Dynamic Seals Lower Life Costs of Wastewater Pumps

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When a plant water supply is used for sealing purposes, an air gap between the incoming water supply and seal water system is required to prevent contamination. Hence, sewage plants often use an independent seal water system. This seal water system normally consists of a tank with overflow connections and a float to maintain the air gap, two small pumps with duplex control panel, Y-strainer, relief valves and isolation valves. The cost of a seal water system with installation and piping cost can be from $10,000 to $20,000.

In addition to the cost of a separate sealing system, the sewage plant also has to consider the cost of power to run the seal water pump and the cost of clean water. A 4X4 sewage pump with 2" sleeve OD can consume 0.5 gpm to 2.5 gpm depending on packing type and lantern ring position. On the other hand, a single mechanical seal can also consume 0.5 gpm to 1.5 gpm of flush water. This means if the pump runs for 24 hours a day, the total consumption of sealing water for just one 4X4 pump can be as high as to tons of water per year. Since this sealing water goes back to the process, these to tons of extra water need to be treated again before it goes back to environment.

To help the water and wastewater community, ITT A-C Pump introduced a patented dynamic seal for sewage pumps. The dynamic seal is not a stranger to the pump industry. It has been successfully used in the Pulp and Paper Industry for years. Functionally, it is just an auxiliary expeller in the stuffing box mounted on the same shaft.

As the pumped liquid enters the dynamic seal chamber, it is opposed by the centrifugal force of the expeller, thus preventing the leakage through around the shaft. The expeller creates a ring of liquid and air phase and maintains equilibrium between the two phases, hence the name Equiseal®.

Two lip seals prevent any leaking during the idle condition of the pump. A bypass line connects the dynamic seal chamber to the suction of the pump, which assures the seal chamber pressure remains equal to the pump's suction pressure.

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Proper operation and sealing capability of a dynamic seal depends on the speed of the pump and the suction pressure. Since a wastewater or a non-clog pump can run very slow or be driven by a variable speed drive, often a single expeller may not be enough to insure sealing. To solve this issue, ITT A-C Pump offers double or two stage Equiseal® options.

Since the dynamic seal works like another small impeller, it consumes power. In equilibrium stage the expeller actually pumps very little water and hence the power consumption is very low. Many operators may be concern about the cost of power draw by a dynamic seal. Although they appear to have higher initial cost and seem to have higher power consumption, the systems can be less expensive to operate if total cumulative cost is considered over the life of the pump.

Cost Comparison

Cost of a dynamic seal for a 4X4 pump is $. Cost of a mechanical seal is $. Since most of pump manufacturers offer the packing as standard, the price is already built in the pump price. Hence the initial cost of packing is zero. However the cost of sealing water, replacement of packing twice a year, and changing the sleeve and lantern ring every year can be significant. Following is a comparison between the operating costs of conventional packing, mechanical seal and dynamic seal.

Why don&#;t you have an online catalogue for standard seal sizes?

You can find our standard inch and metric seal sizes by clicking on the seal profile image on the relevant seal category page. Click the Seal-Size-Selector, select inch or metric seal size, enter the rod, shaft or bore diameter of your seal housing, and you will be offered a standard seal size, including hardware design information.

Also available are custom-made seals and special size seals made to order with very low minimum order requirements. Most of our seals can be shipped within 2-4 days.

Contact us to discuss your requirements of pu dynamic seal. Our experienced sales team can help you identify the options that best suit your needs.