When cutting a new hydraulic hose from a roll of bulk hose, install the new fittings, then flush the hose with a lightweight oil to wash all of the shavings out of the hose. Otherwise, you could introduce rubber and metal braid shavings into the hydraulic system.

When flushing a hose with oil, make sure the flushing oil is compatible with the hydraulic fluid used and that the velocity of the flush is about twice that produced by the system's hydraulic pump. Another way to clean hydraulic hoses is to use pneumatic projectiles (sponges) that push through the hose to clean out debris.

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Book Bits: Planning PM Frequencies

From "Maintenance Planning and Scheduling Handbook"

The PM frequency is one of the most subtle areas for the planner to manage. If a particular piece of equipment fails only once every two years, the appropriate frequency for cleaning or inspection may still be once every month. This is because PM frequencies must be set by age of installation, likely failure modes, and criticality to plant process instead of previous failure rate.

Once the plant installs the equipment, that equipment must work through an early period during which it has a higher than normal chance of failure. Newly installed equipment should be inspected more often than older equipment for signs of failure. After the proving period, PM frequencies might be lessened. Certain equipment also has certain favored failure modes. A valve may exhibit a sticking symptom several weeks before failure to operate. A flange may drip months before leaking bad enough to cause a problem. The sound of cavitation may indicate a future pump problem.

The PM frequency should take into account the time between the appearance of a particular symptom and the time the equipment may be restored to proper operating time without experiencing a failure. In addition, certain failures may not interrupt plant operation because of being in nonessential services or having installed spare equipment the operators can utilize. If these failures do not cause more extensive repair operations than would be necessary to prevent failures, the plant may exercise a strategy of minimal PM effort or attention to set frequencies. On one hand, the planner wants to set PM frequencies to minimize failures and generate corrective work orders. On the other hand, the planner does not want to set excessively short PM frequencies that would overtax personnel resources. The planner must balance these plant needs.

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"About a year ago we ran a lubricant too long in a high-duty gearbox and it oxidized and threw sludge. Since then, we've been watching the oil more closely with oil analysis. The problem is that acid numbers rise and the oil darkens after only one month of service. The lubricant used to last a full year. We keep changing the oil but the problem just repeats. Why does our gear oil have such such a short life?"

It sounds like the gearbox was not thoroughly flushed after the oil oxidized the first time. Typically, a simple drain will leave more than 15 percent of the old oil behind - occluding to machine surfaces and trapped within the casing. This also leaves a host of reactive chemicals (pro-oxidants) behind that rapidly deplete antioxidant additives, leaving the base oil unprotected.

You refer to the gearbox as high-duty, which probably means high temperature and high wear metal production. The temperature and wear particles also accelerate the rate of oxidation, especially when sludge and other pro-oxidants are in the mix. I suggest you perform a thorough flushing of the gearbox. Read more about flushing.

Jim Fitch, Noria Corporation

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