Gene Vogel
EASA Pump & Vibration Specialist
In the beginning, God made water to run freely over the earth. Then Man made pumps to make water run where he wanted it. Then God made leaks. Then Man made pump seals. God laughed. Man continues to struggle with leaking pumps seals.
For those new to pump repair, mechanical seals can be intimidating. It is commonly known that pump mechanical seals are temperamental devices that fail frequently. The fact is, mechanical seals are simple devices that are often misapplied, sometimes installed incorrectly, or perhaps installed on pumps that are not well suited for the application. For many applications, the mechanical seal is robust enough to tolerate less than optimal handling and operating conditions. For more demanding applications, everything must be right.
How a Mechanical Seal Works
Knowing how a pump mechanical seal works will help you understand the concerns for applications, seal selection and installation procedures. The main components of a seal are the rotating and stationary face rings that are held in tension against each other by mechanical spring(s). These form the primary seal (Figure 1), and the contacting faces are precision smooth and flat. The rotating face ring and the assembly that holds it must be sealed to the shaft, and the stationary face ring has to be sealed to the housing. These two secondary seals use O-rings or boots (Figure 2).
Selecting the proper materials for the primary and secondary seal components is important. Carbon-ceramic face material and Buna-N for secondary seals are standard, and they work well with common water pumping applications. When pumping sewage or strong chemicals, alternate materials work better. Material selection is an area where many service centers seek outside help.
Fortunately, many value-added seal distributors will provide that assistance. A value-added provider will ask critical questions about the application and recommend products that will work best. Their price may be more than catalog sales alternatives, but the added value lies in the knowledge to specify the right product. If a provider tries to match a seal by the dimensions only, not considering the application, you may just get a good price on the wrong product.
Precautions Ensure Success
In most cases, installing pump mechanical seals during the repair process is not difficult; a few simple precautions ensure success. Only the proper type of lubricant should be used to ensure the elastomer secondary seals slide into place. Some seal providers offer a water-soluble lubricant designed for this purpose. If necessary, you could even use a lubricant found at your pharmacy. The essential factor is that it be water-soluble so that it is washed away by pump operation. This does not apply to seals installed in oil-filled seal chambers. In all cases, avoid damaging the elastomer secondary seals on shaft edges of shaft shoulders, keys or housings. A sheet of Mylar paper wrapped around the shaft will protect the seal as it slides into place for shafts.
The amount of tension applied by the seal spring assembly can be a concern on some special applications. But on the types of pumps seen most in service centers, the tension adjustment is pre-set by the pump/seal design. Just observe during disassembly if there are any tensioning provisions and document the measurements if there are.
When a seal leakage problem is detected, it is important to carefully inspect the seal to determine its cause. Is it leaking at the primary seal or one of the secondary seals? The primary seal faces should show a smooth, slightly shiny wear pattern. The elastomer secondary seals should be pliable but not soft, and there should be no corrosion on the surfaces that contact the shaft or housing. Corrosion at those contact points would indicate a leak. This is another area where a value-added seal provider can be of assistance. They can provide an analysis of the seal failure and recommend solutions.
Valuable Seal Providers
If you are unsure where to find a good value-added seal provider, start with the EASA Solutions Expo exhibitors. Explore the 2020 virtual trade show at easa.com/convention. Other valuable reference resources are available on the EASA website. Find companies in the Associate Member search at my.easa.com/find/associate. Search the Resource Library using the keyword “seal” for a list of articles, webinar recordings and technical papers.
Leaks may be inevitable, but seals need not be a mysterious part of pump repair.
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