Join Date: Jul 2000
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Unless carefully sized/engineered, an 'inlet' manifold serving several functions can easily be well below the flow requirements of the total requirements ... and 'choke'/cavitate. To do this correctly, you MUST calculate (then test) ALL the 'stack up' of pressure drops at full flow for all the 'branches'. Unless you do this carefully, you risk 'turbulent flow' and the *whole* system will not operate correctly .... the first component/branch to be possibly damaged will be the engine with a 'severely restricted' raw water flow. This is 'especially' pertinent for when in very WARM water so to prevent the inlet water from potentially 'flashing'/boiling when severe pump(s) vacuum is applied when the total 'demand' is the greatest and is becoming 'turbulent'. As S'dog stated, the engine should 'always' be on a totally SEPARATE and independent inlet.
Let me attempt to change your 'bronze apostasy' - There is absolutely nothing 'wrong' with bronze for seawater service - TRUE bronze, not the cheap 'red-brass' that is foisted off to marine consumers as 'bronze'. RedBrass is a 'bronze' that is loaded with zinc to make the bronze 'easily machinable' - can become a boats 'zinc anode' when the other boat zincs fail. "Good Bronze" is a royal bitch to machine and therefore is 'not cheap' because it takes special expertise and specialized tooling to machine it. One of the most stable bronzes for seawater service is Nickle-Aluminum-Bronze (bring your mortgage application with you when you buy NiAlBronze).
Marelon is a nylon co-polymer, Nylon readily 'hydrolyses' (comes apart) in long term water contact; I would rate 'marelon' one step above red brass for seawater service.
Last edited by RichH; 12-08-2010 at 10:51 AM.