If you’re thinking about purchasing a gas compressor from Ro-Flo for your application, you’ve likely noticed that there are two options for the shaft seals: single face mechanical or double bellows. Single face mechanical seals are valued for their simple, robust design that is easily repaired in the field, while double bellows seals offer a second level of protection. Here’s the difference between single and double bellows mechanical seals and the best applications for each type.

Single Face Mechanical Seals

While the concept of a seal is straightforward, in operation inside a rotary sliding vane compressor, the execution is more complex. Single face mechanical seals utilize a spring to press together two flat surfaces (faces), which slide against each other. A fluid film, which is lubricating oil, forms between the two flat surfaces, creating a barrier between the process gas and the atmosphere. This fluid film also reduces wear of the two faces.

Common issues with single face mechanical seals include:

  • quality or quantity of the lubrication oil
  • an accumulation of debris between the sealing faces
  • damage to the sealing faces
  • damage to the O-rings

These issues are all easy to diagnose and repair on-site. The simplicity of the single face mechanical seals makes them the preferred option in most applications.

Double Bellows Mechanical Seals

This type of seal has two sets of contact faces. The two sets of faces are back-to-back, or dual-opposed, separated by a coil spring, thus pushing in opposite directions. The double bellows mechanical seal requires a lube oil support system.  The support system is designed to keep the seal parts submerged in oil and to maintain pressure on this oil system that is greater than the pressure inside the compressor. With this pressurized system, if leakage occurs at the outer seal, it will be towards the atmosphere and air will not be drawn into the compressor. If leakage occurs at the inner seal, lube oil will be pushed into the compressor. Details of the required lube oil support system can be found in Ro-Flo’s Installation, Operation and Maintenance Manual.

It is important to note that the lube oil support system must be pressurized prior to pressurizing the compressor or gas piping system – whether for pressure testing or compressor operation. If the process gas system is pressurized prior to the support system being pressurized, the seal is likely to fail.

Double bellows mechanical seals are used for any application in which the additional protection may be needed. Often, this type of seal is stipulated by safety and environmental regulations. Many users of Ro-Flo compressors are in the oil and gas industry or managing biogas, therefore this type of seal is quite common.

If you’re uncertain which type of seal is the correct one for your application, our engineering team will be happy to help you decide.

Single-Face Mechanical Seal – Replacement & Rebuild Procedure

Double Bellows Mechanical Seal – Disassembly, Inspection and Replacement

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