Top 3 Reasons Why Mechanical Seals Leak

Mechanical seals are an integral part of centrifugal pumps. A mechanical seal is used to prevent liquid from leaking from a pump, as well as preventing outside air and contaminants from entering a pump. Typically, a leakage limit is expressed in terms of volume by a measure such as milliliters per hour. Though infrequent, mechanical seal leaks can definitely compromise a pump’s integrity, resulting in a great need for repairing a pump as soon as possible. The top three reasons why a mechanical seal will leak are due to fluctuating pressure, damaged mechanical seal (or shaft/shaft sleeve) and excessive vibration.

When a pump experiences rapid drops or spikes in fluid pumped, a pump can sometimes struggle to maintain the fluid within. Specifically, a major area of potential damage is the mechanical seal: “Changing operating conditions will lead to an increasing leakage of fluids. Rubber lip seals are more forgiving in these circumstances and are less susceptible to this phenomenon.”¹ Still, a cause of leaks in a pump may also be due to O-ring seals, which are much less costly and easier to replace compared to mechanical seals: “The source of most leakage usually is the interface between the two seal faces, but can also come from secondary seals such as O-rings”² Besides specific parts of a seal, the shaft can also be a cause for mechanical seal leaks.

A damaged shaft sleeve can be the cause of leaks from a mechanical seal. “Make sure that the shaft or the shaft sleeve has not been damaged. If there is a sweat score or nick on the shaft or the shaft sleeve where the mechanical steel fit, you may need to replace the shaft or the shaft sleeve so that the seal does not leak near the shaft. You could have a worn or damaged mechanical seal.”³ Though a mechanical seal leak can be caused due to shaft issues, vibrations are another potential cause of leaks, among other issues for pumps.

One other potential cause of mechanical seal leakage is excessive vibration. Excessive vibrations are altogether a source of a plethora of problems for pumps. “If operating vibration levels are high, the shaft suffers from excessive radial or axial movement or is misaligned excessively, leakage rates tend to be higher.”⁴ Thus, excessive vibration can not only be a cause of leaks, but can also make leaks worse in a mechanical seal.

Mechanical seals are not to be taken lightly. A pump’s integrity can be entirely compromised due to mechanical seal issues, which may only be discovered once a leak is found. The proper remedy of preventing mechanical seal leaks is, besides proper installation according to manufacturer’s instructions, frequent monitoring of a pump so as to prevent major problems before they occur.