This was one of the least complicated systems, a basic RV
plumbing system, with increased capacities. The are only two fixtures, the
bath tub and the toilet.
The original goal was to have a minimum100 gallon fresh water capacity.
Pending experience, this should last for two days, considering the conservation
gained with recirculated wash.
As it turned out, the capacity is about 120 gallons. Fresh water will
be held in a reservoir made of PVC cylinders. These are basic 10" diameter
pipes in a vertical orientation. This allowed fabrication without special
equipment and eliminated "sloshing" in the tank.
Here is a spreadsheet for use calculating tank size
and capacity for either a cylindrical or rectangular tank.
Gray water from bathing will be stored separate from toilet black water.
Gray water holding capacity should be at least half the fresh water capacity.
Custom built tanks are planned to maximize capacity and optimize weight
distribution. It will be acceptable to dump gray water more frequently
than filling fresh water. Capacity of the black water holding tank will
depend on its final location and truck/body details. Depending on final
tank design, a macerator pump may be used to evacuate the gray water tank.
The water heater should have quick recovery and require little maintenance.
A ten gallon Atwood unit with both LP Gas and 110 volt electrical heating was
chosen. Atwood also offers an option to tie the heater into the vehicle's
cooling system to capture additional heat from the engine. This option was
not chosen primarily because of the distance between the engine, in the front,
and the water heater, at the very rear of the vehicle. LP Gas will be the
primary heat source. The electric element will only be used while the
generator is running and only one of the two high power electrical appliances,
Air Conditioner and dryer, is running. A lockout mechanism will be
required to prevent all three systems from being turned on simultaneously.
The vehicle will have an integrated, self-retracting hose system for filling
the fresh water tanks. The hose reel system was custom built by
Hannay Reels, a leader in industrial reels,
to Paws At Your Door specifications. The spring loaded system supplies and
retracts up to 100 feet of 1/2" industrial hose. Filters and pressure
regulator will be integrated in the system for protection.
The version 1 vehicle used the largest available RV pump, the ShruFlo 5.7
SmartSensor. Barb found this barely adequate. Adding a small
accumulator tank, the ShruFlo 24 oz. model, merely demonstrated the effect
of an accumulator tank, but didn't have enough capacity to be practical.
An accumulator tank is intended to be a "cushion" for the water pump.
It reduces the number of times the pump switches on and off, thereby
extending the pump's life. From the faucet's perspective, there is a
strong, steady flow of water, for a brief period, after starting the flow,
until the reservoir is depleted and the flow is just the output of the pump.
Since the accumulator is essentially a balloon system that stores about half
its rated volume in water and keeps it under pressure, the 24 oz. unit was
We ended up selecting a FloTec pump designed to power a small house.
These are typically used for homes withtheir own wells. the 1/2 horse
power pump is rated at 8 gallons/minute at 40 PSI, and incorporates a 15
gallon accumulator tank. This offered plenty of capacity. The
cost of this performance is size and power consumption. The pump runs
on either 230 or 115 VAC, whereas the RV-style pumps run on 12 VDC, and the
accumulator tank was much larger. We have AC power available, the pump
will be powered from the inverter, with a maximum draw of 9.4 amps, and we
found space for the pump/tank assembly.