Liquid chemical feeders can simplify pool maintenance — but an awareness of their workings is crucial for effective use.
For much of the pool industry’s history, chemicals have been added to the water in two basic ways: By pouring solutions into the pool, or by placing tablets in a feeder of some sort. These techniques are both simple and time-tested, but they’re not always ideal — especially for pools with high bather loads, or those that require rapid chemical adjustments.
This has led some manufacturers to develop new types of mechanical feeders which add precise doses of liquid chemicals to the water as needed. Though many of these feeders work in conjunction with automation systems on large commercial sites, they’re also growing in popularity for residential applications.
Here, we talk with experts on liquid chemical feeders to get a sense of how the main types work, where they’re most useful and how they should be maintained. A working knowledge of these devices will enable more effective service practices and promote clearer dialogue with those clients who use chemical automation.
An understanding of liquid feeder applications begins with a grasp of their workings.
Many of today’s liquid solution feeders fall into the category of positive displacement pumps, which means they rely on mechanically applied pressure, rather than suction, to push liquid chemicals — such as solutions containing chlorine, muriatic acid or soda ash — through their lines. The category of positive displacement liquid solution feeders includes peristaltic pumps, diaphragm pumps and piston pumps.
Peristaltic pumps move chemicals through a flexible feed tube, squeezing the tube with a rotating set of rollers and producing an output-side pressure that usually falls between 25 and 100 psi.
The mechanical simplicity of these pumps offers several advantages. “A peristaltic pump is completely self-priming,” says Kevin Boyer, COO of Aquasol Controllers Inc. in Houston. Boyer adds that a peristaltic pump also works quite well with gassing liquids like bleach, because its design simply pumps any gas, along with the liquid, right through the tube and into the line.
Diaphragm pumps move chemicals by rotating a cam or solenoid against a flexible membrane, displacing liquid while its egg-like shape applies varying pressure. As the diaphragm expands and creates a vacuum, a spring-loaded check valve at the pressure side of the membrane’s chamber opens, allowing fluid to flow in. As the solenoid compresses the diaphragm, the pressure forces a check valve at the chamber’s pressure-side out-port to open, allowing the chemical to flow into the feed line.
Piston pumps work in essentially the same way, except that the cam or solenoid pumps a piston, which compresses a similar flexible membrane.
Some diaphragm and piston pumps used to develop issues with gas buildup, which would cause the pumps to lose prime. However, many of today’s have designed their products to be self-venting. “Some of them are now built with a mechanism in the head that vents the gas back into the bleach tank,” Boyer says.
As designs of liquid feeders have improved over the years, their reliability and consistency have risen, and the amount of repair they require has decreased. Even so, a chemical feed system must be sized correctly, and matched with the right application, if they’re to be most effective.
Throughout the past several years, automation systems have become more advanced, and chemical feeders have grown less expensive — allowing a much wider variety of customers to incorporate chemical feeders into their projects. Today, some builders urge all their residential customers to incorporate automation.
“I myself will always recommend automation for residential pools,” says Troy McGinty, product manager at Hayward Commercial Pool Products in Rockville, Md. “And I’d say that every commercial body of water should absolutely have a chemical automation system on it.”
It’s also worth noting that many commercial clients will have already done some research into chemical feeders, and may have detailed questions about how these technologies can meet their needs. In short, it’s more critical than ever for pool professionals to understand which devices are most appropriate for each project.
As with electrolytic chlorine generators (ECGs), the ideal way to assess a pool’s chemical feeder needs is not by gallonage, but by the system’s demand for adjustments to chlorine, pH and so on. Environmental conditions, peak bather loads, and water loss or leakage issues are all major contributors to chemical demand. So it’s important to investigate these factors with the customer before making a feeder recommendation.
After establishing the pool’s chemical demands, the next step is to assess which type of feeder will most efficiently meet them. For many residential and small commercial applications, peristaltic pumps are sufficient. They tend to be less expensive than diaphragm and piston pumps, and a variety of size options are available — many manufacturers offer several tiers of motor size, and several feed tube diameters as well.
Diaphragm pumps are often better suited to large commercial applications because they’re typically designed to deal with more sizable chemical flow. Thus, they tend to be somewhat larger and more expensive than peristaltic pumps.
Also, instead of size variations, they typically deal with varied chemical needs by electronically limiting their output — a limit that may be imposed via an automation controller, or within the pump’s own circuitry, depending on the design.
In fact, automation controllers form a crucial component of many systems that involve liquid chemical feeders. Though some lower-end systems may simply use feeders to add scheduled doses of chemicals to the water, the preferred technique is to use sensors — such as ORP and pH meters — to communicate to a feeder array what chemical adjustments are needed. This sort of setup requires some automation components.
There’s also another impact of these automated adjustments — one that may be closer to home for many customers. “The biggest advantage of a chemical controller is that it’ll save you money on chemicals, because it’s not feeding you chlorine all night long,” says Gus Dabney, owner of Florida Chemical Laboratories in Largo, Fla.
Automated chemical feeders are particularly useful for customers who have electrolytic chlorine generators. Effective real-time monitoring control of the water’s pH and the chlorine levels will ease the burden on the salt cells, increasing their effectiveness and longevity.
Though liquid chemical feeders can do their work without daily input from the user, they’re still subject to their share of potential issues. Frequent system checkups and adjustments — and part replacements when necessary — will go a long way toward keeping these devices efficient and trouble-free.
For a peristaltic pump, the most common issue is wear and tear on the feed tubes. This isn’t caused by any specific flaw in design; it’s simply due to the fact that the pump works by squeezing plastic tubes.
Another potential problem — especially with older peristaltic pumps — is clogging in the lines. Clogs can create back pressure that may damage the pump, so it’s also important to investigate this possibility on a regular basis. Thus, most experts recommend thoroughly checking the tubes of peristaltic pumps for leaks and clogs at least once per week.
In addition, it’s critical to test water chemistry regularly with a manual test kit, instead of trusting a readout on the feeder or controller. Over time, a film can build up over metal chemical probes, and this often skews their readings. Though a soak in muriatic acid or a scrub with a toothbrush will usually remove this film, the easiest way to know it’s become a problem is to “test the tests,” by comparing the system’s electronic readout with other test kit results.
Although some customers might hope that an automated liquid chemical feeder will bring an end to the days of constant maintenance, the fact is that any pool is a constantly changing system, and requires regular checkups and adjustments if it’s to stay safe and efficient. With that in mind, an understanding of chemical feeder mechanics will make it easier to anticipate issues, fix them before they become real problems, and keep the whole system running smoothly.
Source: Ben Thomas- Pool and Spa News | 10.28.2011