Rain barrels are containers that are directly connected to the guttering of a house roof. As rain falls onto the roof, it falls into the gutting and collects into the barrel. Rain barrels can have a variety of uses, such as gardening or washing the car, but applications are often hampered by the lack of pressure coming from the barrel. A simple means to fix this is by using a pressure washer in conjunction with the rain barrel. There a variety of factors that need to be considered before attempting this.
Rain Barrel Output Pressure
Rain barrels often have an outlet connected to a hose allowing direct watering of the garden. The output pressure of the hose is often poor, due solely to gravity, but pressure can be increased by raising the height of the barrel with respect to the hose end. Pressure washers will often require a particular inlet pressure to function. It is important to calculate the pressure at the hose end of the rain barrel in order make sure it is compatible with a particular pressure washer.
Calculation of Rain Barrel Pressure
The pressure at the outlet of a rain barrel is due to the mass of water being pulled down towards the Earth. The pressure of the water can be calculated very simply using the formula:
Pressure = Atmospheric Pressure + water density x acceleration due to gravity x height
Alternatively, one can use a simple rule of thumb that states each 0.3 meters of elevation leads to 0.433 pounds per square inch (psi). Therefore, if the pressure washer requires a 3 psi inlet pressure, the barrel will need to be raised about 1.8 meters.
Water Volume Considerations
Pressure washers typically expel water at a pressure above 100 psi, which means they can use the water within a rain barrel very quickly. As a general rule of thumb, 10 minutes of using a pressure washer at 100 psi will use about 67 liters of water. Since most rain barrels have a volume of 250 liters, there will be about 35 minutes of pressurized water available.
Pressure washers work by using an electrical motor to accelerate water to higher pressures. If particulate matter gets into the rain barrel and passes into the electrical motor it can be damaged or completely broken. To avoid this problem, use a filter. The filter is normally connected directly to the downspout.