Abstract: A lock valve apparatus and a hydraulic system incorporating a lock valve apparatus including a lock valve body with a bore, a first port, a second port, a third port and a fourth port. There is a spool valve with a valve spool reciprocatingly received in the bore. The spool valve, a first one-way valve and a second one-way valve normally prevent fluid flowing between the ports. The first one-way valve and passageways in the valve permit a fluid flow from the first port to the third port when the first port is pressurized. The second one-way valve and passageways in the spool valve body permit a fluid flow from the second port to the fourth port when the second port is pressurized. The spool valve is shifted to align passageways, including a first annular passageway, between the spool and the bore to permit a return flow of fluid from the fourth port to the second port when the first port is pressurized. The first annular passageway receives pressurized fluid from the fourth port.

Abstract: A lock valve for marine hydraulic steering systems includes a valve body with a spool valve reciprocatingly received in a bore therein. A first port and a second port of the valve are connected to a manual pump. A third port and fourth port are connected to a double acting hydraulic cylinder connected to a rudder or steerable motor. There are valves within the lock valve which normally prevent fluid flowing between the ports so the steering system remains in a fixed position when the helm is released. Fluid can flow from the first port to the third port when the first port is pressurized. A return flow of fluid from the fourth port to the second port is permitted only when the first port is pressurized. When the second port is pressurized, fluid can flow the second port to the fourth port. A return flow of fluid from the third port to the first port is permitted only when the second port is pressurized.

Abstract: A lock valve for marine hydraulic steering systems includes a valve body with a spool valve reciprocatingly received in a bore therein. A first port and a second port of the valve are connected to a manual pump. A third port and fourth port are connected to a double acting hydraulic cylinder connected to a rudder or steerable motor. There are valves within the lock valve which normally prevent fluid flowing between the ports so the steering system remains in a fixed position when the helm is released. Fluid can flow from the first port to the third port when the first port is pressurized. A return flow of fluid from the fourth port to the second port is permitted only when the first port is pressurized. When the second port is pressurized, fluid can flow the second port to the fourth port. A return flow of fluid from the third port to the first port is permitted only when the second port is pressurized.