RV Systems – How They Work – Part 1.

Antique RVs







When Lynda and I bought our first motorhome we had no idea all the systems our new home on wheels contained. The salesman gave us a quick overview of how to operate the systems, of course, I retained only about ten percent of what he said.

Fortunately, this wasn't our first RV so I had some knowledge of what was involved. Becoming familiar with all the systems and it's quirks took some getting use to.

In this article, I cover most of the systems found on and in modern RVs.

The First RVs

The covered wagon may have been the first RV. The Pilgrims used it to travel across the continent to a new life. Once the automobile was invented RVs changed.

Drivers began making camping alterations to cars almost as soon as they were introduced. The first RV was Pierce-Arrow’s Touring Landau. The Landau had a back seat that folded into a bed, a chamber pot toilet and a sink that folded down from the back of the seat of the chauffeur, who was connected to his passengers via telephone


The Pace Arrow Landau
The 1910 Pace Arrow Landau

Camping trailers made by Los Angeles Trailer Works and Auto-Kamp Trailers also rolled off the assembly line beginning in 1910. Soon, dozens of manufacturers were producing what were then called auto campers.

The Modern RV

My first RV was a truck camper. The systems would be referred to as primitive by today's standards. The water system consisted of a fresh water holding tank and a manual pump at the sink. The sink drained out the side of the camper via a garden hose into a container, a collapsible thick plastic bag. The electrical system was a 12-volt battery power powering two lights. The stove was a three burner cook top with no oven. The heating system was also simple, radiant heat from a built-in propane heater. Ventilation consisted of a ceiling vent.

That was it, no toilet, no other amenities other than a claustrophobic double bed without enough headroom to sit up. The bed design was referred to as east-west, meaning you slept across the width of the camper, not the north-south direction (the length of the camper).

The problem with this design, if the person in the front sleeping position needed to get out of bed before the other person it was necessary to climb over and no doubt wake the other person. 

My first travel trailer was a 70's vintage model, I don't recall the brand name. The systems were more complicated than the trucker camper, the water system consisted of a 20 gal. fresh water holding tank and a 12-volt water pump to push water to the single kitchen sink tap, bathroom sink tap, and toilet. No shower, tub or hot water tank.The toilet and the sink's grey water emptied into the same holding tank.

The electrical system  was a bit more complicated, two completely separate systems, a 12-volt DC system, and an 110-volt AC system . The 12-volt system received its power from the battery and in turn powered the 12-volt lights and water pump.

The 110-volt system received it's power from an outside source (shore power or plugged into the house) it powered 110-volt home type lights. To finish the system there was one 110-volt powered receptacle (plug). Obviously, the converter had not been invented yet or too expensive to use in an RV.

The heating system was the same as the truck camper, a built-in radiant propane heater. The problem with these heaters, the heat rose to the ceiling so the floors stayed cold and the top bunks were too hot. No other amenities, no shower or tub, no hot water, no A/C.

Modern RV Water Systems

These days RVs are houses on wheels, some are mansions on wheels. The luxurious monster class 'A' motor homes have many complicated systems. The water and waste systems are probably the least complicated. Not too much has changed from the early days of RVing.

The water system begins at the fresh water holding tank with a capacity of at least 50 gal. A 12-volt pump still pushes water through the system albeit the pump is much larger than the old days.

The water pump has a check valve (one-way valve) that prevents water from flowing back into the fresh water holding tank. If, after the water system is pressurized the water pump cycles (comes on) intermittently, a tap may be open, the hot water tank drain valve may be leaking or the water pump check valve is faulty or there is a leak in the system.

Older RVs have two exterior fresh water inlets, one is a garden hose threaded attachment for connecting to city water.  Note: use a pressure reducer or slightly open the city valve, too much water pressure could damage your RV's water system.


There is also a capped fill tube for filling the fresh water holding tank, a hose is placed in the fill tube or if necessary you can pour water into the fresh water holding tank. The RV manufacturers for some strange reason have eliminated the capped fill tube, all that remains is the threaded garden hose attachment. This water inlet is located at your RV's docking station. When the hose is attached, a lever valve controls whether the water goes into the holding tank or the water system.

The elimination of the capped fill tube into the fresh water holding tank can present problems if you need to refill water using a gravity system, the one-way valve on the threaded garden hose inlet may not open without adequate pressure.

Your RV's water system could be relatively simple with a hot water tank, kitchen and bath sink, toilet, shower and probably an outside outlet (shower or spray hose).

Some larger RVs have more complicated systems with all the usual appliances listed above plus a water filter system, clothes washer, a water line to the fridge to supply cold water and ice maker, a dishwasher and possibly some others.

Most RVs have a drain on both the hot and cold water lines situated somewhere at the low point of the water system. These drains are usually visual from under your RV, some are marked red and blue (hot and cold). The fresh water holding tank will also have a drain. If you cannot locate the drain valves refer to your owners manual or contact the RV manufacturer. For more on RV water systems, check out my previous article on "Winterizing Your RV".

The Hot Water Tank

Newer model RVs have duel heated hot water tanks, propane, and electricity. Propane when 110-volt AC electrical power is not available. Both propane and electric may be run at the same time to reduce the recovery time. Check the owners manual for recommendations.

The hot water tank may or may not have a by-pass attachment, this allows water flow into the hot water tank or not. Check the by-pass valve before turning on the hot water tank.

The by-pass system is used for winterizing reducing the amount of anti-freeze required. When winterizing remember to remove the drain plug to empty the tank. Recently RV manufacturers have added a plastic drain plug presumably if the hot water tank is not drained and freezes the drain plug will pop out hopefully preventing damage to the tank. Check out my previous article on "Winterizing Your RV".

There could be other appliances in the water system I have not mentioned.

Modern RV Electrical Systems.

RV electrical systems have probably gone through the biggest changes and have become much more complicated. More systems have been added, 12-volt DC plus 110 & 220-volt AC, in addition, the amperage of the systems has been upgraded to 30 & 50 amps to run several air conditioners and a clothes dryer.

Modern RV electric systems are integrated and for most purposes act as one. This has been made possible by the introduction of converters and inverters into RV electrical systems.

The 12-volt DC Electrical System

This system supplies power to the necessary appliances when not connected to shore power (110-volt AC). The system begins at the battery, supplying electrical power to 12-volt appliances including water pump, fridge (requires 12-volt power to run on propane), furnace fan, all interior and exterior lights , stove hood fan, bathroom vent fan, main area vent fan, propane detector (close to the floor), and carbon monoxide detector.

The 110-volt AC Electrical System

This is where things get a bit more complicated. 110-volt AC comes from a shore power plug with a heavy duty cord or from a generator. Note: to connect a generator, if not built-in, to your RV a special adapter plug may be necessary from a 30 0r 50 amp plug to a regular 3 prong plug

From here the power connects into a transfer relay which directs power to the 110-volt  AC circuits thereby energizing common electrical appliances such as the TV/s, air conditioner/s, microwave oven and electrical plugs that enables the use of such things as a toaster, and other appliances that cannot run on 12-volt DC. Note; the size of the generator is determined by the total wattage of appliances used at the same time, (check the specification sticker for the number of watts), for example, a 2000 watt generator may not put out enough power to run your air conditioner.

The Converter

When traveling and the engine in your motorhome or tow vehicle is running the electrical alternator in  should charge the battery/s in your RV. Note: it may take several hours of running your engine to fully charge your RV battery.

Conversely, if you are in an RV park and plugged into 110-volt shore power, electricity travels through a converter which converts 110-volts AC to 12-volt. The 12-volt power charges the battery/s and supplies power to 12-volt appliances mentioned above.

The Inverter

Inverters are NOT standard RV equipment, an add-on accessory. An inverter operates opposite to a converter, it changes 12 volt DC battery power to 110 AC power. Inverters may be necessary if you plan to live off the grid or boondock/dry camp and need to use appliances that require 110-volt AC such as a TV.

If you choose to equip your RV with an Inverter you will be drawing & relying on your 12 Volt D/C power supply (in other words your deep cycle battery).

Something to keep in mind when considering which Inverter is right for you is the load you will be placing on the Inverter. For example, the load required to charge a cell phone will be much less than the load required to run a microwave oven. If you plan on inverting your D/C power to A/C power you may consider increasing the size of your battery bank (adding more batteries).

It doesn’t take long to draw down your RV batteries when inverting considering the Inverter converts the DC power to AC power at a ratio of 10 – 1! Knowing that for every 1 amp needed to run the appliance approximately 10 amps is drawn from the battery, how long your RV battery will last all comes down to your overall battery capacity.

Check out my article on "RV Batteries – Things You Should Know"

A 1000 to 2000 watt inverter is large enough to run a TV and receiver and other small draw appliances such as a laptop, sewing machine, and chargers. Keep in mind the displayed rating on an inverter is the maximum output for short peak outputs. Check further for the maximum continuous output. 

Owning an RV and contemplating your next adventure is very exciting. Part of the experience is checking out the RV systems, knowing how they work will go along way to trouble shooting and fixing minor problems.

Check back for part 2 of "RV Systems – How they work."


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