Causes of Pump Mechanical Seals

It is important to review how a pump mechanical seal works. First, its main components are the rotating and stationary face rings that form the primary seal (Image 1). The face rings have flat, precision-smooth contact surfaces that are held in tension against each other by mechanical springs.

The rotating face ring and its assembly have to be sealed to the shaft. The stationary face ring has to be sealed to the housing. These two sealing points are called secondary seals and typically use elastomer O-rings or boots .

Pump Seal Materials

Selecting the proper materials for the primary and secondary seal components is important. For common water pumping applications, carbon-ceramic face material and Buna-N secondary seals are standard and work well. Alternate materials work better for pumping sewage or strong chemicals, so many technicians seek outside help on these applications.

 

Precautions Ensure Success

By following a few precautions, it is not difficult to install pump mechanical seals during the repair process. For example, to ensure the elastomer secondary seals will slide into place undamaged, always use the proper lubricant. Some seal providers offer water-soluble lubricants designed for this purpose. Make sure the lubricant is water-soluble (except with oil-filled seal chambers), so that it will be washed away by pump operation. 

In all cases, avoid damaging the elastomer secondary seals on the edges of shaft shoulders, keys or housings. A good way to accomplish this is to wrap a sheet of mylar paper around the shaft to protect the seal as it is slid into place.

While the amount of tension the seal spring assembly applies can be a concern on some special applications, the tension adjustment on common utility pumps is preset by the pump and seal design. Just observe during disassembly if there are any tensioning provisions and, if so, document the measurements.

When a seal leakage problem occurs, carefully inspect the seal to determine the cause. Is it leaking at the primary seal or at one of the secondary seals? The wear pattern of primary seal faces should be smooth and slightly shiny, and the elastomer secondary seals should be pliable but not soft. The shaft and housing contact surfaces should be corrosion free; corrosion at those contact points would indicate a leak. 

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