Cylinder and Packing Lubrication

Lubricated cylinders use a separate mechanical lubricator to force feed, in metered droplet form, a very precise amount of lubricant to specified points. This minimizes the amount of lubricant in the cylinder and allows a lubricant most compatible with the gas to be selected without compromising the frame lubrication system. Lubricant is fed to a point or points on the cylinder to service the piston rings and the packing when required. In a few cases, as in air compressors, the packing is lubricated from the crankcase. On some applications involving wet C02 or H2S in the gas stream, special materials may be avoided if one of the lubrication points is connected to the suction pulsation dampener.

One type of mechanical lubricator is the multiplunger pump, which has a plunger dedicated to each feed point (see Figure 3-20). This arrangement normally includes a sight glass per feed point. Another type of mechanical lubricator is the single metering pump sized for total flow, with a divider block arrangement to separate the lubricants going to different feed points (see Figure 3-21). While there are pros and cons to each system, the compressor vendor will normally recommend a system for any given application.

Because of the small amount of lubricant dispensed, the divider block system must be employed with the mini-lube method of lubrication previously discussed. The special divider block is usually connected to one plunger on a multiplunger pump, taking advantage of the smaller output to do the initial flow reduction. The balance of the pump's plungers may be used where a more conventional quantity of lubricant can be used.


Three methods of cooling are in common use, the pressurized cooling tluid system, the thermosyphon, and the static system. The static system is used on smaller compressors and is probably the least common. Cool-

Figure 3-21. A single lubrication pump with a divider block.

ing fluid is used as a static heat sink and can be thought of more as a heat stabilizer than a cooling system. There is some heat transferred from the system by normal conduction to the atmosphere.

The thermosyphon is a good system for remote areas where utilities are limited, but requires some careful design to ensure proper operation. This is a circulating system with the motive force derived from the change to density of the cooling fluid from the hot to the cold sections of the system. API 618 permits this system for discharge gas temperatures below 210 F or a temperature rise across the compressor of 150°F or less.

The most common system is the pressurized cooling fluid system. In a plant or refinery environment where cooling tower water is available, this system has the highest heat removal capability. In locations where cooling water is not available, a self-contained, closed-cooling fluid may be used. The system consists of a circulating pump, a surge tank, and a fan-cooled radiator or air-to-liquid heat exchanger. The radiator may have multiple sections, one for frame oil cooling and another for inter- or after-cooling. The cooling fluid is either water or an ethylene glycol and water mixture. Allowance must be made in the design to accommodate the inherently higher temperature coming from the air-cooled radiator and also ambient temperature variations.

On all systems using water, the obvious is overlooked all too often. A method of draining the equipment during periods when the equipment is idle and freezing temperatures are a possibility should be provided. The consequences of failing to provide this feature are obvious.

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