Plumbing
Sewage lift station design and pumping field guide
Size the wet well to the cycle, run duplex pumps that alternate, push the force main fast enough to scour, and prove the alarm and the backup work before anyone walks away.
Direct answer
A sewage lift station collects wastewater in a wet well and pumps it through a pressurized force main to the gravity sewer when waste cannot reach it by gravity. It runs on duplex pumps, floats, and a high-level alarm, sized to the peak flow and total dynamic head. The engineer, the health code, and the pump manufacturer control the design.
Key takeaways
- A sewage lift station collects wastewater in a wet well and pumps it through a pressurized force main to a gravity sewer when gravity cannot reach it.
- Use duplex pumps minimum, each sized to carry full design flow alone, alternating lead and lag so either pump runs the station during a failure or service.
- Size wet well working volume to inflow and the pump's max starts per hour; common form is V = T times q divided by 4, targeting a 5 to 15 minute minimum cycle.
- Hold force main velocity around 2 ft/s minimum for self-scouring and under about 8 ft/s, with designs aiming for a 2 to 5 ft/s band at design flow.
- A wet well is a permit-required confined space under OSHA 1910.146 with hydrogen sulfide, oxygen deficiency, and engulfment hazards; pull pumps on the guide rails instead of entering.
What a lift station is, and what it costs you when it fails
A sewage lift station is the pump system that moves raw wastewater uphill when gravity cannot do it. Sewage wants to run downhill in a sloped pipe to the main, and most of the time it does. When the drain leaves the building or the site below the level of the sewer it has to reach, there is no downhill left. The waste collects in a tank called a wet well, and a pump lifts it up and pushes it through a pressurized pipe, the force main, until it spills back into a gravity sewer that can carry it the rest of the way.
This is the one plumbing system that floods the building or the street when it quits. A gravity sewer that clogs backs up slowly and gives you warning. A lift station is pumping raw sewage on demand, and when the pump fails or the power drops, the inflow does not stop. It keeps coming from every fixture upstream, the wet well fills, and it overflows, either back into the lowest fixtures in the building or out of a manhole onto the ground. That is a health hazard and a cleanup nobody forgets.
So the design is not really about the pump. It is about staying ahead of a failure you cannot stop. That means redundant pumps sized to the real flow and head, a wet well sized so the pumps do not destroy themselves cycling, a high-level alarm that tells someone before it overflows, backup power, and safe access to a tank full of sewer gas. This guide covers the full station. For the pump sizing itself and the solids question, see the sewage ejector sizing guide. For the gravity connection on each end, see the building sewer lateral guide.
When do you need a lift station?
You need a lift station when there is no gravity path from the waste to the sewer or septic system that has to receive it. The trigger is elevation. If the invert of the drain serving the fixtures sits below the invert of the public main, gravity will not carry it across, and something has to pump.
The common cases repeat. A finished basement with a bathroom below the building sewer. A building set in a low spot where the street sewer runs higher than the slab. A remote pad, a guard shack, or an outbuilding too far from the main to hold slope. A new development on the wrong side of a ridge from the trunk sewer. Sometimes the gravity run is theoretically possible but so long and so flat that holding slope across the whole site is worse than pumping a short rise.
The judgment call between a single below-grade fixture and a full station is real. One basement bath under the sewer is usually a packaged sewage ejector in a sealed basin, which the ejector sizing guide covers. A building or a site whose entire sanitary load has to be lifted is a lift station with duplex pumps, a designed wet well, and an engineer's stamp. Where you cross that line depends on the flow, the criticality, and what the health department will accept, so confirm the threshold with the authority having jurisdiction early.
The wet well
The wet well is the tank that collects the wastewater between pump cycles. It is the heart of the station, because its volume is what lets a steady trickle of inflow be pumped out in short hard bursts without the pumps running every minute. Sewage flows in continuously and the pumps run intermittently. The wet well absorbs that mismatch.
The working volume is the part that matters: the storage between the level where the lead pump switches on and the level where it switches off. That band of water is what the pump empties on each cycle. Below the off level you keep enough depth to keep the pump submerged and its suction covered, which the pump manufacturer specifies, and above the on level you keep freeboard for the lag pump, the alarm, and the inflow that arrives while the pumps are catching up.
Build it so nobody has to climb in to clean it. The well will collect grease, rags, and grit no matter how good the upstream system is, and the floor should slope or be shaped so solids move toward the suction instead of building a reef in the corners. Size, shape, and submergence are an engineered package, so set them with the engineer and the pump manufacturer's installation data, not from a rule carried over from the last job.
How big should the wet well be?
Size the wet well so the pumps do not start too often. The working volume is set by the inflow and the minimum runtime the pump can stand, not by how much sewage you want to store. Store too little and the pump short-cycles, starting and stopping every couple of minutes, which overheats the motor and burns it out long before its time. Store too much and the sewage sits, goes septic, and stinks.
The cycle math is straightforward. Cycle time equals 60 divided by the allowed starts per hour, so a pump rated for 6 starts per hour wants a 10 minute cycle. A common form for the working volume is V = T times q divided by 4, where T is the cycle time and q is the pump capacity, and that quarter factor falls out of the worst case, which is inflow at half the pump rate. Ten States Standards practice commonly targets a minimum cycle on the order of 5 to 15 minutes at design flow, but the controlling number is the pump manufacturer's maximum starts per hour for the motor you actually buy.
This is exactly where field habit gets people in trouble. A wet well sized by gut, or shrunk to fit a tight excavation, short-cycles the pumps and you are back replacing motors in a year. Run the cycle calculation against the real inflow and the real pump curve, and hedge the final volume to the engineer and the manufacturer's start limit.
Two pumps, never one
A lift station serving a building or a site gets two pumps at a minimum. Never one. A single pump on a station means the day it fails, or the day it clogs on a rag, the station is down and the sewage has nowhere to go. With one pump there is no maintenance window either, because you cannot pull it to service it without taking the whole station offline.
Duplex means two identical pumps, each sized to carry the full design flow alone. One is the working pump and one is the standby. They share the load over time by alternating, but the sizing logic is that either pump can run the station by itself, so a failure or a service pull on one still leaves a full-capacity station running. On larger or more critical stations the design steps up to triplex or more, with the spare capacity scaled to how bad an outage would be.
This is the redundancy that separates a real station from a basement ejector. Spend the money on the second pump. The cost of the spare pump is trivial next to the cost of sewage on the floor and the call at 2 a.m. with no way to clear it.
Alternation and the lead-lag sequence
The two pumps alternate so they wear evenly. The controller picks one as the lead for this cycle, runs it, and then hands lead to the other on the next cycle. Without alternation one pump does all the work and wears out while the standby sits dry, seizes, and is not actually a standby when you finally need it. Alternation keeps both pumps exercised and spreads the run hours.
On high inflow both pumps run. The lead pump starts when the level reaches the first on point. If the inflow is faster than one pump can keep up, the level keeps rising to a second, higher on point, and the lag pump starts so both pumps run together until the level drops back to the off point. A storm event, a slug of infiltration, or a peak draw is what calls the lag pump in.
The alternation lives in the control panel, in a mechanical alternator relay on simple stations or in the pump controller or PLC on anything modern. Confirm it actually flips. A panel set up wrong, or a failed alternator, can quietly run one pump for months, and you find out when the overworked pump dies and the never-used one will not start.
Grinder or solids-handling pump?
Match the pump to the waste and the force main. The two families are solids-handling pumps, which pass whole sewage solids through a large impeller, and grinder pumps, which cut the solids into a slurry before pumping. The choice drives the pipe size, the head capability, and the maintenance for the life of the station.
Solids-handling pumps move volume. They use a non-clog impeller built to pass a sphere of a given diameter, and the practical rule for raw municipal-type sewage is the pump and the discharge should pass solids around 3 in so rags and debris go through instead of jamming. They want a discharge line that matches, commonly 3 in or 4 in and up, and they shine when you need gallons per minute and the lift is moderate. Grinder pumps trade flow for head. They grind everything to a slurry and push it through a small-diameter force main, often 2 in or smaller, and they generate the high head you need to drive sewage a long way or up a steep hill, at the cost of a cutting mechanism that wears and needs more attention.
Pick by the system, not by price. A central station with gravity-fed lines and a reasonable lift is usually solids-handling. A long, small force main or a serious uphill push is grinder territory. The solids decision is the same one the sewage ejector sizing guide walks through, so cross-check it there, and confirm the pass-through and the family with the pump manufacturer for the actual waste stream.
Submersible vs dry-pit, and the guide rail
Most stations today run submersible pumps that sit down in the wet well, in the sewage, sealed and cooled by the liquid around them. The alternative is a dry-pit design, where the pumps sit in a separate dry chamber next to the wet well and draw the sewage across, which keeps the motors out of the liquid and makes them easier to get at but costs more to build.
The detail that matters for the life of the station is the guide rail. A submersible pump is set on a rail system with an automatic discharge connection at the bottom. The pump slides down two guide rails and seats itself against the discharge elbow under its own weight, sealing the connection without anyone going into the well. To service it, you hook the lift chain and pull the pump straight up the rails and out, and it reseats when you lower it back.
That rail is the serviceability of the whole station, and it is why you do not enter the wet well to work on a pump. Specify the rail system and a lifting chain or cable rated for the pump, and keep the rails plumb and clear so the pump actually seats. A bent rail or a fouled guide means a pump that will not seal on the elbow, and then you are recirculating in the well instead of pumping out.
How do you size the pump?
Size each pump to the peak flow and the total dynamic head, then read where it lands on the pump curve. Peak flow is the design inflow the station has to clear, in gallons per minute. Total dynamic head, TDH, is everything the pump has to push against, in feet: the static lift from the low water level in the wet well up to the discharge point, plus the friction head, which is the loss through the force main and every elbow, valve, and fitting at the design flow.
Flow is not something you simply pick. The pump delivers what the system lets it. Plot the pump's curve, head against flow, and plot the system curve, the TDH the piping demands at each flow. Where the two cross is the operating point, the duty point, and that is the flow and head the pump will actually run at. Choose a pump whose duty point sits on a workable part of its curve, near its best efficiency point, not way out at the end where it cavitates or runs hot.
The friction half of TDH is where field results drift from the submittal. A force main that is longer than the plan, has more fittings, or has roughened with age raises the friction head, moves the duty point, and drops the flow. Size with the routed length and the real fitting count, build in margin, and hedge the TDH and pump selection to the engineer and the manufacturer's certified curve. The flow-and-head method is the same one the ejector sizing guide details on the pump-curve side.
The force main
The force main is the pressurized pipe that carries the pumped sewage from the station to the point where it can flow by gravity again. Unlike a gravity sewer, it runs full and under pressure whenever a pump is running, so it does not need slope and it can go up and over high points. It ends at a manhole or a structure where the sewage drops back into a gravity line, and that gravity line is the building sewer lateral or the public main covered in the lateral guide.
Size it as a balance. A smaller force main is cheaper and keeps the velocity up so solids stay suspended, but it raises the friction head the pump has to fight, which costs energy and can push the duty point out of range. A larger main cuts the friction but can let the velocity fall low enough that solids drop out and the pipe silts up. The diameter that holds the right velocity at the design flow is the one to build.
Put a check valve and an isolation valve on the discharge of each pump, normally in a valve vault between the station and the buried main. The force main material, the thrust restraint at bends, the air-release valve at high points, and the connection back to gravity are an engineered set, so detail them with the engineer and the local standards rather than improvising at the trench.
Force-main velocity
Velocity in the force main is what keeps it self-cleaning, and it has a floor and a ceiling. Too slow and the solids the pump worked to suspend settle out in the pipe, build up, and eventually choke the main. Too fast and the friction climbs steeply, wasting head and energy and scouring the pipe wall over time.
The common target is a minimum self-scouring velocity around 2 ft per second at pumping flow, which is the speed that keeps grit and solids moving instead of dropping. The upper end is usually held under about 8 ft per second, and many designs aim to sit in the 2 to 5 ft per second working band. Those figures track Ten States Standards practice, but the exact number is the engineer's call against the pipe, the solids, and the pump.
The velocity trap shows up on oversized mains and on stations that pump far less than their design flow. A main sized generously, or a station running at a fraction of capacity because the building never filled up, can sit below scour velocity for years and silt closed slowly. If a station's flow has dropped well below design, raise the velocity question with the engineer rather than assuming the original size still works.
Check and isolation valves
Each pump discharge gets a check valve and an isolation valve, and they earn their place every cycle. The check valve stops the column of sewage in the force main from running backward into the wet well when the pump shuts off. Without it, every time the pump stops the main drains back, the level rises again, and the pump restarts, which short-cycles it and floods the well with what it just pumped out.
The isolation valve, usually a plug or gate valve, lets you close off one pump to service it while the other keeps the station running. That is the whole point of duplex redundancy made usable. Put both in a valve vault outside the wet well so they can be reached and worked on without entering the confined space.
Watch the check valve slam. When a pump stops and the check closes against a moving column, it can slam hard enough to hammer the piping and the joints over time. The fixes are a check valve type chosen for the service, a cushioned or swing check sized right, and on larger stations a controlled-closure valve. A check that is sticking or worn is a common quiet failure, so it goes on the maintenance list.
Level controls and floats
The controls watch the level in the wet well and run the pumps to match. The simplest and most common sensors are float switches, sealed floats on cords that tip and make contact at set levels. Larger or more demanding stations use a pressure transducer or an ultrasonic sensor that reads the level continuously, which lets the controller and a variable-speed drive modulate instead of just switching on and off.
The level sequence has a fixed order from the bottom up: pump off, lead pump on, lag pump on, and high-level alarm at the top. The lead float starts the working pump. If inflow outruns it and the level keeps rising, the lag float starts the second pump. When the level drops back to the off float, the pumps stop, leaving the suction submerged. The alarm float sits above all of it.
Floats fail in ways you can see if you look. Cords tangle, floats hang up on the rails or the piping, and grease binds them so they stop tipping. A float stuck on means a pump that runs dry. A float stuck off means a pump that never starts and a well that fills toward the alarm. Set the float levels deliberately, keep the cords clear of the rails, and test that each float does what it is supposed to.
The high-level alarm
The high-level alarm is the device that tells someone the station is losing before the wet well overflows. It sits above the lag-pump-on level, so it trips only when the pumps are not keeping up, whether a pump failed, the power dropped, a float hung, or the inflow simply beat both pumps. By the time the alarm float lifts, the station is already behind, and the time between the alarm and an overflow is the only warning anyone gets.
It has to reach a human. A local audible horn and a flashing light on the station are the minimum, but a horn nobody hears at 3 a.m. on an empty site is no protection. The alarm should also dial out, by autodialer, cellular, or into a SCADA or building system, so an operator is notified wherever they are. A power-loss alarm matters as much as a high-level alarm, because the most common reason a station stops is that it lost power and the pumps are simply off.
No station should be without it, and a dead alarm is worse than no alarm because it teaches everyone to ignore the panel. Test it on every service visit. Lift the float, confirm the horn, the light, and the remote notification all fire, and log it.
Backup power
A lift station cannot take a break, so it needs a plan for when the power goes out. The inflow keeps arriving during an outage whether the pumps run or not, and a station with no backup overflows on the first storm that knocks out the grid, which is exactly when the inflow is highest.
The usual answer is a standby generator with an automatic transfer switch that starts the generator and carries the station when utility power drops. On stations without a permanent generator, the design provides a connection for a portable generator and counts on staff getting there fast, which only works with a reliable power-loss alarm and a response plan. Some critical stations add a second utility feed or limited emergency storage. The right level of backup depends on how fast the well fills during an outage and how bad an overflow would be at that site.
Size and detail the backup with the engineer and the health authority. Many jurisdictions set minimum standby requirements for sewage pumping, and the standby has to actually carry the pump starting load, not just the running load. A generator that cannot start the pump is decoration. Exercise it on a schedule so it starts when it is needed, not just when it is tested.
Odor and hydrogen sulfide
Sewage held in a wet well goes septic and gives off hydrogen sulfide, the rotten-egg gas, along with the rest of the odor load. The longer the sewage sits, the worse it gets, which is one more reason not to oversize the wet well into a holding tank. H2S is the gas behind both the complaints from the neighbors and the corrosion inside the station.
It is also dangerous and corrosive at the same time. Hydrogen sulfide is toxic and, at higher concentrations, deadens the sense of smell so the warning goes away while the hazard climbs. It is heavier than air, so it pools in the bottom of the well exactly where someone would step. And it attacks the station from the inside, converting to acid on damp concrete and metal surfaces and eating them over time.
Control it with venting and, where the load justifies it, active odor control. The wet well is vented to carry the gas away from people and from the structure, and on stations with real odor or corrosion problems the vent runs through a treatment unit such as a carbon or chemical scrubber or a biofilter. The right approach depends on the flow, the detention time, and the neighbors, so set the odor and H2S strategy with the engineer.
Ventilation, corrosion, and coatings
Ventilation does double duty: it protects anyone near the station and it slows the corrosion. The wet well is vented so sewer gas leaves instead of building up, and when entry is ever required the space is force-ventilated with a blower first, because the resting atmosphere in a wet well is not safe to breathe and not safe to assume is safe.
The corrosion is relentless on the wrong materials. H2S turns to sulfuric acid on damp surfaces above the waterline and in the headspace, and it eats bare concrete and unprotected steel. Bare concrete wet wells crumble at the gas line, and ordinary steel hardware rusts away. The defense is materials and coatings: protective linings or coatings on concrete, plastic or fiberglass basins on smaller stations, and stainless steel for rails, chains, hardware, and fasteners that live in the corrosive zone.
Specify the corrosion protection up front. Retrofitting a coating into a working wet well full of sewage is far harder than building it in, and the rails and lift chain are the parts that strand a station when they corrode through, because then you cannot pull the pump. Match the materials and coatings to the H2S exposure with the engineer and the manufacturer.
The wet well is a permit-required confined space
Treat the wet well as a permit-required confined space, because that is what it is. It is an enclosed space not meant for continuous occupancy, with limited entry and exit, and it holds the hazards that define the category: hydrogen sulfide, oxygen deficiency, flammable gas, and engulfment from the inflow that never stops. People die in wet wells, and the second death is usually the one who climbed in to save the first.
OSHA's permit-required confined space standard governs entry, and it is not paperwork to wave off. Entry requires a written program, atmospheric testing before and during entry, forced ventilation, an attendant outside, a retrieval system, and a rescue plan that does not rely on the attendant climbing in. H2S deadens the nose, so you do not trust your senses, you trust a calibrated gas meter. None of that is optional, and none of it is something a two-person crew improvises on a Friday.
The whole point of the guide rail is that you do not have to enter. Pull the pumps up the rails, work on them at grade, and lower them back. If a job genuinely requires entry, it runs under the full confined-space program with trained people and the right equipment, or it does not happen. Blunt version: if you are not certain the air is safe and you have a rescue plan, you do not go in.
Packaged vs built-up stations
A packaged lift station ships as a factory-assembled unit, typically a fiberglass or polyethylene basin with the pumps, rails, piping, valves, floats, and control panel already built in and tested. A built-up station is constructed on site, usually around a cast or precast concrete wet well, with the components specified and assembled in place.
Packaged stations win on smaller flows and faster schedules. The factory build quality is consistent, the unit drops into the excavation in one piece, and the corrosion-resistant basin sidesteps the concrete-and-acid problem. The limits are size and access. There is a practical ceiling on how much flow and head a packaged unit covers, and a buried fiberglass basin needs careful handling and anti-flotation. Built-up concrete stations carry the larger flows, allow custom geometry and dry-pit layouts, and are the standard for municipal-scale work, at the cost of more field labor and the corrosion protection the concrete demands.
Pick by flow, head, site, and who maintains it. A small commercial or site station is often a packaged unit. A large or municipal station is usually built up. Either way the sizing logic for the wet well, the pumps, and the force main is the same, and the engineer's design governs which form fits.
Setting the basin and anti-flotation
The install that gets skipped is anti-flotation, and an empty buried basin in a high water table will float up out of the ground like a boat. A wet well is a large, mostly empty volume sitting in saturated soil, and the buoyant force on it can exceed its own weight, especially before it is filled and connected. A floated basin shears the piping, breaks the connections, and wrecks the station before it ever runs.
Guard against it with ballast. The basin is anchored against buoyancy with an anti-flotation collar or ballast slab, with concrete backfill or a deadman as the design calls for, sized to the groundwater the site actually has. Set it on proper bedding so it beds evenly and does not settle or rack, and dewater the excavation during the set and backfill so the empty basin is not fighting groundwater before it is anchored. Plumb matters too, because the guide rails have to stay vertical for the pumps to seat.
Then the rest follows the design: the inlet at the right invert, the force main and valve vault piping, the electrical and the controls in proper enclosures, and the vent. The buoyancy detail and the bedding are engineered to the soils and the water table, so build them to the geotechnical and the engineer's drawings, not to whatever the last basin needed.
Maintenance and PM
A lift station is a machine pumping an abrasive, stringy, corrosive liquid, and it needs a maintenance schedule or it fails on its own timeline instead of yours. The station that gets visited fails predictably. The station nobody touches fails the night of a holiday.
The recurring tasks are clean the wet well of the grease cap and the solids that build up, check and exercise both pumps so the standby actually runs, test every float and the high-level alarm by lifting them and confirming the sequence, inspect the check and isolation valves for slam and leak-back, and start the standby generator under load. Watch the pump run times and starts logged by the panel, because a lead pump logging far more hours than the lag pump means the alternation has quit, and a climbing start count means the wet well or a float is short-cycling it. Pull and inspect the pumps on the rails on a schedule, before a bearing or a seal tells you by failing.
Do the clean and the inspection from outside the well, with the pumps on the rails and the controls at the panel. The maintenance-by-topic carries the same lesson here: the cheapest failure is the one you catch on a scheduled visit instead of a callback.
Who has to approve a lift station?
A lift station is engineered and approved work, not a fixture you set and move on from. The design carries a professional engineer's stamp on most jobs, and the local plumbing code, the health department, and the sewer authority all have a say in whether and how it gets built and connected to their system.
The adopted plumbing code, IPC or UPC depending on the jurisdiction, governs the building-side plumbing and the sewage pumping requirements. The health department and the wastewater authority govern the discharge to the public system, the standby power, the alarm, and often the wet well and force main details, frequently through standards that track Ten States Standards practice. The connection back to the gravity main is the sewer authority's call, the same approval the building sewer lateral guide covers on the gravity side. Where these overlap, the strictest requirement controls.
Get the authorities involved before the design is final, not at inspection. The flow they will accept, the standby they require, the alarm and telemetry they want, and the force-main connection details vary by jurisdiction, and finding out at the trench is the expensive way. Confirm the requirements with the engineer, the adopted code edition, and the authority having jurisdiction up front.
What to document
A lift station is too important to live in someone's memory. The records are what let the next person service it, the operator respond to the alarm, and the authority sign off, and they are exactly what a field tool like FieldOS is for: capture the pump and panel data, the wet well and force main dimensions, the control settings, and the test results in one place that survives the crew that built it.
Record the equipment and the design basis together. The pump make, model, and curve point. The wet well dimensions and the float or transducer setpoints. The force main size, length, and material. The control panel and alarm details and how the alarm dials out. The standby power arrangement. And the operations and maintenance manual that the manufacturer and the engineer hand over, because the setpoints and the start limits live in it.
| Component | Requirement | Note |
|---|---|---|
| Pumps | Duplex minimum, each at full design flow | Make, model, and curve duty point |
| Wet well | Working volume sized to the cycle | Dimensions and float setpoints |
| Pump type | Solids-handling or grinder, matched to waste | Solids pass-through diameter |
| Force main | Velocity holds 2 to 5 ft/s at design flow | Size, length, material, fittings |
| Check and isolation valves | One each per pump in a valve vault | Type, and check for slam or leak-back |
| Controls and floats | Off, lead-on, lag-on, alarm sequence | Setpoints and alternation confirmed |
| High-level alarm | Audible, visual, and remote notify | Tested, with dial-out verified |
| Backup power | Standby per the authority | Transfer scheme and exercise log |
| Anti-flotation | Ballast sized to groundwater | Per geotechnical and engineer |
| Approvals | Engineer, code, health, sewer authority | Stamped design and connection permit |
Common mistakes
- Running a single pump with no standby, so a clog or a failure takes the whole station down with no way to clear it.
- An undersized wet well that short-cycles the pumps and burns out the motors years early.
- A force-main velocity below scour, so solids settle out and silt the main closed over time.
- No high-level alarm, or a dead one, so nobody knows the station is losing until sewage is on the floor.
- No backup power, so the first storm that drops the grid overflows the station when inflow is highest.
- Entering the wet well without the confined-space program, instead of pulling the pumps out on the rails.
- Setting an empty basin in a high water table with no anti-flotation, so it floats and shears the piping.
- Mixing up solids-handling and grinder duty, so the pump or the force main jams or runs out of head.
Field checklist
Want this checklist to run itself on every job — with photo proof and a signed record crews can hand the customer? That's FieldOS.
Standards and references
The framework is the engineer's design plus the adopted code and the local authority, and on a lift station the engineer owns the calculations. The local plumbing code, IPC or UPC, governs the sewage pumping and the building-side plumbing. The health department and the wastewater authority govern the discharge, the standby power, and often the wet well, controls, and force main, frequently through requirements that track Recommended Standards for Wastewater Facilities, the document the trade calls Ten States Standards.
Hedge the sizing, the velocity, and the cycle to the people who own them. The wet well volume and the minimum cycle come from the pump manufacturer's maximum starts per hour and the engineer's flow numbers. The force-main velocity target, commonly 2 ft per second minimum for scour and under about 8 ft per second at the top, is the engineer's call against the pipe and the solids. The pump selection rides on the manufacturer's certified curve at the system's TDH. Confirm all of it against the project documents and the adopted code edition.
Three things do not bend. The pumps are duplex, sized to the flow and the TDH, with a wet well sized so they do not short-cycle. The force main holds a scouring velocity, and the station has a working high-level alarm and a backup power plan. And the wet well is a permit-required confined space under OSHA 1910.146, entered only under the full program, which is why you pull the pumps on the rails instead of climbing in.
Units and terms
Lift station work mixes pump terms, hydraulics, and code language, and the same idea shows up under different names across a pump curve, a spec, and a control drawing.
Flow is gallons per minute, GPM, sometimes million gallons per day, MGD, on larger stations. Head and TDH are in feet. Velocity is feet per second. Pump capacity and starts per hour come off the manufacturer's data, and the cycle time in minutes falls out of them. Keep the units straight between the curve and the calculation, because a head in feet read as anything else moves the duty point.
- Lift station
- A pump system that collects wastewater in a wet well and pumps it through a force main to a gravity sewer when it cannot get there by gravity
- Wet well
- The tank that collects the incoming wastewater between pump cycles; its working volume is the storage between the pump-on and pump-off levels
- Duplex / alternation
- Two pumps, each at full design flow, that alternate the lead so they wear evenly; the lag pump joins on high inflow
- Solids-handling vs grinder pump
- A solids-handling pump passes whole solids around 3 in through a non-clog impeller; a grinder pump cuts solids to a slurry for a small, high-head force main
- Force main
- The pressurized pipe that carries pumped sewage from the station to the point where it can flow by gravity again
- Total dynamic head (TDH)
- The total head a pump must overcome, in feet: the static lift plus the friction head through the force main and fittings at the design flow
- High-level alarm
- The audible, visual, and remote alert that trips above the lag-pump level when the pumps are not keeping up, before the wet well overflows
FAQ
What is a sewage lift station?
A sewage lift station is a pump system that moves wastewater uphill when gravity cannot. Sewage collects in a wet well, and duplex pumps lift it through a pressurized force main to a gravity sewer that carries it the rest of the way. It is used wherever the drain sits below the sewer it has to reach.
What is a wet well?
A wet well is the tank in a lift station that collects incoming wastewater between pump cycles. Its working volume is the storage between the level where the pump switches on and the level where it switches off. That volume is sized to the inflow and the pump's start limit so the pumps do not short-cycle and overheat.
Why do lift stations need two pumps?
Lift stations run duplex pumps because the inflow never stops. If a single pump clogs or fails, the sewage has nowhere to go and the station overflows, with no way to service the pump without taking the station down. Two pumps, each sized to full flow, give a standby and a maintenance window.
What is a force main?
A force main is the pressurized pipe that carries pumped sewage from a lift station to where it can flow by gravity again. It runs full and under pressure whenever a pump runs, so it needs no slope and can go up and over high points. Its size is set to hold a self-scouring velocity at the design flow.
How big should a lift station wet well be?
Size the wet well working volume to the inflow and the pump's maximum starts per hour. A common form is V = T times q over 4, where T is the cycle time and q the pump rate. Targets often land at a 5 to 15 minute minimum cycle, but the manufacturer's start limit and the engineer control it.
What force main velocity keeps sewage solids moving?
A force main should hold a self-scouring velocity of about 2 ft per second minimum at pumping flow, with the top end kept under 8 ft per second. Too slow and solids settle and silt the pipe closed; too fast and friction and wear climb. The engineer sets the number against the pipe and the solids.
Grinder or solids-handling pump, which do I need?
Solids-handling pumps pass whole solids around 3 in and move volume at moderate head, fed by a 3 in or larger force main. Grinder pumps cut everything to a slurry and push it through a small, high-head force main. Match the family to the waste and the force main, and confirm it with the pump manufacturer.
What do I do when the lift station high-level alarm goes off?
Treat it as the station losing before it overflows. Check whether the power is on, whether both pumps are running, and whether a float has hung up, because the alarm trips above the lag-pump level when the pumps are not keeping up. Get a pump running, by portable generator if it is a power loss, and clear the cause.
Can I enter a wet well to service the pumps?
Not without the confined-space program. A wet well is a permit-required confined space under OSHA 1910.146, with hydrogen sulfide, oxygen deficiency, and engulfment hazards. The guide rails exist so you pull the pumps out on a chain and work on them at grade. If entry is required, it runs under a written program with testing, ventilation, an attendant, and rescue.
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