A bailer is a length of pipe with a check valve at the bottom that lets slurry in as it drops and holds it in as it is raised, and it removes the loosened cuttings from a drilled hole every 30-50 drops of the bit. Lower it to the bottom, work it up and down a few times so it fills, haul it out, empty it, and add water first if the hole is dry, because the bailer only lifts slurry, not dry dust.
Part of Deep Wells
A bailer is the scoop used in cable-tool and auger drilling to lift cuttings out of a borehole. It is lowered on the same rope as the bit and is emptied at the surface.
The Valve Lets Mud In And Keeps It There
A bailer is a pipe closed at the bottom by a one-way valve that opens inward. When the pipe drops into the slurry at the bottom of the hole, the valve is pushed open and slurry rises inside. When the pipe is lifted the weight of the slurry shuts the valve, and the load comes up. The check-valve designs in Hand Pumps work here: a flap of stout leather hinged over the opening, or a ball resting in a tapered seat. A ball valve is more robust against grit.
What You Need
- A pipe — steel or other strong pipe, narrower than the hole by enough to slide freely; 1-2 m long
- A valve — flap or ball, at the bottom, with a seat that grit cannot hold open
- A bail at the top — a loop or a shackle to take the rope
- Water — to add to the hole if it is dry
- A tub or pit for cuttings — kept away from the borehole mouth
Method: Wet, Drop, Work, Lift, Empty
Step 1: Pull the bit. After 30-50 drops, haul the bit out and set it aside where nobody can step on it.
Step 2: Check there is water. If the hole is dry, pour water in so that the cuttings form a slurry. The Deep Wells guide adds water to dry holes for this reason.
Step 3: Lower the bailer. Let it fall the last metre or so onto the cuttings so the valve opens. Do not let it slam into the bottom hard enough to bend it.
Step 4: Work it. Lift it a short way and drop it again several times. Each drop pushes more slurry through the valve. Stop when it has had several strokes and feels clearly heavier on the lift than when empty.
Step 5: Lift and empty. Haul it up steadily, tip it into the tub, and check the valve is clean and seats properly. Look at what came up.
Step 6: Resume drilling. When the bailer is coming up with little but clear water or a thin silt, the hole is clean and the next 30-50 drops can start.
Worked Example: What One Trip Lifts
A bailer made from 80 mm pipe 1.5 m long holds π ÷ 4 × 0.08² × 1.5 = 0.00754 m³, which is 7.5 L. Full of water it weighs about 7.5 kg, and with cuttings in it more than that, plus the pipe and the rope. At that size, a 150 mm hole advances π ÷ 4 × 0.15² = 0.0177 m² per metre, 17.7 L for every metre of depth, so a full bailer clears the cuttings from about 7.5 ÷ 17.7 = 0.42 m of new hole in the best case. At 0.42 m per load, a metre of new hole takes 1 ÷ 0.42 = 2.4 loads, so a bailer this size goes down more than twice for every metre drilled, and cuttings that swell when loosened need more trips still.
The Cuttings Are The Log Of The Ground
What the bailer brings up is your log of the ground. Lay out a sample from each trip in order, labelled with the depth. Clay comes up as sticky balls; sand and gravel come up as loose grains that settle fast in the tub; a trip that suddenly runs clear and full of coarse sand or gravel marks a water-bearing layer. Note the depth and keep a sample, because it decides where the screen goes (Screen Section).
Common Mistakes
- Dry bailing. No slurry, no load; the valve stays shut.
- A valve held open by grit. The load pours out on the way up; clean the seat every trip.
- A bailer too wide for the hole. It jams, and a stuck bailer is a stuck hole. Keep clearance all round.
- Leaving cuttings at the mouth. They wash back in and the pile is a trip hazard.
Safety
A full bailer is a heavy load on a rope over an open hole
Keep people clear of the line of the rope and do not lean over the borehole. Never put a hand into the hole or under a bailer being lowered or lifted; tools and the bailer itself should be on a line so they cannot be lost down the hole. Cover the hole when work stops. Nobody enters a drilled hole to clear a stuck bailer (Safety Protocol).
What’s Next
- Learn next: Well Casing — lining the hole once the cuttings are clear
- Combine with: Percussion Drilling — the drilling cycle the bailer serves