The trial run before a machine is shipped usually takes place twice, once at no load and once under load. The two runs do not look for the same problems: the no-load run checks the assembly, the load run checks the performance. Treating the two as one thing produces the familiar result that the commissioning passes and the machine misbehaves a few days after it reaches site, because a small mechanical deviation is not visible at no load and is amplified as soon as the load is applied. The order of the two runs cannot be reversed either.
No-load commissioning: checks the mechanics, not the performance
On the no-load run no oil is flowing in the system, the pipework is dry and the pump runs at low load. The purpose of this run is to confirm that all the mechanical and electrical connections are right: if the motor rotation does not match the specified direction of the pump, a reversed rotation drives the pump straight back; coupling misalignment usually cannot be seen at this stage, but it shows up first as vibration; and leakage at the sealing faces, flanges and joints is almost invisible without pressure and only appears once the oil circuit is connected.
There is one step on the no-load run that is easily skipped, and that is listening to the noise. The mechanical noise of the pump, the periodic impact of the coupling and the abnormal friction of the fan all differ in pitch and rhythm. With no oil masking them at no load the sounds are clearest, and an experienced ear can pick the direction after a few seconds of listening. Once the machine runs under load, the same sounds are covered by the oil flow and the heating elements, and the same problem becomes hard to tell apart.
On the electrical side, every action has to be run through at no load: the switching of each circuit, the correspondence between the indicator lamps and the buttons, and whether the interlocks trigger as designed. Phase-loss and phase-sequence protection are best verified at this stage, because there is no oil being processed in the circuit and the consequences of a false trip are at their smallest. The action of the heating and temperature control circuits is also confirmed at no load, so that after assembly only the parts that can be verified with oil remain.
Load commissioning: checks the performance, and checks it in the steady state
Load commissioning means connecting the oil circuit, filling it with the oil that is actually to be processed and running the machine in the rated mode. This run looks at whether the performance figures hold in the steady state: whether the working vacuum settles inside the -0.08 ~ -0.0999 MPa range, whether the processing flow rate reaches the rated 6000 L/h, whether the temperature control holds the oil temperature inside the set range, and whether the heating capacity is enough to bring the oil up to the target temperature.
The key word here is steady. During the first few minutes the oil temperature has not come up, the vacuum has not been established and the elements are not yet wetted, so the readings move all the time and cannot serve as a criterion. What has to be recorded is the stretch after the machine has run for a while and the readings have stopped drifting. A vacuum level that will not hold under load usually points to the pumping speed of the pump set not matching the oil feed, or to a leak at a sealing point; a temperature control that will not hold under load usually points to the heating capacity being small for the flow rate.
Which early problems each of the two runs catches
Setting the commissioning items against the early faults seen on site shows why both runs have to be done: a wrong rotation direction, a coupling that is not aligned, a phase sequence error in the wiring, a loose fastener and foreign matter in the pipework are problems the no-load stage can find, and once they reach site they mean a shutdown for repair; a vacuum that will not build, insufficient flow, oil that will not come up to temperature and outlet oil with water content or gas content out of limits only show up with oil and under load, and belong to the load stage.
- What the no-load run covers: rotation direction, coupling alignment, sealing leaks, electrical operation and interlocks, abnormal noise.
- What the load run covers: the stable working vacuum range, the processing flow rate, temperature control and heating, and the indicators of the outlet oil.
- Most of the problems that occur often in the first weeks on site can be stopped in one of the two rounds, and the only cost is the commissioning time.
One further practical point: for the load run, if the conditions allow, use the oil the customer actually has to process rather than new oil. Different oil types differ in viscosity, water content and additive system: the viscosity affects the pumping speed, the water content affects the heating load and the additives affect how fast the elements take up dirt. Running one round with oil close to the real duty is what gives the later operating parameters any reference value.
The no-load run checks the assembly, the load run checks the performance; confirm there is no mechanical problem first, then take the performance readings, and the order of the two rounds cannot be reversed.