Machinery Lubrication

Machinery Lubrication May-June 2019

Machinery Lubrication magazine published by Noria Corporation

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ML the main line will be present in the pilot line. Returning to the spring, notice the diagonal arrow. In schematic symbols, a diagonal arrow means that its related component is variable or adjustable. In this case, the relief valve has an adjustable spring and has been adjusted so that a pressure of 500 pounds per square inch (psi) will develop enough force to compress the spring and open the relief valve. e resistance in this direction is therefore 500 psi. Tracing the fl ow to the right, you encounter a symbol for a manual valve. is could be a ball valve, gate valve, butterfl y valve, etc. e valve can be open or closed. e notation indi- cates that it is open, so there is no resistance in this direction. e line terminates into an open drum. When the pump is turned on, as shown in the schematic at the top of page 22, the path of least resistance in this case is to the drum, not through the relief valve. e pressure reading on the gauge is 0 psi. Clearly, the reason the gauge reads so low is because there is no resistance in the system. However, I have seen many pumps replaced for no other reason than because the pressure in the system was low. Over the years, I have received numerous phone calls that started out, "Well, I have changed the pump, but my pres- sure is still low. What else should I look for?" In fact, a pressure problem in a hydraulic system is rarely the pump. It is almost always another bad component in the system. e pump should never be the fi rst component to try but rather your last resort when a pres- sure problem exists. In the example shown, replacing the pump would deliver exactly the same result. In the schematic at the bottom of page 22, the manual valve has been closed, blocking fl ow to the drum. e only remaining fl ow path is through the relief valve. For fl uid to pass through the relief valve, a resistance of 500 psi must be overcome. Once pressure builds to 500 psi, fl ow is delivered through the relief valve and back to the tank. On many occasions, I have heard remarks such as, "My pump is putting out 1,500 psi." is illustrates the misconception that pres- sure originates at the pump. As you can see, what is being read on the gauge is not how much pressure the pump is putting out but rather the amount of resistance currently being overcome in the system. Without a fi rm understanding of this concept, becoming a troubleshooter is impossible. 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 telecommunications equipment operation and repair for the Central Intelligence Agency at American embassies overseas. RECOGNIZED FOR QUALITY. PREFERRED FOR SERVICE. Summit: Your responsive partner in compressor lubrication. When you partner with Summit, you can expect even more than the highest quality air, gas and refrigeration compressor lubricants. @V\NL[[OLJVUÄKLUJL[OH[VUS`JVTLZ^OLUWHY[ULYPUN^P[O an industry leader who's dedicated to your success. With unmatched access to lubrication experts, the latest technology and personalized customer service, you can count on the right solutions exactly when you need them. Klüber Lubrication NA LP Partner with us. www.klsummit.com 800-749-5823 www . machinerylubrication.com | May - June 2019 | 23

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