Piston-rod

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. 

Piston-Rod Packing Proper piston-rod packing is important. Many types are available, and the most suitable is determined by the gas handled and the operating conditions for a particular unit. 

Fig. 1.2. A close-up of the mechanical lubricator on the traction engine. Unless the bore of the steam cylinder is kept oiled it will become worn and scored. The lubricator pumps small metered quantities of steam oil into the cylinder to stop this happening. The drive is token from the piston rod by the ratchet and pawl arrangement.

A pump which has been running without glycol for some time should be checked before returning to normal service. The pump will probably need at least new O rings. The cylinders and piston rods may also have been scored from the dry run. ... 

PISTON ROD OIL SCRAPER LEAKS 1. Worn scraper rings. 2. Scrapers incorrectly assembled. 3. Worn/scored rod. 4. Improper fit of rings to rod/side clearance. 

Oil wiper rings remove excess oil from piston rod and seal the frame. 

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

The piston is located at the end of the piston rod and acts as a movable barrier in the compressor cylinder. It is generally made from materials such as aluminum or cast iron and has a hollow center. Small-diameter high-pressure cylinders may be provided with a combined piston and rod machined from a single piece of bar stock. 

The major source of fugitive emissions from a gas compressor cylinder is the piston rod packing. Other sources of fugitive emissions are around the cylinder valve covers, unloader covers, unloader actuator packing, and clearance pocket gasket and actuator packing. 

Here are two more examples of penny-pinching. The piston of a reciprocating engine was secured to the piston rod by a nut, which w as locked in position by a tab washer. When the compressor was overhauled, the tightness of this nut was checked. To do this, the tab on the washer had to be knocked down and then knocked up again. This weakened the washer so that the tab snapped off in service, the nut worked loose, and the piston hit the end of the cylinder, fracturing the piston rod. 

Stroke, -schimmel, m. club mold (Aapergillus sp.). -stauge, /. piston rod. -stoss. m. (Mack.) piston stroke. -trMger, m. flask support, flask stand. 

Direct steam piston direct connected to liquid piston or plunger through piston rod. 

The capacity of a pump is given in manufacturers tables as actual, after deducting for volume occupied by piston rod and slippage. Slip varies from 2-10 percent of displacement, with 3 percent being a fair average. 

For multiple cylinders, multiply the capacities just obtained by the number of cylinders. If the piston rod does not replace pumping volume as in some arrangements, the last term of the double acting capacity equation is omitted. 

End view showing male and female rotors and slide valve on an 85-ton intermediate compressor. The robust design of the Series R compressor can ingest amounts of liquid refrigerant that would severely damage reciprocating compressor valves, piston rods, and cylinders. (Used by permission Cat. RLC-DS-2, Aug. 1995. The Trane Company.)... 

Note that the crank end (Figure 12-2F) always has the piston rod running through it, while the head end usually does not, but may, if a tail rod (Figure 12-2L) is used. 

PISTON RINGS are normally cast-iron of the single-piece snap-ring type, although other materials may be used when conditions require. PISTON ROD is carbon-steel, flame-hardened over packing travel area. 

PISTON ROD is carbon-steel, flame-hardened over packing travel area unless otherwise specified. 

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

See Figure 12-7. Piston rods are usually forged and hardened steel or alloy. 

The motion of the piston rod is reciprocating through this packing as contrasted to the rotating motion of the centrifugal compressor or pump shaft. In many applications, it is important to prevent any part of the shaft that has heen inside the cylinder and exposed to the gas from being... 

Figure 12-7. Piston rods. Precision-manufactured rolled threads and induction hardening provide high fatigue strength and long life in heavy duty service. Standard rod material is AISI 4142 carbon steel other materials are available as required. Tungsten carbide coatings are also available for maximum surface hardness. Pistons are locked securely onto the rods. For higher pressure, smaller bore cylinders, the piston may be integral with the rod. (Used by permission Bui. 85084, 1992. Dresser-Rand Company.)...

Figure 12-8A. Piston rings. The piston rod is manufactured from heat-treated stainless steel and is coated with wear-resistant overlays, such as ceramic, chromium oxide, and tungsten carbide applied by plasma techniques. Piston rod cross-head attachment has mechanical preloading system for the threads. Rider rings and seal rings are manufactured from PTFE filled resins fillers are matched to the gas, piston speed, and liner specifications. Typical fillers are glass, carbon, coke, or ceramic. (Used by permission Bui. BCNA-3P100. Howden Process Compressors Incorporated. All rights reserved.)...

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