Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1222953
ML www . machinerylubrication.com | March - April 2020 | 19 ML A hand pump can be used to test a directional valve for bypassing. A good way to test a directional valve for bypassing is to remove the lines from the manifold, cap off its "A" and "B" port lines and attach a hand pump with a gauge to the "P" port line. e "T" port can be run to a bucket so you can observe any oil that bypasses. In the case of the example, notice the tandem center position. Because of the tandem center, you can only test the valve when it is in its "A" and "B" positions. Manually shift the valve to its "A" position, holding it shifted while operating the hand pump. Bring the pressure up near the normal system pressure and see if it holds. Try the same with the valve shifted to the "B" position. Pressure should hold for at least one minute with no bypassing to the tank. If pressure drops immediately, the valve is bad and must be replaced. If the valve is good, test the cylinder. Remove any load from the cylinder. is may require disconnecting the rod from whatever it moves and may be time consuming, which is the primary reason testing the cylinder should be last. Fully extend the cylinder, then shut down the system and bleed any pressure, leaving the cylinder extended. Install a flow meter in the cylinder's rod-side line. Power up the system and apply pressure to the full piston side of the cylinder. ere should be no flow reading on the flow meter, and you should not be able to see fluid moving inside. 4. Make Good Decisions Use a logical progression of trouble- shooting. Often, I see the "shotgun" method of simply changing parts until the problem goes away. is is wasteful not only in part costs but also downtime as well. Never remove a component unless you have good reason to believe it is bad. Whenever something is removed from the system, the lines are open to airborne contaminants. Contaminants much too small to see can do serious damage. While you may be fixing a problem today, you very well may be adding more problems later. ML About the Author Jack Weeks is a hydraulic instructor and consultant for GPM Hydraulic Consulting. Since 1997 he has trained thousands of electricians and mechanics in hydraulic trou- bleshooting methods. Jack has also taught radio-wave propagation for the U.S. Air Force and telecommunica- tions equipment operation and repair for the Central Intelligence Agency at Amer- ican embassies overseas.