Let’s be honest, we all know that simpler is better. The simplicity of a peristaltic style metering pump makes it a very reliable method for injecting a wide variety of chemicals into water treatment applications. Understanding the variables that result in wear on the pump components, especially wear to the pump tube assembly, can assist the reader in properly specifying the pump for a specific application.
Peristaltic pump technology
The human body uses “peristalsis” action to move food through the digestive tract. The wave-like muscle contractions progressively squeeze the digestive tract, essentially “pushing” the food through. It doesn’t get any simpler than that.
One of the greatest benefits of a peristaltic pump is its functional simplicity. Peristaltic pumps utilize a circular pump “head” and simple rotating roller that is designed to pinch the tubing and gently squeeze the fluid through specially designed tubing, as shown in Figure 1.
Figure 1: Typical peristaltic pump
They can effectively pump both fluids and gasses, eliminating the possibility of siphoning, vapor locking or loss of prime even when operating at very low output rates. Nearly continuous output results in a finer dispersion of chemical in the piping system when compared to pulsating type pumps such as diaphragm pumps. Figure 2 shows the near continuous output of chemical in the flow stream when using a peristaltic pump versus the interrupted chemical dispersion when using a diaphragm pump.
Figure 2: Intermittent vs. continuous flow
Fewer components result in very low maintenance costs when compared to the cost of rebuilding more complex pumps that require a large number wetted components such as metal springs, o-rings, valves, check balls, etc.
Commonly called a squeeze tube pump, the new generation of peristaltic chemical metering pump is quite different from the low-pressure laboratory pumps most people are familiar with seeing in a hospital setting. These industrial workhorses are now capable of pumping aggressive chemicals such as 12% sodium hypochlorite (chlorine), 50% sodium hydroxide, 97% sulfuric acid, and 85% phosphoric acid against system pressures up to 125 psi. Some models include such features as tube failure detection systems, flow verification sensors, and sophisticated control electronics for PLC interface and connection to SCADA systems.
Pump System Components
For analysis purposes, the peristaltic pump assembly can be broken down into five main components; 1. pump tube, 2. pump head and roller, 3. motor, 4. control electronics and 5.motor/electronics housing. Note that in some models, the control electronics (VFD, motor starter, PLC, etc.) are housed in a separate enclosure.
Variables to tubing wear
Many manufactures rate the life of their tubing by the number of effective operating hours before failure. While this rating may be effective for comparing the life of tubes used in the same pump under a specific set of operating parameters (for example; pumping water with a specific pump head type, at 0 psi, at a fixed RPM), there are many variables that will affect the number of hours a given tube will last in an actual application. Care should be taken to specify the pump components and operating parameters to achieve the greatest tube life possible in an application.
- Tubing materials – The tubing material must withstand the chemical being injected, return to its original shape after many thousands of occlusions (compressions), and operate at the required system pressure. Specifying the optimum tubing material is critical for a successful application.
- Chemical resistance – Chemical incompatibility will result in a breakdown of the tubing material properties, often manifested as a change in the stiffness of the material, either softening or hardening. In most cases, chemical resistance problems will be apparent within the first few days of use. However, in some cases, the chemical will attack the tubing material slowly over a long period of time, reducing the life of the tube.
- Dimensions – Larger tube diameters and thinner wall thicknesses will generally result in reduced tube life expectancy.
- Material properties – The physical properties of the tubing material will greatly influence not only its suitability for general use in a peristaltic pump, but also the amount of time the tube will last in a particular application. The peristaltic pump tube must be capable of precisely returning to its original shape many thousands of times after being squeezed by the roller. Many tubing materials lack this memory making them unsatisfactory for peristaltic pump applications. Tubing manufacturers offer a variety of tubing formulations, many of which are suitable for use in peristaltic pumps and many which are not. The end user must be cautious when selecting the tubing material for the application. Most pump suppliers will either offer assistance with the tubing selection or offer pre-assembled “tube assemblies” designed specifically for their peristaltic pumps, greatly reducing the possibility of miss-application.
- System pressure – The pressures acting on the tubing will directly affect the tube’s life. Both the inlet and outlet pressures should be considered and particular attention should be paid to “hidden” variables that can add to the system pressure such as piping system components and fluid viscosity.
- System pressure – The most obvious (and perhaps most influential) variable affecting tube life is the piping system pressure. But often, system components and installation factors that can increase the pressure at the pump tube are overlooked. For example, most manufacturers recommend installing a check valve in the discharge piping directly after the pump tube to prevent the system fluid from flowing back through the pump during routine pump maintenance or pump tube rupture. A spring loaded check valve or back pressure valve will increase the pressure at the pump tube by a value equal to the cracking pressure of the valve. For example, if the system pressure is 50 psi and the back pressure valve is set at 20 psi, the effective pressure at the pump tube is 70 psi. Therefore, valves with high cracking pressures should be avoided.
- Another often overlooked variable that can increase the pressure at the pump tube is the physical distance from the pump to the point where the chemical is injected into the system, especially important to consider when injecting viscous fluids. The pressure at the pump tube will increase as the distance from the injection point increases, the chemical viscosity increases, and the discharge-piping diameter decreases. Imagine trying to drink a thick milkshake through a skinny, 100 foot straw! Small diameter orifices in fittings should also be avoided when pumping viscous chemicals.
- Number of occlusions – The tube life is affected by the number of times the tubing must be pinched (number of occlusions) in order to pump a given amount of chemical. Reducing the number of occlusions will increase the life of the tube. Four variables affect the number of occlusions required to inject a given amount of fluid; the diameter of the tubing, the diameter of the pump head, the number of rollers on the roller assembly (occlusions per revolution), and the motor rpm. Some manufacturers use the total number of occlusions, rather than time, when estimating their tube life expectancy.
- Tubing diameter – A larger diameter tube will inject more chemical per occlusion (trap more chemical between two pinched rollers) than a smaller diameter tube. Therefore, a large tube can output more chemical with less occlusions, resulting in less wear, than a smaller tube.
- Pump Head Diameter – Similar to the tubing diameter, the pump head diameter will affect the amount of chemical per occlusion. Larger diameter pump heads will result in more chemical being pumped per revolution.
- Number of rollers – A given peristaltic pump model may have anywhere from one (offset cam type roller) to six or more individual rollers which squeeze the tube, pinching off the captured fluid and delivering it to the discharge end of the pump tube. Multiple rollers per assembly result in slightly smaller volumes of chemical injection per revolution, less pulsation and a reduced likelihood that an individual roller will wear out resulting in lost pumping capability. However, since tube life is directly proportional to the number of times the tube is pinched per revolution, the cost associated with the higher number of rollers is tube life.
- Motor rpm – Unlike many types of pumps, peristaltic pumps are capable of operating at very low revolutions per minute (rpm) while maintaining very high accuracy, repeatability and priming capability. Therefore, to increase tube life, specify the pump so that the typical operation of the pump is at the lower end of the operating output adjustment range, resulting in the fewest number of occlusions. The maximum possible rpm of a specific pump model will vary from manufacturer to manufacturer with maximum motor rpm of 650 being not uncommon, though at this high rpm, tube life will be greatly diminished. Some pump models have effective turndown ratios of up to 10,000:1 resulting in a minimum effective rpm of 0.01!
- Amount of tubing squeeze – Simply pinching off (occluding) the tube is not enough, the rollers must squeeze the tubing the exact amount required to ensure that the fluid being pumped is effectively trapped in the tubing and delivered to the injection point. Factors such as system pressure, suction lift, fluid viscosity, tube material, and others will affect the amount of squeeze required for a particular application. If the tube is under-squeezed, the fluid can escape or flow backward toward the suction side of the pump tube when the roller rotates in the head. This can occur when the pump is operated against a higher system pressure than recommended. If the tube is squeezed too much, it is being subjected to more force than is necessary and tube life will be diminished. Properly matching the roller design with the type of tube being used will result in the most efficient pump design and longest tube life for a particular application. Figure 3 shows the squeeze action of a peristaltic pump.
Pump Head and Roller Design
The roller diameter, roller materials, type of bearing surfaces, and pump head design can also affect the life of the pump tube as well as the life of the roller assembly. Schematic of a pump head is shown in Figure 4.
Figure 4: Schematic of pump head
Roller diameter – A large diameter roller will pinch off a greater surface area of the tube while rotating, resulting in lower tube life; however, large rollers will rotate fewer revolutions per roller assembly revolution, potentially resulting in longer roller life.
Roller bearings – The roller must rotate on a shaft, therefore the type and design of the bearing surfaces can increase or decrease the life of the roller. The design of the bearing surface can also assist in preventing chemicals and debris (from tubing surface wear) from entering the roller axle area causing drag on the roller.
Roller material – The roller assembly materials of construction should be of sufficient strength to withstand the repeated compressions of the pump tube while offering resistance to the chemicals that may potentially be spilled in the pump head area. The roller assembly must also have the dimensional stability to withstand variations in ambient temperatures and rotational forces without affecting the amount of squeeze on the pump tube.
Pump head – As with the roller assembly, the pump head materials of construction must also withstand any spilled fluid that may enter the head. The diameter of the head will also affect the amount of fluid pumped per revolution, with larger pump heads discharging more chemical per revolution than smaller pump heads.
All of the parameters such as system pressure, number of occlusion, tube chemical resistance, tube squeeze and roller bearing inefficiency impact tube life as shown in Figure 5.
Figure 5: Components affection tube life
Chemical spills – If left alone, the pump tube will eventually fail. Depending on the operating pressure, type of tube, and many other factors, the chemical may leak out slowly or squirt out dramatically. Manufacturers offer a number of different methods for protecting the roller assembly, pump head and area surrounding the pump from chemical spills. Some manufacturers include drain ports to remove chemical, float switches to shut down the pump when a spill occurs and a cup fills, and electronic sensors to shut down the pump when chemical is detected in the pump head area. Some methods are more effective at quickly turning off the pump and reducing the amount of chemical spilled. Based on the effectiveness of the method, the pump head and roller assembly may incur damage resulting in drag on the roller assembly and reduced roller and tube life.
A variety of motors ranging from small, fractional horsepower shaded pole AC gear motors, to large C-frame AC and DC powered gear motors are used with peristaltic pumps. Many peristaltic pump manufacturers include the motor as part of the pump assembly which helps take the guesswork out of specifying the correct motor to use for a given pump assembly. As with any pump, care should be taken to properly specify the motor for the pump and the intended operating environment.
The control electronics must be carefully selected to properly control the motor as well as providing for any remote control and communications capabilities such as analog input motor speed control, analog output pump speed feedback to SCADA, alarm outputs, pump status, etc. As with the motor, many pumps include the control electronics as part of the assembly.
Typically, a peristaltic pump enclosure protects the motor and control electronics from the operating environment while the pump head area of the pump is either unprotected or sealed in its own enclosure separate from the motor and controls. Manufacturers offer a variety of enclosures for the motor and control circuitry ranging from small plastic housings to explosion proof metal enclosures. Many pumps are supplied without any enclosure at all. As with the motor and control electronics, the user should take care to specify the pump system with a proper enclosure that is designed to provide the protection needed for the application environment, as shown in Figure 6.
Figure 6: Fully enclosed peristaltic pump
A typical setup of peristaltic pumps with integral motor and controller provides the necessary chemical feed to the cooling water system is shown in Figure 7.
Figure 7: Peristaltic pumps providing chemical feed
Many variables affect the service life and maintenance requirements of a peristaltic pump. By carefully assessing the application, the user can properly specify the pump and components to minimize service and maintenance requirements and maximize the life of the pump.
Mr. Bill McDowell is a Sales Engineer with Blue-White Industries and has over 29 years with the company. He has held various positions with Blue-White Industries including Project Engineer and Director of Engineering. Additional information can be obtained from Blue-White Industries at, 5300 Business Drive, Huntington Beach, CA 92649. Phone 714-893-8529, Fax 714-894-9492, or email@example.com; www.blue-white.com
A search for technology to increase system accuracy, reduce maintenance costs, and enhance an advanced SCADA system led a Rancho Cucamonga, Calif., utility to replace its diaphragm-type pumps and gas–chlorine injection system with peristaltic pumps.
BY Bill McDowell
Built in 1989, the 60-mgd Lloyd Michael Treatment Plant (LMTP) in Rancho Cucamonga, Calif., treats raw water from the California Aqueduct system to provide drinking water for a multicity service area. In November 2012, the Cucamonga Valley Water District began upgrading the plant to enhance treatment processes and comply with new federal water quality standards. The upgrade is expected to be completed by spring 2014.
As part of the upgrade, the anionic and cationic polymer, ferric chloride 43 percent, sodium hydroxide 50 percent, and gas–chlorine chemical-feed systems will be replaced. Jerry Griffith, plant mechanic, began looking for new technologies to increase each system’s accuracy, reduce maintenance costs, and integrate operations into an advanced supervisory control and data acquisition (SCADA) system.
The plant’s diaphragm pumps and gas– chlorine injection system had a variety of problems that needed to be reduced or eliminated during the upgrade. Challenges included system maintenance, chemical metering accuracy, ease of use, SCADA system requirements, system flexibility for emergency operations, and limited space requirements.
The pulsating diaphragm pumps required frequent adjustments and maintenance. “They always needed cleaning, the oil needed to be replaced frequently, and the stroke length needed to be adjusted manually,” said Griffith.
The pulsating diaphragm pumps were also hard on the piping system, causing occasional leaks. Piping and ancillary components, such as pulsation dampeners, calibration columns, and pressure regulator valves, also required additional maintenance and floor space and made the system more complex. In addition, the diaphragm pumps weren’t providing much information to the SCADA system.
As part of the upgrade, the gas–chlorine injection system will be replaced with a liquid chlorine and ultraviolet (UV) system.
The gas system is expensive to maintain, costing $10,000 per year for scrubber and injector cleaning and maintenance. Using lower-concentration liquid chlorine and UV technology will help the plant maintain lower trihalomethane (THM) levels. The new liquid chlorine system, which uses peristaltic pumps, will be installed in the chemical room. When the gas–chlorine system is removed, the area will be transformed into a much-needed workshop.
CHOOSING THE RIGHT CHEMICAL PUMP
After reviewing and testing various types of pumps on the market, LMTP personnel chose peristaltic-style metering pumps to replace the diaphragm pumps in all applications, including gas–chlorine injection, for several reasons.
Low Maintenance. Although peristaltic pumps require periodic tube changing, such maintenance is predictable and inexpensive. For example, Griffith replaces the pump-tube assembly of the new anionic polymer system every six months, regardless of wear.
Ease of Use. The peristaltic pump is easy to use, and the pump-tube assemblies can be replaced quickly and easily. In addition, the menu-driven software and display allow operators to quickly adjust the pump’s many electronic features.
Higher Accuracy. Even when pumping high-viscosity polymers, the peristaltic pumps are accurate to within about 3 percent over their operating output range and over the life of the tube. The SCADA system can easily set and maintain 1 ppm without requiring operators to make manual adjustments.
SCADA Ready. The peristaltic pumps communicate with the SCADA system better than the diaphragm pumps did. Now more process information is available to the SCADA system, including multiple alarm outputs and output volume data. In addition, the system can react more quickly to commands, such as a quick shutdown of the system. The highly automated plant is monitored and controlled in real time using handheld devices. Rob Hills, water treatment superintendent, can now access and control anything in the plant with his smart phone or personal digital assistant.
Flexibility. The peristaltic pumps are self-contained. The motor and controller are located inside the pump enclosure for portability. The pump’s small size and light weight allow operators to move the pump to a remote location if treatment is required at a different injection point. For example, if a system failure requires a particular section of pipe to be shutdown, the pump can be relocated as required and run manually to prevent plant shutdown. With the San Andreas Fault less than a mile away, LMTP operators are alert to potential damage to piping systems from earthquake activity. They try to maintain as much system flexibility as possible.
Space Requirements. The peristaltic pumps occupy a smaller footprint, further increasing efficiency in the chemical room and reducing maintenance. The entire gas chlorination system will be replaced by peristaltic pumps and relocated to the chemical room with the other systems.
Quiet Operation. The new peristaltic pumps produce significantly less noise in the chemical room. Operators didn’t realize how loud the diaphragm pumps were until they were gone, according to Griffith. Less noise helps reduce the stress of working in the chemical room for extended periods.
Consistency. With the features and capabilities to handle all applications, the peristaltic pumps reduce the complexity and amount of operator training required as well as the number of spare parts necessary for system maintenance.
Customization. Custom designed by LMTP staff, the new anionic and cationic polymer, ferric chloride, and sodium hydroxide chemical systems feature
- a plastic texture-coated flooring grate system over the containment area.
- a below-grate flushing pipe system.
- quick-release polyvinylidene fluoride cam-lock inlet and outlet pump fittings.
Peristaltic pumping technology has simplified maintenance and helped LMTP personnel function more efficiently, maintain and upgrade plant equipment, and comply with federal water quality standards.
Bill McDowell is a sales engineer with
Blue-White Industries (www.blue-white.com),
Huntington Beach, Calif.
Article available on Opflow Magazine’s Website: http://dx.doi.org/10.5991/OPF.2013.39.0020
Maintaining the correct amount of chlorine for effective drinking water system disinfection in a large municipal drinking water system can be challenging. Piping system lengths, variable flow rates and demands, and other factors contribute to the difficulties in maintaining the optimum level of free chlorine throughout the entire system.
One method of increasing the length of time that the chlorine remains effective in the system is to add ammonia. With the addition of ammonia, chloramines are formed resulting in not only a more stable and longer lasting disinfecting residual than free chlorine, but also the additional benefit of a reduction in the amount of initial chlorine injection required and a similar reduction in unpleasant chlorine odor and taste.
Although the mixing of ammonia with chlorine to form chloramines is a safe and effective means to treat drinking water, the addition of ammonia can create a potential hazard if the chlorine is not present. The proper chlorine/ammonia ratio must be maintained to form the chloramines. For this reason, system designers are careful to select the most reliable injection system components possible that also allow for variable flow rate requirements and permit continuous monitoring and remote control by SCADA systems.
Chuck Boone, the Mechanical Maintenance Supervisor at the Irvine Ranch Water District (IRWD) in Irvine, CA, became concerned about the new IRWD reservoir management system (RMS) pilot project when the diaphragm pumps chosen for the chlorine injection task repeatedly failed. Although sensors in the system detected the failure and safely shut down the system, it became obvious that a more reliable chlorine injection pump system was required.
The cause of the diaphragm pump failures was traced to the pumps losing prime due to vapor locking. Vapor locking is caused by gases escaping from the fluid and building up in the pump head preventing the valves from operating correctly. This phenomenon commonly occurs when the pump is sitting idle, such as at night or when the system demands are low. The IRWD maintenance mechanics worked with the diaphragm pump manufacturers to install de-gassing valves and other devices that would permit the pump to automatically expel the built up gasses from the pump head, but these measures were unsuccessful. Looking for a better way to inject chlorine, the IRWD team turned their focus to peristaltic pump technologies.
Commonly called “squeeze tube pumps,” the new generation of peristaltic pump is quite different from the low pressure, non-industrial peristaltic pumps most people are familiar with seeing in a hospital setting. These industrial pumps are now capable of long tube life and output pressures to 125 PSI. Some models also include such features as tube failure detection systems, flow verification sensors, heavy duty weatherproof enclosures and sophisticated electronics for connection to SCADA systems.
Peristaltic pumps use a circular pump “head” and simple rotating roller design to gently squeeze the fluid through a piece of specially designed tubing. With no valves to clog, metal springs to corrode or ball seats to fail they can effectively pump both fluids and gasses, eliminating the possibility of vapor locking and loss of prime. A peristaltic pump’s output is not affected by changes in the system pressure (it therefore does not have a pump output curve) making its output much more consistent than a diaphragm pump.
In a chloramine application, it is critical that the ammonia pump inject at a proportional rate with the chlorine pump and automatically deactivate in the event of a chlorine pump failure. The new generation of variable speed peristaltic pumps meets the requirements for both the chlorine and ammonia pumps in a chloramine application.
Manufacturers of these pumps include many of the features used by large municipal water treatment systems such as scalable 4-20mA (analog) and high speed pulse (digital) input and output signals. These I/Os not only permit the SCADA system complete control of both pumps but they can also provide solutions for external data logging, remote diagnostics and driving multiple pumps and devices from the primary pump.
The scalable analog output signal provided the IRWD team a simple method for proportionally driving the ammonia pump directly off of the chlorine pump.
The pumps offer outputs to 33.3 gph, a 100:1 turndown ratio and continuous feed. With output pressure ratings to 125 psi and its ability to pump gases, they are suited for use in chlorine dosing applications.
|Article Peristaltic Pumps Excel in Chloramine Application|
Diaphragm Metering Pumps
This type of metering pump will require you to be a bit more knowledgeable about the pump valves, as well as proper priming and adjustment characteristics. Once you understand the pump and work within its normal limits, you should be assured of a successful program.
Peristaltic Metering Pumps
Peristaltic metering pumps are a good choice when pumping dirty fluids that may contain trapped gases or particulate matter, into lower pressure systems. Newer peristaltic pump designs are capable of pressures to 124 psi.
There are more tubing options available for modern peristaltic metering pumps, offering more chemical resistance and longer tube life.
Tube failure has been well addressed with Blue-White’s Exclusive, Patented Tube Failure Detection system (U.S. patents 7,001,153 and 7,284,964).
These pumps are initially easier to begin using than diaphragm metering pumps.
Peristaltic & Diaphragm metering pumps –
Diaphragm metering pumps excel at pumping clean, aggressive chemicals into high-pressure systems, and require very little maintenance. A variety of wetted parts materials are available for chemical resistance. However diaphragm pumps can lose their prime, and can be difficult to prime, especially if the fluid is dirty or contains trapped gases.
Peristaltic metering pumps excel at pumping dirty fluids that contain trapped gases or particulate matter into lower pressure systems. Modern peristaltic pump designs are capable of pressures to 124 psi. Peristaltic pumps will require periodic changing of the pump tube.
Research and a good understanding of both the installation requirements, and the pump’s operating parameters and maintenance requirements, are vital to choosing the best pump for your application.
If you are in the water conditioning or water treatment industry, manage a store, or are an installation professional, odds are excellent you know more than most about pumps including chemical feed pumps. Here are a few things I’m fairly sure you didn’t know.
Most adults own at least six pumps:
- Fuel pump
- Washing machine (water pump)
- Oil pump
- Vacuum cleaner
- Dishwasher (water pump)
- Air conditioner
I’m sure I’ve left some out, but you get the point. Pumps are a very important part of nearly everyone’s lives. Below I’ve listed some historic information on pumps.
Pumps are not a new technology – only the power used to drive pumps (and control) are new. Pumps date back to Alexandria (Greece) 100 BC; animals, yes-even humans, powered pumps.
Christopher Columbus (1451–1509) used bilge pumps on his ships (pumps were made out of lead, with leather strips for flapper type check valves). It was written that he said “an efficient bilge pump was the most important piece of equipment on a ship”. I believe now we’ve established the historic aspect of pumps, it’s important we understand the basic classification of pumps.
Today’s water conditioning & w/ treatment installations include one or more of the above pumps. Centrifugal pumps are used for pumping large amounts of water, of particular importance in water recirculation. Piston pumps are of importance in water reclamation, such as reverse osmosis systems, due to their very high pressure capability. Displacement style pumps (diaphragm, or peristaltic), is a common way to pump chlorine, or other water treatment chemicals, we know them as; chemical feed pumps, metering pumps, chlorinators or injection pumps.
Now we’ve established the importance of pumps in our lives and in particular, the water conditioning & w/treatment industry, allow me to focus in on pumps used for chemical delivery in our industry. Although these pumps are properly called displacement, pumps (remember) both reciprocating diaphragm, and rotary peristaltic, in this article for diaphragm pumps I will use the name; chemical feed pump, the rotary peristaltic is often referred to as a tube, or squeeze tube pump, I’ll just use the name peristaltic pump.
Now that we’ve covered some of the history, I’d like to share some of what I’ve picked up over the years. Working for a well-known chemical feed pump manufacturer for thirty-three years has taught me quite a lot. Some of what I have learned may be valuable to you, a water conditioning & treatment professional. I would like to clear up some myths, or assumptions I’ve been asked about from time to time.
Do you as a manufacture build in planned obsolescence?
Nothing could be further from the truth; to the point, the question is almost humorous. When a particular chemical feed pump is designed, there are countless kinds of destructive testing conducted. We deliberately try to cause the product to fail. Product improvements are an ongoing process that just never ends. When we force a breakdown, that particular part or area is redesigned until it’s corrected.
Metering pumps should be trouble free.
Of all your equipment you work with, the metering pump will require the most attention. The model you purchase is important, and the brand reliability, remember you are dealing with far more than a mechanical pump, you are dealing with; water chemistry (ph & chlorine levels, to name a few), the possibility of serious bacteria, water temperature & pressure, and a multitude of other factors. When you put them all together, there is far more involved than a chemical feed pump. The “perfect chemical feed pump” will not overcome a poor installation. If any of the above items are neglected your job will become infinitely more complicated.
Which type of pump is better, peristaltic or diaphragm?
As a manufacturer of both I can tell you with some expertise they both have their strengths and weaknesses. I will also tell you there really is no definitive answer. It would be similar to asking what’s better a Jet pump or a Submersible pump? Peristaltic pumps are a bit easier for the novice, but if not maintained are far more problematic than diaphragm pumps. If you have a good working knowledge of diaphragm feed pumps, and understand the basics of maintaining check valves, this type pump is more cost efficient. I believe in choice, and I’ll let the market decide that question.
Chlorine is on its way out.
We have a Love/hate relationship with Chlorine. This is a case where the good definitely outweighs the not so good. Don’t even try to imagine our lives completely without chlorine as a disinfectant. Alternative forms of disinfectants play a larger role in our industry, and that is a good thing. However, make no mistake chlorine is still the disinfectant of choice in our industry, it simply works well and the cost benefit isn’t worth arguing.
Most water conditioning & W/treatment professionals have their favorite type of chlorine. As a manufacturer, I do too. Let’s go over them. Liquid chlorine (sodium Hypochlorite) is usually purchased at your favorite dealer/distributor, or chemical company, some regions the chemical is delivered on a route basis. This industrial strength chlorine runs anywhere from 9% to 15% active chlorine. The chlorine you purchase at the supermarket is considerably weaker about 5% chlorine. Sodium hypochlorite, or liquid chlorine is the chemical of choice for most mechanical chlorinators, some will argue that point, but for the most part hands down its liquid chlorine. The problem with liquid chlorine is; it is heavy, cumbersome, and transporting it can be hazardous. Liquid chlorine weakens over time. Dry (chlorine) or calcium hypochlorite also has its advantages, and disadvantages. It is certainly easier to store and does have a longer shelf life. Some of the challenges are obvious; you have to mix slurry (dry chemical & water), so it can be pumped. The amount of undissolved solids will over time foul check valves, and plug injection fittings. Peristaltic pumps are recommended if you choose to pump chlorine slurry. Peristaltic pumps easily handle chlorine slurries, because they have no check valves.
Some tips on maximizing the performance of your mechanical chemical feed pump (diaphragm, or peristaltic style)
- Keep variables to a minimum. Such as, chlorine strength, type of chlorine used, and the feed rate setting on chemical feed pump. Example; if you keep the chlorine strength consistent, during the summer months, you’ll need to increase the amount of chlorine to be fed. On a peristaltic pump, adjust the on time up (pump longer), with a diaphragm pump increase the cam setting, or pulse rate. If you tamper with chlorine strength (usually a problem with slurries), and chlorinator feed rate, you will just drive yourself crazy. Minimize your variables.
- Avoid running chemical container dry, while the pump may not be mechanically harmed, pumping air will cause the valves to build up a residue of dried chlorine (salt).
- After changing out chemical containers make sure, the chemical feed pump is primed and most air is purged out of the pump head & discharge line.
- At least every six months inspect, and if necessary, replace the diaphragm. Also, inspect the top and bottom valves; clean or replace. If you are using a peristaltic feeder, change pump tubes out regularly, Also keep your eye on the roller assembly; the rollers do require periodic lubrication, and replacement. Rollers that are frozen, not rolling correctly will dramatically shorten the life of the pump tube.
- Keep spare liquid ends (assembled pump head kits) handy, as we all know Murphy’s Law, “Problems usually occur at the most inopportune times”, it’s far easier to replace a diaphragm and pump head assembly with valves (usually just 4 screws) than detailing every o-ring and ball seat. Using peristaltic pumps? keep pump tubes and roller assemblies on hand. Time is money.
- Inspect the foot valve strainer quarterly, or as frequent as necessary.
- Chemical feed pumps are easy to prime when the discharge (pressure) line is removed or vented. After the pump is primed re-attach the discharge line to the top pump head valve, or close the vent relief.
- Keep the pump room clean & well ventilated – Too many pump rooms are a mess. The rooms should be neat & clean (not a storage area for junk) spare parts should be available at the site. An installation, instruction booklet should be mounted on the wall at or near the chemical feed pump, this will have a parts schematic complete with part numbers.
- Always wear eye protection when working on chemical injectors or when changing out containers, or adding chemical. This is something that cannot be over stressed.
- Avoid changing chemical brands without researching the compatibility regarding your chemical feed pumps.
- A flow indicator installed on the suction tubing of your injector is an outstanding diagnostic tool, at a glance you can see if the pump is working properly. Some manufacturers offer them as standard equipment.
- Never mix different chemicals in the same solution tank.
- Never inject chlorine and pH adjusting chemicals near one another, always use caution.
- Your Chemical feed pump must shut down when the water recirculation pump is not running. The chemical feed pump should operate in concert with the water pump, never by itself.
- Chemical feed pumps – Double ball check valves just work better than single ball check valves.
- The weakest side of a diaphragm chemical feed pump is the suction side (the ability to draw chemical), always keep your suction run as short as possible (5’ or less). Discharge runs are not as critical.
- Most all warranty and out of warranty work is related to poor maintenance.
- Peristaltic pumps have an amazing ability prime, up to 18’ (without discharge backpressure), it’s true, but please keep the suction run a short as possible.
- Your pumps injection fitting is the single most neglected part of your system. When your injection fitting begins to clog, the chemical feed pump works harder & harder to overcome the blockage (sound familiar). Change or clean them regularly.
- Peristaltic pumps – Are easier (more forgiving) to use, but if neglected could be a serious problem. Pump tubes need to be changed with regularity; many are not & eventually could leak corrosive chemicals. Changing a pump tube is not complicated, and just takes minutes.
- Peristaltic pumps – Older peristaltic pumps benefit from changing out roller assemblies, as these rollers age (wear), slowly you lose critical squeeze tolerances and the pump gradually will lose the ability to inject chemical. Often the pump tube is blamed, but the problem is really the roller assembly.
- Suction & discharge tubing needs to be replaced regularly. This is one area where I see widespread neglect. Tubing is available practically everywhere and is rather inexpensive.
- Chemical controllers (pH, ORP & TDS) are of growing importance to our industry. This is an area you absolutely need to hire the most qualified, and service after the installation is an absolute. Most controllers work well with chemical feed pumps; Stick with the industry leaders, those controller companies with a proven track-record. Avoid elaborate so-called turnkey systems that claim to do everything. Caveat emptor.
- There is no perfect chemical feed pump or system – No matter the cost or what you were led to believe. The success of a particular job, or system is directly related to the installer & quality of equipment, but most importantly how the equipment is installed & maintained. As a manufacturer, we do our best to manufacture the finest equipment, but we are only as good as those who do the installation, service & maintenance work.
In summary, pumps have a very long history dating back 100 BC. Pumps are crucial to our lives, and particular importance to the water conditioning/treatment industry.
Robin Gledhill, President
Huntington Beach, CA, USA