Like gaskets, a mechanical seal stops fluids leaking into places they are not supposed to be. The difference is that gaskets are for static applications like pipe flanges while mechanical seals prevent leaks from around rotating shafts. Hennig Gasket & Seals is in the business of cutting gaskets to shape and supplying gasket material, but we do offer a mechanical seal repair service. Here’s a primer on mechanical seals for those who’d like to know more.
The Shaft-Sealing Challenge
Pumps, compressors, and similar rotating machinery are built around a rotating shaft that passes into or through a housing. Bearings hold the shaft in place but don’t stop the fluid from escaping. Historically, this was done with gland packing material. This looks like rope and is packed around the shaft to prevent leaks.
Gland packing has several limitations:
- Wears out, requiring adjustment and eventually, replacement
- Can wear the shaft
- Creates friction for the motor to overcome
Modern gland materials incorporate PTFE, graphite or other friction-reducing compounds, but the risk of leaks remains. As awareness of the environmental and health and safety consequences has grown, many machinery manufacturers have replaced packing with mechanical seals.
Mechanical Seal Basics
In principle, mechanical seals are straightforward. They comprise one element fixed to the shaft and a second element on the housing or body. These are arranged with surfaces that are perpendicular to the shaft axis and are brought together so the rotating shaft element rubs against the fixed housing element.
This perpendicular configuration accommodates runout between shaft and housing. A small gap – less than 0.0001″ – between the two contacting surfaces stops particles getting into the fluid but can allow a degree of leakage. The alternative is to put combinations of low friction materials like graphite and ceramic or carbide in contact. This drives leakage rates almost to zero. For additional sealing, many modern mechanical seals spring-load one element to push it against the other.
Contact Hennig
Hennig Gasket & Seals are experts in all types of gasket and sealing applications. Contact us for gasket materials or mechanical seal rebuilds.
