Principle of viscotherm is that in a laminar flow the drop of pressure fluid is directly proportional to the drop in pressure. A sample of fuel is pumped through a capillary tube at a constant rate . Tapping points are provided so that the pressure difference can be measured using a differential pressure gauge.the gauge is calibrated directly in terms of the viscosity. a differential pressure transmitter is provides a signal and controls the fuel heating.
Since very small needle lift is obtained in the test equipment result in an unequal pressure distribution in the cut off shaft resulting in a hard contact in a small area along with high frequency oscillations, low lubricity of test oil will increase the chance of seizure. Full lift and high lubricity of heavy oil eliminates this risk of seizure during normal operation.( Always open and clean slide type valves before testing as cold sticky heavy oil along with small clearances can cause restriction in the movement of the spindle).
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