Tech Tip: Hydraulics & Pneumatics

Enhance your employees’ product and industry knowledge with PTDA’s Tech Tips. This library of online tips, hints and techniques may be used to educate new and current employees on power transmission/motion control (PT/MC) products, technologies and concepts and serve as reference and reminder for more experienced staff. Tech Tips are based on the expertise of PTDA member companies and content from PTDA’s Power Transmission Handbook^®, the definitive resource and training tool on PT/MC products.

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Why are pipe connectors not recommended?

When pipe thread is properly installed, they do so by connecting the crown and root of the thread form. This causes contamination that can enter the system. Further, because of this interaction, the thread form becomes distorted and should not be reused. Often, the Teflon tape is added to the thread but this is a lubricant and not a sealant. If Teflon comes off the thread, it can enter the system as a contaminate. 

Flow equals pressure in a hydraulic system, is that correct?

While you need flow to create pressure, flow in a hydraulic system determines the rate of speed the actuator (cylinders and motors) of a certain size will travel.

What is hydraulic pressure?

Pressure is resistance to flow.  You can also create pressure by trapping fluid under a load.  In a hydraulic system with a pump creating flow, the resistance is what causes the pressure.  This resistance can be from many sources, the actual load and the resistance created when pushing oil through lines, components and filters.

A Common Cause for Hydraulic Pump Failure

Trouble encountered often in a hydraulic system is cavitation of the hydraulic pump inlet caused by a dirt build-up on the suction strainer.  It produces symptoms such as a loss of high pressure, speed and increased pump noise.  The strainer is either located in the pump suction line, accessible from the top of the reservoir or it will be found immersed below the oil level in the reservoir.  Many operators of hydraulic equipment rarely give the equipment any attention or maintenance until it fails.  Eventually, the suction strainer will probably become restricted enough to cause a breakdown of the entire system and damage to the pump.  Some organizations are now recommending that the in tank immersed inlet strainer be removed to avoid cavitation from occurring.  If an inlet strainer is to be used, an accessible above tank style is recommended.

Filtration, a Key to Hydraulic Reliability

Hydraulic fluid contamination is generally considered to be the dirt, water, and air that will find its way into the hydraulic system.  Most hydraulic manufacturers also admit that hydraulic contamination causes approximately 80 percent of hydraulic system failures.  This makes high quality filtration a good investment that pays for itself very quickly.  When the customer's hydraulic pump fails, also check the filtration system because there is a high possibility your customer will need either new filters or a better filtration system.

Recirculation Loops—Filtration for Modern Systems

Many modern hydraulic systems use a pressure compensated piston pump as the main system pump. But often this pump is only being used to hold system pressure and is not flowing fluid through the system. This creates a dilemma for the hydraulic filter as it needs continuous flow to get the fluid clean. Therefore on many modern systems, a recirculation filter system should be used.  A recirculation system (or kidney loop) is a small pump, motor and filter system that continually circulates fluid from a hydraulic reservoir through a filter. This system is designed to run continuously so that the filter is always cleaning the hydraulic fluid. As more than 80 percent of all hydraulic failures are caused by contamination, this continuous filtration is critical to the health of the hydraulic system.

Relief Valve in a Hydraulic System

You always need a relief valve in a hydraulic system because a pressure compensator may not react swiftly enough to prevent a pressure spike that could damage the equipment or injure an operator.  Consult an experienced system engineer for more information.


The information provided in Tech Tips is not meant to be all-encompassing, but rather to draw attention to and provide information about the particular subjects covered. All suggestions and recommendations contained in Tech Tips are based upon information that is believed to be accurate to the best of the experience and knowledge of PTDA’s contributing members, but are made without guarantee or representation as to results. PTDA and Tech Tip contributors expressly disclaim any warranties or guaranties, express or implied, as to the accuracy or completeness of any information published in Tech Tips, and disclaims and makes no warranty that the information in Tech Tips will fulfill any of your particular purposes or needs. PTDA and Tech Tip contributors disclaim liability for any personal injury, property, or other damages of any nature whatsoever, whether special, indirect, consequential, or compensatory, directly or indirectly resulting from the publication, use of, application, or reliance on Tech Tips.