SLIDE 1 Compressor Over Lubrication:
Is It a Problem?
Gulf South Rotating Machinery Symposium
John P. Miguez
March 20, 2007
Sealing Solutions
SLIDE 2 # 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
SLIDE 3 We often don’t think of the additional costs involved with over
- lubrication. The chart below lists several average compressors
and the cost of oil, along with the cost of over lubrication by twice as much. It does not include hidden costs, such as disposal costs, packing, downtime and mechanic’s labor.
Costs of Over Oiling
SLIDE 4
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
SLIDE 5
Mechanical packing uses the cylinder’s internal pressure to collapse the three ring segments around the rod. As the pressure rises in the cylinder, the three segments are squeezed tighter and tighter around the rod’s OD, keeping the gas from escaping along the rod and into the distance piece and atmosphere.
How Packing Works
SLIDE 6
How Packing Works - 2
SLIDE 7 As the pressure is released with the opening
- f the discharge valve(s), pressure behind
the rings will cause the ring segments to move forward toward the piston end of the
- cylinder. At the same time, the rod reverses
direction with the start of the suction cycle. The resulting drag of the ring on the surface
- f the rod will result in the ring’s OD moving
faster than the ID, causing the ring to bow.
How Packing Works - 3
SLIDE 8
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 rings before they close up again to seal on the next compression cycle.
How Packing Works - 4
SLIDE 9
How Packing Works - 5
SLIDE 10
# Faster Speeds # Shorter Strokes # Type of Packing # Rods # Lack of Education on Oil System
Why Problem?
SLIDE 11 As compressor speeds have gotten shorter and the RPM increased, the time the packing rings have to seat themselves upon the start
- f the compression cycle has decreased.
A quick example will help to illustrate.
Why Problem?
Faster Speeds and Shorter Strokes
SLIDE 12 PA compressor with a 12" stroke running at 400 RPM will take (60/400)/2 = 0.075 second
- r 5/64th of a second to complete the
compression cycle, then reverse itself. PAt 1000 RPM, it takes 0.03 or 1/32nd of a second to travel the same 12". PAt 1800 RPM, we get 0.016 or 1/64th of a second.
Speed & Stroke
SLIDE 13
Stroke
To further compound the rings problems, as the time to seal gets shorter, the stroke goes from 12" to 5-6" to 3-4".
SLIDE 14 It is a tribute to engineering and manufacturing that this happens more
- r less correctly 99% of the time.
So, not only do the rings need to collapse around the rod in 1/64th of a second, they have only 3" in which to do so.
SLIDE 15
Rod Condition
Out of Roundness
SLIDE 16 Rod Condition - 2
RMS - Roughness of Surface
We want rods to have some roughness to them. The roughness allows the packing to wear to the proportions of the rod and seal better. The roughness also provides something for the oil to grab and hold on to as the gas pressure attempts to blow it out
- f the back of the compressor cylinder.
SLIDE 17 Importance of Lubrication
PServes as a coolant PWashes away particle matter and helps sealing PPrevents corrosion PReduces friction
The difference between perfect lubrication and no lubrication can be as high as a factor of 40. What this means is, the friction generated between a ring and rod with no lubrication vs. a properly lubricated ring would be the same as having 40 times more gas pressure on the same ring and rod. As an example, at 100 psi internal pressure, a frictional factor of 40 would generate the same amount of heat as having 4000 psi of pressure on the ring.
SLIDE 18 Importance of Oil - 2
Under normal circumstances, oil should be evenly applied to a film thickness of about 0.002 inches.
SLIDE 19 Oil Distribution System
Divider Block Systems
Yesterday Today
Drops per minute Drop size varies depending on pressure, temperature and viscosity of oil. Pints per day 28.876 cu in. in a pint 0.002 cu in. in a drop Divider Blocks distribute so many “cu in.” of oil per stroke.
SLIDE 20
Potential Problems with Divider Block Systems
PBlocks wear out PWrong size blocks PPump not adjusted correctly
Too much oil can lead to over lubrication problems!
SLIDE 21
Two Types of Over Lubrication
Too much oil is used during assembly
Can lead to failure to seal properly
SLIDE 22
Two Types of Over Lube - 2
Too much oil going into cylinder can lead to excessive heat, wear and premature failure of packing.
SLIDE 23
If rings don’t seal on start-up, look for little or no sign of wear marks on bore of packing rings. Packing that has been in a while will often be saturated with oil. Sometimes the radial and tangent rings will be stuck together. You may see forward extrusion and overheating.
Symptoms of Over Lubrication
SLIDE 24
Examples of Over Lubrication
SLIDE 25
Before anything else!
Ensure system is operating according to manufacturer’s specification.
PCheck pump size PCheck pump rate PCheck divider blocks PCigarette paper test
SLIDE 26 Checking Divider Block Sizing
Assumes the blocks are working correctly
P Measure divider block cycle time. P Calculate the recommended oil rate in pints per day. P Calculate time needed to inject above pints
- f oil into your cylinder.
SLIDE 27
Using a stopwatch or the second hand of a watch, measure the time for one complete cycle of the pin or LED flash. Record this time.
Divider Block Checking - Step 1
Measure divider block cycle time
SLIDE 28 Each manufacturer has published formulas used to calculate the normal rate of oil for its compressors. Most manufacturers call for one pint of oil per every 2,000,000 ft2 of cylinder surface area to provide a 0.002" oil film. Arial Compressors is 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 2
Calculate the recommended oil rate in pints per day.
SLIDE 29
- 1. Record the numbers stamped on the divider blocks. Add the
numbers 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 your cylinder.
SLIDE 30
If the timing is way off, you should get a qualified person to inspect the system.
Divider Block Checking
Your measured time and calculated times should be the same or close.
SLIDE 31 Example of an Ariel JGC 10" cylinder: Cylinder bore x factor of 0.5 (Factors are 0.3, 0.4, & 0.5 according to frame 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
SLIDE 32 P Warning: Oil usage should not be reduced
without considering each operating factor. Gas composition, gas pressure and separation equipment must all be factored into the equation.
P It is best to get a lubrication system expert involved
before reducing lubrication levels.
P Always follow the manufacturer’s recommended
procedures for reducing lubrication.
Solving the Problem
Remember, packing is cheaper than rods & pistons.
SLIDE 33 PWhen you lower the pump rate, you lower the
- il 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 before lowering the rate once again.
Too little oil will produce rapid wear of piston rings. Grit from the rings may plug up valves and be seen on packing rings.
Solving the Problem - Part 2
SLIDE 34
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.
SLIDE 35
Ariel’s Response
Ariel engineers were asked why they recommend so much more oil than other compressor manufacturer’s?
SLIDE 36
Ariel’s Response - Part 2
SLIDE 37
Ariel’s Response - Part 3
SLIDE 38
Ariel’s Response - Part 4
