Negative seal

Performance of user seal checks and whether positive and/or negative seal checks are... 

Q. Can you please clarify whether both or either of the positive and negative seal checks described in Appendix B-1 are required when donning a respirator ... 

B. Pre-Use Self-Testing is a routine requirement for all employees who wear respirators. Each time the respirator is used, it must be checked for positive and negative seals. The Safety Division will train supervisors on this procedure. Supervisors are responsible for training employees in their individual workcenters. 

Cell Assembly. The methods for cell assembly, starting with the processed plaques depend on whether the cells are to be vented or sealed. For vented cells, processed plaques are usually compressed to 85 —90% of their processed thickness allowing sufficient porosity for electrolyte retention and strengthening the plate stmcture. For sealed cells, sizing of the negative plaques is usually avoided because maximum surface area is important to oxygen recombination. 

The positive plates are siatered silver on a silver grid and the negative plates are fabricated from a mixture of cadmium oxide powder, silver powder, and a binder pressed onto a silver grid. The main separator is four or five layers of cellophane with one or two layers of woven nylon on the positive plate. The electrolyte is aqeous KOH, 50 wt %. In the aerospace appHcations, the plastic cases were encapsulated in epoxy resins. Most usehil cell sizes have ranged from 3 to 15 A-h, but small (0.1 A-h) and large (300 A-h) sizes have been evaluated. Energy densities of sealed batteries are 26-31 W-h/kg. 

Eig. 4. Constmction of a sodium—sulfur battery. A, Negative terminal B, springs plus graphite felt C, sulfur D, carbon E, sodium reservoir E, positive terminal G, iasulator H, aluminum sealing gaskets 1, steel case J, film of sodium K, P-alumiaa tube L, carbon felt M, wick N, aluminum can (67). 

Gas flow in these rotary dryers may be cocurrent or countercurrent. Cocurrent operation is preferred for heat-sensitive materials because gas and product leave at the same temperature. Countercurrent operation allows a product temperature higher than the exit gas temperature and dryer efficiency may be as high as 70%. Some dryers have enlarged cylinder sections at the material exit end to increase material holdup, reduce gas velocity, and minimize dusting. Indirectly heated tubes are installed in some dryers for additional heating capacity. To prevent dust and vapor escape at the cylinder seals, most rotary dryers operate at a negative internal pressure of 50—100 Pa (0.5—1.0 cm of water). 

To prevent dust and vapor escape at the cylinder seals, a negative internal pressure of 50—100 Pa (0.5—1.0 cm of water column) is maintained. 

On the negative side, the MCFC suffers from sealing and cathode corrosion problems induced by its high-temperature molten electrolyte. Thermal cycling is also limited because once the electrolyte solidifies it is prone to develop cracks during reheat-... 

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