RV Water Pump Basics for Motorhomes, Fifth Wheels & Travel Trailers.
When not hooked up to an external supply, fresh water must be pumped from the on-board RV water tank using an RV water pump. When the power is switched on, the pump works automatically whenever a faucet is turned on. It's normal for the pump to pulsate. The water pump is preset to keep a more-or-less constant water pressure. When the pump senses a drop in pressure, because you're using water, it runs long enough to restore the pressure and then shuts off. Depending on the demand for water that pressure can be restored rapidly causing the pulsing.
You can install a device called an accumulator tank that will minimize the pulsating. Also new model RV water pumps are available that claim to eliminate the pulsation and noise.
If your motorhome, fifth wheel or travel trailer water pump is excessively noisy check to see how it's mounted. The pump's mounting screws should go through rubber grommets and the screws should NOT be tightened down on the mounting grommets thus allowing the pump to 'float' on it's mounting. This floating helps insulate the vibration of the water pump from the RV's frame making operate more quietly.
It's a good idea to switch off the pump when not in use... especially when leaving the RV unattended but it is OK to leave it on if you want.
IMPORTANT: If the water pump runs periodically when all faucets are off you have a leak in the water system. The leak may be in the plumbing or it could be in the pump itself. If you are sure that your plumbing is not leaking then the leak is most likely in the pump's internal check valve. This check value is needed to keep water from flowing back through the pump into the freshwater holding tank when your motorhome, fifth whee or travel trailer is connected to an external water system. In fact, if you notice that the water level in the freshwater tank is rising it's good sign that the pump is at fault. There are rebuild kits for most water pumps or, depending on how old the pump is, you may want to replace it.
We've been in parks where the water pressure has been very low so we had to use our water pump to boost the park's water pressure to take showers. It works because the pump draws additional water from the fresh water tank to supplement that coming from the park.
If the pressure of the water coming from the hook-up is less than the pre-set low pressure of your fresh water pump then water will be pumped from your fresh water tank to increase the pressure to that of the pre-set high pressure of the pump. If you do not want to pump water from your freshwater tank turn the water pump off.
The two most common fresh water plumbing systems are:
1: A hose connection which bypasses the fresh water tank and RV water pump and a separate fill spout used to fill the fresh water tank directly.
2: A hose connection with a valve somewhere near the connection or in a utility area... turn it one way to fill the fresh water tank the other way for direct use.
There is a check valve in the plumbing system that permits the outside water supply to charge the system without going into the freshwater tank. This could be a check valve inside the water pump and it may be the only one or there may also be an external check valve on the discharge side of the water pump.