Troubleshooting hydraulic components: Maintaining fluid power systems
Troubleshooting industrial hydraulic components %%MDASSML%% such as pumps, cylinders, valves, actuators, and hydraulic motors %%MDASSML%% requires a sound understanding of the operation and functional relationship of the components in the system.
This article addresses the principles of diagnostics and testing, as well as common issues associated with hydraulic maintenance, such as the causes of noise and reasons for leakage.
Troubleshooting occurs at either start-up or breakdown. Taking a systematic approach to diagnostics and testing helps identify problems and provides the information needed to quickly repair or replace hydraulic components.
Some basics to remember
Take nothing for granted: When a problem occurs, make sure a safe condition exists and find out whether this or a similar event has happened before. Resist the temptation to “dive in” with repairs before asking the right questions. Review a system schematic, determine whether the machine is an open- or closed-loop system, and think through different problem scenarios.
Know the system : While reviewing the schematic, identify the recommended system pressure, pump types, valves, accumulators, and actuators, and the machine’s sequence of operation. Review any available service bulletins.
Visually inspect and operate the machine : Get familiar with the machine’s mechanisms and general layout. Ask the machine operator pertinent questions. Then, only after you have determined that a safe operating condition exists, operate the machine to identify system pressure, whether manual controls are hard or sloppy, and to see if there are any unusual odors or visible external leaks.
Check all services to the machine : Identify electricity to the machine, high-pressure steam pipes, gas lines or other power devices, and determine whether accumulators should or have been discharged.
Isolate legs of the circuit and avoid open lines : Always think about safety first. Understand that a problem in one leg of the circuit may be caused by a problem in another leg of the circuit, such as slow actuator speed.
Identify the problem : There may be hidden causes. Make a list of all possible causes Consider what you found while operating the machine and focus on the most likely cause. Remember that one failure may be the result of another failure.
Match the problem to the cause : Compare your list of possible problems with the principles of component and system operation. For example, pressure equals force and flow equals speed.
Reach a conclusion and test it : Review your list of causes and decide which are the most likely and which are the quickest and easiest to test. Test components before replacing them; analyze the information gathered and eliminate possible causes.
Report your findings : Make notes of your findings on the schematic, talk with plant decision makers, and create a machine file so that your findings are well documented. This will help to establish failure patterns.
Repair and/or replace components : This is a stop-gap measures. The continued repair and/or replacement of a component is solving a symptom of a problem rather than solving the real problem. What is causing the component to continually fail? Answer that question and you have truly solved the machine problem.
While doing troubleshooting and repair work, think in terms of preventive maintenance, which is essential to extending uptime, increasing production, and enhancing quality.
Common maintenance issues
Common issues associated with hydraulic maintenance include the causes of noise and reasons for leakage. Noise comes from pumps, fluid velocity, aeration, cavitation, and valves, to name a few. Leakage is often the result of poor system design, substandard component quality, improper installation, system abuse, or a combination of two or more of these reasons.
Hydraulic System Noise and its Sources
Noise in hydraulic systems comes from a variety of sources, including, but not limited to:
Noise generating sources such as internally generated sounds and vibrations that transmit sound waves through pump casings, valves, filters, motors, and other components; and
Noise transmission sources such as structure-borne vibrations and sound waves amplified by reservoirs, pumps, valves, and machinery frames, to name a few.
The sources of noise in a system are typically classified as generated, transmitted, or amplified (See Figure 1 %%MDASSML%% Sources of Noise).
Pump noise often results from pressure changes within the system. Other causes of pump noise in hydraulic systems include pump housing expansion and contraction noises, as well as pressure ripple noises and vibrations.
Electrical motors generate turbulent air stream noises within the motor as the armature rotates and additional loud windage sounds and “siren” noises result from the transmission and amplification of air-borne and structure-borne vibrations and noises through the motor’s cooling fan and shroud.
Other reasons for noise generation throughout the hydraulic system include:
Changes in fluid velocity caused by flow restriction or sharp turns in the pipe, resulting in turbulence;
Aeration, resulting in air bubbles that explode when exposed to higher pressure;
Cavitation bubbles that collapse when exposed to higher pressure; and
Contamination from foreign objects, sludge and dirt that may cause vibration, friction, chattering and overheating.( See Figure 2 %%MDASSML%% Insert Permissible Noise Exposure)
Hydraulic system leaks and their sources
The four primary reasons for leakage in hydraulic systems include poor system design, substandard component quality, improper installation, and abuse.
Design %%MDASSML%% Excessive strain on hydraulic lines, because of a design that fails to allow for expansion and contraction, as well as improper clamping and spacing, may lead to leaks. It is critical to allow for movement under load. For example, cylinders with non%%MDASSML%%centerline mountings tend to sway under large loads. Rigid tubing connected to the cylinder end caps will be subject to forces and movement, and may leak. Overhung cylinders require additional support to prevent cylinder movement on the unsupported end. It should be noted that cylinder length changes with pressure and temperature.
Quality %%MDASSML%% Unless quality fittings, tubing and mating ports are used during installation, the hydraulic system may be exposed to potential leaks because of faulty material. Off center ports or ports too close to a component’s edge will cause future problems as well. Using quality fittings and ensuring proper installation are the best ways to reduce future maintenance activities.
Installation %%MDASSML%% Improper tube preparation and assembly may lead to hydraulic system leaks. Prying a poorly bent tube in place strains the joint making it prone to leakage. Improper cutting, flaring, and brazing all lead to potential leakage. Cut tube should have no more than a 2° angle and the ideal flare surface is 37% 1/2°. Tube overflare interferes with nut ID. Guard against improper flareless (bite type or compression type) preset, which can result in a misaligned or uneven bite, or an overset or underset ferrule that won’t provide the required added strength.
Proper brazing the face seal requires that the sleeve be positioned onto the tube with no more that a 0.60” gap (preferably with a zero gap), and the sleeve face must be perpendicular to the centerline of the tube. Poor braze joints are caused by improper placement or misalignment of the sleeve over the tube, improper cleaning and/or fluxing (uneven or insufficient heat), or braze overflow on the sealing face. New technology eliminates the brazing process and its problems. In place of the brazing procedure, an orbital cold forming process produces a flat, smooth, rigidly supported sealing surface on the tube end. This process is known as flanging.
Incorrect torque, alignment, and positioning can affect the assembly of fittings. Burrs, scratches, nicks, foreign particles, pinched o-rings and faulty sealants may also cause leakage.
When troubleshooting fitting failures, determine the location of the leak, then check the joints for proper tightness. If the leak persists, check for correct assembly. It may be necessary to remake the joint.
Abuse Failures %%MDASSML%% There are multiple ways to abuse hydraulic system components. Common examples are:. Do not remove protective caps and plugs from components until ready to assemble. A leak does not always equal tighten the fitting. Never use tubing as structural support.
Filtration systems and components present another potential source of hydraulic system leaks. A filter maintenance schedule should be set up and followed diligently.
Different filter media and different types of filtration systems present an array of different advantages and disadvantages.
The main types of filter media are depth and surface type elements. The advantages of depth filter media include cost effectiveness, high dirt capacities, and high efficiency. Disadvantages include cleaning difficulty, media migration possibilities, limited chemical compatibility, shelf-life limitation, and higher initial pressure differential requirements.
Advantages of surface filter media include freedom from media migration, resistance to fatigue, easy to clean, controlled pore size, and low initial pressure differential requirements. Disadvantages include high costs, initial inefficiency, and limited dirt holding capacity. (See Figure 3 %%MDASSML%% Filtration)
Four filter installation alternatives include:
Suction Filter and Strainer %%MDASSML%% Protects the pump and the system from dirt introduced in the reservoir. Suction filtration is not suitable for many variable displacement pumps.
Pressure Filtration %%MDASSML%% Can provide specific component protection, but is expensive because of the need to withstand system pressure flows.
Return Line Filtration %%MDASSML%% Is inexpensive because it is a low-pressure application and protects the reservoir from dirt generated in the system.
Off-Line Filtration %%MDASSML%% Servicing an off-line filter can be accomplished without a loss of production, though the initial cost of the installation is relatively high.
When filter elements are removed from the system, inspect them for signs of failure. Inspecting filter elements and studying the results from fluid sampling help to determine appropriate intervals between inspection and predict potential system problems.
At the end of the day, filtration is an inexpensive form of system insurance. However, it is only as good as it is maintained. Keeping the oil clean will help prevent costly downtime due to contamination-related component failures.
The Bottom Line…
Hydraulic system noise and leakage often result in system downtime.
Leaks are often the result of poor system design, substandard component quality, improper installation and abuse.
A filter maintenance schedule should be established.
Taking a systematic approach to diagnostics and testing helps identify problems quicker and provides the needed information to repair or replace hydraulic components.
Lawrence Schrader Jr., Global Motion & Control Training Manager, Parker Hannifin, can be reached at 216-896-2574 firstname.lastname@example.org.
Gorbel Inc. introduces new G-Force intelligent lifting device
Gorbel, Inc. introduced the press to a new member of its G-Force family of intelligent lifting devices on Tuesday, March 28 at NA 2006, the Material Handling Industry of America’s biennial trade show being held at Cleveland’s I-X Center.
Featuring a modular design for increased functionality and flexibility, the new device has a 660-lbs capacity—up from 380 lbs in previous designs—and is said to be more precise than hoists and more responsive than air balancers. It provides precision placements at speeds of up to 60 fpm and replaces the operator present switch (OPS) with a photo sensor. This feature senses the presence of the operator’s hand without requiring a switch to be depressed, resulting in smoother operation because the OPS is not available for use as a start/stop control.
The unit’s handle, which has been redesigned to be more ergonomic, features a standard LCD that displays operation modes, programming menus, fault codes and weight readout. On-board diagnostics and preventative maintenance indicators are included to help keep the unit in working order, alerting users when regular wear items like wire rope need replacement or when the unit is due for inspection.
Also demonstrated was a 5-ton capacity Tarca Track crane system. Pre-engineered, Tarca Track has a three-piece welded construction with a compound section of mild steel top flange and web and a specially rolled, high-carbon steel lower rail. It offers a raised tread and high-carbon track to promote even wear patterns and provide durability and flexibility. Runways, end trucks and crane drives are amongst the features included with the crane system.