... pumps (including one-piece pumps, combination pumps),a series of rod pumps and special pumps such as viscous oil pumps, sand anti-wedgingpumps and anti-gas-locking pumps ... oil pumps, gas-proof pumps and sand-proof pumps, inclined well pumps, hydraulic feed back pumps for heavy crude oil, pumps with forced mechanic valves, gas-proof pumps with ...