On Day 1, we chose a high quality hydraulic fluid based on some pretty harsh testing. On Day 2, we took our first stab at choosing the correct oil viscosity. Now it’s time to to check if this viscosity will allow the machine to start up on the coldest day. So let’s look at the generic graph of a VG32 oil below. I’ve added the blue line in the centre of the VG32 range.

Coldest Allowable Temperature for pump start-up1

At the far left, I’ve drawn a yellow vertical line, where the VG32 curve intersects 1,600 mm2/sec, which is the highest allowable viscosity for start-up. Following the yellow line down to the X-axis tells us that the coldest start-up temperature is about -15°C. However, this is only for the warm-up phase. You can’t run the machine at full speed, until the oil reaches about 0°C, as you can see from the green line. Therefore, if your machine automatically runs at full speed right away, then your coldest start-up temperature is 0°C.

Conclusion:

If your coldest start-up temperature is between 0° and -15°C, then a heater is recommended, especially if you cannot run the pump at lower speeds until the oil reaches 0°C.

However, anything below -15°C definitely requires a heater.

In an industrial application, it’s relatively easy to install an oil heater. For mobile machinery, it’s a little more complicated and sometimes very impractical. In that case, we need to look for a lower viscosity oil. We’ll look into that tomorrow.

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