Pump Systems for Rainwater Catchment
by Verne Wood, CEO of PWS, Inc, Keaau, Hawaii

Understanding how water gets from the catchment tank to the faucet can help people on rainwater catchment systems feel more comfortable with their system and be more self-reliant.

A normal pump system is composed of a pump, a pressure tank, a pressure switch, and a check valve. These main components all work together automatically to supply pressurized water to your point of use.

Catchment pump systems draw water from the tank, pressurize it, and store it in a pressure tank until you need it. There is a one-way valve called a check valve (also called a foot valve) between the water tank and the pump; this valve prevents the pressurized water from returning to the water tank, and it simultaneously creates a closed system between it and your faucets.
When you open a faucet, water is delivered under pressure. The subsequent pressure drop activates the pump switch and the purup turns on, drawing more water from the tank and delivering it, under pressure, to the pressure tank and thence to the faucet. When you close the faucet, the same switch senses the pressure build-up and, at a prescribed pressure, shuts the pump off.

Shallow-well pumps, which are commonly used for catchment systems, are designed to push water rather than to pull it. For that reason, the most appropriate place for the pump is at the same level (elevation) as the water storage tank. The pump can be placed elsewhere, but the efficency and the life of the pump will be compromised as the demand to "pull" increases. The diameter of the supply line from the tank to the pump also affects the pump's performance. This pipe should be a minimum of 1 inch diameter - larger if possible--to reduce strain on the pump.

Changing filters on a regular basis will give you better water flow and reduce work for the pump. It is possible for a dirty filter to impede water flow com-
pletely.

Your pump will also give you better service if you have a large pressure tank in the system. The larger the pressure tank, the less the pump will turn on and off, which in turn will extend the life of the pump and consume less electricity. It is possible to add a multiple number of pressure tanks in your system.

You can improve the pump's performance and reduce electrical consumption by using a 220-volt pump. Higher quality water pumps are configured to run on 220 volts, and these pumps will lower electrical consumption and improve the performance of your system. Some pumps have a "dual-voltage" feature whereby you select either 110 volts or 220 volts as your power source. From the point of view of pump operation performance, the 220-volt option is preferrable. *

The correct pressure setting between the switch and the pressure tank will ensure that the pump does not run any longer than it needs to. It should shut off promptly once it has delivered water to your point of use and refilled the pressure tank.

The pressure switch on the side of the pump should cycle freely without sticking. A switch that is dirty can stick and cause the pump to run longer than it needs to. Sometimes ants nest in the switch and cause it to stick. Also, the check valve must work properly and prevent water from returning to the tank. If debris gets stuck in the check valve, the valve will not close tightly, and pressurized water will leak back into the tank. You may notice this problem if your pump turns on when you are not using water.

Many times when people think a water pump is broken and needs repair, the problem is actually in the switch, the check valve, or the pressure tank. Understanding how the system works could save you from the inconvenience of no water or an unnecessary service call.

Some simple checks that can be done prior to having a service call are (I) make sure that the pump is getting water from your tank, and (2) make sure that the pump is getting electricity.

After this, a more technical investigation begins, and you may want to call a service person. If you feel capable of continuing the process, the next step is to check to see if the air pressure in the pressure tank is correct. Open the valve stem and let some air out. If water comes out or there is no air in the pressure tank, place a tire gauge on the pressure tank valve stem. The pump needs to be turned off (or isolated) so that the water pressure can be drained down. The tire gauge should read between 18 and 38 pounds of pressure. When the system is turned on again, the pump switch should activate the pump when the pressure gauge reads 2 pounds above what the tire gauge reading was (it should be between 20 and 40 pounds). If these numbers do not correlate, then it is necessary to add air or adjust the switch. If your pump turns on when you are not using water, the first thing to look at is the check value. It could be releasing pressurized water back into your water tank.

Most problems with pump systems are actually a failure of one of the components and not the pump itself, although a sustained malfunction of one of the components can damage the pump.

If the pressure setting is not matched between the air tank and the switch, the pump can cycle repetitively and damage the pump motor. The motor also can be damaged if the check valve leaks or if there is an air lock in the system.

The pump can also be damaged from overheating. This is the single biggest cause of water pump damage. Water moving through the pump housing cools the pump. If the water supply is severed or the water does not get pumped out of the housing, the pump will overheat. This circumstance will lead to a burnt motor, a damaged impeller, or a warped shaft and seal.

If you ever run out of water or lose water flow for any reason, the pump should be shut off immediately. To further protect your pump, there are two types of sensors that can be installed at the switch that will automatically shut off the pump before any damage occurs. One unit senses heat in the electrical wire, and the other one reacts to a drop in water pressure.

*Editor's note: All electrical installations and electrical troubleshooting should be done by a qualified electrician. A 220-volt system can be much more hazardous a 110-volt system. Pump housings should be locked prevent unauthorized access.

Many thanks to Vern Wood, CEO of PWS, Inc of Keaau, Hawaii for permitting the reprint of this article

Related Links

Rainwater Harvesting - Pumps or Pressure Tanks
Pump Sizing for Rainwater Catchment Systems
Free Rain, Free Watering and Exercise All in One (Bicycle Pumps)
University of Hawaii - Rainwater Catchment Guidelines
State and City Programs and Vendors

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