A leachate pump that has quit in January usually isn't broken. The air line feeding it froze solid somewhere between the compressor shed and the well, and nobody noticed until the sump started filling. If you run a landfill or a transfer station, you probably have a compressor out back that nobody thinks about until that day. This is a guide to making it one you don't have to think about.
Here's the short version of compressed air for landfills: the biggest user is not the shop. It's a field of pneumatic pumps on wells and sumps, some of them a thousand feet from the building, running year round in whatever weather you get. That changes how you size the compressor, how dry the air has to be, and how you pipe it.
Why a landfill is not a normal compressed air job
Most plants put the compressor next to the thing that uses the air. A landfill spreads its load across acres. Leachate collection wells, gas collection condensate sumps and pump stations each pull a little air on a cycle, and every one of them depends on one shared supply line that runs outdoors.
That gives you three problems a machine shop never sees. First, long pipe runs, so pressure drop matters more than it does anywhere else in the system. Second, freezing, because water in a buried or exposed line turns to ice and blocks it. Third, heat. Waste Today has reported that the thermoplastic pumps and tubing used in many wells aren't rated past 150°F, while some elevated temperature landfill zones have reported temperatures of 190°F and higher. Exhaust and supply air that carries heat, water and oil into a hot well is a recipe for early failures.
The transfer station side is simpler and looks more like a heavy repair shop: a maintenance bay, impact wrenches on loader and truck tires, grease and tool air, and cylinders on gates, doors and balers. Same compressor, very different demand pattern. Plan for both.
What the pumps actually need
Take a real example. The QED slider pump, an air-powered leachate pump sold for low angle landfill sideslope risers, is specified for an air supply of 0 to 100 PSI and lists air consumption of 7 SCFM. It lifts as much as 200 feet and needs a riser at least 4 inches inside diameter, Schedule 40. Those are the manufacturer's numbers, so check the spec sheet for whatever pump you run, because models differ.
Two things fall out of that. Lift is pressure: water needs about 0.433 PSI per foot of vertical lift, so a pump working 100 feet down needs roughly 43 PSI just to get liquid to the surface, before friction and the discharge line. And 7 SCFM per pump is not a lot, until you multiply it by every well on the site.
| Load | Typical air need | Duty pattern |
|---|---|---|
| Pneumatic leachate pump (per well) | About 7 SCFM while pumping, per one common model | Cycles with liquid level, can be all day in wet weather |
| Pump controllers and level sensors | Very small, but needs clean dry air | Continuous |
| Maintenance bay tools | 4 to 10 SCFM per tool in use | Bursts |
| Baler or gate cylinders at a transfer station | Depends on bore and stroke, size from the machine data plate | Intermittent |
Sizing the compressor
Don't add up every pump and buy that. Pumps cycle, and they rarely all discharge at once. But in a spring thaw or after a heavy rain they might, so be honest about the worst day. Here's a worked example, an illustration rather than a prescription.
Say 30 pumps at 7 SCFM each. If every one ran at the same instant that would be 210 SCFM. Realistically maybe a third are discharging at any moment in wet weather, so about 70 SCFM, plus 30 or so for the shop and a 15 to 20 percent margin for leaks and growth on a pipe network this long. You land near 120 SCFM, which is where a 25 to 30 HP rotary screw sits. Compare that to a 10 HP machine and you see why undersized compressors show up as pumps that stall on the worst days.
A rotary screw is the right call for a site that runs air around the clock. Piston machines are fine for a small transfer station with a single bay, but a screw handles continuous duty and gives you far better efficiency. Waste Today notes the Department of Energy puts the overall efficiency of a typical compressed air system as low as 10 to 15 percent, and a site with a 100 HP compressor and two 30 HP units can spend over $50,000 a year in electricity at full load. Leaks across a field of pump connections make that number worse, so find them with an ultrasonic detector once a year.
Browse our rotary screw air compressors if you're replacing a unit, and think about a second compressor for backup. A landfill that loses air loses its leachate control, and leachate has regulatory consequences.
Drying the air so it doesn't freeze
This is where most landfill air systems fail. A refrigerated dryer cools air to about 35 to 38°F and delivers a pressure dew point near 38°F. That's fine in a heated shop and wrong for a line that runs outside in January. If the line temperature drops below the dew point of the air inside it, water drops out, and below 32°F that water freezes. Waste Today says as much: moisture can constrict lines, and if it freezes pumping stops.
The fix is a desiccant dryer. A common rule of thumb is to specify a pressure dew point at least 18°F below the coldest temperature the line will see. Where winter lows reach 0°F, that means a dryer rated for -40°F pressure dew point, which a heatless or heated desiccant dryer can hold. Pair it with a coalescing filter ahead of it so liquid oil and water never reach the desiccant, and a particulate filter behind it to catch dust. Our desiccant air dryers cover the range, and you'll want to read up on coalescing air filters for the front end.
Don't put a lubricator on the line unless the pump manufacturer calls for one. Many leachate pumps are designed to run on dry, clean, unlubricated air, and oil in the exhaust can end up in the well or the discharge. Read the pump spec.
Piping a field system
- Size for the far end. Pressure drop on a long header eats into the very pressure your deepest pump needs. Go a size larger than the tables suggest, and keep velocity down.
- Add storage at the far end. A receiver near the pump cluster smooths the cycling and lets the compressor ride through a pump start without a pressure dip.
- Drain every low point. Even with a dryer, a rare upset sends water down the line. Put a drip leg and an automatic drain wherever the pipe dips.
- Pick a pipe that doesn't corrode. Our air pipe and fittings include aluminum and polyamide systems that don't rust inside and are quick to add a drop to when you drill a new well.
Mistakes we see on waste sites
Skipping the dryer because "the compressor has an aftercooler" is the classic. An aftercooler pulls out bulk water, not enough to protect an outdoor line. Another is feeding a freezing winter line from a refrigerated dryer, then blaming the pump. A third is sizing the compressor to the average day and not the wet one. And finally, nobody owns the system, so nobody drains the receiver or checks the dryer's dew point until pumping stops.
What we sell, and what we don't
We sell the air side: compressors, dryers, filters, receivers and pipe. We don't sell the pumps themselves, and we don't design the well field. Bring us your pump's air spec, the longest run and your winter low, and we can match the compressor and a dryer that will survive it.
Frequently Asked Questions
How much compressed air does a leachate pump use?
It depends on the model. One common air-powered leachate pump lists 7 SCFM at up to 100 PSI. Check the spec sheet for yours, then multiply by the number of pumps that can run at once on your worst day.
Why do my landfill air lines freeze?
Water vapor in the air condenses when the pipe gets colder than the air's dew point, then freezes below 32°F. A refrigerated dryer delivers a dew point near 38°F, which isn't low enough for an outdoor line in winter. A desiccant dryer fixes it.
Do I need oil-free air for pneumatic pumps?
Often it's the pump manufacturer's call, not a code. Many are designed for clean dry air with no lubricator. A coalescing filter after the compressor keeps oil carryover out of the line either way.
Should I use a rotary screw or a piston compressor?
For a site that needs air around the clock, a rotary screw. A piston compressor can work at a small transfer station with a single shop bay and no pump field.
