Seals, pump shaft

The traditional function of a PWR reactor coolant pump is to deliver cooling water to the reactor during both normal operations at power and for fission product heat removal when shutdown. The reactor coolant pump type adopted in the US for currently operating plants is the shaft seal pump, which can be made large and can have high hydraulic and electrical efficiencies. The potential design options for the AP600 were numerous ac powered shaft seal pumps, dc powered safety pumps, canned motor pumps, no pumps (natural circulation) and others. 

Because the motor and the pump bearings are within the coolant boundary, the caimed motor pump also allows the designer to eliminate the shaft seal pump support systems, such as seal injection, seal leak off, lubricating oil and fire protection systems. This avoids complexity, and results in lower overall cost. 

Higher intrinsic reliability than shaft seal pumps. 

Seal-less motor pumps are not as efficient as shaft seal pumps. 

Unlike shaft seal pumps, seal-less pumps cannot be repaired in situ, requiring a design to be developed for quick removal and replacement of entire pumps. 

Unlike shaft seal pumps, canned motor pumps of the size required for the AP600 had not been built before. This led to the decision to use two canned motor pumps, of modest extrapolation, for each steam generator loop. 

Sealing tlie Centi-ifiig Chemical Pump Altliougb detailed treatment of. shaft seals is presented iu tbe subsection Sealing of Rotating Shafts, it is appropiiate to mention here tlie special problems... 

Factiiring in general, we observe that there are more eentrihigal pumps. About 90% of the pumps in industry are eentrifugal pumps. And the PD pumps found in industry have much in common with their eentrifugal sisters. They are mostly rotary designed pumps, with precision bearings and a shaft seal. Much of the theory, and system needs, are applicable to both types of pumps. 

The outside diameter of the lip. seal fits and seats into the housing bore (transmission or pump). The inside diameter, with the elastomeric lip, rides onto the spinning shaft (whether vehicular drive shaft or pump shaft). 

In the CCPS taxonomy, where the equipment boundary for a motor-operated pump includes the motor, shaft, seals, casing, impeller and the circuit breaker, then the demand-related failure is attributed to the pump. 

Pumping of liquids is almosl universal in chemical and petrochemical processes. The many different materials being processed require close attention to selection of materials of construction of the various pump parts, shaft sealing, and the hydraulics of the individual problems. A wide variety of qqtes and sizes of pumps have been developed to satisfy the many special conditions found in chemical plant systems however, since all of these cannot be discussed here, the omission of some does not mean that they may not be suitable for a service. 

Shaft seal requirements and two common types of seals, packed stuffing boxes and simple mechanical seals, are described and discussed in this section. A packed box typically is used on slow- to moderate-speed machinery where a slight amount of leakage is permissible. A mechanical seal is used on centrifugal pumps or other type of fluid handling equipment where shaft sealing is critical. 

This highly pressurized fluid also flows around the impeller to a lower pressure zone where, without an adequate seal, the fluid will leak along the drive shaft to the outside of the pump housing. The lower pressure results from a pump design intended to minimize the pressure behind the impeller. Note that this design element is specifically aimed at making drive shaft sealing easier. 

I. Leakage—joints and packing this factor accounts for the possibility of leakage from gaskets, pump and other shaft seals, and packed glands. The factor varies from 0.1 where there is the possibility of minor leaks, to 1.5 for processes that have sight glasses, bellows or other expansion joints. 

Standard 682 Shaft Sealing Systems for Centrifugal and Rotary Pumps... 

API Std 682 Shaft sealing systems for centrifugal and rotary pumps ... 

In order to ensure a proper seal against the process medium In the pumping chamber the shaft seal Is of the axial face seal type - a sealing... 

API Standard 610, Centrijugal Pumps for Petroleum, Petrochemical, and Natural Gas Industries, Adoption of ISO 13709, October 2004 API Standard 613, Special Purpose Gear Units for Petroleum, Chemical and Gas Industry Services, February 2003 API Standard 614, Lubrication, Shaft-Sealing, and Control-Oil Systems and Aunliaries for Petroleum, Chemical and Gas Industry Services, April 1999 API Standard 616, Gas Turbines for the Petroleum, Chemical, and Gas Industry Services, August 1998... 

Sealing the Centrifugal Chemical Pump Although detailed treatment of shaft seals is presented in the subsection Sealing of... 

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