Guide
Troubleshooting a carbide-to-water acetylene plant: what the symptom is telling you
Acetylene plant faults show up in 1 of 5 ways: a generator alarm (water level, temperature or instrument air), no gas or low pressure, a hopper that will not vent, a falling yield per kg of carbide, or a compressor that trips or runs grey oil. Nearly all trace to water ratio, agitation or sludge.
- Generator trips
- Low water level
- Temperature ceiling
- 70 °C; set point starts at 58 °C
- Water-to-carbide ratio
- 6 to 8 litres per kg; a high-temperature alarm with the ratio well below that is the commonest cause
- Agitator
- 5 minutes in every 15; a shaft that is not turning at the drain-valve end is broken
- Pressure drop diagnostic
- A drop of about 0.21 kg/cm²g below normal between generator and compressor means sludge in the arrestor line
How to use this page
A carbide-to-water acetylene plant has a small number of ways of going wrong and a large number of ways of telling you. This is the fault register KIGL issues with its plants, condensed by symptom. It assumes the plant is being run to the maintenance checklist; a plant that is not being run to it will show several of these at once, and the checklist is the cure.
One rule overrides everything below: a leak is repaired with the plant stopped and purged, never running.
Generator alarms
| Alarm | Probable cause | What to do |
|---|---|---|
| Low water level | Water below the low-level check valve; slurry drain valve leaking; instrument-air leak to the drain valve | Confirm at the check valve; switch off the control circuit and add water through the bypass; check the drain valve for an obstruction under the seat and the air line from the I/P converter for leaks |
| High water level | Slurry drain valve not opening; level transmitter diaphragm fouled | Confirm at the upper check valve; drain down; remove and clean the transmitter diaphragm, replace if punctured; check the drain valve diaphragms and spring |
| High temperature | Water-to-carbide ratio too low; water supply pressure low; water-inlet valve not opening; spray nozzles dirty; alarm set below the water-controller set point | Raise water supply pressure; check the air-operated inlet valve; clean nozzles; set the alarm above the controller; lower the controller set point if the ratio per hopper is below the band |
| Low instrument air | Air compressor stopped, tank valve shut, filter clogged, line leaking | Everything but the agitator stops on air failure by design; restore air, then reset and restart |
| Bell rings, no lamp | Lamp burnt out | Replace it — and find out which alarm it was |
Temperature pattern on the tank
| What your palm finds | Cause | Remedy |
|---|---|---|
| Warmer above the water line than below | Water not added to compensate for the shutdown temperature drop, or slurry not agitated | Keep generator pressure low by venting while water is admitted through the bypass; confirm the agitator timer; with dusty carbide, lengthen the agitator run |
| Bottom not the same as just below the water line | Sludge settling, insufficient agitation | Check the shaft turns at the far end; check the timer; check carbide fines |
| Anything too hot to touch | Reaction running away | Stop the carbide feed, vent, admit water, find out why the high-temperature trip did not act before restarting |
No gas, or pressure that will not come back
| Symptom | Cause | Remedy |
|---|---|---|
| No generation at all | Hopper empty; carbide too large and bridging at the hopper neck; screw feed or hydraulic pump running in reverse; hydraulic pressure low; carbide valve disc not opening | Recharge; weed out oversize lumps; tap the hopper neck with a wooden mallet; correct rotation; reset hydraulic pressure; inspect the disc |
| Pressure drops below the low switch and stays there | Screw feed will not run (electrical); safety-valve vent lever left open; hydraulic valve not opening; hydraulic oil low or bypass open too wide | Check starters and overloads; close the lever; check hopper, tank and arrestor pressures in turn; top up oil and set the bypass so pressure falls as slowly as it rises |
| Positive pressure in the generator, nothing at the compressor | Outlet pipe, wet arrestors or outlet non-return valve full of sludge | Vent, open the plugs, flush with a water jet, clean the non-return valve covers; a 0.21 kg/cm²g drop at the arrestor gauge is the diagnostic |
| Pressure above the working maximum, safety valves venting | Water not added after a cold shutdown; start-up on cold water after generation | Hopper switches off, auxiliary off, check water flow and level, check the agitator, feel the tank; find out why the alarm did not act |
| Selected hopper will not run, pilot light drops | High-setting pressure switch set too low; overload tripped | Reset the switch; reset the hopper starter overload |
Hoppers and screw feed
| Symptom | Cause | Remedy |
|---|---|---|
| Hopper will not vent down for filling | Carbide lodged between feed valve and seat; equaliser valve open; damaged valve disc; build-up around the tube end | Run the empty hopper a minute or two, revent; shut the equaliser; inspect the disc; clean the tube end at the next tank clean |
| Acetylene smell at the fill cap | Carbide on the seating; dry gasket; dry lugs; worn gasket | Brush the seat; film of Vaseline or silicone on the gasket; grease the lugs; replace the gasket |
| Screw-feed motor overloads or shear pin breaks | Carbide chips between screw and housing; worn shaft and bushes; sprockets misaligned; hydraulic seat not operating | Clear the chips; renew worn parts; realign; set the oil pressure |
| Gas leaking at the screw-feed shaft | Oil seals in the feed bush worn | Replace |
| Reduction gear hot, noisy or leaking | Wrong or low lubricant; damaged bearing or seal; foreign matter | Fill to level with the specified grade; replace the bearing or seal; drain, clean and refill |
Hydraulic pump
No pressure: reverse rotation, faulty gauge, low oil, bypass wide open, relief valve passing, choked line, leaking cylinder seal or piston rings. Noise: air lock in the casing or suction, worn coupling bushes, excessive vane clearance. Reservoir level falling fast: a leak in the piping or the cylinder shaft seal.
Slurry drain and water control valves
| Symptom | Cause | Remedy |
|---|---|---|
| Drain valve does not open on rising level | Instrument-air leak; punctured diaphragm (air escaping at the outlet or at the spring adjuster); spring tension too high; faulty level controller | Arrest the leak; change the diaphragm; ease the spring; have the controller set right by an instrument engineer |
| Valve open but slurry not draining | Line clogged with lime | Drain through the bottom plug, remove the valve, clean the generator outlet and pipe |
| Slurry drains while the level is low | Foreign matter between the seats; faulty controller | Open fully to pass it, else drain and clear the valve; check the controller |
| Controller reads high while the level is low | Impulse line from generator to transmitter choked | Remove, clear, refit |
| No water feeding at high temperature | Air leak from the temperature controller to the water valve; punctured valve diaphragm | Arrest the leak; change the diaphragm |
| Water valve passes when it should be shut | Dirt on the seat, or a worn seat | Clean or lap |
Agitator and safety valves
Agitator gland leaking: tighten the nut moderately; a slight initial leak often seals itself with lime, otherwise renew the packing. Motor overheating: too much solid in the tank, gland too tight, or misalignment. Safety valve passing below set pressure: dirt on the seat or the setting disturbed. Safety valve failing to lift: impulse line clogged. Gas at the manual vent arm: diaphragm ruptured.
Downstream of the generator
| Symptom | Cause | Remedy |
|---|---|---|
| Gas leaving the cooler-condenser above room temperature | Insufficient cooling water; air trapped on the water side | Increase flow; vent the water section |
| Flow restricted with arrestor gauge normal and valves open | Distribution holes in the scrubber inlet clogged; lime build-up in the line or cooler outlet (typically after years of operation, sooner with dusty carbide); dirt in the check valve ahead of the scrubber | Isolate, drain the scrubber, remove and clean the inlet pipe; clean the line where the build-up is; clean the check valve |
| Purifier fails the silver nitrate test | Bed saturated, channelling, or flooded with undrained condensate | Out of service at once; regenerate; shorten the interval in the rotation; repack when regeneration no longer restores it |
| High-pressure drier drain open but nothing comes | Drain valve clogged | Stop the compressor, isolate, vent the drier, remove and clean the valve; flush the drier bottom with more water in future |
Compressor
| Symptom | Cause | Remedy |
|---|---|---|
| Will not start | No supply; starter defective; suction too low (low-pressure switch); overloaded | Check three phases; check the starter; raise generator pressure; check free rotation with interstage purge valves open |
| Trips while running | Single phasing; excessive load; low-pressure switch (not enough gas); high-pressure switch (cylinders full, or a blocked HP line) | Check supply; check for mechanical damage; check generator pressure; check whether filling is complete or the line is blocked |
| Interstage pressure low | Not enough gas at suction; choke in the suction line | Improve generator pressure; clear the line |
| A stage pressure too high | Valve on the next stage not working | Remove that head, clean or replace the valve |
| An interstage safety valve blows | Leaking valves on the next stage; clogging downstream | Clean or lap; clear |
| Final-stage safety valve blows | Manifold isolation valve shut; manifold non-return valves or pressure controller not operating; HP driers clogged | Open; readjust; clean — and check the high-pressure switch acted, with no valve between the switch connection and the compressor |
| Oil pressure low | Oil-pump belt broken (it drives by cogs, not tension — do not stretch it over the flange); oil low; suction near zero; pump suction clogged | Replace the belt correctly; top up; restore suction; clean |
| Oil grey | Water: traps not drained, overdue change, detergent oil, leaking trap drain valve | Drain all and refill with SAE 30 non-detergent; find the leaking valve with the compressor stopped and vented |
| Oil level rising with no oil added | Water not drained from the crankcase after a long shutdown; leak in the oil-pump suction tube inside the water tank; crankcase leak | Drain the grey mixture and refill; pressurise and bubble-test the tube; repair |
| Stops before full charging pressure | Momentary power failure; starter not holding; high-pressure switch set low; suction fell to the low switch | Restart; reset overloads; recalibrate the switch against the manifold gauges; trace the flow restriction back through drier, purifier, arrestors and generator gauges |
| Not pumping to capacity; slow filling | First-stage valves leaking; worn piston rings | Clean, then lap the valves; replace rings |
| Belts wearing fast | Misalignment | Realign |
Instrument air
Air pressure not holding: holding relay dropped out, pressure switch out of adjustment, receiver drain left open, intake filter clogged, a line leak, head valves leaking, belt loose. Leaks with the compressor stopped: the check valve or the centrifugal unloader. Instrument-air pressure low with the screw feed still running: the air-pressure control switch is disturbed or defective, or its impulse line is choked — this is a safety function and is corrected before the plant runs again.
When the symptom is not on this page
Log it. The hourly shift log — carbide per hopper, water meter, level, temperature, pressure, every compressor stage, purifier state, yield per kg — is what turns a vague fault into a timed one. KIGL audits customers' plants against this register and the checklist, and supports plants of any make on site.
Troubleshooting — frequently asked questions
The high-temperature alarm keeps tripping. What do I check first?
The water-to-carbide ratio. If less water than the band is reaching the generator per kg of carbide, the reaction runs hot. Check water supply pressure, that the water-inlet control valve is opening on rising temperature, that the spray nozzles are clean, and that the alarm set point sits above the water-controller set point — otherwise the alarm fires before the controller has acted.
Why is the generator warmer above the water line than below it?
Because the slurry is not being stirred, or because water was not added to compensate for the temperature drop over a shutdown. Confirm the agitator shaft is turning at the far end and that the timer gives it its 5 minutes in 15; then check the carbide for excessive fines, which need longer agitation.
The hopper will not vent down for refilling. Why?
Carbide is lodged between the feed valve and its seat, holding it open to the generator. Run the empty hopper for a minute or two to clear it, then vent again. If it still will not fall, the hopper equaliser valve may be open, or the rubber disc on the carbide valve is damaged.
There is positive pressure in the generator but no gas reaching the compressor.
Sludge. The outlet pipe to the wet flashback arrestors, the arrestors themselves or the non-return valve on the outlet has filled with lime. A pressure reading about 0.21 kg/cm²g below normal at the arrestor gauge is the tell-tale. Stop, vent, open the pipe plugs and flush with a water jet; clean the non-return valve covers.
My yield per kg of carbide is falling. Where is the gas going?
Usually one of four places: wet or dusty carbide, a flooded purifier, a leak, or a generator running outside its water ratio. Yield is computed every shift for this reason; it moves weeks before any alarm does. Check the water meter total against carbide weight for the week first.
The compressor oil has turned grey.
Water in the oil. Either the condensate traps were not drained on schedule, the oil is overdue for a change, a detergent oil was used by mistake, or a trap drain valve is leaking. Drain the whole charge and refill with non-detergent SAE 30; if the level keeps rising without oil being added, look for a leak in the oil-pump suction tube inside the water tank.
The purifier is failing the silver nitrate test.
Take it out of service at once and switch to the standby purifier. A bed that fails before its regeneration interval is either saturated, channelling, or flooded with condensate that was not drained from the bottom every shift. Regenerate, and shorten the interval in the rotation; repack when regeneration no longer restores it.
Can I fix a leak while the plant is running?
No. Stop the plant, purge the section with nitrogen or a water flush, never carbon dioxide, repair with spark-resistant tools, purge the air out again before restart. A leak is found by smell and confirmed with soap solution — never with a flame.
References
- Bureau of Indian Standards. (2003). Acetylene Generators — Requirements (IS 8471:2003, First Revision).
- Bureau of Indian Standards. (2024). Dissolved Acetylene (Gas) — Specification (IS 308:2024, Fourth Revision).
Enquiries
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State the gas or equipment, the quantity or capacity, and your location. KIGL will confirm the grade, the cylinder or plant size, and whether the location can be served from Noonmati, or through the agent network.