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Raritan Engineering Company your marine hardware supplier would like to share with you these topics we thought would be of interest to you this month regarding 

Pressurized Freshwater Systems

The freshwater pump

Freshwater pumps provide water to fixtures onboard a boat. Pressurized water systems make life onboard more pleasant by providing water “on tap” for dishwashing, showers and various other applications. The intricacy of installing and maintaining one will depend on the number of outlets and accessories you choose.

Precisely where they are used: On all boats bigger than runabouts and day-sailers, fresh water on board is both a convenience and a requirement. The freshwater pump is at the center of the delivery system which ensures a continuous supply to the fixtures in galley, head and shower.

Qualifying Questions

Do you really want on-demand water supply?

Let your marine water heater company help you with some advice on this topic. On-demand pumps have a pressure switch that makes the pump build up pressure in the fresh water line. Any time water is required and the faucet is opened, a flow of pressurized water will be available. The pump turns on to preserve this pressure as required. By comparison, manual pumps have no pressure switch, and must be switched on by hand (via an electric switch) prior to when the water is needed.

How many outlets does the pump need to serve?

Freshwater pumps are frequently described by how many outlets they can supply (“for 2-3 faucets”). Extra taps or fixtures in the system might cause a decrease in flow capability, erratic flow, or extreme pump cycling if several were “open” at one time.

How much capacity do you want?

Pumps will generally be chosen by how many gallons per minute (gpm) they can pump, and/or by just how much pressure they can create. The freshwater pumps we provide have capacities between 1.1 and 11 gallons per minute. A few general standards for sizing the pump:

Number of fixtures

Recommended gpm


Up to 3.0 gpm.


Up to 4.0 gpm.


More than 4.0 gpm.

Do you want an electric or a manual pump?

Some pumps make use of electricity to operate, and others use muscle power. But almost any type of pressure water system should possess a freshwater and/or saltwater manual pump and spigot as backup. Electrical pump failure should not remove your accessibility to fresh water.

Do you want to pump both fresh and saltwater?

Many galley pumps can not be utilized with saltwater, because salt is going to damage the valves and seals or corrode internal metals. Nevertheless, to conserve freshwater, especially on small vessels with minimal tankage, you might wish to utilize saltwater for dishwashing. A preferred technique utilizes a bucket for the very first wash cycle before rinsing the clean dishes with freshwater, either in the galley sink or using the deck shower system. If you want to pump both fresh- and saltwater, select a saltwater-capable pump.

You can find more information as well as get assistance on a boat water heater at

Where would you mount the pump?

This question determines whether you need a self- or non-self-priming pump. Non self-priming pumps need to be installed at or below the water level, so water is already in the pump chamber. They can force water uphill against gravity. Self-priming pumps can be situated above the water level, since they can draw the water upward to them whenever they are turned on.

Exactly what type of electrical system does your boat have?

Is it 12V or 24V? We offer several pumps for both. Amperage draw varies by capacity, however the 24V model of a given pump might draw approx. half as much current as the 12V equivalent. NOTE: Starting amperage draw may be considerably more than operating draw. See individual product information in the Master Catalog.

Which port size do you need?

Greater capability pumps will possess port sizes of 3/4 or 1″ to enable even more flow. Some shower pumps provide multiple port sizes in between 3/4″ and 1 1/2″. Otherwise 1/2″ NPT ports are typical on freshwater pumps.

What to look for.

The significance of multiple pump chambers: Additional chambers typically imply smoother operation, along with less pulsation, in diaphragm pumps.

Variable Speed: New variable speed pumps offer a noticeable enhancement over accumulator tank systems. They change the speed of the motor to deliver the precise quantity of water wherever it is needed. There’s virtually no lag time, and there’s no drastic distinction in pressure if two or more faucets are open simultaneously.

Rated gpm: Gallons per minute. Explains the pump’s output under ideal (open flow) conditions. This does not take into consideration head height, friction in the system and other elements which will decrease output. For most boats, high gpm pumps may not be a benefit, especially if the fixtures only permit a restricted amount of water to flow.

Run dry capability: A few electric pumps could be damaged by running dry. This implies that the mechanism burns up or wears out when there is no fluid present. To avoid this problem, some pumps have “run dry” sensing units that spot a lack of water flow and shut off the pump to protect it.

Vibration dampeners make certain electrical pumps somewhat quieter, by absorbing some of the shock in the pump action.

A check valve is a mechanical valve which only permits water flow in 1 direction. It will also stop city water pressure (which is more than the pump can deal with) from going into the pump. Most diaphragm pumps have check valves built-in.

A pressure switch opens up the electric circuit to a pump (and turns it off) when the water in the system reaches a pre-set pressure, typically 35-60psi. It closes the circuit (and turns the pump back on) whenever the pressure falls below that point. It is the device that makes on-demand pumps work automatically.

The rest of the system.

Your boat water heater company recommends this…Freshwater Tank: We believe the finest tanks are made of thick-walled, high-density polyethylene, but versatile tanks can operate in an odd-shaped or inaccessible area. Tank size depends upon the space available and your requirements (anywhere from one to ten gallons per individual per day might be consumed). Ensure your tank’s deck fill has a snug seal and that your tank’s vent terminates the boat so your drinking water supply won’t be fouled by outside water.

Hose: Most pumps and fixtures are developed for 1/2″ ID hose. Be sure the hose you choose can deal with 35-40psi and is made from FDA-approved (nontoxic) products. Hot-water hoses must be reinforced to withstand high temperatures.

Strainer: Any type of electric pump ought to be protected by a strainer or in-line filter. Water system and washdown pump manufacturers typically sell strainers which could be attached upstream from their pumps.

Accumulator Tank: A sealed air chamber combined with a water reservoir offers expansion volume to reduce pump cycling from minor pressure modifications and provide a constant flow. Bigger tanks can easily store enough water to eliminate pump cycles when modest quantities of water are required. Up until a few years ago, this was the last word for functional pressure water systems aboard.

Freshwater Systems.

Municipal Water Inlet: Simply by connecting a drinking-water-safe garden hose in between a municipal water inlet and a faucet on shore, you’ll possess a constant source of pressurized water at the dock without ever having to fill up the tank or run the pump. To protect and isolate your pump and accumulator tank from possibly damaging high pressure, set up a one-way check valve as revealed in the diagram.

Water Heater: The water heaters we carry can be run at the dock by AC power or underway by getting heat from your engine’s cooling water. Also a small, 6-gallon heater is enough to offer hot water for washing dishes or taking a short shower.

Faucet/Shower: Showers, whether in the head or out on the swimstep, can greatly improve your quality of life on board. Higher capacity pumps with big accumulator tanks will provide the most home-like shower. When including an interior shower, it is required to possess a shower sump so you don’t satisfy up your dry bilge with slimy water each time you shower.

Final notes.

Add a water system purifier to your tank periodically in order to inhibit the growth of algae. The clarity of your water will improve and your system won’t grow a permanent green lining. Boat owners that venture far offshore should think about adding a watermaker to their freshwater system. Use high quality hose and hose clamps and examine the whole freshwater system frequently. Sailboat owners ought to consider putting in a siphon break in the drain lines of sinks, or turning off sinks’ thru-hulls when not in use. It’s feasible to heel over to where the sink is below the waterline, establishing a siphon that can flood the interior of the boat.

So don’t forget these beneficial stats on what type of freshwater or saltwater pump you need for your boating needs.

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