I wish I knew before about Eng-tips web site. Anyway, I am Engineering operator on a ship and I am learning the steering system. Looking at the manual and the technical drawing, I understand the entire system except 2 components in the system which are the "shuttle valve" and the 2 "Check-Q-Meters".

Let me explain the system more in details:

2 Hydraulic pumps are supplying the system, a main pump and a standbye pump. From the Directional valve, the flow goes to the "Check-Q-Meter" and also the shuttle valve (connected to the return line) . Then after the "Check-Q-Meter" it goes to your 2 steering motors and then the flow goes back to another "check-Q-Meters" and the the shuttle valve again (which is between the supply and the return side) and then back to the directional valve.

A shuttle valve is a type of directional control valve which permits a system to operate from either of the two fliud power sources. In you circuit is is probally acting as a safety.  In the event that the main pump can no longer supply the power to operate the downstream devices, the shuttle valve will shift to allow fluid to flow from a secondary backup pump.

In other words, a shuttle valve will always select from the highest input pressure and route that flow to the output pory if the valve.

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