Quote:
Originally Posted by neelie
Without going into details, I am considering using a couple of schedule 40 in-line PVC ball valves, hose barbs and assorted fittings to direct and control the flow of cooling seawater to A/Cs and water maker.
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There is nothing wrong with using plastic
fittings and valves as long as they are protected (just as any small diameter pipeword should be even if metal). Contrary to the responses from some others I take it that you are not talking about using rigid PVC pipe, just fittings and valves.
I would recommend though that if it is below the water line you use threaded engineering polypropylene fittings which are good for typically close to 250 psi (there are also fibre reinforced ones but are harder to find) and plastic engineering ball valves. These are normally available from any plumbers merchant - I am not familiar with what
USA Home Depots stock, but may be available from them too. Above the waterline (say at least 200mm above) then rigid PVC is fine and often the material of preference in high quality builds (eg as Sandy points out, for black water).
In our own boat we have the polypropylene fittings and plastic ball valves (it was a professional custom build) below the water line for the seawater distribution headers after the seacocks with no problems at all. They are located so that they are protected from accidental physical damage. Our
engine exhaust, which discharges above the waterline, is an example of something we have fabricated from rigid PVC pipe.
From the surveys I have seen the greatest cause of flooding accidents in
boats is by far from failed metal pipework (ie after the seacocks) so metal solutions are not free from their own problems. Plastics will last the life of the boat, they (like any small diameter fittings and pipework whatever the material) just need to be protected from physical damage.
Regarding passing survey for
commercial vessels, in the jurisdiction I
work in plastics are accepted by local rules as it has been in vessels built to the rules of classification societies that I have been involved with. The usual limitations just being that the material is suitable for the task, including suitability for the fire rating of the compartment they are in, and properly installed for the
service. Personally, I believe that would exclude the use of rigid PVC below the waterline in seawater services - it does not exclude other plastics however.