| 摘要 |
A fluid pressure powered apparatus comprises a double-acting member, a first pilot valve, a second pilot valve, and a switchable valve is disclosed. The double-acting member is operable between a first stroke end and a second stroke end by fluid pressure from th e switchable valve. The first pilot valve is configured to supply a biasing fluid pressur e to a first bias surface of the switchable valve. The first pilot valve is actuatable by the double-acting member when at the first stroke end to reduce the biasing fluid pressure on the first bias surface. The second pilot valve is configured to supply a biasing fluid pressure to a second bias surface of the switchable valve. The second pilot valve is actuatable b y the double-acting member when at the second stroke end to reduce the biasing fluid pressure on the second bias surface. In operation, the reduction of biasing fluid pressure on either the first bias surface or the second bias surface, respectively, triggers the switchable valve to swit ch between a first stroke position and a second stroke position, respectively. A method of reciprocating a fluid pressure powered apparatus is also disclosed. The fluid pressure powered apparatus and the method disclosed herein provide a zero-emissions pumping system for injectin g chemicals or conditioning agents into a natural gas pipeline.
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