Are mechanical seals and barrier fluid tanks the only way to ensure dilution reduction? Is there an effective way to use less water? 

Mechanical seals, invented in the early 1920s, became the go-to rotating shaft sealing method in the 1990s, becoming common in most process industries and applications. Their perceived ability to seal rotating equipment better than the traditional braided packing methods was evident. Over the last 30 years, their usage has become a standard procedure for many application maintenance programs. 

They have recently fallen out of favor due to their high cost and sometimes low reliability. Installing these seals on equipment with shaft runout, a scored sleeve, or worn parts almost always leads to premature failure and costly downtime. Many process engineers and reliability supervisors find that the investment return is unrealized and are thinking about switching to lower-cost methods. The promise of infinite life and problem-free running has faded alongside increased knowledge that mechanical seals require both mechanical conditions and plant operations to be near-perfect for long term success.

Methods of automatic dilution reduction:

• Double mechanical seals with barrier tanks.
• Single mechanical seals with an O-ring mount bearing at the throat, ahead of the seal.
• Stuffing box bearing with integral lantern ring and application required packing.

Dilution to the process while using mechanical seals occurs mostly when single seals are used on solids applications which, to keep the solids from compacting around the OD of the seals, the user connects a fluid or gas line to the flush port in the gland. The flush fluid or gas then flows to the process and dilutes the medium. The introduction of the flush into the medium inevitably leads to extra evaporation processing steps for removal. These extra steps can be costly and time-consuming.

Double seals with captive barrier fluid tanks ensure a coolant flows underneath each sealing face without going to process. While effective at keeping flush out of the process, double seals can add thousands of dollars to the cost because of their complex nature. Their complexity also adds to the potential for mechanical failure.

An efficient and cost-effective way to reduce dilution to the process is to utilize a close clearance bearing ahead of the mechanical seal or packing. Stabilizing bearings designed to be in contact with shafts automatically throttle flush to the process. Reducing bearing clearances and extending the bearing length can further reduce flow through. In addition to the bearing system, flow control mechanisms can be installed to create a hydraulic balance entirely within any stuffing box, totally self-contained, with virtually no dilution to process. The type of flow control equipment in this scenario is critical, though, and should not be overlooked. 

See SealRyt Flow Control options here

Flow systems should be unimpeded flow-through designs, rather than those that use needles or seats for throttling. Flow controls that use a diminished channel to alter pressure suffer from clogging that can result in total flush loss causing equipment overheating and failure. Using flow controls with a flow-through design continuously feed the rotating seal even if the meter is clogged because of less than perfect flush quality. 

See SealRyt Bearing (patented) options here

There is some debate on the use of bushings or hydraulic stops to control process dilution. Bushings allow flush to circulate more freely inside the stuffing box, but they don't limit or regulate flush volume independently. The varied designs on the market can alter the fluid dynamics inside the stuffing box environment. There are a few designs of bushings to operate with mechanical seals, but because of their nature, they have minimal effect on flush throttle. Hydraulic stops are equally unreliable. Hydraulic stop systems utilize a pressure differential between the inlet port and the outlet port of the stuffing box. The differential creates a pressure lock inside the stuffing box that's balanced with the process side being pumped. These systems fail because of their reliance on intermittent and unpredictable flush supply in the plant. 

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