Packing Problems

Some common problems associated with packing repairs in the field are as follows 1. Segment reversal. This term refers to the mismatching of the individual ring segments. Rod packing segments are match-marked at the factory in some manner to assure proper assembly. Improper assembly of ring segments can result in excessive leakage and premature packing failure. 2. Mislocated packing. This term refers to having single-acting packing where double-acting packing should be installed. 3. Wrong side...

Packing Rings

Packing rings are the heart of the packing assembly, sealing along the piston rod and between themselves and the packing case (see Figure 3-29). The tangent ring is cut into three segments so that each cut lies on the side of an equilateral triangle. The cuts of this ring maintain sealing contact regardless of variations of the ring's inside diameter. As wear occurs, the ring segments will close radially to compensate while still maintaining sealing contact at the tangential joints, Figure 3-30...

Packing Types

There are several types of packing available. These include 1. Fully lubricated. Oil is supplied to the packing from the mechanical lubricator. The cases are drilled so that oil will be carried to the oil cups and then to the piston rod through a drilled hole in the oil cups. 2. Mini-lubricated. Same as fully lubricated, except that oil to the packing is decreased approximately 30 percent of normal flow. 3. Micro-flow. There is no oil supplied directly to the packing. The only oil that reaches...

Piston Failures

Figure 4-31 explains typical compressor piston defects and failure locations. A. Piston mating surface fretting and wear on two-piece pistons. maximum Allowable Cylinder Bore Diameter Before Oversize Pistons Are Required Maximum Bore Diameter Increase Allowed Before Oversize Piston is Required Maximum Bore Diameter Increase Allowed Before Oversize Piston is Required maximum Allowable Cylinder Bore Diameter Before Oversize Pistons Are Required All Piston Materials With Non-Metallic Rings &...

Piston Ring Clearances

The suggested minimum side clearances between ring groove (side) and end (gap) clearances for piston rings of various material are given below. Caution should be taken to make sure that each ring has the minimum end clearance. Unless there is sufficient clearance, ring ends may butt together from thermal expansion, causing ring wear, cylinder scoring, and other damage. The end clearances shown in Table 4-4 are for butt cut or step joint rings, as shown in Figure 4-27. For angle cut joints,...

Piston Ring Function

Two principal functions of piston sealing rings are To prevent gas from blowing by the piston. To transfer heat from piston to the cylinder walls and hence to the water jackets. Piston ring groove width variations can have a significant effect on these functions. To ensure proper operation, good contact is required between the ring and the side of the groove. If the grooves become tapered or edges dragged over as shown in Figure 4-22, poor sealing or ring fracture may be expected. If shoulders...

Piston Ring Installation

Care should be taken when expanding rings over the piston. To prevent permanent deformation or breakage, they should be spread no further than necessary to clear the outside diameter of the piston. Thin steel strips placed as shown in Figure 4-29 will help prevent damage from overstress or catching in unfilled grooves. Four strips are usually sufficient, one near each ring end and the other two evenly arranged on the opposite side of the piston.

Piston Rod Oil Wiper Packing

The stuffer in the frame head of the cylinder housing or crosshead guide contains a set of piston rod oil scraper rings and a gland (see Figure 3-51) that prevents crankcase oil from being carried out of the crankcase along the rod. A typical gland is designed to allow no more than .005 total side clearance for the scraper rings, generally .002 to .003. If the clearance is insufficient for the rings to float on the rod, they will not function properly. Too much clearance will cause the rings to...

Pistonto CylinderLiner Bore

The piston-to-cylinder or liner bore clearances vary with piston design and piston ring configuration. Oil-Lubricated Cylinders with No Rider Band The clearance between the piston-to-cylinder bore or the liner bore on an oil-lubricated cylinder can be determined as follows Cast iron piston .00125 inch bore diameter Example 20 diameter cylinder 20 x .00125 .025 clearance Aluminum piston .003 inch bore diameter Example 20 diameter cylinder 20 x .003 .060 clearance Oil-Free Cylinder Rider Band See...

Planning for Preventive Maintenance

Preventive maintenance for reciprocating compressors focuses on Restoring and upgrading compressor equipment. Involving operation and maintenance personnel and upgrading their knowledge and skills on compression equipment. Implementing effective maintenance planning and scheduling techniques. Identification of qualified vendors, suppliers, and contractors. Preventive maintenance includes periodic inspection to detect conditions that might cause breakdowns, production stoppages, or detrimental...

Plasma Spray

Development of plasma spray and suitable coatings allow piston rods not only to be reconditioned but to be given a surface treatment superior to that originally on the rod. Overlays of tungsten carbide and chrome oxide can give the piston rod longer wear life. Care must be taken to check the rod for straightness after spraying. Plasma spray has superior bond strength over conventional metal sprays and is less likely to flake off in service. This technique is used to restore piston rods to their...

Ported Plate Valves

Ported plate valves are similar to the concentric ring valves, except the rings are joined together into a single element (Figure 3-17). There are two advantages to this when compared to the concentric plates The number of plate edges available for impact is reduced. Mechanical damping by using damping plates to absorb opening impact is easily introduced. Spring is generally provided by coil springs that directly contact the plates, eliminating the buttons used in concentric ring valves. The...

Preliminary Checks if Runout Exceeds Limits

If the guidelines above have been closely followed and runout cannot be set at the proper limits, the following checks are recommended. Figure 4-10. Allowable piston rod runout vs. cylinder running clearance. .010 .020.030.040 .050.060.070 .080.090.100 .110.120.130.140.150 .010 .020.030.040 .050.060.070 .080.090.100 .110.120.130.140.150 First, ensure that all the housing nuts are torqued properly. Second, ensure that the packing and scraper assembly are not binding the rod. If the proper runout...

Prevent Gas Leakage

A means of preventing gas from leaking into the compressor during overhaul is necessary. Any gas trapped inside the compressor may leak into the room when the equipment is opened up. When opening up the compressor part of the machine, pancake skillet blinds should be placed between flanges or a blind flange installed on existing piping. Those positive shutoffs are easier said than done at most installations. A double block and bleed valve combination is satisfactory if the bleed line (for...

Preventive Maintenance for Reciprocating Compressors

It may be either impossible or utterly uneconomical to design and manufacture machinery for zero maintenance or perfect reliability with infinite life. Realistically, two principal maintenance philosophies are prevalent in industry Do nothing until the equipment breaks down or an emergency occurs. The compressor is repaired as quickly or as cheaply as possible and is returned to service. Inevitably, the next emergency is just around the corner. Maintain the equipment in excellent condition,...

Principle of Operation

An unloading device (see Figure 3-61), is fitted to each suction valve. At partial loads, this device does not allow the suction valve to close when the piston is in its bottom dead-center position, but delays this closing in a controlled way. Thus, a certain amount of gas, which is stepless-ly adjustable, is allowed to return towards the suction manifold before the compression starts. Figure 3-61. Reverse flow unloading device, schematic view (Source Hoerbiger Corporation of America, Pompano...

Procedures and Specifications

The following questions can be used to evaluate the vendor's procedures. 1. Does the vendor have a written quality control manual Are its procedures and work processes adhered to by shop employees, or is the manual just for show 2. Does the vendor have written specifications and procedures for reconditioning or manufacture of compressor components for which they are quoting If the vendor has the specifications, have they been made a part of his quotation without being requested Are the...

Procedures for Inspection of Compressor Piston Rods

Use the following procedures to inspect compressor piston rods 1. Remove piston from piston rod. 2. Place piston between centers (be sure existing centers are in good condition) or in V-blocks (see Figure 4-40). 3. With dial indicator, indicate over length of rod. Rod should not run out more than .001. 4. Measure diameter to be sure rod is round within .001 and not tapered more than .001 over its length, or worn undersize. If rod is found to be worn not more than .005 undersize and still round...

Program

Although monitoring of reciprocating compressors is not as simple and definitive as monitoring other rotating equipment, there are some things that can be and should be monitored. The first step in the program is to decide what is to be monitored. An effective predictive maintenance program should include the following 1. Daily operating reports and logs. These are used to observe operating parameters, pressures, temperature, flows, etc. These are often overlooked and recorded as part of the...

Pulsation Form

Pulsation is caused by the periodic action of compressors propelling gas through a pipe. The piston-crank-valve mechanism generates a variable pressure which, over time, creates a pressure wave in the suction and discharge piping that resembles a composite wave as shown in Figure 2-56. This composite wave is made up of a number of waves that are multiples of the fundamental sine wave. The multiples make up the composite wave form. Therefore, multiple frequencies of pulsation exist that can...

Pumps for Divider Block Systems

There are three basic types of pumps used for these systems. All pressurized inlet pumps must have an adequate supply of pressure and volume to handle the required flow rates. The typical range of inlet pressure varies from mere inches of water column to 30 psi. The first type of pump is the box lubricator converted to pressurized inlet. The sight glass and drip tube are replaced by a cap with inlet fittings for the supply lines. The suction tube is removed or plugged. Typically, two pumps are...

Pumps With Pressurized Supplies

Rotation of the lubricator cam actuates the pump rocker arm assembly to operate the pump piston. On the piston downstroke, spring pressure is exerted on the piston causing it to follow the cam. As it moves down, a pressure reduction (vacuum) is created between the piston and the discharge check valve, and the valve closes. This allows the pressurized supply to unseat the supply inlet shutoff ball and pressurize the piston bore with lubricant. On the piston upstroke, the piston forces the supply...

Pumps With Sight Glass

Rotation of the lubricator cam actuates the pump rocker arm assembly to operate the pump piston. On the piston downstroke, spring pressure is exerted on the piston causing it to follow the cam. As it moves down, a pressure reduction is created between the piston and the check valve and Figure 3-3. Force-feed box lubricator with sight glass (Source Lubriquip, Inc., Cleveland, Ohio). Figure 3-3. Force-feed box lubricator with sight glass (Source Lubriquip, Inc., Cleveland, Ohio). the valve...

Quantity of Material to be Removed When Reboring

The maximum diameter to which a compressor cylinder can be rebored is usually limited by the counter bore. Generally, the counter bores are V to V larger than the cylinder bores. While a cylinder may have sufficient strength to be bored larger than the counter bore diameter, it may be impractical to do so because there would be no way to center the heads without major redesign (see Figure 4-16). Figure 4-16. Cylinder bore and counter bore configurations. Figure 4-16. Cylinder bore and counter...

Rebuilding Compressor Pistons

There are several types of repair and rebuilding needed with worn or scuffed compressor pistons. These include 1. Remachine piston ring lands to correct worn grooves, then install wider piston rings. 2. Turn OD of piston to remove any scoring or scuffing. Build up OD with metal spray of proper material and remachine OD to original diameter. 3. Repair cracks in ribs or hubs in cast iron pistons by appropriate grinding, cleaning, and welding. Piston must be remachined after welding on OD, hub...

Reconditioning and Rebuilding

The valves removed from the compressor should be sent to the valve manufacturer's shop for cleaning, reconditioning, installation of all new components (sealing elements, springs, etc.), and testing. Operation and Maintenance of Reciprocating Compressors 1 63 ICOQK MANLEY HSRI Operation and Maintenance of Reciprocating Compressors 1 63 ICOQK MANLEY HSRI Figure 3-22B. High-security valve restraint (Source Cook Manley, Houston, Texas). Figure 3-22B. High-security valve restraint (Source Cook...

Record Keeping

Experience has also shown that a systematic study of valve problems will provide the best and often the quickest solutions to valve problems. Record keeping is necessary to successfully evaluate and solve valve problems. It is obvious that records should be sufficiently detailed to show which parts are involved and where these parts were located in the compressor. A picture of some sort is helpful in spotting a pattern of valve failure. A typical valve location chart is shown in Figure 3-20....

Regular Inspection and Maintenance

Compressor installations should be inspected regularly at intervals that will have to be determined by the severity of operating conditions. Necessary maintenance work such as replacing worn or broken parts installing new packing changing crankcase oil cleaning the crankcase, the force-feed lubricator and the air filter and removing deposits from valves, discharge passages, coolers, and water jackets should be carried out promptly. Following an overhaul, the entire system should be thoroughly...

Rod Position Monitoring

This monitor enables the user to detect when the rider ring bands have worn away enough to require shutdown before the piston contacts the cylinder. A proximity probe is mounted vertically next to the cylinder to observe the piston rod position. The new monitor provides two modes of operation average and instantaneous rod position. The instantaneous position measurement uses a Keyphasor transducer to provide a once-per-turn crankshaft revolution reference signal for sampling the rod drop probe....

Rod Under Tension

As the piston discharges toward the crank end on the return stroke, as seen in Figure 2-43, the net force of the suction and discharge pressures results in a tension load on the rod. This is called rod load tension. The operator can damage the compressor by decreasing the suction or increasing the discharge pressure too far above the design pressures. Figure 2-43. Piston rod stretch during compression in crank end portion of cylinder. Figure 2-43. Piston rod stretch during compression in crank...

Safety Precautions Read Carefully Before Installing the Compressor

Where lubricating oil is present in the compressor discharge, an aftercooler should be installed in the final compressor discharge line. It should be mounted as close as possible to the compressor. When installing a new compressor, it is essential to review the total plant air system. The use of plastic or carbonic bowls on line filters without metal guards can be hazardous. A pressure relief valve must be installed in the discharge piping between the compressor and any possible restriction,...

Sample Calculation A New Machine

Process gas molecular weight 17.76 k-value 1.26 Suction temperature 60 F Suction pressure 150 psia Compression ratio 6.67 overall, or V6.67 2.58 per stage From Figure A-l, we obtain a discharge temperature of 308 F. Specific gravity of gas 17.76 28.97 0.613 Compression efficiency from Figure A-7, ead 80 * Compressibility factor Zs is obtained from Figure A-8. General HP formula Figure A-7. Estimated efficiency as a function of compression ratio reciprocating compressors. Figure A-7. Estimated...

Sealing Elements

Materials used for sealing elements fall into two classes high strength steels and plastic composites. Feather valve strips, valve channels, and springs are made of steel, usually 410 stainless that is stress relieved, hardened, and tempered for maximum wear resistance. For more corrosive applications, channel may be made from 316 stainless. Feather valve strips may be made of Inconel 17-4 PH materials for greater corrosion resistance. As indicated in Table 3-6, valve discs or plates may be...

Service Condition Changes

A change in suction or discharge pressure may cause problems. Observing these pressures should be part of any troubleshooting effort. A plant operator advised that he had purchased a 12 x 9 single-stage horizontal compressor and that he was using it for 100 psi pressure. He inquired about the working conditions for which this machine was suit able and, upon investigation, found that the compressor was designed and built for a maximum air pressure of 40 psi. The operator was, accordingly,...

Setting Piston End Clearance

Whenever the piston rod has been removed or even turned in or out of the crosshead, it is necessary to check the piston end clearance and make any adjustments necessary to restore it to the proper amount. If the piston has not been removed from the rod, the original clearance can easily be maintained by center punching both the rod and the crosshead and making a suitable scribing tool, as shown in Figure 4-39, before removing the rod from the crosshead. Note The length of the scribing tool will...

Tapered Piston Rods

Because lubricating oil films may tend to fill up some small passages, packing can usually function in the presence of slight piston rod taper. Generally, tapered conditions are found at either end of the stroke, while the in-between portion of the rod may remain unaffected. Excessive amounts of taper will destroy the seal in the following manner. When the rings are riding on the tapered part (see Figure 3-45), one edge of the ring bore is in contact, while the other edge is away from the...

The Effect of Unbalance

Compressor inertia forces may have two effects. One is a force in the direction of the piston movement, and the other is a couple or movement that is developed when there is an offset between the axis of two or more pistons on a common crankshaft. The interrelation and magnitude of these forces will depend upon such factors as number of cranks, their longitudinal and angular arrangements, cylinder arrangement, and extent of counterbalancing possibility. Two significant vibration (movement)...

The flow of the gas

The flow of gas through the seat keeps the sealing element open. As the flow diminishes due to decreasing piston speed, the springs or other cushioning elements found in most valves force the sealing element to return to the seat lands and close the valve. Preferably, the valve is completely closed when the piston is near dead center. Figure 3-12. Valve seat land and lift representation.

Thermostatic and Thermosyphon Systems

These systems may be used where a small amount of cooling is advisable but the expense of a system involving a pump does not seem justified. They make use of the natural thermal circulation that results when the cooling water is heated in the cylinder. In these systems, the jackets are filled with water, oil, or ethylene glycol, and the heat of the cylinder is distributed by convection currents. The thermosyphon system is used with gases having a k value of 1.26 and below and with cylinder...

Thin Film Lubrication

During operation, fluid oil films exist between bearing surfaces. However, while stopped, adequate fluid films can no longer be maintained, and some metal-to-metal contacts may occur. Under these conditions, and regardless of bearing type, the film strength property of oil is of increasing importance. An oil having adequate film strength will resist rupture and, thus, minimize metal-to-metal contact, friction, and wear. Diester and polyalpha-olefin (PAO)-based synthesized hydrocarbon oils are...

Troubleshooting Valve Problems

Insufficient or improper lubrication 4. Pulsations on both suction and discharge 2. Cylinder jacket water temperature is lower than 3. Gas may be wet and washing inlet lubrication 1. If failures occur in winter months only, liquid is the probable cause and piping should be insulated or steam traced and or knockout pots placed close to the cylinder tightening or being knocked loose due to liquid 1. Valve loose by improper tightening 2. Valve tightened against broken pieces of 3. Improper...

Types of Cylinder Bore Wear

Cylinder bores usually wear in the following ways. 1. Compressor cylinder bores generally wear in a barrel-shape manner, that is, they wear more in the center than at either end of the compressor stroke (see Figure 4-15). 2. Bores may also wear out of round, that is, larger in the vertical than horizontal direction, or the reverse. 3. Taper wear may also be evident, that is, larger at the head end than crank end, or the reverse.

Undersized Piston Rods

If a piston rod is undersized but concentric and there is no taper, the packing can form an effective seal within reasonable limits because bore contact will be in the center of each segment and the cut in each ring is overlapped by its mate. Nominally sized rings can be used if the piston rod undersize dimension does not exceed .002. Whenever certain under-size conditions exist, wear-in time is required before the packing will properly seal. If the piston rod is greatly undersized, leakage...

Valve Failure Record

How long has valve been in service (hours) Is lubrication on cyl. bore and valve adequate (lubricated units only) Figure 3-21. Typical valve failure record (Source Dresser-Rand, Painted Post, New York). 1. Install new valve seat gaskets of the proper diameter, thickness, and material. 2. Place valve assembly on seat, taking care that the gasket stays in place and is not pinched. 3. Place yoke against valve and tighten set screws to hold assembly in position (lower valves). Extreme care must be...

Wear and Fatigue

Wear, as such, cannot be completely eliminated. It can be minimized by proper lubrication, design, and selection of materials. Most valves require some means of guiding. Wear at the guides, if severe, can result in sloppy action, cocking, poor seating, and failure. Wear must never be permitted to develop to this degree. Fatigue is the result of repeated cyclic stress. The stress level, as well as the stress range, must be considered in any design. However, barring abnormal action, well-designed...

Weld Repair Procedure

It is important that the proper weld procedures be followed when making weld repairs on crankshafts. An approved procedure will go a long way towards maintaining the integrity of the crankshaft. 1. Cracks in the crankshaft shall be removed by grinding. 2. Crankshaft shall be inspected with magnetic particle method to ensure that the cracks are removed. 3. Crankshaft shall be preheated to a temperature between 350 F and 800 F. This preheat temperature shall also be the minimum interpass...

Torque Values For Crosshead Nuts

On those piston rods that use a nut tightened to the face of the crosshead, it is important that the proper torque value be achieved to prevent loosening or overstressing the rod. Table 4-9 gives torque values for various size piston rod thread sizes at the crosshead end. Note It is very important to properly block the crosshead to prevent it from cocking when tightening the nut. Failure to take this precaution can damage the crosshead pin bushing as well as the connecting rod bearing.

Rod Under Compression

Consider first a double acting cylinder, as shown in Figure 2-42. As the piston pumps toward the head end, the discharge pressure (P9) on the piston tends to compress and buckle the piston rod. At the same time, gas is entering the cylinder behind the piston, exerting suction pressure force (Pj) on the back side of the piston. Two forces are opposite in direction, but since the discharge pressure is greater, the net result is a force com pressing the rod. This is called rod load compression. It...

Types of Compressors

The principal types of compressors are shown in Figure 1-5 and are defined below. Cam, diaphragm, and diffusion compressors are not shown because of their specialized applications and relatively small size. Compressors Dynamic I Displacement Figure 1 -5. Principal compressor types used in industry. Positive displacement units are those in which successive volumes of gas are confined within a closed space and elevated to a higher pressure. Rotary positive displacement compressors are machines in...

Effectiveness of Preventive Maintenance

Preventive maintenance, when used correctly, has shown to produce maintenance savings in excess of 25 , but beyond this, its benefit quickly approaches a point of diminishing return. It has been estimated that one out of every three dollars spent on preventive maintenance is wasted. A major overhaul facility reports that 60 of the hydraulic pumps sent in for rebuild had nothing wrong with them. This is a prime example of the disadvantage of performing maintenance to a schedule as opposed to the...

What is a Compressor

Before discussing the types of compressors and how they work, it will be helpful to consider some of the basic gas laws and the manner in which they affect compressors. By definition, a gas is a fluid having neither independent shape nor form, which tends to expand indefinitely. Gases may be composed of only one specific gas maintaining its own identity in the gas mixture. Air, for example, is a mixture of several gases, primarily nitrogen (78 by volume), oxygen (21 ), argon (about 1 ), and...

Crosshead Guide Repair

Crosshead guides are either built integral with the compressor frame or are separate and bolted to the frame. The guides form slides for the crossheads they must have a good surface finish and must be in line with the centerline of the cylinder. Crosshead guides can be rebored in place or in the service center. This is usually a field job because it is much cheaper to machine a guide in place than it is to remove the guide from the foundation. Removable guides, such as tail rod crosshead...

Rod Load Assignment

The rod can easily absorb most excessive tension and compressive forces, but other parts, such as pistons, connecting rods and bolts, crossheads and shoes, bushings and bearings, are also stressed. The most highly stressed part, therefore, determines the rod load assigned by the compressor builder. This value is different for each model of compressor, but generally crosshead pin bushing pressures are limiting. Rod loads can be calculated by simple arithmetic, but in operation, suction and...

Proximity Probe Method of Monitoring

A more efficient method of measuring rider band wear is to use a proximity probe, mounted vertically to the packing case, to measure the position of the piston rod. Probe gap voltage can then be read with an electronic rod drop readout device. Monitors such as Bently-Nevada's Six-Channel Rod Drop Monitor use a Keyphasor , probe to provide a once-per-revolution crankshaft pulse. This pulse is used as a reference, so an instantaneous rod position can be displayed. There are three main advantages...

Compressor Pistons

Figure A Conventional small diameter piston without rider rings. Material Iron, steel or aluminum. Single bolt piston to rod attachment. Figure B Two piece small diameter piston with single rider ring. Material Iron, steel, aluminum or combinations thereof. Single bolt piston to rod attachment. Figure C Three piece piston with two rider rings. This design utilizes two rider ring carriers and one piston ring carrier. Materials as In B. Single bolt piston to rod attachment. Figure A Conventional...

Valve Temperature Monitoring

A modern 32-channel temperature monitor provides increased productivity and efficiency. The monitor detects changes in valve condition by using differential measurement of valve temperatures. This allows you to make shutdown decisions based on real machine conditions rather than preset maintenance schedules. Reduced machine maintenance cost is also a benefit of this system. Temperature trends can be used to schedule maintenance to minimize downtime and to provide information to help diagnose...

Compressor Piston Rod Packing

Piston rod packing is almost always the full floating type. It consists of several annular cups, segmental rings, and a flange-like gland held in the cylinder head stuffing box as a complete assembly by properly proportioned studs and nuts that secure it against a sealing gasket. The segmental packing (sealing rings) is contained in the cups and is held together as an assembly by garter springs that hold the rings firmly on the piston rod. These rings are free to float in the cups. This packing...

Reapplication of Babbitt Sprayed Rider Bands

The following procedures should be followed when reapplying babbitt-sprayed rider bands. 1. Clean all old babbitt from the rider ring grooves by machining to base metal. Take extreme care at this point to assure that all babbitt is removed, while keeping the depth of the groove to a minimum. If machining is not necessary, sandblast the rider groove to bare metal. 2. Thread rider ring groove in accordance with instructions given in Figure 4-34. 3. Keep the cleaned area free of all oil and spray...

Disc Valves

The geometry varies from a single small disc in small valves to multiple discs in large valves. They can be found in applications ranging from a few hundred psi, as in poppet valves for gas transmission compressors, to over 50,000 psi in poppet valves for hyper compressors. The design characteristics of poppet valves for gas transmission service are multiple nonmetallic and streamlined sealing elements in single-or double-deck valves. (See Figure 3-18)....

Foreign Materials

Foreign materials may be listed in the following categories Liquid carryover from a process or from interstage coolers is apt to cause premature failures, particularly on intake valves. A slug of liquid is particularly hard on valves and may even break a seat. Liquid also destroys lubrication, thus, accelerating wear. Carryover can result from poor separation of condensate ahead of the compressor, or improperly designed piping where low spots permit liquid accumulation. A sudden flow change can...

What To Watch

The following checkpoints should be watched An example of the seriousness of these fires and explosions can be seen with the case of a soot-blowing compressor. This was a 200 HP, three-stage machine with a 500 psi discharge. It experienced an explosion in the discharge line between the compressor discharge and the aftercooler. The explosion ruptured a 4 pipeline. In another case, a 2000 HP air compressor in an automobile plant had an explosion in the air discharge of the high pressure...

How Compressor Packing Works

As previously described, a packing set consists of a series of sealing units. Compressor packing is not bottle-tight, but the amount of leakage is extremely small, a fraction of one percent of the capacity of the machine and usually within tolerable limits. In case of toxicity of the gas or danger of explosion or corrosion, leakage may be vented to a safe place. Because the individual rings will leak slightly, it is through the series of rings that the pressure is broken down from discharge to...

Disassembly Assembly and Inspection Procedures Disassembly

Refer to Figure 3-22A for a typical valve assembly with conventional restraint. 1. Remove valve screw cap and back off valve jam screw a minimum of four complete turns. 2. Remove valve cover nuts and remove valve cover. 3. Loosen set screws holding valve yoke and remove yoke. 4. Remove cover and valve seat gaskets and discard. 5. Carefully clean gasket seating surfaces on valve covers and valve seats. 6. Visually inspect valve seats for any signs of damage such as burring, wire drawing, and...

Splash and Flood Lubrication

Many horizontal compressors use the flood system for bearing and crosshead lubrication. Oil is elevated from the reservoir by discs on the crankshaft and is removed from the discs by scrapers. Some oil is diverted to the main and crankpin bearings, and the remainder is led to a large pocket over the crosshead from which a stream of oil flows to the crosshead pin and crosshead bearing surfaces. In some designs, the main bearings are lubricated from this pocket and the oil flows through external...

Troubleshooting Lubrication Systems

The following lists will help identify the cause of some of the more common compressor lubricating oil systems problems. 3. Defective pump or relief valve 4. Relief valve on header faulty 5. Worn bearings or excessive clearance 1. Relief valve in header faulty 5. Pressure regulating valve set too high Excessive Oil Consumption 1. Oil level too high in crankcase 3. The oil pressure may be too high 4. Piston rings and cylinder are worn Force-Feed Lubricator Incorrect Delivery of Lubricator 3....

High Pressure Cylinders

High-pressure cylinders, as shown in Figure 2-9, are made from a steel forging, with only nominal water cooling as compared to the other cylinders. Because the smallest possible number of openings in the forging is desired, capacity control mechanisms are not normally provided. Tie bolts may be installed perpendicular to the bore to pre-stress the forging, decreasing the maximum tensile stress induced by the gas pressure. Valve ports are finished to a highly polished surface, which reduces the...

Reconditioning of Compressor Piston Rods

If a rod is scratched, nicked, worn, or a slight shoulder exists, it is possible to recondition. If previous inspection has revealed any indication of cracks, inclusions, or imperfections in material, the rod must be scrapped. Note Do not attempt to weld piston rods. Regrinding Piston rods may be ground undersize, and the standard packing rings can be used. Generally .002-.003 per inch of piston rod diameter can be ground for medium pressures, but as the operating pressure increases above 1000...

Case Histories From Service Technician Reports

Service technicians compiled examples of problems that could have been prevented by more-detailed or careful examination of early symptoms. The following are some of the typical problems they described. Symptom Compressor would not unload, pumping until safety valve blew. Excessive blow-by existed at the piston rod packing. Findings The unloader piston was found to have rusted in its cylinder due to excessive condensation. Jacket water temperature at 50 F was increased to 100 F outlet. Unloader...

Compressor Component Repair and Rebuilding

In the overhaul and maintenance of the reciprocating compressor, many repairs can and are made to the major components. When making repairs, several things must be considered to prevent jeopardizing the integrity of the part and to ensure that it performs as good or better than the original installed in the compressor by the manufacturer. Here are questions to ask Is the repair made with sound engineering judgment Is the repair done with care and proper manufacturing techniques, such as,...

Web Deflection Measurements

Web deflection measurements are thus required for determining deviations in the crankshafts of large industrial marine engines and reciprocating compressors. These measurements and their interpretation are vital in disclosing conditions that can lead to disastrous and expensive crankshaft failures. Accurate periodic measurements, combined with careful analysis, will permit such conditions to be corrected before they cause problems. Web deflection is defined as any movement of the crank webs...

Valve Cover Bolting

Compressor valve covers should be checked to make sure they are fully bolted rather than short bolted, meaning they have only some of the threads of the nut in contact with the stud bolt. Full-thread contact is necessary to reduce the risk of the compressor valve cover being blown off. There is a remote possibility that a longer stud could have been substituted, which gives the appearance of short bolting. But this is unlikely. Figure 7-t. Noninterchangeable valves. Figure 7-t....

Routine Maintenance is Sufficient in Fouling Service

The excellent performance of the labyrinth-piston compressors in fouling service at Plant A can be attributed to the routine maintenance the units receive. Six four-throw, two-stage machines are given routine overhauls after every 8,000-10,000 operating hours. Three of the six machines are always in service, and there are times when all six machines are online. Overhauls are generally completed in three to four working days, with three or four machinists working 12-hour shifts. Typical tasks...

Repairing Foundation Cracks

The notch provided in the top of a foundation for the oil pan creates a perfect location for stress risers. A moment is created by lateral dynamic forces multiplied by the distance between the machine base and transverse reinforcing steel in the foundation below. The possibility of foundation cracking at this location increases as the depth of the notch increases. The farther the distance between the horizontal forces and transverse reinforcing steel, the greater the moment. Figure 4-11...

Inspection of Cylinders

Cylinders are inspected either visually or, with greater precision, by measuring bore size. Visual inspection should be done at every shutdown, for example on the occasion of a valve change-out. This can be accomplished by looking through the valve ports and inspecting the bore for any sign of scuffing or scoring. Also, the amount of cylinder oiling should be determined, that is, determine whether the cylinder is being over-oiled or not enough oil is being fed to the cylinder. Adjustment to...

Cylinder Bore Measurements

Compressor cylinder bore measurements are taken in the vertical and horizontal directions and in at least three locations along the bore, each end of ring travel, and in the center (see Figure 4-14). All measurements are taken with a micrometer and should be recorded on appropriate inspection report forms. One form should be used for each compressor cylinder and all pertinent data entered. Figure 4-14. Measurement locations along cylinder bore. Figure 4-14. Measurement locations along cylinder...

Rider Ring Clearances

The suggested minimum side and end clearances for rider rings of different materials are shown below. Minimum Side and End Clearances for Rider Rings of Different Materials Minimum Side and End Clearances for Rider Rings of Different Materials End Clearance (Per inch of cylinder diameter) The clearances shown in Table 4-5 are for butt cut or step joint rings as shown in Figure 4-27. For angle cut joints multiply value in table by the amounts shown in Figure 4-28. The side clearance for Teflon...

Inspection and Reconditioning Piston Rods

Before installing the piston piston rod assembly in the compressor cylinder or attempting to recondition a piston rod, inspect and measure it thoroughly. An important part of this inspection is checking the piston rod and the piston to be sure the assembly is able to run true to the centerline of the cylinder bore. Inspection is done by the following method 1. Visually inspect for signs of scuffing, longitudinal scratches, damaged or pulled threads. 2. Measure all diameters and lengths to...

Reverse Flow Control

The reverse flow regulation used by Hoerbiger is a stepless capacity control system that can be used on reciprocating compressors. It allows close adjustment of the output of a piston compressor to the demands of a process. It can follow variations of gas demand, gas composition, and Table 3-1 1 power Consumption of Compressor at Different Load Conditions Table 3-1 1 power Consumption of Compressor at Different Load Conditions *Kilowatts required bhp x. 746 motor efficiency *Kilowatts required...

Emergency Repairs Should Be Minimized

Plant systems must be maintained at their maximum level of performance. To assist in achieving this goal, maintenance should include regular inspection, cleaning, adjustment, and repair of equipment and systems. On the other hand, performing unnecessary maintenance and repair should be avoided. Breakdowns occur because of improper equipment operation or failure to perform basic preventive functions. Overhauling equipment periodically when it is not required is a costly luxury. At the same time,...

Operational Problems and Maintenance of Compressor Valves

In a reciprocating compressor cylinder, the valves, without a doubt, have the greatest effect on the operating performance of the machine, both from an efficiency standpoint and from a mechanical reliability standpoint. The valves are installed in the compressor cylinder directly in the air or gas stream, and are subjected to considerable abuse. It is surprising that we generally have as little valve trouble as we do. Stop and consider for a moment just what is expected of a compressor valve....

Remanufacturing of Shell Type Bearings

Remanufacturing or rebabbitting of shell-type compressor bearings should be done only to specific styles. The old bearing shells with thick babbitt, usually .032 to .064, can be rebabbitted by a shop experienced in this type of work. Centrifugal casting or spraying of the babbitt has been found superior to pouring babbitt in these shells. The newer shells with reduced babbitt thickness (.007-.015), can be rebabbitted by centrifugal casting if the backing is made of cast iron or steel. Bearings...

Rate of Leakage

Leakage amounts depend upon the amount of misfit between the rings and the piston rod. Leakage can also be the result of disturbances along the faces that must be in contact to form proper seals, as described for the various ring styles. Under the best of circumstances, packings will weep or bleed in small amounts that cannot be detected by ordinary means. Some of this escape is due to separation at the various points of contact as might be caused by vibration or temporary lubrication loss....

Excessive Rod Load

Most major damage to compressors is caused by exceeding recommended rod loads. For this reason, it is important that operators and mechanics understand rod loads before they start a compressor. Figure 2-41. Unloader with Teflon bushings are used with non-lubricated compressors (Source Plant Engineering, October 18,1979).

Piston Rod Column or Frame Loading

Each compressor is subject to a piston rod column or frame load limitation. The size of each compressor establishes a maximum allowable frame or piston rod column load. Keeping within this allowable load ensures that the frame castings and running gear parts, such as crankpins, crosshead pins, main bearings, crossheads, and connecting rods are not subject to loadings or stresses beyond their design points. Piston rod column or frame load is the force that the pressure in a cylinder exerts on...

Air Filtration

Another area requiring special attention for successful trouble-free operation of non-lubricated air compressors is proper filtration of the incoming air. Figure 2-39. Truncated piston for conventional non-lubricated compressor pistons (Source Joy Manufacturing Company, Division of Gardner-Denver, Quincy, Illinois). Figure 2-39. Truncated piston for conventional non-lubricated compressor pistons (Source Joy Manufacturing Company, Division of Gardner-Denver, Quincy, Illinois). Figure 2-40....

Characteristics of Reciprocating Compressors

Reciprocating compressors are the most widely used of all compression equipment and also provide the widest range of sizes and types. Rat- 100 150 200 250 DISCHARGE PRESSURE-PSIG Figure 1-15. Power vs. capacity and pressure for various air compressors (general approximations). 100 150 200 250 DISCHARGE PRESSURE-PSIG Figure 1-15. Power vs. capacity and pressure for various air compressors (general approximations). Figure 1-16. Altitude correction factors for air compressors applied to Bhp 100...

Servicing Pressure Packing

When cleaning packing rings, wire edges may be found around the bore of the rings if considerable wear has occurred. These wire edges must be removed with a file. However, care should be taken to not break the corners where any two surfaces of a packing ring match. If packings are to be paired with old rods, check the rod for size and trueness. If scores or shoulders are present, the rod should be refinished or replaced. All scores and abrasions should be removed by stoning. Packing cups may...

Divider Block Components

These systems are equipped with main line flow switches and mechanical counters for monitoring. The newest type of monitoring and protection device for the lube system is the electronic monitor. These devices give accurate control over the oil-feed rates and protection to the compressor in the event of system or oil supply failure. Figure 3-6 shows a Trabon MV system arrangement and Figure 3-7 a Watchman Lubemation System. Hcwilt tdjuitmoiil toi ttiirnlN Input flow to ayal.m. K. l.t.ra 9 Count....

Maintenance Costs Revealing

Six plants owned by a large corporation and six owned by other firms in North America and Europe were investigated. Not surprisingly, no two locations used identical data-collection and data-reporting methods. Some of the plants monitored repair cost and downtime data whereas, others kept track primarily of spare-parts usage, or perhaps, only the number of outages. However, all of the available statistics did prove relevant. Exceptionally detailed records have been kept for six machines in...

Manufacture of Compressor Piston Rods

Piston rods may be manufactured if proper attention is paid to selection of material, machining accuracies, heat treatment of materials, surface treatments, and surface finishes. Note Do not attempt to manufacture piston rod without first asking questions and consultation on the various aspects of piston rods. Before deciding to manufacture piston rods, the following factors should be considered 1. Determine operating conditions of compressor. 2. Material may be substituted from original design...

Frame Vibration Monitoring

Compressor Unloader Operation

The benefits of frame vibration monitoring are the prevention of catastrophic failure and the reduction of the amount of damage to a machine. This is accomplished by detection of small changes in the case motion. With modern 32-channel reciprocating compressor monitoring systems and associated seismic transducers, companies such as Bently-Nevada offer the user many advantages over the traditional, and often unreliable, g-switch type of detector. Bently-Nevada, one of a number of capable...

Typical Compressor Problems

For possible solutions to typical problems, check Troubleshooting Chart, Table 5-1. Always be sure to study and consult the compressor instruction book. And DO NOT FORGET TO CHECK THE PRESSURE GAUGES. Air discharge temperature above normal Piston ring, piston, cylinder wear excessive Piston rod or packing wear excessive Intake pipe restricted, too small, too long Table 5-1 (Continued) Troubleshooting Chart Table 5-1 (Continued) Troubleshooting Chart Air discharge temperature above normal Piston...

Evaluating Inspection Data

Recording inspection data serves several purposes 1. To establish the exact condition of all wearing parts. 2. To establish the wear rate of parts, which, if promptly replaced, will not deteriorate to such a degree that associated parts will be damaged and will also require replacement. 3. To determine which parts require reconditioning and which parts can be reconditioned to like-new condition. Compressor-Piston Rod Inspection Form U-2.995 0-2.998 T-2.998 Note U Undersize 0 0ut Round T Taper...

Major Sources of Packing Problems

There are several indicators of troubles with metallic packing that are frequently misunderstood and in reality are a manifestation of trouble originating elsewhere. Excessive or rapid wear is an example of this. Barring improper selection of mating materials or of materials and gas, excessive wear can be caused by several factors. To fully understand and diagnose abnormal wear, normal wear should be understood. Figure 3-43. Pressure balance set with seal ring fastened directly to the packing...

Design and Materials for Reciprocating Compressor Components

Today's modern, heavy-duty, continuous-service reciprocating compressor cylinders can be attached to a single horizontal or vertical frame. When more than one cylinder is used, the various configurations are almost endless. As previously seen, these machines range from simple one-cylinder, single-stage compressors for air service to multi-stage, multi-service process gas compressors. Regardless of the service, from the smallest to the largest, reciprocating compressors share both the same...

Procedure for Torquing Piston Nuts

The following procedure has been developed for the torquing of piston nuts when installing cast iron, aluminum, and steel pistons, either two pieces or one piece, with straight bores. It must not be used for pistons that use piston rods with taper fit to the piston. 1. Clamp piston rod behind the collar in a suitable fixture similar to the one shown in Figure 4-36. Care must be taken not to clamp on any coated surface if the rod has been coated, because cracking or breaking the bond will...

Design Overview of Labyrinth Piston Compressors

Earlier in this chapter, we alerted the reader to a special non-lubricated reciprocating compressor configuration, the labyrinth piston, or Laby machine. Although available since the mid-1940s, labyrinth compressors are not as well known in the United States as they are in other parts of the world. In labyrinth piston compressors, an extremely large number of throttling points provide the sealing effect around pistons and piston rods. No contact seals are used. Whereas plastic sealing rings...

Calculations

Reciprocating Compressor Curves

Solving compressor problems by the use of the ideal gas laws has been reduced to a relatively simple sequence of applying a few basic formulae and obtaining values from some basic curves. In order to help in the understanding of these terms and equations, the first chapter of this text covers some basic thermodynamics. Also, following the sequence of events as they occur in a compressor cylinder may help develop an understanding of the terms encountered in most reciprocating compressor problems...

Theory of Reciprocating Compressors

Reciprocating compressors are the best known and most widely used compressors of the positive displacement type. They operate on the same principle as the old, familiar bicycle pump, that is, by means of a piston in a cylinder. As the piston moves forward in the cylinder, it compresses the air or gas into a smaller space, thus raising its pressure. The basic reciprocating compression element is a single cylinder compressing on one side of the piston (single-acting). A unit compressing on both...

Excessive Oil Feed

All oil fed to the cylinders is subjected to oxidizing conditions. Under prolonged heating, even the best quality compressor oils will oxidize to some extent. Therefore, feeding more oil than is actually needed results in increasing the amount of oxidation products formed. Because the highest temperatures are encountered on discharge valves and in discharge passages, and most of the oil fed to the cylinders eventually leaves through the discharge valves, it is here that deposits tend to...