure. 4. Cold oil. 5. Incorrect oil. 6. Knock is actually from cylinder end. 

In unloaded or part-load operation, rod reversals must be of sufficient magnitude to provide lubrication to the crosshead bearings. The bearings are lubricated by the pumping action of the opening and closing of the bearing clearance area. 

Couplings specification information, 451 Critical pressure, 35 Critical temperature, 15 Crosshead type,... 

Crosshead guides are cast integrally with engine frame. 

Crossheads, running in bored guides, have shim-adjusted babbitted shoes at top and bottom and either full-floating or fixed crosshead pins. Suitable for addition of balance weights. 

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-... 

The crankshaft rotates about the frame axis, driving the connecting rod, crosshead, piston rod, and piston. 

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. ... 

The frame lubrication system circulates oil to the frame bearings, connecting rod bearings, crosshead shoes, and can also supply oil to the packing and cylinder lubrication system. Splash lubrication systems are... 

In a forced-feed lubrication system, a pump circulates lubricating oil through a cooler and filter to a distribution system that directs the oil to all the bearings and crosshead shoes. Figure 11-23 is a schematic of a typical system. The details of any one system will vary greatly. Major components and considerations of a forced feed lubrication system are as follows ... 

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. 

In this method [89], a single fiber is taken and partially embedded in a drop of uncured resin placed on a holder. The resin is then cured with the fiber held upright. The holder, with resin and fiber, is held in a grip attached to the crosshead and then pulled out from the resin. The force pulling the fiber out of the resin is balanced by shear stress at the resin-fiber interface holding the fiber in place. The maximum shear stress occurs as the embedded length tends to zero and is given by ... 

For example, an HHE for a three cylinder application has three crankthrows set at 120°. Piston weights may he balanced or balance weights added to the active crossheads to obtain zero unbalanced primary forces. By comparison, a fixed angle crankshaft requires four crankthrows with either an additional compression cylinder or a balance weight dummy crosshead to obtain acceptable unbalanced forces. ... 

The minimum number of cylinders are not locked into even numbers to handle compression problems. The minimum number required are used therefore, balance weight dummy crossheads are not necessary. ... 

Crosshead pressure-lubricated through drilled passages in crosshead body. Piston rod threaded and locked into crosshead. 

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

Vane Liquid ring Screw Screw Roots Trunk Crosshead Labyrinth Diaphragm... 

It should be noted that test information would vary with specimen thickness, temperature, atmospheric conditions, and different speed of straining force. This test is made at 73.4°F (23°C) and 50% relative humidity. For brittle materials (those that will break below a 5% strain) the thickness, span, and width of the specimen and the speed of crosshead movement are varied to bring about a rate of strain of 0.01 in./in./min. The appropriate specimen size are provided in the test specification. 

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