As seen in Speedboat Magazine’s April 2020 Issue.
I’m plumbing a twin-engine power steering with pressure from both pumps. I have a return line question. If I run a single line thru the straight part of a tee to a second cooler then branch from tee to first cooler, will it show preference or overload second reservoir? Or should I turn the tee and branch and run 2 sort of equal length lines to coolers to better balance the flow? Or, should I run sealed reservoir caps with hose reservoir cap to reservoir cap to balance? I am wondering if a closed system will present problems. My experience is with Sea Star style hydraulic steering which is fairly basic. My new boat requires new knowledge.
Thanks for any info you may have.
Todd Buchanan Lake Isabella, MI
Full Hydraulic Steering for Twin Engine Applications
You are doing the right thing by using two power steering pumps, which provides for redundancy and increased safety.
First of all, in order to properly plumb your steering system, it should incorporate a priority valve that the pressure lines from the pumps are connected to. The priority valve has check valves in it that prevent backflow to a pump of an engine that is not running. Using a priority valve will insure that you still have power steering when only one engine is running or in the event that a pump were to fail, or lose a belt.
The return line from the helm should be connected to a tee that splits the return to each engines’ power steering cooler. Many priority valve assemblies that are available have the return line tee already incorporated in them. A couple of decent choices are IMCO and Latham Marine.
The type of power steering pumps you have on your engines will dictate exactly how the return lines will be connected to the pumps. If your power steering pumps are the Saginaw (GM style) with the reservoir “can” on the back, connect the return line from the power steering coolers to the return port on the back of the pump. The two reservoirs that
are integral on the pumps normally have a cap on them. This cap needs to be removed and replaced with an adapter that seals on the neck of the can and has an NPT port on it (IMCO is one of the common ones). Then adapter is connected to the two pump reservoirs to a common reservoir that is mounted remotely and above the level of the power steering pumps. In lieu of using the caps that seal with an o-ring, a plate with a 3/8” NPT port can be welded to the top of the tin reservoir. Teague Custom Marine has billet reservoirs available for the Saginaw pumps that incorporate all the features you will need for proper plumbing.
If your power steering pumps are not the Saginaw style, the plumbing of the remote reservoir will be different. Some of the pumps on the later Mercury engines and Ilmor engines have a plastic reservoir that is remote from the pump. This is the case on most later model engines with serpentine accessory belts. The best way to plumb the return lines on these engines is to return from the power steering cool-ers to a common reservoir that is mounted higher than the power steering pumps on the engines. Then, from this same common reservoir, a supply hose is routed to the inlet of each power steering pump.
The cap on your remote reservoir needs to be vented. The fluid in the steering system expands and contracts depending on temperature. A sealed system is not an option.
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