Gas lock occurs when the pressure built up in the compression chamber on the down stroke is not sufficient to open the traveling ball and seat. The graph below is a result of data gathered from compression testing 2" bore RW standing cages from different manufacturers.
The tests were done by stroking a one foot long plunger inside a 2" bore RW barrel tube with the bottom of the traveling cage coming within 2-1/4"; 1-1/4"; and 1/4" of the top of the standing cage.
The traveling cage used was of API design with a blank disc in place of the seat to simulate hydrostatic load on the traveling ball which would keep the ball on the seat during the downstroke of the plunger.
The standard API seat plug and the recessed seat plug were both used to illustrate the importance of close valve spacing.
The tests were done using a 24" plunger stroke.
All values shown in the table below are in PSIG.
|STANDARD SEAT PLUG WITH 2-1/4" CAGE SPACING|
|STANDARD SEAT PLUG WITH 1-1/4" CAGE SPACING|
|STANDARD SEAT PLUG WITH 1/4" CAGE SPACING|
|RECESSED SEAT PLUG WITH 1/4" CAGE SPACING|
It is evident from the above information, that it is the proximity of the balls and seats that determines compression, not the proximity of the cages.
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