Clarifiers are expensive, to buy or repair, and their downtime can be costly in fines imposed by regulatory agencies and in community ill will. Regular maintenance, an annual inspection of the mechanism and an occasional touchup of the paint or coating system are simple and inexpensive proactive steps that will usually prevent most problems. Three components of all clarifiers require maintenance: the effluent system, the sludge removal system and the drive. The effluent and sludge removal systems require maintenance only occasionally, whereas the drive requires regular maintenance.
The effluent system usually consists of a V-notched weir attached to a launder. The weir must be kept level, and the weir and launder must be clean and free of algae. Regular cleaning with brushes and even some chlorine will accomplish this. Some operators coat the launders with epoxy paint to aid in cleaning.
One cleaning system consists of spring-loaded brushes attached to the rotating mechanism which clean the weir, launder walls and scum baffle. An effective method of preventing algae growth is to install opaque launder covers to prevent the entry of growth-promoting light.
Sludge Removal System Maintenance
Most sludge removal systems have squeegees that sweep the tank floor. It is important that they sweep the floor clean. Therefore, they should be inspected and adjusted whenever the tank is drained. Suction clarifiers have seals at all rotating/ stationary points. “Short-circuiting” occurs when influent is drawn directly into the underflow through leaky seals. This can be prevented by replacing the seals as they become worn.
Suction clarifiers are also susceptible to plugging. Riser pipe valves can plug if the flow rate is low. Suction header orifices can also plug with foreign debris. The tank should therefore be cleaned regularly. Some operators schedule tank cleaning for fall to remove dead leaves.
Clarifier Drive Maintenance
Good drive maintenance requires attention to six things:
- Condensate removal
- Proper functioning of the torque control
- Maintenance and/or replacement of reducer bearings and seals
- Chain maintenance
- Strip liner wear monitoring
Water condenses and collects in all clarifier drives and, if allowed to accumulate, can cause the main gear and bearing to rust and fail quickly. The regular removal of this water is, therefore, the single most critical aspect of drive maintenance. Clarifier drives have cock-type valves through which condensate is drained. The operator should drain the condensate at least weekly and more often in areas of high rainfall or humidity. The operator should monitor how quickly condensate accumulates in a particular drive and drain the condensate accordingly.
The primary and secondary reducers and the main gear and bearing require lubrication. The reducers and main bearing run in grease or oil and may share a common oil bath with the main gear, which usually runs partially immersed in oil. The reducers, main bearing and main gear casing have grease fittings or oil fillers and oil drains. An oil sight glass or dipstick is usually provided for checking the oil level.
The operator should grease the reducers, where possible, and check all oil levels weekly and should also drain and replace the main gear oil every 6 months. In an increasing number of drives, the main bearing and gear run in grease rather than oil and condensate drains continually from the drive casing through small “weep” holes.
This system has two advantages over the conventional, oil-lubricated main gear. First, it prevents condensate accumulation and eliminates oil changes altogether. Second, grease is a better lubricant than oil for slow-moving gears and bearings, and its stickiness prevents water and other contaminants from coming in contact with gear and bearing surfaces.
Proper Torque Control Functioning
An occasional check to ensure that the torque control is functioning properly can prevent catastrophic damage to the drive and clarifier that might occur in the unlikely event of a malfunction. Many torque control mechanisms have a manual bypass and a visual torque indicator that make it easy to check their functioning.
The operator should work the bypass through the range of the visual indicator while the drive is running. If the torque alarm or the motor cutout fails to actuate at the designated torque levels, the torque control mechanism should be repaired immediately.
Maintenance and/or Replacement of Reducer Bearings and Seals
In all types of primary and secondary reducers, bearings and seals must be lubricated regularly and replaced when necessary. When seals and bearings wear out, they must be replaced according to manufacturer’s instructions. Worn seals will leak oil or grease. Worn bearings will make noise or get hot. They should then be replaced before they damage the rest of the drive mechanism.
Many newer drive units have cycloidal or planetary-gear reducers that are coupled directly to the drive motor and main gear. Such designs are safer, more efficient and reliable and require less maintenance than old-fashioned drive chains. Most older drive units, however, link the primary reducer to the secondary reducer through a drive chain and sprockets. The drive chain must be lubricated and tensioned and the alignment of the sprockets checked. Improper lubrication can cause the drive chain to wear out prematurely and improper tensioning and/or sprocket misalignment can cause it to come off the sprockets.
The operator should lubricate the drive chain weekly with WD-40 or foaming chain lube. Such lubricants are ideal since they penetrate and lubricate chain pins and rollers without causing excessive buildup. The operator should also check the alignment of the sprockets with a straightedge and adjust the drive chain so that it does not have excessive slack. When properly tensioned, the chain will not have more than about one inch of slack at its midpoint.
Monitor Strip Liner Wear
Many older drive designs have hardened steel strips, known as “strip liners,” as their main bearing surface. Strip liners have a life of only 10 to 20 years. The precision main bearings used by some manufacturers, on the other hand, will easily outlast the rest of the clarifier mechanism if properly maintained. Either excessive noise or a notable lowering of the top of the drive, which may cause the scrapers to drag on the clarifier floor, may indicate the need to replace the strip liners.
A thorough, well-thought-through program of regular clarifier maintenance, together with an annual inspection of the mechanism and an occasional touchup of the paint or coating system, will yield big payoffs in longer equipment life and avoided downtime. This small investment of oil and time might just prevent a lot of headaches as well.