![\"Hydraulic](\"https:\/\/hydroazma.ir\/wp-content\/uploads\/2022\/11\/Vickers-PVB-pump-repair.jpg\" "\\"Hydraulic")
<\/figure>\n\n\n\nAs usual, the estimate got approved by the client, the work was performed by most skilled specialists, the pump was tested and upon the successful test shipped out\u2026 to come back on the very next day with a shattered slipper retainer ring and an angry owner, carrying it in a bucket.<\/p>\n\n\n\n
Now I would like to let you in on a little secret \u2013 the parts used for this repair were\u2026 well\u2026 it\u2019s not that they were \u201cpirate\u201d or \u201cwhite-market\u201d or something, no, of course not\u2026 \u2013 they were\u2026 hm\u2026how do I put it?\u2026not quite original, or genuine, if you like\u2026 yes, that\u2019s what they were\u2026 Anyways, the shop foreman was aware of the \u201csham\u201d, therefore a decision was made to assume the warranty claim and quietly replace the damaged parts with original Vickers. The pump was, once again, repaired and delivered to the rightful owner. However, the next day\u2019s morning brought along a beautiful sunrise and the already familiar bucket with the very same pump inside!<\/p>\n\n\n\n
The damage was another \u201cdeja-vu\u201d \u2013 the shattered retainer plate with mashed piston slippers and what not\u2026 It was at that time that the questions were made about the pump\u2019s working conditions. Naturally, the first suspect was the excessive case pressure \u2013 which would be the most common cause of this type of failure \u2013 and the client was asked to confirm how many hoses were connected to the pump. Since it was the man himself who\u2019d dismounted the pump, he was sure about the answer and said \u2013 two hoses \u2013 one for the suction line, and the other for the pressure line. And what about the drain line? \u2013 Nope! No drain lines here \u2013 just these two\u2026 All the other \u201cpump holes\u201d are plugged\u2026 Aha! \u2013 So it is your fault! You can\u2019t run these pumps without drain lines! \u2013 To which the man responded that of course, he knew nothing about oil hydraulics and them pumps, but he was one hundred percent positive that it\u2019s the way this machine had been for the last five years, and he owned two more equal haulers that had these hydraulic pumps connected in exactly the same manner\u2026<\/p>\n\n\n\n
The argument went on and on \u2013 with one party pointing out the obvious fact that no pumps of this type could possibly survive working with a plugged case line, while the other party saying that despite all this at least three machines had these pumps mounted with all case ports plugged and only two hoses connecting to the pump, being those the pressure and the suction lines\u2026 The endplate of the pump was inspected from all possible angles \u2013 to see if there was a \u201chidden\u201d passage or a check valve that would connect the case to the suction line, which indeed would allow this pump to work without an external drain line, however, no such passage was found \u2013 the endplate was a solid chunk of metal, with isolated tank and pressure sides \u2013 so, \u201cmechanically speaking\u201d this pump had to have a drain line \u2013 otherwise the internal leakage would cause the case pressure to go up and eventually break the retainer plate \u2013 with all the following\u2026<\/p>\n\n\n\n
As I \u201cdropped by\u201d \u2013 my opinion on the subject was asked. I was even asked if I could dislocate to the client\u2019s business site to check if these pumps indeed were connected the way the man was saying they were. When I saw the pump lying on top of a workbench \u2013 one small detail caught my eye, and to confirm my suspicions I asked if I could remove the shaft \u2013 \u201cto check something\u201d.<\/p>\n\n\n\n When I removed and inspected the shaft \u2013 I knew exactly what was going on here\u2026 And immediately voiced my \u201cverdict\u201d that both<\/strong> arguing parties were right! The workshop was right to defend the fact that this pump couldn\u2019t work without a drain connection, and the owner made no mistake when he said the pump had only the pressure and suction lines connected to it, and all the drain ports were plugged. But how?!!<\/p>\n\n\n\n The answer is \u2013 this pump is the tail pump in a two-pump tandem assembly, and its case oil is being drained thought the shaft bearing<\/strong> into the case of the front pump \u2013 which also means that it can only work without a shaft seal!!!<\/strong> But how could we know that? Well \u2013 first of all, the mechanic who disassembled the pump should have noticed and questioned the fact that it didn\u2019t carry any shaft seal in the first place, but even if he didn\u2019t, or if a different mechanic were to assemble the pump \u2013 there were still three sure tell signs present.<\/p>\n\n\n\n First \u2013 there was no mark on the sealing surface of the shaft (sorry \u2013 no picture here) \u2013 any shaft seal leaves a mark, especially after several thousand hours of work.<\/p>\n\n\n\n Second \u2013 the drain port was plugged, and the plug was properly tightened \u2013 in most cases, you can tell a difference between a plug that\u2019s just been lightly tightened for transportation purposes and a plug that\u2019s been sitting there untouched for the last couple of years.<\/p>\n\n\n\n Third \u2013 the front bearing had no shields. In a standard PVB the front bearing is shielded and has grease inside \u2013 in this case, the shields were removed to let the oil flow through the bearing. It was this \u201csmall detail\u201d that caught my attention when I saw the unit lying on the workbench.<\/p>\n\n\n\n So, there you have it, folks, \u2013 some hydraulic equipment manufacturers opt for replacing the standard external drain connections of pumps and motors with removed shaft seals. Obviously, this solution is only viable for relatively low drain flow rates and only for tandem units, or when a pump (or a motor) is connected to a gearbox, in which case the leakage oil also serves for the gearbox lubrication\/cooling purposes (older Atlas Copco core drilling units, for example). It is very important to identify these units and serve them adequately, and if the shaft seal is needed to perform bench tests, it should be removed after the tests are finished \u2013 otherwise, there is a serious risk of \u201cover-fixing\u201d the unit and causing serious damage to the client\u2019s machine as well as the shop\u2019s reputation!<\/p>\n\n\n\n![\"Hydraulic](\"https:\/\/hydroazma.ir\/wp-content\/uploads\/2022\/11\/Vickers-PVB-pump-repair2.jpg\" "\\"Hydraulic")
<\/figure>\n\n\n\n![\"Hydraulic](\"https:\/\/hydroazma.ir\/wp-content\/uploads\/2022\/11\/Vickers-PVB-pump-repair3.jpg\" "\\"Hydraulic")
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