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Oil well pumps may be classed as either tubing or rod
pumps. In the case of tubing pumps, the barrel is run on the tubing
and the plunger is run on the rod string. In the case of rod pumps,
the complete unit is run on the rod string. Rod pumps have the
advantages of being more easily removed for servicing and less
susceptible to damage in running, but they offer less working area
for the plunger, since the maximum bore of a rod pump is
necessarily less than the maximum bore of a tubing pump for the
same size tubing.
Pumps may be further classed by the nature of the barrel.
Liner barrels are made up of jackets with sectional or one-piece
liners held in position by collars. Full barrels are one-piece tubes
threaded at each end.
Tubing pumps may be equipped at the lower end with
regular shoes or with extension shoes and nipples. The latter
arrangement permits a longer plunger stroke for a given length
pump barrel. In the nonextension style, however, there is less
space around the standing valve for accumulation of sand deposits.
Rod pumps are of either stationary barrel type with top or bottom
hold-down, or traveling barrel type. Stationary barrel pumps have
reciprocating plungers actuated by valve rods. In traveling barrel
pumps the barrel reciprocates over the plunger assembly.
The American Petroleum Institute has adopted a
classification system based on the above characteristics. Figure
20.2, which shows the five classifications, is taken from API
Standard 11 A, which is also the reference for all specifications
pertaining to oil well pumps, and for recommended field practices
pertaining to care and use of pumps. Class 1 is a tubing type with
regular shoe. Class 2 is a tubing type with extension shoe and
nipple-Class 3 is a rod type, stationary barrel, with top hold-down.
Class 4 is a rod type, stationary barrel, with bottom hold-down.
Class 5 is a rod type, traveling barrel. In Fig. 20.2, the first letter of
the abbreviated designation is either "T" indicating tubing type
pump or "R" for rod type pump. The second letter is either "W."

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