Compressor OverLubrication:Is It a Problem?

Gulf South Rotating Machinery SymposiumJohn P. Miguez

March 20, 2007

Sealing Solutions

# Costs of the problem

# History of compressors

# Review of how packing works

# Why are we now having a problem?

# Types of over lubrication

# How to determine if you are over lubricating

# What to do about over lubrication

We Will Discuss

We often don’t think of the additional costs involved with overlubrication. The chart below lists several average compressorsand the cost of oil, along with the cost of over lubrication by twiceas much. It does not include hidden costs, such as disposalcosts, packing, downtime and mechanic’s labor.

Costs of Over Oiling

P First compressors were steam engines

P Early packing rope and axle grease

P Late 1800s - Charles Cook: Mechanical Packing

P 1900 - A. O. France: Modern Packing Design

P 1960 - Ray Farrell: Liquid Cooled Packing Case

P 1980s - Ariel Compressors dominates market

P 1990s - Faster speeds and shorter strokes

A Brief History of Compressors

Mechanical packing uses the cylinder’sinternal pressure to collapse the three ringsegments around the rod. As the pressurerises in the cylinder, the three segments aresqueezed tighter and tighter around the rod’sOD, keeping the gas from escaping along therod and into the distance piece andatmosphere.

How Packing Works

How Packing Works - 2

As the pressure is released with the openingof the discharge valve(s), pressure behindthe rings will cause the ring segments tomove forward toward the piston end of thecylinder. At the same time, the rod reversesdirection with the start of the suction cycle.The resulting drag of the ring on the surfaceof the rod will result in the ring’s OD movingfaster than the ID, causing the ring to bow.

How Packing Works - 3

You can also get a torque effect on the ring,which causes it to spin around the rod.

The end result is a three dimensional opening,closing, flexing and spinning of the ringsbefore they close up again to seal on the nextcompression cycle.

How Packing Works - 4

How Packing Works - 5

# Faster Speeds

# Shorter Strokes

# Type of Packing

# Rods

# Lack of Education on Oil System

Why Problem?

As compressor speeds have gotten shorterand the RPM increased, the time the packingrings have to seat themselves upon the startof the compression cycle has decreased.

A quick example will help to illustrate.

Why Problem?

Faster Speeds and Shorter Strokes

PA compressor with a 12" stroke running at400 RPM will take (60/400)/2 = 0.075 secondor 5/64th of a second to complete thecompression cycle, then reverse itself.

PAt 1000 RPM, it takes 0.03 or 1/32nd of asecond to travel the same 12".

PAt 1800 RPM, we get 0.016 or 1/64th of asecond.

Speed & Stroke

Stroke

To further compound the rings problems, as the time to sealgets shorter, the stroke goes from 12" to 5-6" to 3-4".

It is a tribute to engineering andmanufacturing that this happens more

or less correctly 99% of the time.

So, not only do the rings need tocollapse around the rod in 1/64th of

a second, they have only 3" inwhich to do so.

Rod Condition

Out of Roundness

Rod Condition - 2

RMS - Roughness of Surface

We want rods to have some roughness to them. The roughness allows the packing towear to the proportions of the rod and seal better. The roughness also providessomething for the oil to grab and hold on to as the gas pressure attempts to blow it outof the back of the compressor cylinder.

Importance of Lubrication

PServes as a coolant

PWashes away particle matter andhelps sealing

PPrevents corrosion

PReduces friction

The difference between perfect lubrication and no lubrication can be as high as afactor of 40. What this means is, the friction generated between a ring and rod withno lubrication vs. a properly lubricated ring would be the same as having 40 timesmore gas pressure on the same ring and rod.

As an example, at 100 psi internal pressure, a frictional factor of 40 would generatethe same amount of heat as having 4000 psi of pressure on the ring.

Importance of Oil - 2

Under normal circumstances, oil should be evenly applied to a film thickness of about0.002 inches.

Oil Distribution SystemDivider Block Systems

Yesterday Today

Drops per minute

Drop size variesdepending onpressure,temperature andviscosity of oil.

Pints per day

28.876 cu in. in a pint0.002 cu in. in a drop

Divider Blocksdistribute so many “cuin.” of oil per stroke.

Potential Problems with DividerBlock Systems

PBlocks wear out

PWrong size blocks

PPump not adjusted correctly

Too much oil can lead to over lubrication problems!

Two Types of Over Lubrication

Too much oil is used during assemblyCan lead to failure to seal properly

Two Types of Over Lube - 2Too much oil going into cylinder can leadto excessive heat, wear and prematurefailure of packing.

If rings don’t seal on start-up, look for little or nosign of wear marks on bore of packing rings.

Packing that has been in a while will often besaturated with oil. Sometimes the radial andtangent rings will be stuck together.

You may see forward extrusion and overheating.

Symptoms of Over Lubrication

Examples of Over Lubrication

Before anything else!

Ensure system is operating according tomanufacturer’s specification.

PCheck pump size

PCheck pump rate

PCheck divider blocks

PCigarette paper test

Checking Divider Block Sizing

Assumes the blocks are working correctly

P Measure divider block cycle time.

P Calculate the recommended oil rate inpints per day.

P Calculate time needed to inject above pintsof oil into your cylinder.

Using a stopwatch or the second hand of a watch,measure the time for one complete cycle of the pin orLED flash. Record this time.

Divider Block Checking - Step 1

Measure divider block cycle time

Each manufacturer has published formulas used to calculate thenormal rate of oil for its compressors.

Most manufacturers call for one pint of oil per every 2,000,000 ft2 ofcylinder surface area to provide a 0.002" oil film. Arial Compressorsis the major exception to this formula.

Example of CP/EI/Gemini compressor FE650 (D Series):

(Bore (in) x Stroke (in) x RPM)/31,800

10"x 6.0" x1000 = 60,000

60,000/31,800 = 1.89 pints/day

To this we must add the packing case needs.

2" rod uses 1.5 pints/day.

Total oil needed is 3.38 pints per day for this cylinder.

Divider Block Checking - Step 2Calculate the recommended oil rate in pints per day.

1. Record the numbers stamped on the divider blocks. Add thenumbers and multiply by 6.

2. Divide the result by the recorded cycle time and compare the two.

Example of CP/EI/Gemini compressor:

(Value of divider blocks) x 6/number of pints per day

(9 + 6) = 15, 15 x 6 = 90

90/3.38 = 26.6 seconds

Divider Block Checking - Step 3

Calculate time needed to inject 3.38 pints of oil into yourcylinder.

If the timing is way off, you should get aqualified person to inspect the system.

Divider Block Checking

Your measured time and calculated timesshould be the same or close.

Example of an Ariel JGC 10" cylinder:

Cylinder bore x factor of 0.5 (Factors are 0.3, 0.4, & 0.5 according toframe model)

10" x 0.5 = 5

For the rod, the OD is doubled and the same factor is used.

2.5 x 2 = 5 5 x 0.5 = 2.5

So the number of pints recommended by Ariel is 5 + 2.5 = 7.5 pt/day.

Checking an Ariel Compressor

P Warning: Oil usage should not be reducedwithout considering each operating factor. Gascomposition, gas pressure and separationequipment must all be factored into the equation.

P It is best to get a lubrication system expert involvedbefore reducing lubrication levels.

P Always follow the manufacturer’s recommendedprocedures for reducing lubrication.

Solving the Problem

Remember, packing is cheaper than rods & pistons.

PWhen you lower the pump rate, you lower theoil rate to each part of the system. < Consider resizing divider blocks.

POnly reduce oil flow by about 5% at a time. Allow the compressor to run a week or two.Then inspect for excessive ring wear beforelowering the rate once again.< Too little oil will produce rapid wear of piston rings.

Grit from the rings may plug up valves and beseen on packing rings.

Solving the Problem - Part 2

P Ariel Compressor (arielcorp.com)

P AAVOLYN Corp. (aavolyn.com)

P Hanover Compression (hanover-co.com)

P M&J Valve Services (mjvalve.com)

P Pro-Gress (progressive-equipment.com)

P Hasu Gajjar & Assoc. (Hasugajjar@aol.com)

Thank You!

The following companies helped me with this presentation, Listing their names is not meant to imply endorsement of

any kind. It is to thank them for helping.

Any errors are mine, and mine alone.

Ariel’s ResponseAriel engineers were asked why they recommend so much

more oil than other compressor manufacturer’s?

Ariel’s Response - Part 2

Ariel’s Response - Part 3

Ariel’s Response - Part 4