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Technical Paper Series I00-9.7

Evaluation of Hydraulic Fluid Lubrication by Vickers Vane Pump Testing: Effect of Testing Conditions Dr. George E. Totten, Union Carbide Corporation Roland J. Bishop, Jr., Union Carbide Corporation G. Michael Gent, Conestoga Inc.

Presented at the International Exposition for Power Transmission and Technical Conference 4-6 April 2000

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I00-9.7 E V A L U A T I O N OF H Y D R A U L I C F L U I D L U B R I C A T I O N BY V I C K E R S V A N E P U M P TESTING: E F F E C T OF T E S T I N G C O N D I T I O N S

George E. Totten and Roland J. Bishop, Jr. Union Carbide Corporation, Tarrytown, NY G. Michael Gent, Conestoga Inc. Pottstown, PA

ABSTRACT

One of the most commonly used tests to evaluate the antiwear properties of a hydraulic fluid is ASTM D 2882 which is based on a Vicker's V-104 vane pump. Although this is a commonly used test, the results are subject to numerous potential problems in both testing procedure and pump hardware. In this paper, the particular focus will be placed on potential problems that may be encountered with testing of water-glycol hydraulic fluids which may lead to erroneous and nonreproducible results.

or susceptibility of the wear data obtained to fluid contamination. [8,9]. Recently, as part of an ongoing project within ASTM D.02 N.07, G.M. Gent has conducted a survey to determine the most common causes of unexpected vane pump failure. [10] Some of the test variations found as a result of this study were: [11] 1. Part Preparation - Due to relatively poor precision in the manufacture of the parts, extensive inspection and hand preparation is often necessary. 2. Rotor Failure - Rotor failure was often unavoidable

even after extensive inspection and preparation.

INTRODUCTION

The Vicker's V-104 vane pump has been used, following a variety of test methods, to evaluate hydraulic fluids for over 40 years. [1] More recently, an ASTM testing procedure, D 2882 [2] was developed to evaluate the antiwear properties of both non-aqueous and aqueous hydraulic fluids. A schematic of the V-104 vane pump is provided in Figure 1. /,4~I¢~¢lSLICD P'OIt LJrJrT ~ JmO'CA~1Obl

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3. Bushing Failure - The occurrence of bushing failure

could be minimized with careful part preparation. 4. W e a r Results - Not surprisingly, material variation

and vane geometry significantly affected pump wear. 5. Torquing - There was a wide variety of torquing methods used by different laboratories. 6. P u m p Maintenance - There was a wide variety of pump maintenance procedures used by different laboratories.

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7. Flushing Procedures - Not one of the laboratories

surveyed used the same flushing procedure. 8. Test Conditions - Some laboratories have slightly reduced the required pressure to reduce rotor failure. Figure 1 - Illustration of the components of a Vicker's V104 vane pump.

Although various attempts have been made to develop bench testing procedures for evaluating the lubricating properties of hydraulic fluids, most have provided poor correlation with hydraulic pump performance, such as that obtained by ASTM D 2882. [3,4]. One of the long-standing problems with the ASTM D 2882 test and its European counterparts, also based on the V-104vane pump, DIN 51389 and BS 5096 [1], is problems with premature breakage of the rotor [5,6,7]

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9. Filtration - Although ASTM D 2882 requires 25 IJ. filtration, almost all of the laboratories used 10 p. filtration. The difference in wear rates obtained by 10 and 25 p. filtration is illustrated in Table 1.[15] In this report, the effect of a number of specific variables [10,11] on the wear rate of water-glycol hydraulicfluids will be discussed. These test variables will include: ring rejection, vane inspection, system pressure calibration, water and reserve alkalinity fluid maintenance [12,13], dismantling and cleaning procedures, filtration and filter materials, and temperature fluctuation control.

Table 1 - Vickers V-104 Vane Pump Wear Rate Variation with Filter Size by ASTM D 2882 Pump Pressure Filter Size Wear Rate (psig) # (mg/hr) 1000 10 0.1 1000 25 0.1 1250 1250

10 25

0.1 0.1

1500 1500

10 25

0.1 1.0

1750 1750

10 25

10.0

B~~ R°t~iOn A

DISCUSSION 1.

Ring Inspection

Hydraulic pumps are designed for industrial operation. They are not designed for use as precision tribological testing instruments. One area where this is particularly evident is when the cartridge rings (see Figure 1) are inspected prior to use. Machining marks and scoring on the inner surface renders the rings unacceptable for use in the ASTM D 2882 test. It is not unusual to reject as many as 50-60% of the rings as received from the distributor.

2. Vane Inspection The only wear that is actually quantified in the D 2882 test is the sliding wear that occurs on the vanes and the ring. The wear reported is the total weight loss of the vane and the ring after 100 hours. Therefore, to optimize the precision of the test, it is essential that the vanes used at the beginning of the test conform properly to the design lines of contact as shown in Figure 2. Since it is possible to obtain vanes with uneven chamfers and surface roughness, as shown in Figure 3, it is important that the condition of the vanes be scrutinized very closely before use and replaced, if necessary.

B Figure 2 - A. Three lines of vane contact with the rotor and the ring and B. Illustration of desired vane chamfers [11]. 3. System Pressure Calibration Good laboratory testing practices must be employed with hydraulic pump testing as with any other testing procedure. For example, since the wear obtained is dependent on the pressure, it is important to perform the test with the proper pressure. Since the pressure gauge can drift, it is critically necessary that it be calibrated prior to and checked after the test. Ideally, the system pressure will be monitored throughout the test.

4. Maintenance of Water and Reserve Alkalinity Water-glycol hydraulic fluids contain water for fire resistance and a somewhat volatile additive for solution and vapor phase corrosion protection. [12,13] Since both the water and the corrosion inhibitor can affect performance, both are volatile, and the test is performed at 65 C where some water evaporation can occur, it is recommended that both water content and reserve

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alkalinity (corrosion inhibitor) be periodically monitored. If a significant water loss is observed, it should be replenished as recommended by the fluid supplier. The use of a Teflon, or fluid-compatible plastic film over the fluid reservoir as shown in Figure 4 provides an excellent barrier to reduce water losses during the test. Fluid sampling can even be performed through the film using a hypodermic syringe.

Figure 4 - Illustration of the use of a Teflon film barrier over the fluid reservoir. 5. Dismantling and Cleaning

Pump surfaces are susceptible to contamination especially when they are subjected to different fluid types, running conditions and deposits such as sludge and varnish. The flushing procedure cited by ASTM D 2882 is often inadequate. In this case, the only good way to assure appropriate cleanliness and minimum contamination is to completely dismantle the system including the pump, hoses, relief valve, reservoirand heat exchanger. For water-glycol hydraulic fluids, each part must be thoroughly washed with water before solvent washing. One of the system components that is particularly susceptible to contamination is the heat exchanger. As shown in Figure 5, the inner tubes of the heat exchanger should be thoroughly washed with water using a longhandle brush. After the parts are all thoroughly cleaned with water, they are rinsed with acetone and dried with compressed air as shown in Figure 6. The outer water cooling jacket of the heat exchanger is capped off to prevent any residual water from contaminating the solvent bath. The parts are then placed in an openmesh basket together and immersed into a Magnus AJA LiP solvent bath containing 50% isopropanol and 50% naphthalite as shown in Figure 7. [14] The bath is automatically agitated up and down at 1.64 cycles/s with a 1.5 inch stroke for a total of one hour. The parts are removed, drained and dried with compressed air before reconstructing the pump. This washing procedure is used after every pump test. Note: it is critically important not to wash pumps run in other fluids, e.g.

A

B Figure 3 - Variation of "as-received" vane chamfer: A. top view and B. side view.

283

polyol esters, and mineral oils in the same bath used for pumps run in water glycol. Also, water-glycol hydraulic fluid control should be periodically to assure the system is operating correctly.

Figure 7 - Parts prior to solvent cleaning in 50% isopropanol/50% naphthalite. 6. Filter Material Figure 5 - Illustration of proper heat exchanger water cleaning procedure.

One potential problem encountered with ASTM D 2882 testing of water-glycol hydraulic fluids is the failure to change from cellulosic filters, often used for nonaqueous fluids, to a water-glycol fluid compatible filter material such as fiberglass. Cellulosicfilters are not compatible with water-glycol hydraulic fluids and typically break through after relatively short running times. Of course, the filter is not effective when this occurs.

The breakthrough process is shown in Figure 8A where pressure spikes and a loss in pressure was observed after 60 hours. However, when the fiberglass filter was used, as shown in Figure 8B, the system did not show the pressure spikes or undesirable break through during the test.

7. Heat Exchanger Installation

Figure 6 - Water cleaned and air dried pump parts prior to solvent cleaning.

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One problem that may be encountered is relatively poor system temperature control. This is caused by high flow rates of cold water through the heat exchanger resulting in temperature swings of _+ 5 °C or more. This problem is readily resolved by reducing the water flow. In this way, temperaturecontrol to _+1 °C is possible.

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10

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80

90

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Figure 9 - Visual and tactic assessment of bearing wea r. 10 5 0

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B Figure 8 - A. Pressure versus time trace for a cellulosic filter used with a water-glycol hydraulic fluid. B Pressure versus time trace for the fiberglass filter at twice the flow rate. 8. Final Part Inspection

ASTM D 2882 only requires the quantitative measurement of total wear of the vanes and ring. Although inspection for other sources of wear are to be reported, there is no requirement for photographic documentation or gravimentric weight loss of other parts. However, there are other sources of potential wear which include bearing wear and cavitation erosion wear, especially of the endplates. Bearing wear may be an extremely important indicator of wear. In some systems, it is possible to have significant bearing wear precede vane and ring wear. However, before the conclusion of the 100 hour test, the system may fail catastrophically and the root cause may not ever be known since only vane and ring wear is observed. Since the shaft and bearings are reused in the test, it is critically necessary to at least visually and tactically assess bearing wear as shown in Figure 9. Another source of vane pump wear that may be encountered is end plate cavitation. As a minimum, visual inspection for end plate cavitation must be made as shown in Figure 10.

285

Figure 10 - Illustration of end-plate cavitation on a Vickers 20VQ5 vane pump. CONCLUSIONS

In order to minimize experimental variations when testing water-glycol hydraulic fluids and presumably any hydraulicfluid, the following precautions must be taken: 1. The ring and vanes must be inspected for machining irregularitiesand precision. 2. The system pressure gauge must be calibrated before and checked after every run.

3. Fluid composition, water, and reserve alkalinity should be maintained. To minimize evaporative losses, either a Teflon film or water-glycol compatible plastic should be used. 4. To minimize the potential for system contamination, which may have disastrous consequences, the hydraulic system must be dismantled, scrubbed, and water washed followed by a solventwashing after every run. 5. Water-glycol compatible fiberglass filters should be utilized. Cellulosic filters should be avoided. 6. System temperature variation may be controlled by adjusting water flow through the heat exchanger. 7. It is insufficientto only weigh ring and vane loss. The complete system, including end plates and bearings must be inspected and wear recorded, preferably photographically. If these precautions are taken, the quality of the ASTM D 2882 wear rate data and reproducibility will be sign ificantly improved.

6. Gellrich, P., Kunz, A., Beckmann, G. and Broszeit, E., "Theoretical and Practical Aspects of the Wear of Vane Pumps - Part A. Adaptation of a Model for Predictive Wear Calculation", Wear, Vol. 181-183, 1995, pp. 862-867. 7. Kunz, A., Gellrich, R., Backmann, G. and Broszeit, E., "Theoretical and Practical Aspects of the Wear of Vane Pumps - Part B. Analysis of Wear Behaviour in the Vickers Vane Pump Test", Wear, Vol. 181-183, 1995, pp. 868-875. 8. Tessman, R.K. and Heer, D.J., "Pump Tests for Fluid Qualification", in Tribology of Hydraulic Pump Testinq, ASTM STP-328", Ed. by G.E. Totten, G.H. Kling and D.J. Smolenski, American Society for Testing and Materials, Philadelphia, 1995. 9. Thoenes, H.W., "An Analysis of the Problems Associated with the Use of Hydraulic Media", 4. Aachener Fluidtechnisches Kolloquium, Fochgebeit Hydrauilk, Band 2, 18-20 March, 1980, pp. 231-250. 10. "ASTM Conference: D2882-90 Collaborative Investigation", Report available from Conestoga USA, Inc., Box 3052, Pottstown, PA, 19464.

REFERENCES

1. Totten, G.E. and Bishop, R.J., Jr., "Hydraulic Pump Testing Procedures to Evaluate Lubrication Performance of Hydraulic Fluids", SAE Technical Paper Series, Paper Number 952092, September, 1995. 2. "Standard Test Method for Indicating the Wear Characteristics of Petroleum and Non-Petroleum Hydraulic Fluids in a Constant Volume Vane Pump", ASTM D 2882-90. 3. Totten, G.E., Bishop, R.J. and Kling, G.H., "Evaluation of Hydraulic F l u i d Performance: Correlation of Water-Glycol Fluid Performance by ASTM D 2882 Vane Pump and Various Bench Tests", SAE Technical Paper Series, Paper Number 952156, September, 1995. 4. Bishop, R.J., and Totten, G.E., "Tribological Testing with Hydraulic Pumps: A Review and Critique", in Tribology of Hydraulic Pump Testing, ASTM STP-328", Ed by G.E. Totten, G.H. Kling and DJ. Smolenski, American Society for Testing and Materials, Philadelphia, 1995. 5. Broszeit, E., Steindorf, H. and Kunz, A., "Testing of Hydraulic Fluids with Vane Cell Pumps", Tribologie & Schmierungstechnik, Vol. 37, No.4, 1990, pp. 202-209.

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11. Gent, G M , "Review of ASTM D 2882 and Current Possibilities", in Tribolo,qy of Hydraulic Pump Testinq, ASTM STP-328", Ed. by G.E. Totten, G.H. Kling and D.J. Smolenski, American Society for Testing and Materials, Philadelphia, 1995. 12. Totten, G.E. and Bishop, R.J., "Historical Overview of the Development of Water-Glycol Hydraulic Fluids", SAE Technical Paper Series, Paper Number, 952076, September, 1995. 13. Wachter, D.A., Bishop, R.J., McDaniels, R.L. and Totten, G . E . , "Water-Glycol Hydraulic Fluid Performance Monitoring: Fluid Performance and Analysis Strategy", SAE Technical Paper Series, Paper Number 952155, September, 1995. 14. This particular model is available from Magnus Division, Economics Laboratory, Inc., South Plainfield, NJ. 15. Unpublished work by Lewis, W.E.F., Union Carbide Corporation, Tarrytown, NY.