summary compressor training

7/31/2019 Summary Compressor Training

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SUMMARY OF DRESSER RAND RECIPROCATING

COMPRESSOR TRAINING


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INTRODUCTION

Types of compressor

1. Reciprocating compressor

Lubricated type - separate lubrication provided to cylinder & packing rings

Non lubricated type no separate lubrication provided to cylinder & packing rings

2. Screw compressor

3. Centrifugal compressor

Reciprocating Compressor

Basic components:


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Compressor frame and running gear:

Frame and Yoke

Crank Shaft

Connecting rod

X-Head

Bearings: main bearings / crank pin bearing / X-head bearing

Frame oil pump

1. Frame and Yoke

Is a single piece cast iron, heavily ribbed andreinforced casing for supporting of movingparts

All forces & moments generated from moving parts are transmitted to frame rigidlymounted on skid or foundation.

2. Crank Shaft

A rotating steel shaft driven by a power source such as an electric motor or engine.

The shaft has arms at right angles which can impart circular motion at some distancefrom the crankshaft centreline.

3. Connecting rod

A part that transfers rotating motion of the crankshaft to reciprocating motion of thecrosshead


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4. X Head / cross head and pin

High-strength nodular iron crossheads

Shim-adjustable aluminium on top and bottom

Full floating Crosshead pins

Integral crosshead guide housings

Assure positive alignment with the frame

5. Bearings

Aluminium sleeve-type


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Compressor Gas End

Cylinder

Piston / piston rings / wearing rings

Piston rod / packing rings / oil scrapper rings

Inlet valves

Discharge valves

Lubricator

1. Piston rod

A steel shaft that connects the piston to crosshead, and transfers reciprocating motion

from the slider-crank mechanism to the piston.


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2. Piston

A circular part usually made of metal that fits inside a cylinder. As it slides back and forth,

the volume chamber is reduced or enlarged causing an alternating increase and

decrease in gas pressure.

3. Cylinder

An enclosed container where compression of gas occurs by means of a moving piston.Usually made of cast iron or forged steel, it must be strong enough to withstand the

maximum allowable working pressure.

Two type of cylinder

i. Single acting cylinder

- A compressor cylinder configuration where gas compression only

takes place at one end of the piston. By design, a cylinder can be

single acting on either the frame end (crank end) or outer end (head

end)

ii. double acting cylinder

- A compressor cylinder configuration where gas is compressed on

both ends of piston. Most cylinders are designed to operate this wayto achieve maximum efficiency.

Single acting cylinder Double acting cylinder


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4. Valves

A device that allows gas to flow through its ports due to differential pressure.

Valves are designed to allow gas flow in only one direction.

two types of valves

i. inlet valves allow gas to enter the cylinder on the intake stroke

ii. Discharge valves allow gas to exit the cylinder after being compressed

slightly above normal discharge pressure.


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Auxiliary Equipment of Reciprocating Compressor

frame lube oil console

pulsation dampeners

cylinder lubricator

cylinder / packing coolant console

main drive motor

gas piping / process coolers

control / purge panel

distance piece drain system

1. frame lube oil console

2. pulsation dampeners

Welded steel tank to reduce pressure pulsation within the gas piping.


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3. cylinder lubricator

4. packing coolant coolers


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5. main drive motor

6. gas piping / process coolers


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7. control / purge panel

8. distance piece drain system


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OPERATION OF COMPRESSOR

Use same gas law in compressor

When the basic compressor parts function in proper sequence, the result is gas under

pressure.

Compressor cycle:


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Cylinder Operation

Single acting cylinder

o Compression take place in one side of cylinder only

*the piston sealed with piston rings to prevent gas from escaping through the

clearance area between the piston and cylinder bore.

Double acting cylinder

o Compression take place in both sides of cylinder

*as the piston is displacing volume on one end of the cylinder, it is increasing

volume on the other end. This allows gas to be drawn in and compressed on both

ends of the cylinder. This cylinder is double acting.


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Double acting cylinder process

Outer end compression

o As the piston moves toward the outer end, the volume in the cylinder is decreased.

Since the inlet valve prevents flow back out of the cylinder and the pressure in the

cylinder is still below the pressure in the discharge gas passage, the gas is trapped

and becomes compressed as the volume decreases.

Inner end expansion

o As the piston moves away from the inner end, the volume in the cylinder increases

allowing the high pressure gas that was trapped at the end of the delivery stroke to

expand and reduce in pressure

Outer end - delivery

o As the volume continues to decrease with piston movement, the gas continues to

increase in pressure. Once the pressure in the cylinder is slightly above the pressure

in the discharge passage, the discharge valve opens and gas from the cylinder bore is

allowed to enter the discharge gas passage through the discharge valve

Inner end inlet

o As the volume continues to increase with piston movement, the gas continues todecrease in pressure. Once the pressure in the cylinder is slightly below the pressure

in the inlet gas passage, the inlet valve opens and gas in the inlet gas passage is

allowed to enter the cylinder bore through the inlet valve.


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Outer end inlet

o As the volume continues to increase with piston movement, the gas continues to

decrease in pressure. Once the pressure in the cylinder is slightly below the pressure

in the inlet gas passage, the inlet valve opens and gas in the inlet gas passage is

allowed to enter the cylinder bore through the inlet valve.

Inner end - delivery

o As the volume continues to decrease with piston movement, the gas continues to

increase in pressure. Once the pressure in the cylinder is slightly above the pressure

in the discharge gas passage, the discharge valve opens and gas from the cylinder

bore is allowed to enter the discharge gas passage through the discharge valve.

Outer end - inlet

o As the piston continues to move, the volume continues to increase therefore

maintaining the differential necessary to hold the inlet valve open and draw gas

from the inlet gas passage into the cylinder bore.

Inner end - delivery

o As the piston continues to move, the volume continues to decrease therefore

maintaining the differential necessary to hold the discharge valve open and move

gas from the cylinder bore into the discharge gas passage


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ASSEMBLY AND MAINTANANCE

1. Valves

a. Seat

b. Stop plate a.k.a guard

c. Moving element

d. springs

2. Piston and Piston Rod

3. Packing rings


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Valves

a. Seat

The gas always flow through valve seat first

This is true for both suction and discharge valve

Gas enters through the seat

Moving elements seal against the seat

b. Stop plate (guard)

The gas always flow through valve stopplate last

This is true for both suction and discharge valve

The gas exits through the stopplate

The stopplate limits the travel (lift) of the moving elements

c. Moving Element

Gas pressure pushes the moving elements off the seat and against the stopplate to

open valve

Moving element always seals (closes) against the seat

Common type of elements

i. Channels

ii. Rings

iii. Ported plates

iv. Poppets

d. Springs

Springs provide a force to close the moving element against the seat

Proper springs will close the moving elements before the piston reaches top dead

centre (TDC) and bottom dead centre (BDC)

Basic valve operation

Differential pressure opens the valve

Spring close the valve

Most valves open & close 5 to 20 times per second (300 to 1200 rpm)

Valves will create a pressure drop in the forward flow direction

A proper valve disallows flow in the reverse flow direction (otherwise there is a leakage)


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First step performing any maintenance such as valve cover or valve removal is to lock out, tag

out, depressurize, and purge the unit being worked on. If hazardous gas is involved the unit

may need to be checked with portable gas detector.

Be sure to follow all the safety procedures as prescribed by your station guidelines.

Valve cover

Each valve is sealed to the cylinder by a gasket and held tightly in place by a valve cover and

cage assembly. Shown on the left is a setscrew type valve cover. This arrangement utilizes a

centre sets-crew to apply the necessary force to the cage and valve.

The o-ring style cover on the right holds the valve secure with the force that is generated

and transferred through the cage by the cover while torquing the cover nuts.

Valve covers removal.

Loosen the nut.

Depending upon the style of cover, the next step is to either remove the acorn nut, or

with the seal-nut style cover, loosen the seal-nut. This should be done before trying to

loosen the set-screw. Although the seal-nut isnt considered a jam-nut, the set-screw will

turn easier with the seal-nut loosened. If it is necessary to replace the lead or seal

washer the centre set-screw must be removed from the cover.

Do not completely remove the setscrew at this time. If there is any residual gas pressure

left in the cylinder the set-screw could be ejected from the cover causing bodily injury.


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Valve cover installation

Always use new gaskets when the valves are reinstalled, and in the case of the setscrew

type of cover replacing the lead washer or special sealing is highly recommended.

Process:

1. Install new gaskets

2. Make sure valve is fully seated

3. Torque cover nuts incrementally in a cross pattern

4. Torque setscrew

5. Tighten seal nut

** The seal-nut has no special torque value. After tightening it, pressurize the cylinder and

use soapy water to check for leaks. Over-tightening the nut will only damage the lead

sealing washer and cause it to become wedged into the set-screw threads making it harder

to loosen during the next round of maintenance.

Fastener tightening

Before using any fastener, always check for damaged treads, and ensure that the

mating surfaces to be joined are clean, free of nicks, scratches and burrs. Also ensure

that the seating surfaces are flat and parallel.


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Valve reliability factor

Dirt and debris

Improper lubrication

Liquid carryover

Pulsations

Dirt and Debris

o Causes rapid wear from erosion

o Makes valve disassembly difficult

o Not tolerated well by channel valves due to tight clearances between the channel &

guide and between the channel spring

o Tolerated better by poppet valves because they have large flow areaso Possible cause of dirt and debris

1. Weld slag in pipe

2. Natural gas well franking

3. Catalyst vessels in oil refineries

4. Accumulation of curd in filter screens is suddenly liberated

Improper lubrication

o

Too much lubrication or very tacky oil causes sticking (viscous adhesion of movingelements to seat or stopplate)

o Valve spring must overcome a sticktion force to properly open and close the valve

on time in lubes units

o Sticktion increase opening and closing impact velocities

o Too little oil can cause abrasive action between the moving parts

o Valves should have oily appearance but not have oil droplets showing

o Consult reputable oil supplier for proper selection of lubricant.

o Consult OEM for proper lube rate

Liquid Carryover

o Liquid can wash away or dilute cylinder lube oil

o Liquid slug can cause sudden valve failure

o Dormant liquid in piping gets picked up by directional change in gas flow

o Vapour in the inlet gas piping condenses especially in cold climates

o Cylinder water jacket temp. not 10-15 degrees above inlet gas temp.


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For Best Valve Life

Use limited number of well-trained personnel to work on valves

Compress clean gas

Allow no liquid carryover

Use proper lube oils and lube rates

Use best materials

Keep systematic valve records

Install valve carefully

Fields Condition

Dirt and debris

o

Accelerated wear and/or poor sealingo Flow holes in seat and guard can become blocked

Liquid

o Are incompressible, so slugging can put a high differential across valve bodies

o Too much lube oil increases sticktion

o Too much gas condensation reduces effectiveness of lubrication


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Piston and Piston Rod

Minovar collar


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Packing Rings

Purpose of Packing

In a reciprocating compressor, the piston rod enters the frame end of the cylinder in order

to move the piston back and forth within the cylinder bore.

Clearance around the piston rod prevents interference between the piston rod and the

frame head.

These clearances allow gas from cylinder to leak around the rod and into the distance piece

if not sealed off.

Purpose of the packing assembly is to seal gas within the frame end of the cylinder bore.


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Correct Cup Orientation

Each cup in the packing assembly is numbered sequentially, starting with number one on the

nose, or gasket, cup. This numbering used to ensure that the cups are in the proper location

between the nose cup and the flange.

If the cups are out of sequence, the lubrication passages would not line up correctly thus

disrupting the proper flow of the oil to the sealing rings. The oil entry cup may also be in the

wrong location. This would cause the rings in the lower numbered cups to be starved of oil.

If the vent cup is not against the flange as shown, the packing would not be able to vent

properly. Improper venting would cause the internal packing case pressure to build up,

forcing gas out around the rod and into the distance piece.

If the packing case is water cooled the coolant passages could be blocked. The cups that the

coolant circulates through could end up in the wrong location, leading to insufficient cooling

of the packing case.

Packing cups.


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General packing ring layout

Three segments for each ring (regardless of cut) allow for continuous contact with rod as the

ring

End gaps form when on rod; allow for reduction oh I.D. while wearing

Dowel pin arrangements misalign end gaps of individual rings

Reference marks show segment orientation

Reference marks face the gas they are sealing


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CYLINDER LUBRICATION

Two types of system:

1. Pump to point (commonly used)

2. Divider block

Pump to point


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Pump to point system

Quantity adjustments are made at the lubricator by increasing or decreasing stroke.

Additional pumps are needed for system protection.

o For low oil level an additional pump with a short suction tube.

o For no flow A dead ended pump flow oil to a spring loaded device that drains back to

the primary reservoir.

The only way to ensure working condition of the pumps, is by visual inspection

System requires constant monitoring.

o Ensuring pumps are dripping

o Monitoring flow rates by counting drops per minute

Pump to point lubricators

Single lubricator to supply amount of oil to specific location.

Positive displacement vacuum feed pumpo Vacuum in sight glass

o Capable of very high pressure


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Vacuum pump troubleshooting

Sight glass well runs dry:

o Air leak in sight glass

o Restriction in drip or suction tube

Sight glass fills with oil:

o Leaky inlet (suction) check valve

o Worn piston

o Commonly related to temperature/viscosity variations

Sight glass remains constant & no lubricant drips from tube:

o Pump may be air bound

o Pump regulation set too low

o Cam shaft speed too slow

Over pressurizing the pump

o

Normally due to mechanical failure Other causes of failures

o Broken or loose suction tube

o Cracked sight glass or poor sealing stopper screw

o Bad o-ring seals under sight glass

o Dirt around plunger or check valves


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DO AND DONTS TO COMPRESSOR

Dresser Rand compressors are designed & built for long periods of continuous full load operation &

are equipped with an automatic safety switch to shut it down in case of low frame oil pressure. It

can be equipped with additional safety devices to obtain practically any degree of protection

desired.

Do on reciprocating compressors

Before start up of the compressor always ensure that

Nobody is around the vicinity of compressor or engine

The required inlet & outlet process valves are open

Cooling water inlet & outlet valves are open

Gauges / safety switches are in proper working condition & showing correct readings

Check the oil level in the frame sump & add oil as required Check the lubricator oil level & top up as required. Clean the lubricator sight feed glasses for

visibility as required.

After start up of the compressor always ensure that

To check the oil level in the frame sump at the line on the sight glass

Check the lubricator oil level at regular intervals & top up as required. Clean the lubricator

sight feed glasses for visibility as required

Check the drops per minute passed by each lubricator feed. Make sure all pumping units are

working. A schedule is established to periodically drain the separators to prevent a liquid carryover

into the compressor cylinder

Listen for any abnormal noise while the machine is operating

Drain all low points in the discharge pippings.

Pressure / temperature gauges & instruments visual check for proper functioning

Check / log the parameter readings at regular intervals & compare the same with earlier

readings

Check for any leakages

Keep the exterior of the compressor & the compressor room floor clean


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Donts do on reciprocating compressors

Never disconnect the safety shutdown devices & allow the unit to run unprotected

Never try to open any part of the compressor when the unit in operation.

When the unit is in operation, do not touch any of the compressor parts / accessory / piping

until you have made sure about the temperature as some parts / accessories are extremely

hot.

Do not operate the equipment in excess of its rated capacity, speed, pressures &

temperature because operation of the equipment in excess of its designed conditions will

subject it to stresses & strains which it was not designed to withstand & may result in an

accident causing personal injury or damage to property.


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GUIDELINES FOR RESTARTING COMPRESSOR

Take a close look at the compressor package for any signs of external and or internal damage

such as rusting / broken edges / damaged instruments etc.

If no serious damage is noticed, proceed with the following steps.

o Remove all inspection covers

o Inspect carefully al the internal parts such as crankshaft / connecting rod / bearings /

crossheads / piston rod. Check the bearing clearances. Replace the bearings if

required

o Remove cylinder head & take out piston & rod assembly. Check the condition of

piston rod & clean the same. Replace piston rings / wear rings. Check the clearances

of piston groove to piston rings.

o Inspect & clean cylinder bore. Lubricate the cylinder bore with thin film of

recommended grade of lubricating oil.

o While assembling the piston & rod assembly, check & record piston end ( frame end

& outer end) clearances

o Check & record piston rod run out

o Inspect oil scrapper rings / partition packing / main pressure packing. Replace if

required

o Drain the oil from crank case. Clean the crankcase internally. Flush the lube oil

system. Replace oil filters. Fill the crankcase with fresh lube oil (as recommended byOEM)


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o Start the auxiliary oil pump & check the oil pressure. Run the auxiliary oil pump for

at least 1hr.

o Start cooling water pump & check for cooling water pressure. Check cooling water

system for any leakages.

o Check all the safety switches for its functioning. Check & re-calibrate for alarm & trip

set points of safety switches.

o Remove inline gas suction strainer & thoroughly clean

o Clean the lubricator & fill with fresh lube oil. Check the operation of lubricator feed

pumps for proper functioning up to the end point

o Check for tightness of all the foundation bolts & piping supports

o Recheck the alignment with driver

o Replace all the gasket / O rings while reassembling compressor

o Before start up it is advisable to thoroughly flush the intake gas piping by

disconnecting the same from compressor inlet flange.

o Check operation of air exchangers ( coolers )o Check & recalibrate all the safety valves

o Pay attention while start up (especially lube oil pressure) of the compressor package

o Run the compressor on no-load initially & gradually put on load


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Log sheets / maintaining records

Any rotating equipment needs human intervention /inspection at regular & periodic travels.

It becomes important to note & record the operating parameters when the equipment is

running smoothly.

This helps to identify the trend of the machine performance in the long run

Log sheet records benefit to identify the possible fault that may in the near future, thus

possibly avoiding major failure.


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