Testing Methods III: Shear in Hydraulic Fluids

MolaKule

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Why would one use ASTM D 5621 or equivalent for shear testing of Hydraulic Fluids? Guidelines for the Question of the Day: 1. No Piston Cup Lapel Pin will be awarded to the same person within 14 days of a previous award. 2. Please respond with a complete sentence. 3. Please do not post links. If a question arises as to the need for clarification, then sources and links may be requested. 4. Please, no off topic posts.
 
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One would use ASTM D5621 or equivalent for shear testing of Hydraulic Fluids because shear results in loss of viscosity, and a hydraulic fluid with reduced viscosity can't handle high operating temps as well, which means increase in wear and eventual equipment failure. Lower viscosity also diminishes volumetric efficiency of pumps, from what I've read.
 

MolaKule

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Let me throw some "intrigue" into the discussion. What has been stated is correct. Why would one use this method rather than use other ASTM or CEC test methods to determine shear?
 
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Of the three common tests, the bosch pump/injector, tapered roller bearing (the other question), and the sonic shearing test, the sonic shearing test has been found to more closely match the shearing behaviour of hydraulic lubricants in service. The lubricants are "rated" against their post shear values rather than their straight KV out of the drum. Pertinent, as mid 90s, somebody decided to replace all the ISO 32 hydraulic oils on one of my sites with HV32, high viscosity index "32s", as they would offer better low and high temperature performance...turned out the HV32 became HV24 within weeks of being placed in Voith turbocouplings.
 
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Originally Posted By: Shannow
Of the three common tests, the bosch pump/injector, tapered roller bearing (the other question), and the sonic shearing test, the sonic shearing test has been found to more closely match the shearing behaviour of hydraulic lubricants in service.
But then CEC L45-A-99 (tapered roller bearing) is thought to be even better correlated to actual field performance, based on some Mobil paper that we all must have found by now... <> I suppose the advantage of ASTM D5621 over CEC is that the test is quicker - 40 minutes as opposed to 20 hours.
 

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Very good comments. Another Hint: Consider some aspects of Fluid Dynamics such as cavitation, unsteady flow, shock waves, and the like.
 

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Quattro Pete and Indylan are hereby awarded the Piston Cup Lapel Pin with a Barnes dual-stage hydraulic pump. banana Shannow had the correct answer as well but was awarded his pin just a few days ago.
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Shannow: Of the three common tests, the bosch pump/injector, tapered roller bearing (the other question), and the sonic shearing test, the sonic shearing test has been found to more closely match the shearing behaviour of hydraulic lubricants in service.
All of the tests mentioned can determine shear of hydraulic fluids, but the sonic shear test ASTM D 5621 is most appropriate. While hydraulic fluids are subject to not only mechanical shear in pumps, valves, and to a less extent cylinders, cavitation in a hydraulic system produces acoustic fields which can sonically shear molecules. In the ASTM D 5621 test, the fluid is irradiated with a high frequency "sonic" oscillator for 40 min., after which the viscosity is measured. It has been found that this test better correlates with field experience than does the Diesel Fuel Injector Shear Stability Test, which lacked the severity necessary for testing hydraulic fluids.
 
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Originally Posted By: MolaKule
but the sonic shear test ASTM D 5621 is most appropriate.
Thanks. So Mobil is incorrect in claiming that CEC L45-A-99 even better correlates to actual field performance?
 

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Originally Posted By: Quattro Pete
Originally Posted By: MolaKule
but the sonic shear test ASTM D 5621 is most appropriate.
Thanks. So Mobil is incorrect in claiming that CEC L45-A-99 even better correlates to actual field performance?
That would be a good question for Mobil, i.e., what is their testing philosophy wrt hydraulic fluids.
 
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Now I know why Shannow doesn't chase VI. In a few threads I've read where he observed a ISO 1,000 shearing down to a 450 in a short time. 4 rpm heavily loaded application. If the sonic shear test results were available and not such a top secret prior to purchase, could that situation have been avoided?
 
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