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Old 02-03-2020, 16:14   #1
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PVC for raw water supply lines?

I am rebuilding my various cooling systems, which was built with a variety of brass, bronze and 316 SS fittings, along with a few PVC adapters thrown in for good measure. The 316 SS fittings and valves are perfect after 20 years, while the bronze and brass of course show some corrosion, most of which is cosmetic.

The seawater system consists of a Jabsco 2620 impeller pump for seawater, a plastic/SS pre-filter, bronze "Y" strainer (to catch impeller pieces), then on to two copper/brass heat exchangers (with isolating/balancing valves), a bronze oil cooler, and finally the SS exhaust elbow.

The engine coolant system uses another Jabsco 2620 for coolant, a bronze "Y" strainer for impeller pieces (neoprene impeller life is limited with glycol; nitrile not available for this pump), then through engine block/head, thermostat housing, steel exhaust manifold, two heat exchangers and back to coolant manifold which returns to pump inlet.

I was thinking of using only PVC or SS on the seawater system (PVC for "cold" sections, SS for hot sections at exhaust end), and leave the brass/bronze fittings for the engine coolant system. Both systems will have some sections of rubber hose as well, as necessary.

I know that PVC is only rated to 60C, but seawater should never exceed 30C in my area, and it's unlikely the output from a heat exchange would even approach 60C, although it might if flow is restricted, so I would probably just use it from pump to the manifolds, including valves. I would use threaded PVC fittings so they can be replaced easily.

Any reason not to use PVC in this application?

On a related note, I was also planning to use PVC (and maybe some PEX) for bilge pump lines. It should be more durable and flow better than typical bilge flex.

Thanks
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Old 02-03-2020, 17:21   #2
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Re: PVC for raw water supply lines?

PVC is too fragile.

Only use PP. for sea water handling

Dont know your local supplier

Georg. Fischer Common in European shipyards https://www.gfps.com/appgate/ecat/co...064/index.html

The picture is Fischer PP plumbing system
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Old 02-03-2020, 20:05   #3
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Re: PVC for raw water supply lines?

Quote:
Originally Posted by slug View Post
PVC is too fragile.

Only use PP. for sea water handling

Dont know your local supplier

Georg. Fischer Common in European shipyards https://www.gfps.com/appgate/ecat/co...064/index.html

The picture is Fischer PP plumbing system
That does look nice, but not sure how easy it is to find here. I forgot to mention that I would probable only use PVC fittings and maybe a few small sections of pipe - there would be barbed fittings to rubber hose for longer runs or where flexiblity is needed. PVC Schedule 40 & 80 are commonly used in direct burial applications here, so it is pretty durable. The primary thing I was thinking of using it for is a distribution manifold between the pump and the heat exchangers, and maybe to replace some brass elbows and tees that are were used before.

I'll check around to see if PP fittings are available here.

Thanks
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Old 02-03-2020, 20:17   #4
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Re: PVC for raw water supply lines?

A direct burial application and a boat are VERY different, mainly because of movement and vibration. PVC is brittle, flex it enough and it will crack. In the event of an engine room fire it also fails at very low temperatures, if you get the fire out, you sink anyway.

For hard piped raw seawater service the only reason to use PVC over stainless or bronze is cost. That is not a part of the boat where you want to pinch pennies. If cost is an issue, good seawater rated hose is a better choice... with stainless or bronze connections--NOT BRASS. I have seen manifolds made of heavy brazed copper pipe also that had a long and safe life.

Be prepared for a future insurance surveyor to tell you that a PVC manifold is unacceptable and needs to be removed.
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Old 02-03-2020, 20:36   #5
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Re: PVC for raw water supply lines?

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Originally Posted by billknny View Post
A direct burial application and a boat are VERY different, mainly because of movement and vibration. PVC is brittle, flex it enough and it will crack. In the event of an engine room fire it also fails at very low temperatures, if you get the fire out, you sink anyway.

For hard piped raw seawater service the only reason to use PVC over stainless or bronze is cost. That is not a part of the boat where you want to pinch pennies. If cost is an issue, good seawater rated hose is a better choice... with stainless or bronze connections--NOT BRASS. I have seen manifolds made of heavy brazed copper pipe also that had a long and safe life.

Be prepared for a future insurance surveyor to tell you that a PVC manifold is unacceptable and needs to be removed.
Well I guess that settles it then. The PVC that was in use was well above the waterline, and had rubber hoses at each side, so isolated from vibration, but I won't add any more, and see if I can remove these.

So copper is ok, but brass is not? There are definitely some brass elbows and tees that we're used, and I am pretty sure most of the NPT to hose barb fittings that were attached to bronze or SS tees are also brass. Sometimes it is hard to tell until it's all cleaned up.

There was a brazed copper manifold on the engine coolant side that I may re-use. I will go through my stock of bronze and SS fittings to see what I will need to make it work, and consider making a manifold from copper I guess.

My goal is to simplify the system, reducing the sprawl and points of failure. I removed nearly 100 hose clamps between the two cooling systems...

Thanks
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Old 02-03-2020, 20:37   #6
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Re: PVC for raw water supply lines?

What about pex for long runs instead of hose (not specifically for fire prone areas)?
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Old 02-03-2020, 21:01   #7
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Re: PVC for raw water supply lines?

My boat uses schedule 80 pvc for standpipes and is both ABYC and ABS certified.

Theres also some schedule 40 pvc but never below waterline.
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Old 03-03-2020, 03:32   #8
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Re: PVC for raw water supply lines?

Quote:
Originally Posted by sgwright View Post
Well I guess that settles it then. The PVC that was in use was well above the waterline, and had rubber hoses at each side, so isolated from vibration, but I won't add any more, and see if I can remove these.

So copper is ok, but brass is not? There are definitely some brass elbows and tees that we're used, and I am pretty sure most of the NPT to hose barb fittings that were attached to bronze or SS tees are also brass. Sometimes it is hard to tell until it's all cleaned up.

There was a brazed copper manifold on the engine coolant side that I may re-use. I will go through my stock of bronze and SS fittings to see what I will need to make it work, and consider making a manifold from copper I guess.

My goal is to simplify the system, reducing the sprawl and points of failure. I removed nearly 100 hose clamps between the two cooling systems...

Thanks
Galvanized steel has been used for a very long time

Its heavy , Needs paint but is very long lasting and robust

Copper is a bad choice

Stainless is a bad choice
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Old 03-03-2020, 04:10   #9
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Re: PVC for raw water supply lines?

As the OP noted, the maximum recommended operating temperature for PVC pressure pipe is 140F (60C).
However, the pressure ratings given for PVC pipe are for a 73F (23C) operating temperature.
To reduce the pressure ratings of PVC pressure pipe for operating temperatures above 73F (23C), multiply the pressure rating or pressure class by the published derating factors (ie: at 140F multiply rating by 0.22).
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Old 03-03-2020, 04:43   #10
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Re: PVC for raw water supply lines?

The reason small craft dont use hard plumbing is the expense and difficulty encountered when hanging and supporting the pipe work
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Old 03-03-2020, 06:15   #11
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Re: PVC for raw water supply lines?

For applications requiring temperatures above 140F, CPVC (chlorinated polyvinyl chloride) is recommended. CPVC is rated to a maximum temperature of 200 F (93.3C).

CPVC and PVC piping both test to the same pressure rating at 73F (22.8C), but as the temperature increases, CPVC maintains its pressure rating better than PVC.
See Chart.

Note: When either PVC or CPVC is heated, or melted, fumes (dioxin and hydrochloride26) that are toxic (in high quantities) are emitted.


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Old 03-03-2020, 10:48   #12
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Re: PVC for raw water supply lines?

JMHO, using PVC is an invitation for disaster.
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Old 03-03-2020, 13:14   #13
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Re: PVC for raw water supply lines?

Best to use hardwall water hose which is intended for this purpose. It has a blue stripe and is quite flexible, especially in the sizes you need. Fittings should be bronze. Groco has a full line of NPT - barb fittings.
If you are near Victoria Trotac Marine has everything you need.
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