Medium-Pressure UV Lamp Troubleshooting

Problem

Devitrification is a common issue for UV lamps. Any contaminants that are released as a result of UV-induced breakdown (or present from the start) will not be able to escape the system and may come in contact with the lamp. Water released from any materials in the system is potentially also a problem as this can eventually penetrate the lamp wall and cause the lamp to fail.

The basis of natural “devitrification” occurs when quartz converts back into a crystalline structure which acts as a very poor UV transmitter. This process occurs after surface contamination and is accelerated when the UV lamp becomes too hot. Devitrification appears as many white spots on the surface of the quartz body, which causes a reduction of quartz transparency to UV light.

Prevention

• Ensure the lamp and the surrounding area is clean and dry and operated in a dust free environment.
• Regularly clean the UV lamp as per the manufacturer’s instructions.
• Ensure the lamp is run at the correct voltage and amps and that the UV system is properly cooled.

Problem

If a UV lamp is exposed to a current overload or excessively high temperatures, the electrical connection can break down. Overcurrent situations are generally due to power supply faults, not a fault in the lamp design itself. The electrical connections at the end of each UV lamp are designed to withstand temperatures of no more than 250°C, (482°F).  This problem causes electrical arcing between the lamp and the lamp holder, which can result in a hole being burnt through the cap, destroy the lamp and potentially even damage the UV system.

Prevention

• Ensure the right UV lamp is chosen for your power supply and that the power supply is operating correctly.
• Keep ceramic cap and seal below 250°C, (482°F).
• Ensure the lamp is correctly placed within the lamp head.
• Inspect caps for damage before placing them into the system.

Problem

Whilst not a common problem, UV Lamps can trip out the control systems. UV Lamps operate at high voltages and if they are too close to any metal work or humidity is high, an earth fault can occur, as the arc jumps to the ground.

Prevention

• Ensure the lamp is correctly positioned in its housing.

Problem

Although tungsten has a high melting point, natural “blackening” occurs during the lifetime of a UV lamp, due to very high arc temperatures operating between each electrode. During normal operation, the electrodes start to erode, and the tungsten material starts to sputter depositing on the inside of the quartz body. When the transparency of the quartz body is compromised, UV output potential is significantly reduced.

All lamps will blacken at the ends eventually, although UV lamps used in disinfection systems should experience this more gradually as they tend to be operated continuously.

Prevention

• Alpha-Purify lamps have a “special material” coating on the end of the electrode to prolong the life of the electrodes.
• This problem is usually avoided by not switching the UV lamp on and off, which avoids power cycling.

Problem

UV lamps used in disinfection systems have a propensity to run hot because of their sealed environment, so swelling can be a common failure for these lamps.

Prevention

• The specification and design of the lamp may need to be revisited.
• Check if the lamp is running at an incorrect voltage/current or at too high a power.

Problem

A dirty quartz sleeve will considerable and rapidly reduce the UV wavelength intensity.

Prevention

• Regular checks of quartz sleeves should take place as levels of pollutants will vary according to the surrounding air or water quality.
• Regular cleaning of the sleeves should happen before a build-up occurs. The regularity can be scheduled according to the observed historic rate of the drop-off of UV. This can be once or even twice a week.
• Always use latex gloves when handling a quartz sleeve.
• All surfaces should be cleaned with an isopropanol wipe prior to reassembly.

Problem

In a sealed system such as a water-based system, a UV lamp cannot cool through the usual methods such as air convection. This can lead to overheating of the lamp.

Prevention

• Check the lamp is not being operated beyond the originally designed power levels. Check manufacturer recommendations are being followed on how higher power density UV lamps are thermally connecting to the water.

Problem

Spiralling is when the plasma arc is no longer wall stabilised. The plasma arc spirals out of control, repeatedly hitting the inside surface of the lamp body, softening the quartz. The risk of spiralling is higher when the UV lamp is over 1-metre in length, or the lamp is not mercury based one – both of which are relatively uncommon in disinfection systems.

Prevention

• Check that your lamp is not running on a constant wattage transformer (with secondary series capacitors).
• The lamp is not operating at a higher voltage than intended.

Problem

In the unlikely event that the UV lamp doesn’t strike out of the box, the cause may be due to leaking – which means air is entering the lamp envelope. The only way to confirm this technical issue is by using a high-frequency lamp tester. A constricted purple or blue arc, or no discharge at all, indicates there may be a small leak in the seal, which is unlikely to be visible to the naked eye.

Prevention

• Unfortunately, there is no prevention to this problem. Contact UV lamp manufacturer for assistance.

Problem

UV light can cause some materials within the lamp chamber to breakdown. Similar issues can occur if the chamber has any water or high humidity ingress.

When this happens in a closed system, the materials cannot diffuse away as they would in an open system. This can lead to higher concentrations of some problematic materials depositing on the lamp, reducing intensity levels. In rare cases, it’s even been known for some materials to pass through the wall of the lamp giving rise to surface contamination, devitrification or non-ignition.

Prevention

• Regularly clean the UV lamp as per the manufacturer’s instructions.
• Do not introduce any other materials into the lamp chamber that have not been specifically approved.
• Ensure the lamp chamber is free from water and high humidity.

Problem

If a UV lamp falls below full intensity, the UV light will not reach the necessary levels required for disinfection systems to operate correctly.

A UV lamp’s effectiveness could also be affected by the condition of the water it is operating in. If there is suspended matter or cloudiness in the water, the UV light will not penetrate as effectively.

Many of the UV lamp troubleshooting issues mentioned here will cause UV light to fall below full intensity.

Prevention

• To ascertain if the UV lamp is not producing full intensity access the UV sensors reading (if fitted) or consult the manufacturer.
• Ensure water-based systems are free of foreign particles in the water. Assess the quality of water transparency and adjust the exposure time accordingly.