Sewage Lift Stations are, by their very nature, a harsh environment, and the equipment in this type of pumping station takes quite a beating with time. The general nature of sanitary raw sewage is both corrosive and abrasive to all the equipment contained within. Therefore, periodic repair and replacement of equipment is needed.
This is usually brought about by a failure of one of the pumps. That is when you find that the equipment may be old and worn out. To accomplish repairs or standard maintenance there are many factors to consider and guidelines to follow.
We always test the entire system first. This gives us an indicator of the condition of each part of the system.
First, the floats are tested, to see if they operate all functions intended. Namely, on/off operation of the lead pump, duplexing when the lag float is raised, and alternation is tested. The high water alarm is also tested at this point. Also, check the junction box for wires that are loose, dark burnt marks to indicate bad connections, and look to insure that no fluids are entering the inside of the box. This is important because sometimes the tank may overflow into junction box.
Each pump is run as part of the float testing, and you can observe to see if pumps are noisy, vibrating, and also whether they pump down at the same rate.
A swirling turbulent action in the wet well during a pump run can indicate that the check valve on the off-pump has failed, causing recirculation back through the off pump and back into the well.
When a full repair of the system is required, the first step is to clean out the tank. The entire system must be isolated by plugging the inlet piping. The tank is then pumped down to dry level and the tank is cleaned out by a sanitary vacuum truck, sometimes using a disinfectant spray. A pressure washer is also used to spray down the walls, floor and all internal equipment.
In many sewage lift stations, there is a rail system. The rails are used to allow the user to remove pumps from the station without the need to enter the tank. A small boom crane or lifting device is attached to the pump lifting chains, and the pumps are removed by simply pulling straight up. The connection to the piping is a “quick disconnect” type. The pump slides up on the rails and is free when it reaches the top of the tank.
After the inspection of the system, you will generally decide if the metal parts in the rails are deteriorated to the point that it is time to replace the entire guts of the station. This involves cutting the discharge piping off and connecting new piping, valves and rail system inside the tank.
As you can see from the pictures, the rails in this system were completely broken and had to be replaced. Also, the discharge piping was rotted.
Next, the top lid should be inspected for integrity. In many stations, the cover is simply carbon steel, and will rust badly by the continual wet and harsh conditions. Support structures should be inspected, and the lid should be replaced if rust is too severe.
The tank should then be inspected for breach, and repaired. Particular attention should be paid to the bottom corners, for damage.
Finally, the control panel and components should be checked out for loose wires, correct operation, proper amp draw and error-free pump operation.
One point about entering a lift station to do repairs – a lift station is considered a CONFINED SPACE, which requires that confined space safety rules be used. OSHA laws govern confined space entry, and dictate the required safety equipment at the site, number of workers and their roles, and procedures during entry. In confined space, there must be at least three men to do the job – an authorized entrant, authorized attendant, and stand-by safety personnel.
A safety tripod with removal harness must be in place and used, to allow a means of retrieving a disabled worker.
The job also requires the use of a “sniffer”, an air quality analyzer, which is used to check the tank for harmful or dangerous gases. Because of the nature of raw sewage, methane gas, for one, may be present, and can cause a worker to lose consciousness if exposed. For this reason, an evacuation fan is used to continuously pull the air from the tank and bring in fresh air. The tank air checked during work, to insure that the air quality remains safe for the workers.
If the fan cannot bring air quality to standards for safe entry, a self-contained air pack is required.
Sewage Lift station work involves a combination of plumbing skills, electrical skills, controls experience, structural know-how and a good knowledge of safety practices and rules.
This work is definitely not for the faint of heart.
Robert Brown Associates