by Victor A. Popp
from Hydraulics & Pneumatics, September 98

If there is one thing that engineers can learn from the spin-doctors in Washington, it's how to spin straw into gold. With proper phraseology, product flaws can become features. This lesson could not have come at a more opportune time, because hydraulic component manufacturers with their zero-leakage products, have left OEMs holding the bag on leaks!

The ball is in our court to either learn leak-free technology, or to avoid using the L-word when explaining to our customers how oil got past the seals. We OEMs have always struggled with words to quantify and qualify oil on customer's floors in our noble efforts to justify hydraulics. If Eskimos have some two dozen words to describe snow and ice, shouldn't engineers have an arsenal of terms for oil that doesn't get back to the reservoir?

A seal salesman made me realize the need to redefine the puddle-causing phenomenon. "That's seepage, not weepage," he said, as he observed the oil on my fingertip, which I brought precariously close to his fine silk tie. In my ignorance I did not know the difference. Instead I dumbly point to the large puddle. He was glad to explain that the military defines seepage as oil that can be seen but does not drip. Weepage forms puddles. I explained to him that puddles were forming on my boss's desk, caused by his weeping over this shipment; and that his grieving process would include sabotaging my next performance review.

We did fix the leak, and ship; but afterwards I was unsettled. Perhaps by taking a strictly classical engineering view of things, I had limited myself. Perhaps by enhancing my vocabulary, and spinning a few words, I could have shipped that machine as a "device with non-constrained fluids."

If mil specs can distinguish between weepage and seepage, perhaps I should adopt some new, more-specific definitions to maximize confusion. Stealing from the military (a federal crime in most instances), I propose that we begin with their seepage and weepage.

Seepage--a slow diffusion of oil molecules past a seal. It can be aided by mechanical motion of the sealing surfaces. It will not form a puddle, but can nonetheless ruin a pair of nice trousers!

Weepage--a more rapid passage of oil past a seal, due to scratches and micro surface variations of the seal or sealing surfaces. Get out the Speedi-Dry!

Oozing--caused by insufficient seal stress due to improper tolerancing of parts or machining flaws. Oozing causes puddles--as well as heartburn in field service personnel.

Dripping--produces puddles that show the degree of levelness of the surfaces on which they form.

Spilling--when fluid travels from the aforementioned surface to the floor. As this phase advances, it is called streaming. A puddle whose length-to-width ratio is greater than 10:1 defines streaming also. This ratio was chosen rather arbitrarily--by me. If a more scientific ratio is needed, it will have to be funded by a research grant.

Flowing--when fluid streaming velocity is greater than 1 ips. It is usually characterized by maintenance department padlocks on the electrical disconnects, and visits from the EPA.

Pouring--when the fluid reaches the floor without any seepage, weepage, oozing, dripping, spilling, or flowing. Its first contact is the floor. It is generally caused by the omission of a seal altogether, or a split hose.

Gushing--happens when the bolts are left off a manifold completely, causing the fluid to follow the laws of projectile motion rather than fluid dynamics. It often is followed by cries of "Thar she blows!" in the shop, and overtime pay.

The purpose of this list is, of course, to amuse you, but I also want to prod component manufacturers and OEMs to continue to focus on ways to assemble hydraulic systems so they don't leak. Until that practice becomes common, the rest of us may want to hang onto our mops, shop vacs, cleanup rags, bags of oil adsorbents, and the L-word.

Victor Popp is a priciple engineer at Instron/Schenk Testing Systems in Canton, Mass.
Reprinted with the permission of Hydraulics & Pneumatics magazine.

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