Water pumps lpm importance

[Cornishkiwi]

Hey all

Just wondering if there are any charts or rules of thumb to guy buy when choosing a pump. I'm going for a marco 2.5 bar pump for my fresh water system. I'm supplying 2 sinks and shower through a 44ft yacth. But was wondering the importance of lpm/gph, is more better or is it finding the perfect balance as if have to large are you essentially just wasting water??

cheers

[Lepke]

Depends on how much water pressure you want and how consistent you want that pressure. And are the sinks and shower operating at the same time.

I use an oversize pump with a switch the turns on the pump when the pressure slightly drops. So I have consistent pressure. I don't worry about how much water I use because I have a watermaker sized so I don't have to worry about how much water I use.

[Cornishkiwi]

Well i'm happy 2.5bar will be enough pressure to Supply the boat with a constant pressure.

But what i don't get is if i have a choice to get a pump at 14lpm, or one and 26lpm i would go for the 26lpm, yet can you go to big? is there problems with going overkill?

[Tupaia]

All pumps have an operating curve, as the flow increases the pressure decreases. You need to pick a pump where the desired pressure can be met at the desired flow rate.

A shower uses between 8 and 12 lpm depending on the user preference. Put a bucket in your shower at home and at the required setting and measure the water after 1 minute. This will give you a handle on your preference for volume (flow).

How much pressure you need will be determined by the shower head, pipe size and length. It then depends on how many people are on board and if you expect them to be using the other outlets at the same time.

It is always a balance a bigger pump uses more amps requires bigger wiring.

[tkeithlu]

There's a mixing of pressure and flow in these posts.

All the pumps with the same pressure switch will produce the same STATIC pressure, that is pressure in the pipes when no water is flowing. Liters per minute and pressure out the faucet depends on two factors. First, friction in the pipes drops pressure and flow at the end, so the bigger the hoses/pipes the more consistent the flow/pressure. As flow at the end goes up pressure drops. Second, cqn the size of the pump keep pressure at the start of the system up when use is maximum? If you want consistent flow/pressure at the user end, the pump needs to be sized for it. Beyond enough pump to keep the pressure the same at the pump end, a bigger pump that is switched at the same pressure will not result in greater flow at the other end - the pump will simply run slower.

With constricting/water saving shower heads, flow isn't what it used to be. Even our kitchen faucet (on shore, not the boat) flows less than 1.5 gallons per minute, so I've found that a 2 gallon per minute pressure pump on the boat is plenty, despite 1/2" diameter piping.

[Lepke]

Originally Posted by tkeithlu

With constricting/water saving shower heads, flow isn't what it used to be.

First thing I do with a new shower/sink head is drill out the water saver.