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Machine Design

A seal for hydrocarbons

Refineries and other processing plants that pump light hydrocarbons such as ethane, ethylene, propane, and butane, (specific gravity from 0.4 to 0.6) face a challenge.

Hydrocarbon liquids can flash to a vapor at ambient temperatures and pressures, causing seal faces to run dry and fail. This to dangerous emissions and expensive downtime.

To prevent this, engineers at Flowserve Corp., Dallas, Tex. (, designed the QBQ LZ mechanical seal with wave patterns laser-machined on the seal face. The pattern creates a stable hydrodynamic effect that changes the pressure profile across the seal face to reduce friction and contact loads without increasing leakage. Lower contact loads means less temperature increase on the seal faces. This lets the seal handle liquids with vapor pressure margins between 5 and 50 psi. These seals can also serve on high-pressure pumps above 300 psi at any vapor margin.

The unit's operating range includes pressures from 0 to 750 psi, temperatures from 40 to 400°F, speeds from 20 to 75 fps. It comes in sizes from 1.75 to 5.125 in. The bidirectional QBQ LZ installs on either end without pump modifications normally needed to boost vapor-pressure margins.

According to the manufacturer, this can improve the MTBR on pumps that consistently go down due to vaporization.

TAGS: Materials
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