Maintenance Technology April 2015 - (Page 21)

HYDRAULIC-SYSTEM TIPS Every hydraulic system in a plant should regularly undergo 15-20 reliability tests-while the equipment is running. High-temperature switch While mineral-based oil will start breaking down at 140 F, many systems will not shut down the unit until the oil temperature reaches 160 F. Hydraulic systems are designed to operate below 140 F. For every 15-degree increase in oil temperature above 140 F, the oil's life will be cut in half. An oil temperature above 140 F indicates a problem in the system. This could be caused by a cooler malfunction or excessive bypassing at the pump, valves, cylinders and hydraulic motors. Set the high-temperature switch (#10 in diagram) at 140 F to shut off the pump and prevent oil breakdown. Heat exchanger flushing and cleaning In hydraulic systems, oil flows over the tubes in a shell-andtube-type heat exchanger (#12 in diagram). Water flow is ported through the tubes in the opposite direction. The heat in the oil is transferred from the oil to the water. To achieve the most efficient heat transfer, water flow should be 25% of that of the oil flow. (The flow rate can be controlled with manual valves, a water-modulating valve or an electrical-solenoid.) Circulating hot wash oil or light distillate through the tube side or shell side will usually effectively remove sludge or similar soft deposits. Soft salt deposits can be washed out by circulating fresh, hot water. A mild alkaline solution, such as Oakite, or a 1.5% solution of sodium hydroxide or nitric acid can also be used. The tubes should be flushed in the opposite direction of the normal oil flow. If an air cooler is used, verify that the cooler fan is turned on at approximately 120 F and turned off at about 105 F. Keep the fins so clean that daylight can be seen through them. If necessary, use combs to straighten the fins on the unit. Take special care when cleaning the fins with an air hose so as to not damage the fins. There should be less than 10% difference in flow rates between the two tests. If a pump is badly worn, the flow will be considerably less at the higher pressure. Accumulator testing An accumulator that's used for volume should be pre-charged with dry nitrogen to from one-half to two-thirds of the pumpcompensator setting. When the hydraulic system is turned off, a charging rig with a gauge can be used to check the pre-charge level. To verify that the accumulator is operating properly, the side of the shell can be checked with a temperature gun or infrared camera. The bottom half or two-thirds should be hotter than the top half. If heat is only felt at the bottom, the accumulator may be overcharged. If no heat is felt, the bladder may be ruptured, the piston seals may be bad, the pre-charge may be above the compensator setting or all of the nitrogen has leaked out. If heat is felt all the way to the top, the accumulator is undercharged. Curious about Cotters? Ask our engineer. asktheengineer@diamondchain.com Pump testing On variable-volume pumps, check the flow out of the case drain line by porting the line into a container and timing it. This test should be made with the outlet pressure at maximum. It is not recommended that the line be held during this test. Secure the line to the container prior to starting the pump. The normal case flow is 1-5% of the maximum pump volume. Vane pumps usually bypass more than piston-type pumps. If 10% of the maximum volume flows out of the case drain line, the pump should be changed. An excellent method of monitoring the case-drain flow while operating is to permanently install a flow meter in the case-drain line. Test fixed-displacement pumps by checking the amount of flow through the relief valve. Turn the pump on and record the flow out of the relief-valve tank line for one minute. Then reduce the setting of the relief valve to its minimum setting. APRIL 2015 ©2015 The Diamond Chain Company. DCMT-415 www.diamondchain.com | 1-800-872-4246 Diamond, the Diamond Chain logo, and "Nothing Outlasts a Diamond" are trademarks of Diamond Chain Company, Inc. nothing outlasts a diamond MAINTENANCETECHNOLOGY.COM | 21 http://www.diamondchain.com http://www.diamondchain.com http://www.MAINTENANCETECHNOLOGY.COM

Maintenance Technology April 2015

Table of Contents for the Digital Edition of Maintenance Technology April 2015

Maintenance Technology April 2015 - Cover1
Maintenance Technology April 2015 - Cover2
Maintenance Technology April 2015 - 1
Maintenance Technology April 2015 - 2
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Maintenance Technology April 2015 - Cover3
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