Putting a few data sheets side by side to compare prices, what goes wrong most often is not a wrong judgement but a mismatch of criteria. Both sheets may state a flow of 6000 L/h, while one of them is the rated condition and the other is the best condition. Both sheets may state an accuracy of 1 μm, while one of them refers to the accuracy of the filter medium and the other to the result of a single machine. The numbers themselves are not wrong, but comparing them side by side leads to the wrong conclusion. This article sets out the six indicators whose criteria have to be aligned before any comparison is made.
The six items that have to be aligned
| Item | What to look at | Why the figure on its own is not enough |
|---|---|---|
| Flow rate | The operating conditions it refers to | The ZYD-100 is 6000 L/h, the ZYD-200 is 12000 L/h and the ZYD-300 is 18000 L/h, but a gap exists between the rated flow and the actual figure on site |
| Working vacuum and ultimate vacuum | Whether both figures are given | A working vacuum of -0.08 ~ -0.0999 MPa and an ultimate vacuum of ≤5 Pa do not measure the same thing |
| Filtration accuracy and cleanliness | Whether they are written separately or merged into one sentence | The filtration accuracy of ≤1 μm measures the capability of the medium, while cleanliness of NAS 1638 class 5 measures the state of the oil now |
| Basis of testing | Whether the standard numbers are complete | Water content, gas content and breakdown voltage correspond to GB/T 7600, GB/T 423 and GB/T 507 respectively |
| Total power | Whether it includes heating and vacuum | The ZYD-100 is 72 + 5 kW, and a different breakdown of the figures changes the electricity estimate directly |
| Dimensions and weight | Whether ancillary equipment is included | The 1200×1400×1800 mm and approx. 720 kg set the clearance needed to bring the machine into the room |
What to do when the criteria differ
Where a sheet does not state a condition clearly, the correct approach is not to interpret it in whichever direction is convenient but to list it as an item to be confirmed and to raise it during the technical clarification stage. The following questions have to be asked of practically every data sheet.
- At what oil temperature and in what condition of oil was the flow measured, and was the test run with new elements or with used ones.
- Is the ultimate vacuum the no-load figure or the figure with oil in the machine, and is it measured at the pump inlet or at the chamber.
- Which stage of filtration does the accuracy figure refer to, and does the cleanliness figure refer to the inlet or to the outlet.
- Is the power figure the input power or the total including the auxiliary systems, and are heating and vacuum listed separately.
- Do the dimensions include the inlet and outlet pipework and the maintenance space, and is the weight for the complete machine or for the parts.
- Are the protection functions documented, and do the overpressure alarm with shutdown and the phase loss and sequence protection appear in the configuration.
Turn the data sheet into a checklist
The most useful form for a comparison is not a table of numbers side by side but a checklist aligned item by item: each row carries the same item, each column carries one supplier, and each cell carries the conditions as well as the figures. The advantage of this is that a blank on any side is exposed at once instead of being covered by an attractive number during the comparison.
Just as important is to list the conditions that are not numbers at all: the accompanying documents, the supply lead time for spare parts, the way after-sales support is handled. These are not parameters, but they often decide whether the machine can actually be put to work once it has arrived. The same checklist should form the basis of the technical clarification, be gone through item by item to fill in the blanks rather than leave each side guessing at the quotation stage, and finally be kept as a version confirmed by both sides and filed with the contract.
The difficulty in comparing is not reading the figures but confirming that they were obtained under the same conditions.
