Advice or guidance on piping from tanks to pump

[Uthyrbendragon]

So I am about to embark on a full re-plumb of my 1984 Beneteau First 35.

I have a new Isotemp water heater and going to use Whale 15mm quick connect from the pump/accumulator through to the faucets etc.

I have two water tanks, one each under the port and stbd settees respectively.

Should I go for larger diameter supply pipe (aka old school pvc) from the tanks to the pump or should I go With 15mm throughout? It seems to me that low pressure/high flow rate is better before the pump but looking to you wise folks for guidance!

Thanks in advance.

[leecea]

As an FYI... my Hunter 36 has one water tank under the v-berth and the pump is under the galley sink. The pump is 40 psi 2.8 GPM. I have the same diameter PEX-like plumbing for all the connections.

[Uthyrbendragon]

Originally Posted by leecea

As an FYI... my Hunter 36 has one water tank under the v-berth and the pump is under the galley sink. The pump is 40 psi 2.8 GPM. I have the same diameter PEX-like plumbing for all the connections.

Thats a great reference point, many thanks.

I have seen many diagrams showing 15mm or 1/2” pex running from the tank(s) but I can’t help but wonder if the greater ID of pvc pipe would be better, albeit with the disadvantage of being transparent.

[Jammer]

Unless there is something unusual about your installation, 1/2" (15mm) is more than sufficient. In general, 1/2" is good up to around 5 gallons per minute, and most marine plumbing systems are designed with a capacity around 2 or 3 gallons per minute.


In reality, the less-common 3/8" PEX is sufficient, and lighter, for most marine and RV freshwater systems.



A more analytical answer would require knowing the volume (GPM or lpm) you expect to get through the pump, the vertical separation between the pump and the bottom of the tank, and the overall piping distance between the tank and the pump.

[Uthyrbendragon]

Originally Posted by Jammer

Unless there is something unusual about your installation, 1/2" (15mm) is more than sufficient. In general, 1/2" is good up to around 5 gallons per minute, and most marine plumbing systems are designed with a capacity around 2 or 3 gallons per minute.


In reality, the less-common 3/8" PEX is sufficient, and lighter, for most marine and RV freshwater systems.



A more analytical answer would require knowing the volume (GPM or lpm) you expect to get through the pump, the vertical separation between the pump and the bottom of the tank, and the overall piping distance between the tank and the pump.

Awesome, thanks for taking the time to explain - 15mm throughout it is then.

Interestingly, it also seems that PEX plus connectors may even be marginally (and I mean marginally) cheaper than pvc with a myriad of SS hose clamps and it has the benefit of not being transparent.

Thanks to all the comments and responses to my question.