When we talk about a helm pump, we must also talk about both passive and power steering as that is the part of the system that interacts most with you and the rest of the steering system. Most passive (non-power assisted) systems are set up to be between 5 & 10 turns lock-to-lock on the steering wheel and if we translate into to mechanical advantage, it goes like this—We’ll use total rudder arc at 70 degrees (about 1/5th of a full circle and seems most typical in most steering installation guides) for this example– If it takes 7 full 360 degree turns of the steering wheel to give full stroke or full rudder travel, then you have about a 36:1 gear (actually hydraulic) ratio between the two.. All else being equal, most steering systems fall in the 20:1 to 40:1 ratio range. Think about it—you just went through 7 x 360 degrees of helm pump rotation (2520 total rotational degrees) , but the rudder only rotated 70 degrees of total arc; hence a 36:1 ratio, “on paper”(we’ll get to that later) between you (the steering wheel) and the rudder. Bet you never thought about it that way before!
Also need to mention that with passive steering you have both pressurized 3-line systems and non-pressurized 2-line systems. There are some that think
“pressurized” has something to do with power steering, but it does not. Hynautic (no longer as they were bought by Teleflex) invented the 3-line pressurized system for one reason—to make it simple to bleed and fill and to allow a less critical installation as to elevations of components, etc.. “Gravity” was not a concern with the pressurized systems. But with that, they added something that most don’t
know. It usually has a much higher steering effort because of an added complexity of more lines and valves. It comes down to internal friction that is created when pushing fluid through hose, pipes and fittings.
In a pressurized 3-line system, you typically have between 15 & 25 PSI at all times in the reservoir, “third line and the low pressure side of the pump. In a 2-line non- pressurized system (although you may still have a 3rd line), the reservoir and / or low pressure side on the system is at atmospheric pressure and relays on gravity and height to keep the flows right between multiple stations. That’s also why you can use clear vinyl tubing for supplying fluid between stations and or reservoirs.