| 摘要 |
A downhole pump has a barrel and a plunger which reciprocate with respect to each other. The plunger has a first portion with a first seal, a second portion and a third portion with a second seal. The second portion is intermediate the first and second portions. A balancing chamber is formed between the plunger second portion and the barrel. The balancing chamber communicates with the plunger interior by way of an opening. A sand snare chamber is provided with respect to the opening so as to prevent sand from contacting the seals in the balancing chamber.
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