Pools require chemicals. Processes of disinfection, oxidation and pH control are the most common chemical requirements that necessitate a feeder. Chemical feeders fall into four major categories, and there are several variations of each. Chlorine feed systems vary greatly, and the type of pool may be the greatest influence. Public, institutional and commercial pools use mostly larger-sized liquid or calcium-hypo, erosion feeders. However, the chemical characteristics of the facility water source should be considered. Even geographical influence play a role. Here’s a brief look at them all.
- Liquid Chemical Feeders. A number of liquid chemicals — including sodium hypochlorite (liquid bleach), muriatic acid (hydrochloric acid often diluted to 31 percent concentration) and sulfuric acid — require liquid chemical feeders. Various other chemicals, including hydrogen peroxide and solids such as calcium hypochlorite, sodium bicarbonate, calcium chloride, soda ash, algaecides and cyanuric acid, also can be made into solutions and fed with a liquid feeder system.
Liquid feeders are most often found in three basic types: diaphragm feeders, peristaltic feeders and venturi feeders. Diaphragm feeders, common for large pools because of their higher capacities and higher pressures, are considered “positive displacement feeders.” They deliver a consistent amount of chemical with each pulse of the “diaphragm.” The capacities vary from 1 to more 100 gallons per hour, with pressures of up to 150 psi.
To ensure that liquid moves only one direction, diaphragm pumps are fitted with several check balls and seals. This also prevents any back-flow of pool water through the pump.
Anti-siphon protection is another must for diaphragm pumps, especially on systems with tanks that sit above the pool.
Early on, peristaltic feeders (also considered a “positive displacement feeder system”) generally were found in small pools and used most extensively in low pressure and low feed applications. But today’s large-capacity, high-pressure peristaltic pumps can handle larger pools. New tube assemblies and stronger motors have allowed for up to 10 gpm feed capacities, with some units handling up to 100 psi backpressure.
Peristaltic feeders have few moving parts, making them popular. They work via a roller assembly mechanism that “pinches” off a section of the feed tube and creates a vacuum that eliminates any back flow or siphoning of chemicals.
Venturi feeders are not a new concept; however, fully manufactured feed units with industry approvals have only become available recently. These feeders use the increased pressure and flow of water from a boost pump through a venturi eductor to create a vacuum. This draws the liquid chemical through a flow meter and adjustable flow valve, and ultimately into a circulating water stream that mixes with the circulating water returning to the pool.Venturi feeders can be controlled with automation by turning the boost pumps on and off.
- Dry and Erosion Feed Systems. Erosion feed systems were first developed to handle tricolor and stick bromine. But with the increasing use of calcium hypochlorite as a chlorine source, a number of popular calcium-hypo erosion feeders now are available, some with capacities to handle even the largest of pools.
“Erosion” describes how most of these feeders turn dry tablets, sticks or briquettes into a solution that is fed to the pool. The dry chemical tablets or brickets are stored in a hopper, then washed or sprayed with water, resulting in a cal-hypo solution that is delivered into the circulation system. The amount of chemical delivered at any given time is controlled by the amount of water flowing through the chamber. Some of these types of feeders are automated via chemical controller-operated solenoid valves.
- In-line Chlorine Generation/Feed Systems. These units also act as feeders, using the salt (sodium chloride) that's added to the pool water to a concentration of between 3,000 and 4,000 ppm. As the weak saltwater circulates through a generation cell(s) fitted with anodes/cathodes charged with DC voltage, sodium hypochlorite is generated. These generation cells are plumbed in-line, so that as the chlorine is generated, it joins the pool water returning to the pool.
Unlike conventional liquid chlorine feed systems and brine systems, the TDS (mainly made up of salt) does not continue to rise.
When installing an in-line system, to keep up with demand it is important to understand how much chlorine is used in a busy hour of operation rather than a whole day. So many in-line systems have been inappropriately sized that a number of health agencies require a conventional chlorine feeder for backup.
- Gas Feeders. Though virtually extinct, there are still some pools running on chlorine gas systems, and only well-trained professionals should operate them. Chlorine gas is 100 percent real chlorine, and because it's a gas, safety regulations require that chlorine gas feeders be operated under a vacuum. Special containment chlorine rooms and equipment including self-contained breathing equipment, scales, chlorine gas detectors, chlorine room air scrubbers and alarm systems usually are required. On gas feeders, the venturi ejector creates a vacuum that operates the entire system and literally sucks the gas into the circulating water. A vacuum regulator controls the amount of gas that flows through the system.
In general, chemical injection, almost without exception, should take place downstream of the pump, filter, heater and most all other equipment such as flow meters, gauges and the like. Manufacturers that have fully engineered and tested equipment often carry industry certifications from the National Sanitation Foundation and/or Underwriters Laboratories Inc., or the ETL Mark from Intertek.
It’s also essential that all chemical feeders be tied into the circulation flow. If that’s not possible, they should at least be interlocked with the recirculation pump power so they are secured if the pump is turned off.
When it comes to operating chemical feed systems, it’s important that operators understand swimming pool chemical feeders deliver chemicals, most of which are hazardous to some degree. Depending on the type of system and local health department or fire marshal rules, secondary containment may be required of the chemicals in storage, the pump and the chemical feed lines.
Additionally, each type of chemical feed system has some specific maintenance requirements. In particular, when replacing tubing on a liquid feed system, consult chemical compatibility charts carefully to ensure that you are using the right pump. Tubing, as well as fittings, plumbing and valves, must be compatible with chemicals being used and also rated higher than the pump’s maximum possible pressure.
Most feeders have moving parts within the pump that require care. In addition, suction foot valves and the injectors require routine maintenance. It is not uncommon for liquid chemical feeders carrying high-pH chemicals such as bleach to clog or develop failing check valves due to scaling deposits. Other feeder systems develop worn seals, tubes and diaphragms that all need regular attention. On peristaltic systems, depending upon the amount of use and backpressure, the feed tubes should be replaced at least annually; but whatever your system may be, don’t wait for something to break before you fix it. The results can be messy and costly!
Clean erosion systems by flushing them with de-scaling-type chemicals or, with extreme scaling, use a mild acid-solution. Before you do anything, though, it is imperative that all the chlorine has been removed.
In some cases, depending on the total water balance, on-site chlorine generation system cells without an auto-polarity-reversing feature require frequent cleaning. To clean these cells, soak them in a weak muriatic acid solution, then scrub with a nylon brush under a direct stream of water.
The cost of each type of chlorine feeder varies greatly, so it may be more important to examine the actual cost of the type of chlorine the feeder uses. That includes evaluating how much chlorine is available pound for pound and/or gallon, and actual cost to control pH.
A calcium-hypo erosion feeder may be inexpensive, but cal-hypo costs around $2 per pound and requires 1.5 pounds of chemical for a full pound of real chlorine. At $3 per pound of chlorine, when you add in the cost of pH control and the real cost of chlorine per pound delivered to the pool, you'll find it's about $3.25.
A typical inexpensive liquid feeder delivers a gallon of sodium-hypo, 12 percent of which contains about a pound of real chlorine and costs around $1.25 per gallon, but the cost of pH control increases the real cost of chlorine per pound to around $1.75 delivered to the pool. Finally, a chlorine generation system that costs many times more than either of the aforementioned feeders can make a pound of chlorine for approximately 60 cents per pound.
Depending on the amount of chlorine used, the actual cost of any one of the systems should be examined over several years to determine the real, long-term, operational cost.
About the Instructor
Rich Young has more than 30 years’ experience with municipal, public and commercial pools and waterparks. He has operated and maintained many public and commercial swimming pools as well as several waterparks. Besides being an AFO instructor for the National Recreation and Park Association and technical adviser/board member at the Professional Pool Operators of America, Young has been published numerous times in industry journals.