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Hydraulic Training by J. Eric Freimuth Hydraulic Training Associates What Now?? Don’t you hate it when you have tried everything you can think of, and still can’t find the problem? This happens more than you can probably imagine, yet it is where I find the most fun - help- ing others find their problems, then directing them on how to fix them. Let me give you an example. I re- ceived a phone cal l from a fel low in Alaska. The conversation went some- thing like this: “Good morning HTA, Eric speaking.” “Good morning Eric, this is _____.” (Name removed to protect the innocent.) “I have a problem and I need your help.” “What’s up?” “My customer has a rig up here and they’re having a problem with the top- head drive. They had the pump gone through a couple of months ago, but it doesn’t seem to be working again. They have no pressure and can’t rotate the tophead any more.” “Okay, let’s take this slowly. First I need a schematic to help you.” “Well that’s not possible, there isn’t one available.” “Okay, then we need more informa- tion. What have you checked up to this point?” “All I know is that they have no charge pressure now, before it was down to 190 psi, and now it is totally gone.” “Have they checked the case flow and case pressure?” “No, they took off the pump and brought it in, I took it apart and I don’t see anything wrong...” This was the beginning of a lengthy discussion to get this person to see the big picture, to help him see what he wasn’t seeing. The answer was right in front of him, yet he was looking for some- thing bigger. He ended up taking digital pictures of the insides of the pump, as well as disassembling the motor and sending pictures of it. The customer sent in oil samples to be tested and they removed the filters. I had _____ cut the filters apart and examine it. I asked, “Do you see any indication of a major break- down?” Of course there wasn’t, but I needed to get him to slow down and see what should have been obvious. I end each class with an exercise on how to troubleshoot a system using a schematic. Unfortunately in this case, we didn’t have a schematic. Understanding the basic components used is a good second step. In this case, it was a Sundstrand MPV046 Hydrostatic pump, and the motor used for the tophead drive was a Rexroth bent axis motor. Being it is a hydrostatic system, there are some characteristics that are common, most all have flow going from pump to the motor and back to pump. What is lost through the case drain is made up by the charge pump. There is a charge pump relief which is set higher than the case pressure. This allows the makeup oil to be included in the system from the charge pump. If the charge pump relief pressure reduces due to a bad spring, broken spring, or is readjusted, then makeup oil will not return to the system and the pump and motor will cavitate. Cavitation is the result of lack of oil; it is very damag- ing to a system and in this case reduces flow to the tophead. The symptom was l ack o f p r essu r e and flow to the top- head, and the lines were f lexing vio- lently. Had our cus- tomer called while the pump was still a t t a c h e d t o t h e vehicle, we could have performed a few tests to verify ou r t heo r y. One such test would be teeing a gauge to the case flow side o f t he pump , as well as installing a f low meter in the c a s e l i n e . W e should have seen a marked increase of case flow and case pressure due to the relief opening and sending all charge pump f low to the case s i de o f t he pump. But this isn’t what was presented. So the next step was to help my customer see the big picture. The oil samples came back, and no larger than 15-micron elements were found in the oil. Under- stand here, it takes a 40-micron speck to be seen by the naked eye. There was indication something was starting to happen, but nothing catastrophic in nature. Bronze, aluminum, zinc, and magnesium were found in the oil, each components of brass which is what the shoes and valve plates are made of in the pump. Also found was wood, a very small amount, but nonetheless wood. After asking the customer, it was re- vealed they were using an engineer’s stick to check oil levels - not a good plan. We will have the conclusion next month. Eric admin@ worldwidedrillingresource.com 69 WorldWide Drilling Resource ® JULY 2014 0,2+ 675;,4 -57 5;,7 ',(78 /558, -753 +0--,7,49 35+,28 95 -09 >5:7 4,,+8 "(4.04. -753 36 95 36 4*2:+,8 %,/0*2, :36 #9(7904. (99,7> /(7.04. (4+ (4+ % 95 65<,7 &07,-,,+,78 0. (7708 "5(+ ,74+(2, ,< '571 $,2 (= &,) 809, <<< .,9,* *53 3(02 8(2,8 .,9,* *53 ',(78 5- =6,70,4*, 3(1, 9/08 204, 5- &,2+,78 (4 :43(9*/,+ !:(209> 75+:*9 04 95+(>?8 3(71,9 690548 04*2:+, 49,74(2 7,88:7, 536,48(904. 25< 549752 67,;,4904. (**0+,49(2 5;,786,,+ +(3(., 95 9/, &,2+,7 %,/0*2, :36 #9(7904. %5298 ( ,9,* ,=*2:80;, (99,7> /(7.04. %5298 (4+ % 95 65<,7 >5:7 0. :4 &07,-,,+ 589 536(*9 >+7(:20* &,2+,7 54 (71,9 (049,4(4*, 7,, ,80.4 0./9,89 >+7(:20* &,2+,7 54 (71,9