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Baseline Your Vacuum Pump to Make Troubleshooting Easier

Posted by Tim Collins on Jan 12, 2015 3:00:00 PM

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Overview:

Baselining a vacuum pump helps establish the basic criteria for how it performs in a controlled environment.  This baseline can be used to compare current performance with the originally installed performance.  This article covers the following key aspects of baselining:

  • What do baselines and diets have in common?
  • What are the downsides of not baselining a pump?
  • What is the best way to baseline a pump?
  • How can baseline information be used to solve problems?

To start with... what do baselines and diets have in common?


Diets and Pump Baseline Data have 2 key things in common:

  1. They aren't required (however, manufacturers strongly recommend baselining pumps); and
  2. Most of the free world doesn’t really do them well. 

A good diet has a start point, an end-point, a plan to get there and metrics that illustrate success. For example, I'm 220 pounds now, I'll run 2 times a week and lay off the sweets, and in 3 months I'll weigh 200.

Similarly, a good maintenance program for vacuum pumps used in research or production would involve 1) characterizing the pump, 2) defining acceptable limits for the pump in terms of ultimate base pressure and 3) time to get there, expected maintenance interval, and expected rebuild interval.  This information should be kept in a safe place.

What Are the Downsides of Not Baselining a Pump?

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The vacuum pump is the only source of vacuum in the system and one of the easier parts to analyze when trouble arises, and it helps you understand what is right and what is wrong.  When you originally specified your pump, you probably chose components with engineering margin, meaning they are a little better than what you needed.  This allows you to have an idea of what would work in your application, and what ultimate vacuum pressure would make your system unacceptable.

By documenting the pump baseline, it gives you a reference for comparison.  If you don't have this reference, you are making educated guesses at what will or won’t work.  When your system isn't working and you have 16 variables to consider, wouldn't it be helpful to be able to confidently eliminate at least 1 of the most important variables quickly: the vacuum pump?

What is the Best Way To Baseline a Pump?

Each pump manufacturer has specifications on how their pump is supposed to perform. Baselining a pump, to the manufacturer's specifications, is really simple.  There are 2 things to track: the ultimate base pressure and how long it takes to get there. 

Here is a method for doing a simple pressure vs. time curve:

  1. Start with a brand new or refurbished vacuum pump.
  2. Use an accurate, thus trusted, vacuum gauge on the top of the pump inlet port.
  3. Turn on the vacuum pump.
  4. **Note the start time and pressure (0 seconds and ATM for example).
  5. Take a note of several time and pressure points in between.
  6. Note the ultimate base pressure of the pump and the time it took to get there (i.e., how low a pressure /how high a vacuum).  Typical numbers for a 2 stage pump might be 15 millitorr and 5 minutes. This would be a good time to verify you got the performance that you paid for.
  7. Put this information in a safe place where you can find it, e.g., a dated and signed label on your vacuum pump (best option), in your preventative maintenance log or in the maintenance section on a server. 
  8. Bonus: at the time of baseline, define acceptable limits.  For example, "as long as the pump can achieve 50 millitorr in 20 minutes, my application will still run fine."

How Can Baseline Information Be Used to Solve Problems?

When there is a problem, baseline information is extremely useful.  Often one of the first steps when troubleshooting a vacuum system is figuring out why the system is not achieving the vacuum specified for a process to continue.  This can be due to several things, such as an erroneous gauge reading, a failing vacuum pump, or a leak in the system.  A failing vacuum pump is often the easiest one to eliminate, so start there.  Do a pump-down curvecollecting the data in the same way you did to achieve the baseline data.  Now compare the baseline to the new pump down curve:

  • Has the ultimate vacuum pressure been reached?
  • How long did it take to get there?
  • Are these results the same, or close enough to the baseline for the system to perform as needed?

Knowing how to easily take pressure vs. time curves on both initial install and during maintenance windows can help to quickly eliminate the vacuum pump as the source of a vacuum system problem.  

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Topics: Vacuum Pump Repair, Vacuum Pump Rebuilding, Accuracy, Vacuum Pump Troubleshooting