Remove all failed putty. The substrate must be free of oxidation, dirt, moisture, grease and residual putty, mastic or sealant. An important section of a dry gas seal is the vent system. Special attention is required for the primary vent system (vent system of primary seal). In the primary vent system, a vent rupture disc is typically installed in parallel with the vent line to rupture at a set pressure and prevent excessive pressure to instruments on a primary seal failure. A pressure-relief valve (PRV) may be installed instead of rupture disc, particularly for large machines. This effect should not be confused with the "beading" effect often associated with water repellents.

Since clearances between seal faces are usually less than 4–10 microns, the seal gas passing between faces should be clean and dry. While the seal filtration requirement is 1–3 microns, 1-micron filtration systems are typical for dry gas seals. The next article, in the March 2012 issue, will focus on selecting the proper seal features—face materials, groove geometries, secondary sealing elements and gasket extrusion/explosive decompression—to provide a reliable dry gas seal system. Dry seals offer an alternative for dusty or extremely viscous applications that guarantees complete sealing, minimum maintenance, protection of the other system components such as the wear of the shaft and less energy consumption due to motor friction. Lastly, a system to control flow to the separation seal is required. All these components are needed to provide an efficient system for controlling the supply and quality of gases to the dry gas seal and to monitor the seal’s health.

Dry Gas Seal Panels 

Material selection is critical for sealing elements. The compatibility of sealing element materials with process gas compositions in all operating cases (normal and abnormal) is important. These sealing elements require robust and sound designs to ensure long-term, trouble-free seal operation. Each of these sealing elements (U-ring, O-ring and V-ring) could easily be damaged in a careless installation or overhaul exercise. The deterioration of seal elements (such as different rings) could be due to abrasive wear from dirt or contamination from dirty process gas. Seal gas booster: A commonly reported root-cause for seal failures has been low pressure of seal gas at startup, which resulted in dirty gas moving to the dry gas seal from the compressor casing. It is recommended to install seal gas boosters to ensure supply of seal gas during standstill and transient conditions, if a reliable source of seal gas with suitable conditions is not available for these transient times (particularly the startup). We present the Dry Seals or a sealing system for solids that have a technology to permit a complete seal with no lubrication need.

Any traces of DRY SEAL on glass can be easily removed after a few hours or preferably the next day. To prevent a dangerous condition, process gas cannot leak into the bearing cavity, which could cause an explosion or expose operators or the environment to hazardous or toxic gas. To eliminate this danger, a separation seal (Figure 2) is used on the atmospheric side of the dry gas seal. Since a number of separation seals are available, selecting the correct seal for the application is important.

Flowmeter on secondary vent: A good recommendation is to consider a flowmeter on the secondary vent. This can give good information regarding the secondary seal health and the overall seal system conditions. The inner labyrinth seal (or process labyrinth seal) plays an important role in the performance and reliability of a turbocompressor and its dry gas seals. The differential pressure across the inner labyrinth seal should be carefully monitored. This differential pressure needs to be maintained at a relatively constant designed value for uninterrupted and stable flow. A low seal gas flow (to process side) may cause migration of dirty process gas into the seal. A high flow may cause the flow coefficient in the system to exceed the designed value, creating detrimental flow turbulence, as well as inefficient performance. Finding a sealing element that guarantees sealing without leaks and adds durability to applications of this type poses a difficult challenge. Large numbers of dry gas seal assemblies have problems because of an issue with an O-ring or a V-ring. There are many sealing elements (O-rings, V-rings, U-rings, etc.) in a seal assembly, which can cause seal operational problems. If an O-ring or a V-ring allows gas to bypass, the gas stream would pass up the primary vent. In many cases, the deterioration of a ring or a sealing element may explain the rise in the primary vent flow, which could be confused with seal face deterioration.