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Bald Eagle Photograph by Don Petersen. A lovely reminder of our National Symbol.
The Second Continental Congress selected the Bald Eagle as the U. S. National Symbol on June 20, 1782.
The Bald Eagle is unique to North America, making them our eagle; they are strong and independent; they are survivors. They are majestic, bold, and faithful. They are a symbol of strength and determination.*
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A note from Steve
Happy 4th of July! We hope you all have a fun and safe holiday. It is amazing that we have already moved into the second half of 2023. The first half of the year has been busy for us developing new products and updating software to meet the needs of our customers. The Sentinel - VM has received an important update. I hope you will take a minute to read about all of the improvements we've added in the article below. Warren Laible has written a very informative article for you on diagnosing Suction Valve Leakage.
Steve
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Sentinel® - VM
Our new Sentinel®-VM software
is now available!
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Are you still using the old “Earthquake” switches on your reciprocating compressors to monitor and shut down your units on “Vibration”?
If you are, and have been for very long, you’ve probably seen a compressor fail without tripping the switch. Back in “The Day”, I had one of my mechanics call me late one night only to say the unit had a “Cast Iron Fit”, and parts were laying all over the sight. The earthquake switch never tripped, the panel showed that the unit went down on “Low Compressor Oil Pressure”, which was the first out indication.
Houston, we have a problem!
Well, we now have an affordable solution, and it does a lot more than provide a shutdown!
Our new Sentinel®-VM software is finished and is available. Not only does it provide indication of catastrophic failure, but more importantly it generates a Phased Waveform, in real time, along with an FFT, as well as a Trendline of the unit vibration over a user defined time period.
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While the whole idea of a vibration trace of a recip may be a new concept for many, the increase in electric motor drives, period defined inspections, reduced analyst staff, etc. has created a greater need for closer monitoring of vibration associated with reciprocating compressors.
With our new system and the included diagnostics, we have the ability to diagnose mechanical looseness, and even suggest where the problem might be based on the rotational speed, volumetric efficiency, gas load, inertial load, combined rod loads, and point in the stroke where the vibration occurs.
The alarm options include a normal, high, and high-high, with diagnostics attached.
We’ve also included a short video (below) illustrating the drill-down capabilities of the rotating software. This data was taken remotely from our live demo rotor, to illustrate the capabilities. We think it will be especially attractive for motor drive units.
We are very excited to announce this and include it in our ever-expanding software suite!
If you would like more details, don't hesitate to give us a call.
Bryan
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Drill-Down Capabilities of the Sentinel - VM Rotating Software | |
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Warren Laible, SME
MMS, LLC
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Diagnosing Suction Valve Leakage
In the last newsletter article, my comments centered around reciprocating compressor leakage in general.
This month I will limit the subject matter to suction valve leakage in cylinders with suction pressures above a vacuum.
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The leakage can be through the valve or around the valve via the seat gasket. Anytime that the valve is closed, and the internal cylinder pressure is greater than the suction cavity pressure, gas will leak back into the suction cavity. This will occur during the compression, discharge, and expansion processes in the cylinder end.
The gas temperature in the suction valve cavity will increase because the leaked gas is at a higher temperature than the suction gas. This higher temperature is then re-ingested into the cylinder during the next suction event. This can also increase the temperature of the other cylinder end in a double acting cylinder.
As with any internal recycle leakage, the cylinder discharge temperature goes up as it is directly related to the gas temperature at the suction toe and the compression ratio. This is also true for the other end of a double acting cylinder even if it is otherwise healthy. The cylinder end with the leaking valve will have the greatest increase in discharge temperature. The measured cylinder discharge temperature will be the blended temperature of both the healthy and unhealthy cylinders ends. This affects the flow rate calculations of the healthy end often resulting in a calculated flow balance greater than 1.00. The actual discharge temperature will be greater than the theoretical discharge temperature. The theoretical and more accurate discharge temperature of the healthy end can be calculated if there is a known gas k-value.
If you have access to a PV card, the measured suction volumetric efficiency (VE) will go up. In addition to the normal pressure drop in the cylinder during the expansion process, gas leaks out of the cylinder end causing the internal cylinder pressure to reach suction pressure earlier. The valve opens earlier; however, some of the gas now entering the cylinder was previously compressed. Flow calculations based on suction conditions are erroneously high.
During the compression process, the measured discharge VE decreases for the same reason. Since gas is leaking out of the cylinder during the compression process, a greater portion of the piston stroke is used to reach discharge pressure and the discharge valve opens later. Flow calculations will be lower than those made at suction conditions, but since gas is leaking back into the suction cavity during the discharge event, these calculations will still be too high.
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Some general observations are as follows:
- The valve cap over the leaking valve will get hot, but this is not a good indication as to the actual leak severity or the predictability of future leakage progression.
- In a single stage, low ratio pipeline application, temperature differences between a healthy and unhealthy cylinder may be small.
- In a multi-stage application, the unhealthy cylinder stage may only show a minor temperature increase since the compression ratio may drop because of the lower capacity; however, the discharge delta temperature (difference between measured and theoretical) 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 load in the cylinder may go up, go down, or remain relatively constant; however, in all cases the horsepower/mmscfd of gas moved will increase.
- Debris from a failing suction valve can often lead to discharge valve leakage and cylinder scoring.
- Complete sealing failure or an improperly installed suction valve may totally unload the cylinder end at suction pressure. If this is a crank-end cylinder, insufficient XH pin reversals may occur. The measured cylinder discharge temperature may return toward normal while the theoretical temperature stays high.
Many years ago, I had one customer that would run water on hot cylinders to keep temperature alarms from shutting down the unit if capacity was adequate for the process. One of my main reporting functions was to identify those cylinders that had totally unloaded so they could save cooling water.
Happy monitoring.
Warren
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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".
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!
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Fairview Technology Center
11020 Solway School Rd | STE 105
Knoxville, TN 37931
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