By Hal Voznick
There are many opportunities for pumps in the point-of-use (POU) water treatment industry. Pumps can enhance the performance of any water treatment or bottled water application.
As the popularity of reverse osmosis (RO) systems has increased in recent years, prices for RO pump systems have dropped. In particular, more RO systems are being sold in Asia than ever before and they all have pumps. Competition from new pump competitors there has driven the price down. Installing a pump system for an RO can be an economical way to increase the performance of a customer’s RO system. RO systems are available with booster pumps built in from most system manufacturers. Pumps are also available as add-on kits from distributors and original manufacturers. Systems with RO pumps built in should be used when it’s known that the feed water pressure is very low or the total dissolved solids (TDS) are very high. Add-on pumps are needed to alleviate customer complaints when the faucet delivery flow is not acceptable or the tank doesn’t fill to its maximum capacity on a previously installed RO system.
POU RO systems need a pump when the city water pressure is below 45 pounds per square inch (psi), where the water temperature is very cold (below 45°F), or the TDS level is 1,000 parts per million (ppm) or more to obtain rated performance.
Using a pressure-boosting pump in front of the RO system can control these feed water variable extremes. Pumps are required if the variables go to the extremes mentioned but will enhance any RO performance over its city water ratings regardless of the variables. The pump can be installed in the same area as the RO unit—under the sink, in the basement or out in the garage.
What to look for
According to market sales, the most popular pump available for RO applications is the three-chamber diaphragm pump, which will boost feed water pressure to 80-to-90 psi at the RO membrane. The increased pressure lets the tank fill faster and more completely. And the tank pressure will be at optimal operating specifications, typically 40 psi. These pumps can work on membranes rated up to 150 gallons per day (gpd). Another benefit of a booster pump is higher salt rejection rates from the membrane (in the case of cellulosic membranes).
For proper design, if the throughput is increased because of increased pressure, then the brine flow should be adjusted. This isn’t typically required, however, because there’s enough of a safety factor inherent in the system, i.e., 4/1 vs. 3/1 membrane ratio of concentrate to permeate recovery. Most membranes are functional up to 200 psi—it’s the other RO components that are limited to 125 psi by the manufacturer, i.e., housings, tubing, fittings, etc.
Most RO pump manufacturers offer systems that are ready to install and are usually supplied with ¼-inch tube fittings. The pumps are low voltage (24 volts), and power is supplied from a transformer. A remote pressure-sensing switch installed in the tank line controls pump operation. Switches are factory-set to turn the pump off when the pressure in the tank is 40 psi and restart when the pressure drops to 25 psi.
Choosing a pump approved by NSF International will ensure that the pump complies with all state and local plumbing regulations.
Increasing the flow from an RO bladder tank to the faucet is another opportunity to install a pump. A repressurization or delivery pump may be needed when there’s a long horizontal run of tubing—over 10 feet—from the tank to the faucet (such as from the garage, where the unit may be located, to the kitchen). Energy lost in these long runs is due to friction, distance or height that the water is being pushed.
A pump may also be needed when multiple faucets are connected to one tank or with a vertical run—when the faucet is on an upper floor and the RO unit is in the basement.
The right choice
Select a pump that has a built-in demand system, which incorporates a check valve and pressure switch in the design. When the faucet is open and the pressure drops between the faucet and the pump, the built-in pressure switch senses the pressure drop and switches the pump on. Pumps for this application deliver water between ½ and 1 gallon per minute (gpm), depending upon system configuration.
An option available on some delivery pump systems is a built-in low pressure switch, which monitors pressure in the storage tank and shuts the pump off when the tank is out of water. Diaphragm pumps can run dry without damage for short periods of time. This is to prevent annoying running should the pump get air in it, in which case it won’t shut off until the air is purged.
When selecting a delivery pump, choose one that has fittings and a power cord for easy installation. Choosing a high-quality unit that also has Underwriter’s Laboratory (UL) approval for electrical standards (as well as NSF certification) will help provide customers with years of safe and trouble-free service.
Bottled water pumps
For water retail stores and dealers who handle bottled water, pumps can be used in place of the traditional water cooler, when lifting the bottle to the cooler is difficult for the customer.
The most economical pump for water delivery from the bottle is a battery-operated unit, which is easy to install and operate. The motor, control button and spout are at the top of the unit, and the water intake and pump impeller are in the suction tube. Place the pump unit in the bottle and get immediate delivery of the water from the spigot on top of the unit.
A new, available pump system delivers bottled water to refrigerators with through-the-door ice and water. This system consists of an electric demand pump with automatic self-priming and a timer to shut the pump down when the bottle runs empty. Like RO pumps, the bottled water pump can be located farther from the POU faucet—in the garage, basement or pantry cabinet.
Once the pump and the bottle location have been selected, the tubing—typically ¼-inch diameter polyethylene—must be routed to the back of the refrigerator. Once the plumbing is in place, the unit is ready to run.
Cranking it up
To start the unit, drop the suction tube in the bottle and snap on the bottle cap. Plug the unit into a 115-volt power source and turn on the switch. The pump will fill the line up to the refrigerator, purge the air automatically and then shut off.
Solenoid valves built into the refrigerator door control water delivery to the glass and icemaker tray. Depressing the paddle in the door to fill a glass of water opens the solenoid, which in turn engages the pump to deliver the water.
This type of delivery system provides convenience to the customer and can add profits for the bottled water retailer—i.e., with ice production comes increased bottled water consumption.
When selecting a pump for a particular application, choose one from a manufacturer with a reputation for high product quality and excellent customer service. With new products available and attractive affordability, pumps offer an additional profit opportunity.
About the author
Hal Voznick, a mechanical engineer, is manager of the Water Products Group at SHURflo Pump Manufacturing Co. of Santa Ana, Calif. He can be reached at (714) 554-7709, (714) 265-2127 (fax) or email: [email protected]