Shaft seal failure: what is damaged? - Results of a 4 year research

The purpose of a mechanical seal is to prevent refrigerant leakage by sealing with oil. But all seals leak oil to some controlled degree.

Seal failure means that leakage is extreme & uncontrollable. The shaft seal is broken and needs replacement. Over the last 4 years, RM Support analyzed 110 broken shaft seals of diverse brands of compressors.

In most cases the seal leakage came from the sealing interface (carbon ring). However, in some situations leakage emerged from O-rings (the secondary sealing area). In particular, VSD compressor units that operated for a longer time in a low capacity (below 2500 rpm) have more damage from O-rings. In some cases even a combination with higher oil consumption as know as oil carry over.

Here are some more interesting observations: seal-schade

71% of the seals showed damage to the carbon ring. Symptoms indicated overheating. Overheating/thermal attack results in 3 kinds of symptoms: radial cracking, blistering and spalling.

65% within this category of damaged seals showed a deformation of the O-rings. 33% had binder problems due to the heat caused by chemical attack.
15% showed deformation on the O-rings only. In some of the investigated seals we fitted a silicon part instead of the standard carbon ring.
10% showed copper plating on sealing parts. The use of Freon gas and hydrated oil in the seals influenced the creation of copper plating on mechanical seals.

4% of the defects could be related to incorrect lapping, hammered dowel pins, materials, broken or missing springs and mounting failures.

The conclusion: symptoms indicate the majority of damage is due to overheating (thermal attack). Reducing the heat during the sealing process will reduce the shaft seal damage.

This research was a part of the development of a Heat Reduced (HR) shaft seal.

Please contact us if you want to know more about this research. Read about our soon available HR shaft seal here.