Dynamic Seals Lower Life Costs of Wastewater Pumps

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When plant water supply is utilized for sealing purposes, it's essential to maintain an air gap between the incoming water supply and the seal water system to prevent contamination. Consequently, sewage plants frequently rely on an independent seal water system. Typically, this system is composed of a tank with overflow connections and a float to keep the air gap, accompanied by two small pumps managed by a duplex control panel, Y-strainer, relief valves, and isolation valves. The installation and piping costs for a seal water system can range from $10,000 to $20,000.

Beyond the expenses linked with a separate sealing system, sewage plants have to factor in the costs associated with operating the seal water pump and the consumption of clean water. A 4X4 sewage pump with a 2" sleeve OD can utilize between 0.5 gpm and 2.5 gpm depending on the packing type and lantern ring position. Conversely, a single mechanical seal may consume between 0.5 gpm and 1.5 gpm of flush water. Thus, if the pump operates continuously for 24 hours a day, the total sealing water consumption for just one 4X4 pump can amount to several tons of water annually. This extra water needs to be treated before being returned to the environment since it re-enters the process.

To support the water and wastewater sector, ITT A-C Pump unveiled a patented dynamic seal for sewage pumps. This dynamic seal is well-established in the pump industry, having been effectively utilized in the Pulp and Paper Industry for many years. It functions simply as an auxiliary expeller within the stuffing box, situated on the same shaft.

As the pumped liquid flows into the dynamic seal chamber, it faces the centrifugal force from the expeller, which works to prevent leakage around the shaft. The expeller establishes a ring of liquid and air, maintaining equilibrium between these two phases, thus earning the name Equiseal®.

Two lip seals serve to halt any leakage when the pump is idle. A bypass line links the dynamic seal chamber to the suction of the pump, ensuring that the seal chamber pressure remains equal to the suction pressure of the pump.

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Optimal operation and sealing capability of a dynamic seal depend on the pump's speed and suction pressure. Given that a wastewater or non-clog pump may operate at low speeds or be driven by a variable speed mechanism, a single expeller may not suffice for effective sealing. To tackle this challenge, ITT A-C Pump provides double or two-stage Equiseal® options.

While the dynamic seal functions similarly to a small impeller and consumes power, in an equilibrium stage the expeller transfers minimal water, resulting in very low power consumption. Many operators express concerns regarding the dynamic seal's power draw. Although the initial investment appears higher and it seems to use more power, when evaluating total cumulative costs over the pump's lifespan, these systems can actually be more economical.

Cost Comparison

The cost for a dynamic seal for a 4X4 pump is $. On the other hand, the cost of a mechanical seal is $. Considering that most pump manufacturers include packing as standard, the initial cost of packing is effectively zero. Nonetheless, the costs associated with sealing water, replacing packing twice annually, and changing the sleeve and lantern ring every year can add up significantly. Below is a comparison of the operating costs for conventional packing, mechanical seals, and dynamic seals.