How to Change the UV Lamp for Desmi BWTS: A Step-by-Step Guide for Ship Operators
If you’re a marine professional managing a Desmi Ballast Water Treatment System (BWTS), regular UV lamp replacement is critical to maintaining compliance, water purification efficiency, and system longevity. Desmi’s CompactClean UV-Lamp NEX is designed for reliability—but proper installation and replacement are key to avoiding downtime or equipment damage. In this guide, we’ll walk you through the entire process, from safety prep to final testing, with expert tips to make the task smooth and error-free.
Why Regular UV Lamp Replacement Matters for Desmi BWTS
UV lamps are the heart of Desmi’s BWTS, neutralizing harmful aquatic organisms in ballast water to meet IMO’s Ballast Water Management Convention (BWMC) standards. Over time, UV output degrades—typically after 2,000–3,000 operating hours—even if the lamp appears intact. Skipping replacement can lead to:
• Failed water quality tests and non-compliance penalties
• Reduced disinfection efficacy, risking invasive species transfer
• Damage to quartz sleeves or gaskets from overworking the lamp
• Costly system repairs down the line
Pro tip: Always replace Desmi UV lamps in pairs (1-2, 3-4, etc.) as recommended by the manufacturer. This ensures balanced performance and avoids uneven wear on the system.
Pre-Requisites: Tools & Safety First
Before starting, gather the required tools and prioritize safety—Desmi BWTS involves electrical and water components that pose risks if mishandled.
Required Tools & Parts
• Allen key (H4) for bolt removal/installation
• Cotton gloves (to protect UV lamps and quartz sleeves)
• Cleaning aids (ethyl alcohol + lint-free cleaning tissues)
• Silicone grease (for O-rings and gaskets)
• Secure containers (for storing old lamps/sleeves)
• Replacement parts: Desmi UV Lamp (model 721666, UV LAMP DESMI 6KW SQ), new gaskets (U-manchet, O-ring, flatseal—never reuse old gaskets), and quartz sleeve (720875, 750x44x2.0 mm) if needed.
Critical Safety Precautions
• Shut off power: Turn off the main breaker in the control panel to avoid electric shock.
• Drain the system: Empty all water from the UV unit—water contact with electrical components or open gaskets causes damage.
• Handle with care: UV lamps and quartz sleeves are fragile. Avoid touching their surfaces (oils from skin cause scratches or reduced UV transmission).
• Work in a clean area: Prevent dirt, sediment, or debris from entering the system—this clogs components and impairs performance.
Step 1: Disassemble the Desmi UV Lamp Housing
Follow these steps to safely remove the old UV lamp and associated parts:
1. Remove the lamp cup cover: Use the H4 Allen key to take out the two M5 Allen bolts (DIN912 M5X10 or M5X20) from the lamp cup cover (both sides of the unit).
2. Disconnect the UV lamp: Gently pull the lamp cup cover away, then unplug the lamp from the wiring. Secure the exposed connections to keep out water and dirt.
3. Remove the centering ring: Take off the white PTFE centering ring from both ends of the quartz sleeve.✨ Pro Tip: If you’re only replacing the lamp (not the quartz sleeve), skip to Step 6—you don’t need to remove the outer cup!
4. Take off the outer lamp cup: Use the Allen key to remove the four M5 screws from the outer lamp cup (both sides).
5. Separate the lamp cup and quartz sleeve: Carefully lift the lamp cup, supporting the quartz sleeve to prevent it from falling or scraping.
6. Remove the old UV lamp: Gently pull the lamp backward (it may be tight to reach) and support it fully as you extract it. Place it in a secure container for proper disposal (UV lamps contain mercury—follow local hazardous waste regulations).
7. Remove the quartz sleeve (if replacing): If the sleeve is scratched, cloudy, or damaged, pull it back gently. Be cautious—once it clears the U-manchet, it may drop. Support it fully and store it safely.
8. Replace gaskets (if needed): Remove the old U-manchet (720877) from both sides. Never reuse gaskets—they lose elasticity and cause leaks.
Step 2: Assemble the New UV Lamp & Components
Now it’s time to install the new parts. Follow these steps to ensure a watertight, efficient setup:
1. Clean the system: Wipe away sediment or dirt from the UV unit body, lower cup, and U-manchet grooves (both sides) using ethyl alcohol and a cleaning tissue.
2. Prepare the lower cup: Apply a thin layer of silicone grease to the new O-ring (720879, 62x3.00 Viton) and place it in the lower cup groove. Screw in the four Allen bolts by hand (do not over-tighten—this damages threads).
3. Install the new U-manchet: Apply a small amount of silicone grease to the new U-manchet (720877). Insert it into one side of the unit.
4. Fit the quartz sleeve: Slide the new quartz sleeve (720875) from the side with the U-manchet, guiding it through the lower cup to the opposite side.
5. Secure the second U-manchet: Install the remaining U-manchet over the quartz sleeve on the opposite side.
6. Insert the new UV lamp: Gently place the new Desmi UV lamp (721666) into the middle of the quartz sleeve—ensure it’s centered for optimal UV distribution.
7. Reattach the outer cup: Align the top cup with the lower cup and hand-tighten the four Allen bolts (both sides).
8. Replace the centering ring: Insert the white PTFE centering ring back onto both ends of the quartz sleeve.
9. Reconnect wiring: Loosen the cable gland (718567) and pull the lamp cup cover down the cable. Reconnect the lamp plugs, then position the cup cover back in place.
10. Secure the cup cover: Screw in the two Allen bolts by hand. Push the wires gently to ensure a secure connection, then tighten the cable glands.
Step 3: Final Testing & Quality Check
Before restarting the Desmi BWTS, perform these critical checks to avoid leaks or malfunctions:
1. Fill the UV unit: Add fresh water to the system to test for watertightness. Check around the quartz sleeves, gaskets, and cup covers for leaks.
2. Inspect connections: Ensure all bolts are hand-tight (over-tightening strips threads) and wiring is properly secured.
3. Power on the system: Turn on the main breaker and verify that the UV lamp illuminates (check the control panel for status indicators).
4. Monitor performance: Run the system for 10–15 minutes and confirm that ballast water flow is consistent, and UV output meets Desmi’s specifications.
Expert Tips for Desmi BWTS UV Lamp Maintenance
• Store parts properly: Keep replacement lamps, sleeves, and gaskets in their original packaging until use to protect them from dust and damage.
• Clean quartz sleeves regularly: Even if not replacing, clean the sleeve with ethyl alcohol to remove mineral deposits—this maintains UV transmission.
• Follow replacement schedules: Desmi recommends replacing UV lamps every 12 months or 8,000 operating hours (whichever comes first) to ensure compliance.
• Use genuine Desmi parts or quality aftermarket parts: Bad quality parts may not fit properly or meet safety standards—always use OEM components (e.g., lamp 721666, quartz sleeve 720875).
