Throttle Bushings

Throttle bushings (Fig. 10-117) are commonly used with single internal or external seals when sohds are present in the fluid and the inflow of a flushing fluid is not objectionable. These close-clearance bushings are intended to serve as flow restric tions through which the maintenance of a small inward flow of flushing fluid prevents the entrance of a process fluid into the stuffing box. 

The leak size can be reduced by using double mechanical seals or a mechanical seal and a throttle bush, the space between the two being vented to a safe place. Major leaks may still occur, however, due to collapse of the bearing or seal. LFG pumps should therefore be fitted with emergency isolation valves (see Section 7.2.1), particularly if the temperature is low or the inventory that can leak out is high. 

For single seals, and when specified for dnal seals, a non-sparking floating throttle bushing shall be in-... 

Table 2-4—Floating Throttle Bushing Diametral Clearance...

Figure D-3A—Piping for Throttle Bushings, Auxiliary Seal Devices, and Dual Seals—Plan 52...

USES AN EXTERNAL SOURCE TO PROVIDE A QUENCH WHICH MAY BE REQUIRED TO PREVENT SOUDS FROM BUILDING UP ON THE ATMOSPHERIC SIDE OF THE SEAL TYPICALLY USED WITH A CLOSE CLEARANCE THROTTLE BUSHING. 

P097 Throttle Bushing Required THRT B c 1 lyes (true) Oino (false)... 

For high pressure differences the usual type of sealing device is the mechanical seal, of which there are a range of designs (internal and external single and double mechanical seals with and without throttle bushing, with or without pressure relief). Some of them can be dismantled and replaced in filled tanks under pres-... 

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