How To Bleed A Repaired Hydraulic Cylinder

One of our members writes:

"We have a simple hydraulic system: pump and iv double-acting cylinders. Nigh of the oil between the directional control valve and cylinders 'shuttles' back and along in the lines without returning to tank. The manufacturer of the system, Rexroth, tells me there is never a need for 'haemorrhage' air from the organization. How can this exist? There are occasions when we change a component and air gets into the system. It would seem merely natural to drain the air out. Why would Rexroth say it is not necessary? More importantly, how exercise you bleed such a system?"

More often than not speaking, air will piece of work its mode out of pretty much any hydraulic system over time. Even trapped air volition dissolve into the oil and be transported back to the tank somewhen.

Simply this is non to say that bleeding or purging of air is not a good thought to fast track the process. Reason being, air in the arrangement can exercise damage and consequence in erratic performance until it'southward removed.

Examples of damage caused by air contamination include:
–metal erosion resulting from collapse of air bubbles in the oil nether pressure;
–loss of lubricity resulting in friction, abrasion, scoring and seizing between lubricated surfaces; and
–dieseling in cylinders (ignition of air-oil mixture when compressed) resulting in damage to the cylinder and called-for of its seals.

Given this is the case, why would a manufacturer like Rexroth advise that air haemorrhage/purging is not necessary. My hunch is information technology's considering they have nothing to proceeds and everything to lose. If a pump burns-out due to aeration they get to sell you some other one (there's no warranty for this!). Merely if you get injured while haemorrhage air from the system on their recommendation, it's possible they'll end upwardly paying yous a couple million dollars. Tin you blame them?

Put but, it's a liability outcome for Rexroth — as information technology is for me were I to recommend that y'all do information technology, or tell you how to do it! Let'southward face up it; no one wants to cop a big fine for contaminating a work-site with oil spill, or worse, ending upwards with an oil-injection injury. So if you lot are going to bleed a hydraulic organisation, yous'd better make sure you know what the heck yous're doing. Because yous exercise and then at your ain risk.

But at that place is something I am happy to recommend y'all practice to minimize free and entrained air on start-upwards. And information technology'due south something you lot can do quite safely. I telephone call it: 'filling the voids'. And this principle is woven into the generic start-up procedure I outline on pages 103 to 107 of The Hydraulic Maintenance Handbook.

Basically information technology involves filling all voids with make clean hydraulic oil prior to starting the arrangement. For example, when you install a replacement cylinder, yous fill it with clean hydraulic oil through its service ports, before connecting its hoses. Same with pump and motor cases (e'er!), intake line between tank and pump(s), and and then on.

Sure, information technology'south not possible to make full every pipe, tube and hose in this manner prior to offset-upwardly. So bleeding can nonetheless be beneficial–if y'all accept confidence in yourself to do information technology safely. But if the system is left to purge itself, 'filling the voids' can make a significant divergence to the volume of air that has to be expunged. And that'south a good thing.

Because allowing a hydraulic system to operate while contaminated with excessive amounts of air is a costly mistake. And to discover six other costly mistakes you lot desire to be sure to avoid with your hydraulic equipment, get "Vi Costly Mistakes Virtually Hydraulics Users Make… And How Yous Can Avoid Them!" available for FREE download here.

How To Bleed A Repaired Hydraulic Cylinder,

Source: https://www.hydraulicsupermarket.com/blog/all/how-to-bleed-air-from-a-hydraulic-system/

Posted by: carlintaid1947.blogspot.com

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