The oil inlet being blocked by large particles is a common situation on site, especially where the oil comes from mixed sources, where there is sediment at the bottom of the drums, and where the oil has not been pre-filtered before it is fed in. Most of the problems people run into at this step are not technical but matters of order: dismantling under pressure, loosening the bolts before draining, putting the seals down anywhere. The result is continuous seepage after reassembly.
Eight steps, and a reason behind each one
- Stop the machine: first bring the oil feed back to zero, stop the heating, then stop the main pump and let the machine come down on its own instead of cutting the power directly. If the pipework is dismantled while the oil is still moving, the opening is pushed apart by the flow.
- Release the pressure: close all the inlet and outlet valves and open the vent points to release the pressure in the pipework and in the filter housing. Dismantling under pressure sprays oil, and the volume sprayed depends on the size of the residual pressure; the high-pressure side is the most dangerous.
- Disconnect the power: the power must be off and confirmed dead before the terminal box is opened. With the heating circuit live, residual capacitance at the terminals can discharge.
- Drain: drain the oil held in the filter housing and the inlet pipework into a container. Draining serves two purposes: no residual oil runs out during dismantling, and the oil that comes out is itself the sample used to judge the cause of the blockage.
- Dismantle: loosen the bolts diagonally, in several stages and evenly, and do not remove one bolt in a single go. Place the removed seals and gaskets in order on a clean surface, keeping them apart and none lost.
- Clean: remove the filter element and the strainer and check where and how many large particles have collected. If the particles are concentrated in the outer layer of the element, the pre-filtration was insufficient in the first place; if the whole element is blinded, the problem may lie in the source of the oil.
- Reassemble: wipe the sealing faces clean, fit the new seals in one go, and tighten the bolts diagonally in several stages with a consistent torque, so that uneven local compression does not leave the seal uneven.
- Pressure test in stages: first pass low-pressure air for a leak-tightness check, and once no leak is found raise the pressure step by step to the working pressure, then let the oil through and watch the differential pressure and the outlet condition. Do not go straight to full load.
What it costs to get the order wrong
Skipping the pressure release and dismantling anyway sprays oil; skipping the power disconnection and opening the wiring carries a risk of electric shock; skipping the draining and dismantling anyway lets the residual oil run onto the floor, contaminating the seals and the working area; putting the seals back at random, or refitting the old ones, means the machine leaks after reassembly; starting the machine without a pressure test means that, with the seals not seated, the machine leaks under pressure, and the leak position is usually harder to find than the place that was blocked before.
How to reduce this kind of blockage in daily operation
- Add coarse filtration at the front: use coarse filter elements 150-250-50 or 110-250-50 in the inlet section and hold the large particles back before they enter the machine.
- Add pre-filtration where necessary: where the oil is in poor condition, run a pre-filtration pass first with a JL series portable filtering and filling machine, filtration accuracy 10~25 μm, which one person can push; it belongs at the very front of the line.
- Check the drums before filling: before drawing the oil, look at the bottom of the drum for sediment and water; drums with sediment are dealt with separately and are not fed straight into the machine.
- Drain at regular intervals: include the drain points in the routine inspection; even a small amount each time reduces the deposits inside the filter housing.
- Add a filter basket or a strainer at the suction inlet on the pipework: one more line of protection at the far end costs very little and keeps the large particles outside the machine.
| Symptom | What it points to | How to confirm | Action |
|---|---|---|---|
| The oil feed drops sharply and there is an abnormal noise at the inlet | The inlet strainer is blinded by large particles | Dismantle and inspect after stopping and draining, and look at the particle distribution | Clean it down following the eight steps, replace the strainer and add coarse filtration at the front |
| A large amount is held up in the outer layer of the element while the inner layer is clean | Insufficient pre-filtration; the particles reach the fine filtration stage directly | Compare the dirt holding of the coarse stage with that of the fine stage | Fit a coarse stage and add pre-filtration at the front |
| The element is blinded right through and the oil looks cloudy | The source of the oil is dirty in itself | Take a sample, check the appearance and carry out a cleanliness test | Pre-treat the oil before it goes into the machine |
| It blocks again shortly after the cleaning | The cleaning was not thorough, or the root cause has not been addressed | Re-check the pre-filtration strainer and the draining arrangement | Check whether any residue is left and confirm that the pre-filtration has been completed |
Safety requirements for dismantling and cleaning
Wear protective gloves and goggles throughout, and let hot oil cool before touching it. Clean the removed oily parts with absorbent cotton, and lay anti-slip and absorbent material on the floor. The oil that is drained is handled as waste oil: collect it and hand it to a qualified organisation, and do not pour it into the sewer or spill it on the floor.
None of the eight steps for dismantling and cleaning can be skipped, and in particular the pressure release and the draining. The time these two steps take is far less than the time spent afterwards chasing a leak.