In our dealings with brewers, we have found many are unhappy with the seal life of the pumps used to transfer hot wort. We have found that almost invariably, the pump has an internal seal which consists of a polymer rotary seal riding against a stainless steel stationary surface. We have come to the conclusion (solely our opinion) that many of these seal failures are due to the following circumstances:

• During operation, wort seeps between the rotary and stationary surfaces.
• When the pump stops, the sugar in the wort begins to cool and crystalize, forming a tacky film on each seal surface. If the pump is flushed with cool water, this may accelerate the crystalization rather than flushing the sugar away.
• When the pump finally comes to rest, the sugar "sticks" the two seal surfaces together.
• When the pump restarts, the two surfaces remain "stuck". The pump shaft is forced to turn by the motor. The result is that the shaft turns inside the rotary seal. The o-ring that is supposed to form a simple compression seal between the shaft and the seal is now subjected to a high speed rotary action, wearing it quickly.
• Within a short time, the seal surfaces "unstick" due to the sugar being re-dissolved, but the damage to the o-ring is already done.
• The o-ring may be able to survive several of these cycles, but is eventually worn flat on it's inner diameter.
• Eventually, the pump begins to leak. Replacing the seal is the common solution. Few brewers ever notice that the seal surfaces are not worn -- only the o-ring.

Obviously, we cannot confirm that this is the cause of seal failure in every hot wort application, but we believe it is a sound theory based on what we've seen. We can offer the following solutions to the problem:

• Follow every wort batch with an immediate flush of hot water to remove any sugar. Remember, the water has to "seep" in between the surfaces just like the wort did, so a short burst may not be sufficient.
• Replace the pump with a model which supports a constant water flush to the seal area. This feature is usually available only on pumps with external seals or high quality (and hence, high cost) models with internal seals.
• Replace the pump with a model which does not rely on a polymer vs stainless seal surface. We have found that SPI's model SP pump with it's teflon vs ceramic sealing surfaces does not seem to suffer the same "sticking" problem (you knew we'd eventually get to the part where we try to sell you something!). We have placed SP pumps in hot wort applications that have gone 6 months (and over 60 batches) on the same seal -- with the original o-ring. The SP series pumps are extremely affordable. Use this link to check out the features of this pump on our Brewery Products page.

We hope that this helps to answer some of the questions we've received regarding seal failures. Of course, we would be even happier if we can sell you a SP pump to solve your problem, but we hope just knowing how it happens will help to reduce seal failures on your existing pumps. We will be happy to answer any questions. Please direct e-mail to applications@dairyeng.com.
March 10, 1997