How An RV Water Pump Works


When we purchased our RV we had to get familiar with all its systems. Since water is one of the essentials for life it was pretty important for us to get to know how we would get running water in our motorhome.

An RV water pump works off of your 12V battery. When you open a tap or flush the toilet, and are not connected to city water, the pump detects the pressure drop and will turn on to maintain the pressure. You’ll need to switch power to the pump on and have water in your fresh water tank.

While relatively straight forward, the concept of having a pump for water is unfamiliar to many of us. There are some things to know to help you keep your pump running well.

How Pumps Work

Now I’m going to tell you something very important that I learn in my thermodynamics class at university.

Pumps Pump Liquid.

Diane’s Thermodynamics Professor

I know that seems obvious but the quickest way to damage a pump is to run it dry. Pumps are designed to move liquids from an area of lower pressure to an area of higher pressure, usually against gravity.

In an RV, the water pump is typically a diaphragm pump with 3-5 chambers. The diaphragm is driven by an electric motor to create suction and has a valve on either side of the chamber.

The diaphragm expands creating more volume and lower pressure, the valve at the outlet of the chamber closes, and water then flows into the chamber with the valve at the inlet opens. The diaphragm contracts creating less volume and more pressure, the valve at the inlet closes and outlet opens forcing the water out of the chamber.

Diaphragm pump animated

Courtesy of There’sNoTime / CC BY-SA

12V electric water pumps tend to be low pressure and low flow. A diaphragm pump is well suited to this type of use.

Also, they can handle some dry run time and can self-prime. This means you don’t need to worry about priming your pump after having your system fully drained.

I wouldn’t let it run dry for too long though even if it can handle it. Something is wrong if the pump is running but no water comes out, see the Troubleshooting section below.

Most commonly these pumps are constant speed pumps. They are either on or off causing them to pulsate when in use because they are trying to maintain a preset pressure, learn more in our article about RV water pumps pulsing. The system will reach the required pressure fairly quickly so the pump will turn off but will then turn on again when it drops back below the threshold.

Variable speed pumps do exist which eliminates the pulsating and usually run quieter. They are found in more expensive RVs, though you can upgrade the one in your current rig.

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If you do not have water hookups and are just running off your fresh water tank then it’s okay to leave your pump on. Your pump should not run unless you have a demand for water, such as turning on a tap or flushing a toilet.

You should, however, turn off your water pump while driving. You don’t want a bump or bounce in the road to knock a faucet open and have water running while your driving.

We personally turn our water pump off at night and also if we are not around the RV. This is a just in case measure but I have heard a story about a cat turning on the faucet which led to a flood and massive damage. It’s better to be safe than sorry.

Water Pump Care and Maintenance

Fortunately, water pumps are pretty easy to care for and don’t require a lot of maintenance. Standard maintenance for your water pump includes inspecting the water lines, cleaning the pump strainer, and sanitizing the water system

Inspecting the water lines is straight forward. Just do a visual inspection to check for any leaks, kinks or damage to your water lines. In areas that are hard to see, try to get your hand in there and have a feel to make sure nothing feels wet.

A pump strainer should be installed between the fresh water tank and the pump. This will prevent debris and dust from getting into the pump and causing damage.

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To clean the pump strainer, disconnect the water line from the strainer then unscrew the strainer from the pump. The strainer itself should twist apart and you can access the mesh inside.

Give the mesh a good rinse, for any stuck on debris use an old toothbrush to scrub it. Then put the strainer back together the same way you took it apart and reinstall it on the pump and water line.

To help prevent debris from getting into your fresh water tank in the first place use a filter on your incoming waterline when you fill your tank. These are very inexpensive to buy and will help keep particles out of the water. You never know what quality of water you are getting at a campground or dump site.

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It might surprise you to hear that sanitizing your water system will help keep your pump running longer. One of the leading pump manufactures states that premature pump failure and poor performance are frequently caused by a lack of sanitizing.

Scale build up on the diaphragm and valves can cause low flow and leak back issues. Sanitizing your water system before storing your RV and before the first use of the season will help keep your pump running for a long time.

For more details about caring for you RV water pump, see our dedicated article How to Care for an RV Water Pump. You can also learn best practices for storing your water hose and keeping it clean.

Troubleshooting

Having issues with the water pump in your RV? Here are some common issues and possible fixes.

Why is my water pump so noisy?

RV water pumps tend to be a bit noisy due to the nature of their pulsating. That being said if you pump sounds noisier than it used to there are a few things you can check.

Do a visual inspection of your pump and make sure nothing has come loose or is touching the pump causing vibration. The mounting screws should go through rubber grommets and be neither too tight nor too loose. You want the pump to sort of “float” so that it won’t vibrate against the mounting surface.

If it doesn’t seem to be something physical like the mounting causing the excess noise, check the strainer is clean and there is no build up causing the noise.

Unfortunately, it could be a sign that your water pump is on the fritz. So keep an eye on it.

When I turn on the faucet, no water comes out?

If no water is coming out of your faucet the first thing to figure out is if the pump is turning on or not.

Is the pump making noise?

If the pump is making noise that means it is working but water may not be reaching it.

First, make sure your fresh water tank is full. I know this seems obvious but its best to rule out the easy stuff first. If your tank is low or empty then it makes sense you won’t be getting any water. Remember “Pumps Pump Liquid”

Once you’ve confirmed your tank is full or there is at least some water in it, its time to check for leaks. Do a visual inspection around your water pump to look for any obvious signs of a leak. Ensure all connections to the pump are connected and tight.

Next, disconnect the pump intake line and check for water in the pipe. If there is water then the pump is sucking water from the tank and you may have a leak between the pump and the faucet.

Try turning on all the faucets in the RV and flush the toilet to see if any of your fixtures are getting water. This might help you narrow down where your leak is.

If the intake line to the pump was dry you likely have a leak between the tank and the pump. Check the line for any signs of damage.

If none of these reveals any sort of leak, your pump may have died and will need to be replaced.

Is the pump not making noise?

If the pump is not making noise, then it is not turning on. When you are troubleshooting anything you need to check if its plugged in and turned on, a water pump is no different.

To start, you will need to confirm if power is going to the pump. Check that the pump switch is in the on position. Cycle the switch on and off to see if any sort of reset occurs.

Next, make sure your battery isolation switch is not engaged, see if other things that run on 12V are working or not. Also, check your battery voltage if you aren’t plugged in.

See if you have any blown fuses. Your RV’s manual will tell you which fuse you need to check.

Your last step to check for power will be to take a voltmeter and go directly to the source. Make sure your pump is actually receiving 12 volts from the batteries.

If it’s not then you have a wiring issue which will be a big pain in the butt. If it is receiving power then you likely need a new pump

Why is my pump running when the faucet is off?

If you are hearing your pump running but no one is using water, TURN YOUR PUMP OFF NOW!

RV water pumps are on-demand pumps, if it is running it means your system is losing pressure somewhere. In other words, you have a leak.

Do a full inspection of your water lines to find out where the cracked or damaged line is. It may be something as simple as a loose fitting but you might need to replace some of your piping.

Hopefully its something simple like a running toilet, you can learn how to fix it yourself in our article A Simple Fix to a Running RV Toilet.

Recommended RV Water Products

Water Filter (Amazon) – a basic water filter like this one from Camco helps keep your water system free from sediment, chlorine and heavy metals

Water Pressure Regulator (Amazon) – you never know if an RV park will have strange water pressure so using a regulator will keep your water system safe from high water pressure

Water Hose (Amazon) – using a quality hose for your fresh water is important to prevent unwanted BPA’s and Phthalate from entering your water system. Plus having one that’s UV stabilized will help it to last a long time.

Diane Dee

Diane is a lover of all things travel. She and her young family wanted to explore North America from the comfort of their own home so they bought an RV. After fully rehabbing a 1994 Safari Trek, they set out to explore both Canada and the USA.

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