Abstract: A wellhead assembly to seal and suspend an in-casing hydraulic drive unit for a downhole pump, including pressure-containing wellhead body members with a vertical bore and a production bore at its uppermost portion. A hydraulic pump hanger is retained and sealed in the vertical bore. The hydraulic pump hanger suspends and seals the hydraulic cylinder, includes a bore extending vertically therethrough, forms at least one hydraulic line to communicate with hydraulic fluid supply lines, forms a hydraulic inlet port to each hydraulic line, and provides a check valve sealed in each hydraulic inlet port. The wellhead body member(s) includes a stem port aligned with each hydraulic inlet port, with a valve actuating stem sealed in each stem port to actuate each check valve between a normally closed and open position. The wellhead body member(s) also includes hydraulic injection port(s) formed to supply hydraulic fluid to each hydraulic inlet port.