The flow rate of the ZYD-100 is 6000 L/h, the ZYD-200 is 12000 L/h and the ZYD-300 is 18000 L/h. These three figures are printed on the data sheet, and people comparing models habitually put them side by side and compare their size. But flow is not an inherent property of a machine; it is a result measured under a set of conditions, and those conditions are normally not printed on the sheet. Without knowing them, putting two numbers side by side easily leads to the wrong conclusion.
The four preconditions a data sheet does not print
- Condition of the oil: viscosity, water content and gas content all change the resistance and the degassing efficiency, so the same flow gives a different energy consumption and a different result on different oils.
- Oil temperature: the temperature control range is 45~80 °C, and when the oil is cold the viscosity is higher, the differential pressure across the element and the pipework is greater, and the actual throughput is smaller.
- Element configuration: the fine filtration stage of the ZYD-100 is built from five 150-500-5 fine filter elements in parallel, and the resistance curve changes with any other configuration.
- Pipework and end-point back pressure: the routing, diameter and length of the inlet line, whether the outlet runs into a tank or a drum, and what the outlet end requires all change the resistance of the system.
Which way the actual figure moves
On most sites the actual throughput is lower than the figure on the data sheet, and the reason is usually to be found in the four preconditions above. There are exceptions: when the oil is in good condition, the temperature is fully brought up, the elements are new and the pipe run is short, the actual figure approaches or even reaches the rated value. What matters is identifying which of the four caused the deviation, rather than saying in general terms that "the machine did not reach its rating".
| Condition on site | Effect on the actual flow | How to verify it |
|---|---|---|
| The oil temperature is below the lower end of the temperature control range | Viscosity rises, the differential pressure rises and the actual throughput falls | Record the oil temperature and the flow meter reading at the same time |
| The elements are close to the end of their replacement interval | The dirt holding capacity is higher, the differential pressure rises and the flow falls | Check the differential pressure records and the accumulated running hours |
| The inlet pipework is long and has bends | The system resistance rises and the actual flow falls | Check the length, the diameter and the number of bends in the line |
| The outlet discharges straight into a drum with a small nozzle diameter | The outlet back pressure rises and the flow falls | Check the outlet diameter and the way it is connected |
| The oil is in good condition and the temperature is at the set value | The actual figure approaches the rated value | Take samples continuously during steady running and check them |
Turning the rated figure into working hours
The question that usually has to be answered is not "how much does this machine flow" but "how long does this batch of oil take". Taking the ZYD-100 as an example, if the actual throughput on site is some proportion of the rated figure, the time needed for a batch of 600 L is 600 divided by the actual flow. The denominator has to be the actual site figure; using the rated figure gives a time that is too optimistic.
The second variable that is easily overlooked is the end point. Degassing is not finished when the rated flow has been passed through; the gas content has to reach ≤0.01% (GB/T 423) and the water content ≤3 ppm (GB/T 7600), and the time that takes depends on the incoming oil. The tighter the end point, the longer the actual working time, and that has nothing to do with the rated flow itself.
Allow a margin in the working time, because an actual throughput below the rated figure is the normal case; how much margin depends on the incoming condition of the oil and on the end point, so it is better not to apply one fixed percentage. If a flow meter is already fitted on site, reading the meter is closer to reality than looking up the data sheet.
A flow figure is the result of a set of conditions and not an inherent property of the machine, and a comparison made without those conditions misleads more easily than no comparison at all.
