Valves provide the answer to a faulty blower problem

Water treatment facilities rely on filtration systems to remove waste products as part of the process to recycle water. These filters are periodically cleaned by backwashing them with air bubbles produced by large blowers.

A leading regional utility’s water treatment works operates three blowers as part of a complex cleaning cycle for the media in its filtration system.

When two failed in quick succession the company turned to Sulzer which provided its single source for blower repairs – a contract which enabled it to avoid having to deal with numerous original equipment manufacturers (OEMs).

Repairs were completed at Sulzer’s Bristol service centre and the assets reinstalled by the site’s own engineers.

Shortly after, the blowers failed again. This left the aeration process with only one blower, plus considerable concern for the reliability of the remaining unit.

The units were returned to Sulzer’s service centre. Once they had been stripped down, it was revealed both suffered from overheating which had caused the rotors to expand and seize.

The intensity of the heat in the blowers was such that the plastic cabinet extraction fan on one had melted. Engineers also discovered that the rotor had friction-welded itself to the housing.

The fact that both blowers exhibited the same failure mode, suggested that the cause of the problem was not related to the unit itself; it was more likely to be a restriction, either on the inlet side or in the discharge line.

When the engineers went onsite to inspect the inlet filters along with the discharge pipework using a borescope, they found no obstructions.

Attention then turned to the pressure relief valves (PRVs) inside the acoustic cabinets, which should have lifted in the event of the blowers operating against a restriction or excessive load. Both were removed and found to be seized.

However, while this accounted for the failure of the blowers, these valves were not the cause of the restriction.

Understanding the application

The blowers operate on a 24-hour cycle, producing scour air that backwashes the filter media. During the cleaning cycle, the blowers are not required to operate all of the time and regulated by an unload valve, which vents excess air to the atmosphere. This avoids stop/starting of the blowers during the cleaning cycle.

All three blowers are regulated by this valve, and closer inspection found that the diaphragm chamber was full of water, preventing it from operating. This, combined with the PRV failures, had led to the blowers becoming distressed very quickly; only the proper function of the remaining PRV had prevented the last blower failing too.

The unloading valve was stripped and cleaned, but Sulzer recommended replacing all PRVs and the unloading valve to ensure the blower circuit functioned reliably. While these valves had performed well over 15 years, their operating condition had not been checked via a regular maintenance schedule.

Delivering the solution

The Bristol service centre engineers removed the damaged rotors and, using OEM drawings, machined them and the casing back to original dimensions, ensuring the correct clearances. The blowers were reassembled, returned to site and reinstalled.

Sulzer blower repair engineer Matt Knight commented: “Without the on-site investigation, we could have just repaired the blowers and they would have continued to fail. The combination of our technical expertise and application knowledge has been invaluable in resolving this issue and ensuring long-term reliability for our customer.”