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by Dom Ruggeri


During my career I have seen many configurations for central systems.  You might say I have seen them all.  Then again, every time I have said, “Now I’ve seen everything”, something else happens to prove me wrong.

I was working at a major formulating house and hadn’t been in the field for quite some time.  I was actually enjoying a normal working schedule, but I knew that would change.  One day in early March of 1990, my manager hands me a plastic bag containing aluminum parts.  These parts were used in automotive air conditioning compressors.  A quick inspection revealed a sticky coating on the parts, and small plastic balls sticking to the residue.  My manager informed me that the balls were shot at the machined parts as part of a deburing operation.  The problem was that the residue was compromising this operation.  Of course we were on the verge of losing the business, and the alleged reason was the unresponsiveness of the lab.  I will admit a 50,000-gallon central system is a sizeable chunk of business.

After a meeting with the division manager, I flew out to the account.  My goal was two fold; to ascertain, and if possible, fix the problem on-site.  Experience, the best teacher, taught me that these types of problems could go either of two ways; the customer really wants the problem solved, or you were not responsive enough therefore you lost this system (customer).  I met the salesman and we became fast friends.  He informed me the situation at this account was serious at best.  He also told me this problem had been around for quite some time and the shop managers were at their wits end.

The shop was old circa WWII.  This facility did not number their systems, they named them.  The troublesome system was called the Elfwich System.  I asked why, but no one knew.  I made note they were using a compatible hydraulic fluid so tramp oil was not an issue. 

The salesman and I toured and observed the Elfwich System.  We noticed no coolant related machining problems.  However, when the coolant dried there was a tacky residue left on the parts.  The operators had to clean off this residue with a solvent and the plastic balls were dissolving in the solvent.  All in all, a very bad situation.  I spoke to the shop chemist and checked the system maintenance records.  I had to admit they were real good at controlling the concentration but that was about all they controlled. I suspected a biological problem but this coolant was ester based and the characteristic sweet ester odor masked the biological odors.  I left the shop and assured the shop management team I would solve this problem.  My laboratory work revealed that the tacky residue was from biological contamination.  The lack of biological control and the compatible hydraulic fluid effectively masked the problem until it was out of control.  We did loose that system.  The customer felt we could have solved the problem sooner.

Through out my career there has always been the question of which is better, a central system or single sump machines.  This series will focus on caring for the central system.  After that the editor and I will perhaps discuss the merits and downfalls of both central systems and single sumps.  No matter how many central systems you see, they will all have these same basic elements.  The only difference is in how they are configured:

  1.     A clean tank or clean side: this area will hold and feed coolant to the machining sites. It can be a pit in the floor up to an above ground poly tank.

  2.     A dirty tank or dirty side: this area holds the coolant that is returned from the machining sites.  Once again it can be a pit in the floor to an above ground tank. Here the coolant is allowed to sit quietly so that tramp oil can rise to the surface and be skimmed off and if present, metal fines can settle to the bottom of the tank to be disposed of later.

  3.     Filtration system: These come in many shapes and sizes from a media type such as paper to separation types as a wyer system.  Which is in place best depends on the company and what type of operations they are performing.

  Of course there are many other add-ons to central systems such as magnetic separators, various coalesors and the list can go on. The only limit is the budget. 

 I always found trouble-shooting a central system to be easier then single sump systems.  Why?  Well if the system is feeding 100 machines and you have a foaming problem then that problem will be in 100 machines.*  However, if the problem is occurring in only one or two machines out of 100, that eliminates the coolant as the source of the problem.**  An over simplification, yes it is but for now it will suffice. I will be addressing many problems in this series if you have a particular concern or a question let me know I will be happy to include an answer in a future article.

Good Luck



Editor’s counterpoints:

* This point is a good argument for independent sumps.

** While Dom's generally right, there are exceptions to this rule.  Unfortunately, management of individual sumps is more complicated, and often an individual machine problem with the coolant can occur, similar to the example discussed.  I suppose it really depends on what we classify as “coolant” problems.