The Lifeline of Mechanical Seals: Understanding the Importance of Flush Water Systems

Using clean flush water is critical for the proper functioning and longevity of mechanical seals in pumps. Here’s an in-depth look at why clean flush water is essential and how different flushing systems should be maintained:

Importance of Clean Flush Water for Mechanical Seals:

1. Lubrication:

Mechanical seals work under tight tolerances where the seal faces move relative to each other. The presence of clean water or fluid between the seal faces acts as a lubricant, reducing friction, heat, and wear. Without proper lubrication, seal faces can wear out quickly or fail due to excessive heat generation.

2. Cooling:

The heat generated by the friction between the seal faces can be significant, especially in high-speed applications. Clean flush water helps to dissipate this heat, maintaining the seal materials within their thermal limits and preventing thermal deformation or seal failure.

3. Cleaning:

Clean water flushes away contaminants like solids, abrasive particles, or chemicals that might otherwise accumulate at the seal faces. These contaminants can cause abrasive wear or chemical attacks on the seal materials, leading to premature failure.

4. Pressure Management:

Flush water can be used to manage pressure in the seal chamber, often introduced at a slightly higher pressure than the pump’s seal chamber (stuffing box) pressure to ensure a positive flow outward, which further aids in keeping the seal area clean. If a barrier fluid such as synthetic oil or a water-glycol mix is used, constant pressure must be maintained during the operation of the equipment. When the barrier fluid tanks (seal pots are being refilled, pressure must be maintained, or operation of the equipment must stop, even though this is not frequently done as a part of seal maintenance.

5. Extended Seal Life:

Clean flush water provides ideal operating conditions through lubrication, cooling, and cleanliness, significantly extending the life of mechanical seals and reducing maintenance costs and downtime.

Force-Flow Water Flush:

• Purpose: A force-flow flush, often called API Plan 32, involves injecting clean water at a higher pressure into the seal chamber to prevent the ingress of pumped fluid into the seal area. It is particularly useful with slurries or corrosive fluids.

• Maintenance:
• Flow and Pressure Control: Ensure the flow rate and pressure are correctly set and monitored. Typically, the pressure should be 15 to 20 psi above the seal chamber pressure to guarantee sufficient flushing without waste.
• Water Quality: The water must remain clean; any particulate or chemical impurities can negate the benefits of flushing. Regular filtration or treatment of the flush water might be necessary.
• System Checks: Regularly inspect for blockages or leaks in the flush system. Ensure the flush line remains unobstructed for proper flow.
• Seal Inspection: Even with a force-flow system, periodic inspection of the seal condition is crucial. Look for signs of wear or damage due to improper flushing or unexpected contaminants.

Closed-Loop Flush:

• Purpose: This system circulates a barrier fluid (often water or a suitable liquid) in a closed loop through a cooling system, providing lubrication and cooling without continuously introducing new water into the process. This consequently conserves water and reduces the dilution of the process fluid.
• Maintenance:
• Coolant Purity: The barrier fluid must be kept clean. This might involve filtration or chemical treatment to prevent bacterial growth or contamination.
• Loop Integrity: Check for leaks in the closed loop system. Any leakage can introduce air or process fluid, disrupting the system’s effectiveness.
• Cooling System: Ensure the cooling system (like a heat exchanger) functions correctly. Overheating can occur if the coolant temperature rises too high.
• Pressure Regulation: Maintain the correct pressure differential in the system. The pressure should be slightly higher than the seal chamber to prevent process fluid from entering the loop. A flow meter may be included in the fluid sealing system to indicate a possible inboard face seal leak (shown as higher flow and lower pressure) or a possible filter clog (shown as decreased flow and increased pressure) along with tale-tale pressure gauges to monitor peak operational pressures if deadheading is a suspected as a possibility, this way the mechanical seal can be engineered to handle the correct balance of pressures from the product and atmospheric side.
• Regular Testing: Conduct periodic tests to ensure the system still provides adequate cooling and lubrication. This might include checking the temperature drop across the cooler, flow rates, and the condition of the barrier fluid.

Both flush water systems require regular maintenance to ensure they continue to provide the necessary conditions for seal operation. Proper maintenance not only extends the life of the seals but also ensures operational efficiency, reduces energy consumption and maintains environmental compliance by controlling emissions and fluid loss.