Oct 05, 2006

Eliminating UV System Installation Problems

Understanding possible problems and access to spare parts is critical to UV system installation and maintenance

Metal, glass, water and electricity can be a perfect combination for causing some major UV system installation problems. This article focuses on preventing the problems, recognizing the causes and providing some helpful solutions.

The starting point for a good long-term UV application begins with a water test. Not all applications are good candidates for UV disinfection. That is why proper pretreatment must be considered. Particulate matter can shadow organisms, organics can absorb UV and minerals can coat quartz sleeves. In these types of situations, the UV system may perform and yield a good test on day one, but as time passes, these parameters can interfere with performance and cause a callback to address a failed bacteriological test. Table 1 shows the recommended water quality guidelines for a UV system.

System Location

As a reminder, the UV system should be installed after all other treatments (filters, softeners, reverse osmosis units) and after any storage tank. This is because those treatment systems can be a breeding ground for microorganisms. It is also important to recognize that the UV system should not be looked at as a standalone system. UV systems often require pre-filtration systems to perform properly. UV disinfection relies on the light’s ability to reach the organisms throughout the contact chamber.

You want to ensure that the UV disinfection system is the last stage of treatment on the cold water line, prior to any branches in the distribution system closest to the point of use.

When looking for a good installation point, keep in mind that you will need to have access to the unit for service and that you also will need to be near a ground fault circuit interrupter (GFCI) receptacle. The GFCI receptacle is a great way to protect the unit from electrical surges. Depending on the region you are in, another potential electrical problem may crop up in summer months due to sweating of the piping and pressure vessel. With that in mind, be sure to locate electrical components so they will be clear of dripping water. The wiring should also be done to provide drip loops so that any water that runs down the wiring does not enter the power supply or quartz sleeve, which could cause a short at the lamp connections.

Because you will need to remove the lamp and the quartz sleeve (the glass-like tube that protects the lamp), you need to leave clearance for their removal. In situations where this clearance is not possible, plumb the unit with unions to allow the entire system to be easily removed for servicing.


It is vital to install a shut-off valve prior to and after the unit (Figure 1). This will allow for easy servicing. In addition, it will allow the homeowner or facility staff to be able to shut off the water in the event of a problem.

Once plumbed in, the pipes ahead of the UV system will need to be sanitized. If there is already a suspected microorganism problem, there may be growth in the pipes and fixtures. The installer should introduce a disinfectant into the system and let it reside for a period of time. The U.S. EPA recommends using bleach to provide immediate disinfection. The agency indicates that bleach should be run through the piping while the faucets are open until you smell the bleach. Once the odor is detected, the faucets should be closed. After an adequate residence time (1 to 24 hours), the water should be allowed to flow from each fixture until the smell is gone. At this point, microorganism testing can be done.

Mechanical Problems

As noted previously, UV systems use quartz sleeves to hold the lamps. While fragile, the quartz sleeves have a 1,000-psi tensile strength and should not break. From time to time, operators will find or create a break in the sleeve (Figure 2). Many times, a broken sleeve starts with a chip or small crack, so careful inspection at installation may prevent a return service call or even potential flooding. Most damage occurs during servicing, cleaning or replacing the sleeve; however, breakage can be caused by a water hammer or other unforeseen event.

If breakage occurs during a service visit, the technician will be able to quickly shut off the water. If breakage occurs during a period when no one is present, a severe leaking/flooding problem may occur.

Once broken, the sleeve will need to be replaced. Most often, the technician will have to order the part, and the building will be without water. We have found that carrying 1-in. PVC pipe caps allows technicians to completely remove the damaged sleeve and seal the vessel (Figure 3). While there will be no disinfection, it will stop the leak and allow the water to flow through the building. At this point, the water would be non-potable, but the ability to flush toilets will lessen the immediate need to bring the system back on line 100%.

Electrical Operational Problems

As UV systems have become more sophisticated, technicians have had to become more knowledgeable in the complexities of electrical operational problems. Three sources for potential problems are the UV monitoring system, UV sensor and solenoid valves.

UV monitoring system. The biggest problem with UV equipment tends to be the UV monitoring system and the devices it controls. The problems are widespread across all products from all companies. The main reason for these problems is that as UV lamps get hot, the actual amount of UV light produced falls off.

This occurs when the water sits for a while in the vessel (during weekends or holidays). While the water sits in the vessel without flow, the lamps heat up and the UV output shown on the UV meter will start to fall. If it falls too low and the system has been equipped with shut-off solenoid valves or alarms, it will trigger them. Once a solenoid has been shut, there is no water to the building. And because no cold water will reach the vessel, it will stay in this low UV output period.

To combat the problem, installers now can use a “high heat dump valve.” As shown in Figure 4, this device dumps the hot water to waste when the temperature exceeds 115˚F. Once dumped, cooler water will enter the vessel, and the UV monitor will show much better readings. This dump valve should be considered for any installation site where there may be infrequent water use.

UV sensor. The UV sensor may also cause problems. Generally, a UV sensor looks at a UV lamp through a port with a window on the side of a vessel. Poor water quality can cause this sensor window to foul. If fouled (i.e., covered with iron), it will cause the UV monitor to record low readings.

At this point, the system would need to be depressurized and the window removed for cleaning. During this process, the operator should also look for chips on glass or water damage to the actual sensor. If any of these components have been damaged, they will need to be replaced. It is a good idea to keep extra O-rings, windows and sensors in the truck. When replacing these parts, ensure that everything has been dried with a lint-free cloth. This will prevent moisture from fogging and damaging the components.

Solenoid valves. Many systems have integrated solenoid valves into the overall system (Figure 5). A solenoid valve, which is normally closed, remains open if the lamp is working or if the UV output of the system is above a certain point, usually 70%. The actual valve is labeled for water “IN” and “OUT.” It is important to install according to the flow arrows. If the solenoid closes, water will not be available to the home or building. This closure is generally a result of low UV or lamp out.

As with all equipment, the actual solenoid valve can fail. To check a solenoid valve for operation, you can plug it into an outlet. This will bring power to the valve and should open it. If it opens, that means that the problem is something other than the solenoid valve.

In the event that it does not open, you will need to investigate further. When re-testing the solenoid, plug it in and listen to the valve for a “click.” If no click is heard, suspect that the actuator coil is defective and order a new one. If a “click” is heard and the water does not run, suspect that something is caught in the diaphragm. If this is the case, the valve will have to be removed and cleaned.

I hope this article provides some helpful suggestions and recommendations. Please remember that understanding the various problems is important, but having access to spare parts is critical to servicing and maintaining these systems.

About the author

Robert Voitle is a senior manager overseeing residential, commercial and industrial products for Sunlight Systems. He can be reached by e-mail at [email protected].