mini logo.png

Our customers come first.

Visit our Website

September 2023 Newsletter

A note from Donna

At MMS we believe in putting our customers in the forefront of our business. Our team is focused on developing machinery health monitoring products with the latest technologies. We know our customers’ success is enhanced, not only by training users to use the new equipment but also by sharing knowledge which comes from decades of experience.  


Our team of Subject Matter Experts have a collective goal of being good stewards in the industry by providing basic technical education for the next generation of oil and gas professionals. All too often valuable “hands on” knowledge and lessons learned through experience are lost from one generation to the next. Understanding the “why” behind equipment issues is valuable when diagnosing problems when they arise. Our self-paced basic technical courses are available online for a nominal cost.  


We hope you have found the new series of articles by our Compressor Professor, Warren Laible beneficial over the past few months. Warren’s past articles are always available on our website at https://mmsysllc.com/newsletters. In this month’s newsletter Warren is discussing Ring Leakage. We invite you to offer topic suggestions you are interested in for future articles.  

Donna


Donna J. Stewart

VP Marketing & Training

The Compressor Professor

Warren Laible, SME

MMS, LLC

Ring Leakage



In past newsletter articles, my comments centered around reciprocating compressor suction and discharge valve leakage. This month I will limit the subject matter to piston ring leakage.

Ring leakage is a recycle leakage between the cylinder ends. The leakage can be over the rings, through the rings, under the rings or around the rings (through the piston).

My comments here are limited to a double acting cylinder with the rings leaking relatively the same in both directions (broken and/or missing rings). Yes, it is possible for rings to leak in one direction and not the other.


As with any internal recycle leakage, at a constant ratio of compression, the cylinder discharge temperature goes up as it is directly related to the gas temperature existing at the suction toe and the compression ratio. The actual discharge temperature will be greater than the theoretical discharge temperature.


I will attempt to explain the leakage characteristics using the attached PV illustration as an example.

When the piston is at the BDC position, there is maximum cylinder volume and low pressure in the head-end and minimum cylinder volume and high pressure in the crank-end. At this condition, gas is leaking from the crank-end into the head-end. This is like a suction leak to the crank-end and a discharge leak to the head-end. This condition continues at a diminishing rate until the differential pressure across the rings equalizes. In our example, this occurred around 10%-cylinder displaced volume. For the rest of the piston travel toward TDC, the pressure is higher in the head-end than the crank-end. This becomes suction leakage to the head-end and discharge leakage to the crank-end. This transition near the pressure reversal point, from discharge to suction leakage, creates a “hump” in the pressure trace. From this point until the second pressure reversal occurs, gas continues to leak from the head end to the crank-end.


As the piston approaches TDC, and if the leakage rate is great enough, there may be a premature pressure drop in the head-end cylinder and a corresponding pressure rise in the crank-end cylinder, creating “rounded suction and discharge toes”. As the piston now moves toward BDC, the head end continues experiencing suction leakage and the crank-end, discharge leakage until the pressure reversal again occurs, in this example, approximately 10% into the stroke (there is that “hump” again). The conditions again reverse and now the head end is experiencing discharge leakage, and the crank-end, suction leakage. This continues back to BDC and again, we see the “rounded toes”.


It's all rather complicated but wait till you have a cylinder with multiple defects. We will save that conversation for a later article.

Some general observations for pure ring leakage are as follows:


  • The discharge delta temperature will increase significantly.
  • Calculated flow balances will be greater than 1.00 on both cylinder ends and calculated flows will be excessively high.
  • Leaking rings alone do not raise the cylinder suction cavity temperature.
  • In a single stage, low ratio pipeline application, discharge temperature differences between a healthy and an unhealthy cylinder may be small.
  • In a multi-stage application, the unhealthy cylinder stage may only show a minor temperature increase since the stage compression ratio may drop because of the lower capacity; however, the discharge delta temperature will go up.
  • The horsepower, rod load, and pin reversals in an unhealthy cylinder are still measured accurately by the analysis equipment, whereas the accuracy of theoretical models may suffer significantly. 
  • The actual horsepower/MMSCFD will go up.
  • In multi-stage applications, healthy stages may experience higher than normal discharge temperatures and changes in rod loading and pin reversals due to higher ratios of compression pressure.


Happy monitoring,


Warren

We'll be at the GMRC in Phoenix.

Visit us in booth 211.

Training and Development

Have you hired an intern this year?

If you have new technical staff or interns you may want to provide them with the Engine Mean Peak Firing Pressure Balancing course offered by our team at MMS. It contains relevant information about engine balancing provided by industry experts. 


Why using the right equipment is important in Engine Balancing

The pressures being collected by the balancer must be an accurate representation of the combustion pressures in the cylinders. The condition of the pressure sensor, the condition of the indicator passage and valve, the presence of resonant pressure waves in the pressure trace, or leakage in the indicator path will prevent an accurate balance.


Engine Mean Peak Firing Pressure Balancing is a course designed to support our

customers' needs for training both new and/or inexperienced personnel the theory (why) and the basics (how) of balancing an engine and why balancing is important to the health and safety of the equipment. This course is offered as a self-paced course through the mmsysllc.com website.


This dynamic course was developed by the MMS team including Warren Laible, the well-known Subject Matter Expert for engine health and Bryan Stewart, who has over 40 years of experienced with gas engines.


To learn more about the theory and practical application of balancing an engine or for more information about the Engine Mean Peak Firing Pressure Balancing course contact MMS or your Exline Sales team. You can also Contact Us through our website.

MMS Learn

Building a Community

Gear Head Blog


Have you visited the blog yet? You will find some great images of what our friends in the industry are doing in their spare time with their own "Rides". 


Check out Kent's sailboat post!


We invite you to participate in the Gear Head Blog found at https://www.mmsysllc.com/blog/ “Tell Us About Your Ride” Take a look at what great projects are posted there and provide comments to keep our conversation going. 


We look forward to hearing from you! 

Gear Head Blog
mini logo.png

Fairview Technology Center

11020 Solway School Rd | STE 105

Knoxville, TN 37931


Contact Us