Checking a lift station

The short answer

• On every visit: alarms, each pump’s switch in Auto, the wet well level and floats, how each pump sounds, leaks, and signs of an overflow outside.
• Read each pump’s hour meter. Pumps that take turns should run about the same; the one that runs longer is usually moving less water.
• A drawdown test measures what a pump really moves, with no flow meter.

Pump rate in gallons a minuteGallons a foot of the wet well × feet drawn down ÷ minutes, plus what flows in meanwhile

A wet well is a confined space. Read it from the top, and go in only under your utility’s confined space procedures.

On every visit

The same things, in the same order, every time, so a change stands out:

• Outside. Gate, fence and hatches locked. Wet ground, rags or paper around a hatch or manhole mean it overflowed since the last visit. A stronger smell than usual is worth a note.
• The control panel. No alarms, and each pump’s switch in Auto, not left in Hand or Off. If the panel shows motor amps, compare each pump with what it usually draws.
• The wet well. The level, from the gauge or the level sensor. Floats hanging free, not tangled or coated in grease. A grease mat or a raft of rags on the surface.
• The pumps. Listen to each one run. Grinding, rattling or a pump that runs without the level dropping needs a look. A check valve that slams when a pump stops is worth a note too.
• Leaks. At pump seals, valves and the discharge piping.
• Standby power. If the station has a generator: fuel, battery, no alarms on its controller, and when it last ran.

What the run hours say

A pump’s hour meter is the station’s memory between visits. Subtract the last reading from this one for the hours it ran since. Where two pumps take turns, the hours should come out about the same. The one that ran longer is usually moving less water each time: a worn impeller, a partial clog, or a check valve that sticks. Or the pumps aren’t taking turns.

Run time also climbs with the weather. Hours that jump after rain, and fall back after, are rain and groundwater getting into the sewers. Hours that creep up in dry weather, with the same homes and businesses on the line, point at a pump losing capacity.

If the panel counts starts, divide them by the hours between visits. The same 48 hours with 214 starts is about 4.5 starts an hour. The motor’s maker sets how many an hour it can take; a float set too close together, or a stuck one, can push a pump past it.

The drawdown test

Most lift stations have no flow meter, so a pump’s real flow comes from the wet well itself: how many gallons it holds a foot, and how fast a pump lowers it.

1. Work out the wet well’s gallons a foot. A round one is 3.1416 × the inside diameter × the inside diameter ÷ 4 square feet, and a rectangular one its inside length × width. Each square foot holds 7.4805 gallons a foot of depth.
2. With the pumps off, time the level rising a measured distance. That’s what flows in.
3. Run one pump, and time it lowering the level a measured distance. Stay between the levels where the pumps normally start and stop.
4. Gallons drawn down ÷ minutes, plus what flows in, is the pump’s gallons a minute.

Compare each answer with the pump’s rated flow on its curve, or with the station’s first test. If both pumps moved 260 gallons a minute when they were new, Pump 2 has lost about 18%, which is why it ran 68% longer. Do the test when what flows in is steady, not in a storm, and do it two or three times.

From run hours to flow

With each pump’s gallons a minute, the hour meters say roughly how much the station moved: each pump’s rate times the minutes it ran.

It’s an estimate: a pump moves a little more with the wet well high and a little less with it low. Where the station has a meter, its readings are the better number, and the meter readings to MGD guide turns them into a day’s flow.

Keeping track of it in ShiftRounds

Each lift station is a checkpoint, on a route of its own or at the end of a plant’s, so the round to every station works with no signal and sends once there is one.

• The checklist. The lift station checklist asks for the wet well level, each pump’s status (on, off, auto or fault), whether the alarm is clear, a leak check, and a photo and note. A pump in fault is a critical finding, and an alarm that isn’t clear a yellow one.
• Run hours. Add each pump’s hour meter as an item counting hours. The keypad shows the hours since the last visit, and an expected range turns a pump that ran far more or less than usual yellow.
• A station you can’t get into is skipped with a reason: locked, flooded, not safe to enter, or out of service. The report lists it, so nobody mistakes it for one that was checked.
• An NFC tag at the panel or the hatch shows the round reached the station.
• A fault or a leak opens an issue that a supervisor assigns and closes. Seen again on the next round, it goes on the same issue.

ShiftRounds doesn’t work out a drawdown test for you: note the levels and times on the round. More on rounds for wastewater plants and lift stations.