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  • Low-Speed, High-Torque Motor has Wealth of Features

    1. Applications requiring heavy loads to be accelerated from rest, such as this portable concrete mixer, stand to benefit from Fluidyne Fluid Power’s new 500 Series low-speed, high-torque motors.

    ​Geroler-type hydraulic motors have a great reputation for delivering low-speed, high-torque power. Their compact design also makes them the first or only choice when space is tight — especially because they drive loads directly without needing a speed-reducing gearbox.

    However, some designs of geroler motors exhibit internal leakage that prevents them from starting loads effectively from rest. The internal leakage allows fluid to bypass pressure chambers and some of it flow through the motor’s case drain. The result of this bypass is reduced starting torque.

    2. Fluidyne’s heavy duty 500-Series motors target low-speed, high-pressure applications.

    ​Fluidyne Fluid Power, Fraser, Mich., resolves this issue with its new heavy duty 500-Series Motors. The 500-Series motors are available in 11 nominal displacements from 125 to 750 in.3/rev. (7.20 to 45.45 cc/rev.). The motors’ valve-in-rotor design efficiently distributes oil and reduces overall motor length. A pressure-compensated balance plate improves volumetric efficiency at low flow and high pressures. They feature bi-directional rotation and a high-pressure Viton shaft seal that eliminates the need for a case drain.

    Joan Armstrong, engineering manager at Fluidyne, explains, “These motors are especially suited for low-speed, high-pressure applications with smooth rotation throughout speed transitions. The hydrostatic balance pressure plate flexes to allow for proper lubrication and high operating efficiency. Plus, the combination of shafts, mounts, and displacements let you configure these motors to almost any application requirements.”

    For more information on the 500 Series motors and other products, call (586) 296-7200, or visit www.fluidynefp.com.

    From hydraulicspneumatics Thursday, May 5, 2016
  • Hydraulics Serves Aussie Navy

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    The HMAS Canberra docks down in Sydney Harbor to receive an LHD Landing Craft containing a powerful hydraulic ventilation drive. (Courtesy of Royal Australian Navy)

    For nearly 40 years, Fluidmecanica SAU, Pontevedra, Spain, has designed and manufactured marine machinery, hydraulic controls and transmission, and pneumatic systems. Last year, four military landing craft worked on by Fluidmecanica were delivered to the Royal Navy of Australia at its HMS Waterhen Naval Base near Sydney. The landing craft operate in conjunction with two Canberra-class landing helicopter dock ships and are qualified under NATO requirements.

    Each landing craft is 23.30 meters long and can achieve speeds exceeding 20 knots. Fluidmecanica designed and built the ventilation system for the engine room of each craft. A ventilation system may seem like overkill for a hydraulic system, but the rigors of the application requires the high power density and durability of hydraulics.

    Hydraulics on the Move

    Two pairs of hydraulically powered blowers rotate at 2,900 rpm to move up to 17,000 m3 of air per hour (10,000 cfm). Each hydraulic gear motor (two connected in series) driving a fan is fed by a variable-displacement hydraulic piston pump powered from each of the landing craft’s two 809-kW (1,080 hp) engines. Hydraulic pressure for each circuit is 280 bar, and maximum flow is 10 lpm.  This is where the versatility of hydraulics is important, because fan speed must be controlled independent of engine speed.

    Fluidmecanica’s Francisco Oliver Rivera explains that a variable-speed electric drive would not have been practical for this application. “An electric drive is more bulky and weighs about 60% more. It would also be prone to failure under high shock and vibration. NATO shock requirements are especially demanding in boats like this, which may have to operate near shelling fire during operations.”

    Fluidmecanica tests a ventilation fan driven by a hydraulic gear motor. Two pairs of these fans are used in landing craft designed and built for the Royal Australian Navy.

    The pump that drives the fan has variable displacement, so its output per revolution increases or decreases inversely with engine speed, says Rivera. “Each pump has a load-sensing control, so we achieve fixed flow with a metering block. In this case, the flow remains fixed over the engine’s complete range of speed—from 1,000 to 2,800 rpm.

    Rivera also says that because the landing craft are designed for use in combat, simplicity and rugged operation were high priorities. “Each hydraulic pump is directly coupled to the engine, so the system automatically starts with the engine. There is no need to switch the fan on or off, because if the engines are not running, the fans are not needed.”

    Looking for parts? Go to SourceESB.

    From hydraulicspneumatics Wednesday, April 13, 2016
  • Hydraulic-Electric Analogies: Part 2—Adding a Variable to Positive Displacement

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    2. The stationary body parts consist of the ports that carry fluid into and out of the pump, and provide a sealed housing to capture internal leakage.

    The vane pump is a positive-displacement pumping mechanism with an assembly that starts with a body containing the plumbing ports for connecting the inlet and outlet to the hydraulic system. A simplified cutaway diagram is shown in Figure 2. Four internal kidney-shaped ports are arranged in inner and outer configurations.

    The two outer ports, which transfer the majority of fluid from the inlet to the outlet, are necessarily the larger pair. The inner ports carry the respective pressures of the outlet and inlet ports to the undersides of the sliding vanes and contribute a small amount of pumping action. Their main purpose is to apply some pressure on the underside of vanes to force them into the cam ring, thereby forming a seal between the inlet and outlet ports. Internal flow paths are machined or cast into the body so that all of the yellow areas have essentially the same pressure, whereas all aqua areas are at the inlet pressure.

    3. Inserting a vane into each rotor slot builds the rotating group of a vane pump.

    The vane pump’s moving parts consist of a slotted rotor into which rectangular vanes are inserted, one vane for each of the slots (Fig. 3). Clearances between the vanes and slots are such that a compromise is made between having the vanes freely sliding within the slots and forming a fairly high impedance (low internal leakage) path between the high- and low-pressure sides. The pump design in Figure 3 has 12 vanes, but any even or odd number of vanes can be used.

    4. The vane pump’s rotor has all vanes in position so that the rotating group can be inserted into the cam ring.

    Figure 4 shows all of the vanes inserted into the rotor and the rotor assembly inserted into its cam ring. The sliding fit between the rotor slots and the vanes ensures that the vanes can move outward from centrifugal force to make positive contact with the inner periphery of the cam ring. The cam ring constrains the outward (radial) motion of the vanes while the eccentricity between it and the rotor’s center of rotation controls the pump’s displacement.

    Figure 5 shows the full rotor assembly nested inside its cam ring. The ring is drawn at its most extreme upward position, which produces the maximum amount of eccentricity between the rotor’s spin center and the cam-ring center and results in maximum pump displacement.

    5. When the rotor assembly is nested inside the cam ring, the ring constrains the outward vane motion while the relative up and down sliding of the ring controls the pump displacement.

    The Moving Parts

    The vane pump has three groups of moving parts in the vane pump. First, the rotor spins about the shaft center line. Second, the cam ring moves up and down to control the displacement. Third, the vanes undergo both sliding and rotating motion. Note that the cam ring does not rotate; it can only move up and down. The assembly consisting of the rotating group and the cam ring are now ready to be installed into the pump body, getting a step closer to a functioning pump.

    Pumping action can be visualized with the aid of the body and rotating group, partially depicted in Figure 6. It all takes place in the volumes bounded by the rotor, the cam ring, and a pair of consecutive vanes. With the rotor spinning as indicated, look at the pair of vanes near bottom dead center, where the rotor is almost touching the cam ring. The volume trapped in the chamber between the vanes is nearly zero.

    6. The rotating group and cam ring are inserted into the pump body, and again, the eccentricity of the shaft and cam ring are apparent. The pumping chambers (the circular trapezoids bounded by the rotor, cam ring, and consecutive vanes) absorb the inlet fluid and expel the outlet fluid.

    However, realizing that rotational motion is taking place, the volume will increase as the rotor drags the vanes along with it. The increased trapped volume reduces pressure within the expanding chamber, causing atmospheric pressure within the reservoir to push fluid into the chambers.

    Eventually, the small chamber rotates to the top position, which has the greatest trapped volume and is filled with its maximum gulp of fluid. After crossing over top dead center, the filled chamber comes into hydraulic communication with the high-pressure outlet port. Thus, the large trapped volume undergoes an extremely rapid increase in pressure.

    At that same time, the vane shown at the 12 o’clock position forms a seal to separate the high- and low-pressure ports. Thereafter, further rotation causes the volume to decrease in the chamber, and the rotor-to-vane coordinated motion, relative to the stationary cam ring, pushes the high-pressure fluid through its kidney port (yellow) and out to the hydraulic system.

    The kidney ports are arranged so that all of the chambers on the left half of the rotor are at high pressure, while those on the left half are at low inlet pressure. With counter-clockwise rotation, as indicated in Figure 6, the right-hand external port is the pump inlet while the left-side port is the outlet.

    Dealing with Leakage

    Sealing between the high- and low-pressure sides is imperfect—and important. Internal leakage can make its way from the high-pressure side to the low-pressure side via several paths: An imperfect seal exists at the vane tip, as does clearance at the sides of the vanes, requiring a close fit in the axial direction between the rotor, vanes, and the stationary parts. Some small amount of leakage makes its way between and around the vanes and their slots through the clearance that’s needed between the ends of the rotor body and the stationary mating parts.

    Much of this internal leakage finds its way into the pump body (commonly referred to as the case), shown in pale green in Figure 6. In that pump body, it must leak back into the low-pressure port to be recirculated into the pumping chambers. Thus, the pump body can reach internal pressures that approach the supply pressure.

    Containing the pressurized fluid in the body requires the use of a high-pressure dynamic shaft seal. In many pump designs, a third hydraulic port is created that carries the internal leakage back to the reservoir. This greatly reduces the internal pressure and lowers the demands on the shaft seal. Modern sealing technology can eliminate external leakage from hydraulic machines if the system is properly maintained.

    Taking a Position

    The pumping elements in Figure 6 are shown in the maximum displacement position. The cam ring has been positioned in its maximum up position, resulting in the maximum eccentricity between the center of rotor rotation and the center of the cam ring.

    If the rotor and cam ring are perfectly concentric, the displacement will be zero. If the cam ring is dropped below the concentric point, the inlet and outlet ports will be reversed, and so will the output flow without changing the direction of shaft rotation. Such pumps are variable displacement, and said to be capable of over-center operation, meaning the displacement can take on either positive or negative values.

    7. Stroking pistons plus external access through hydraulic ports allow the cam ring and displacement to be varied.

    Now, though, the need arises for some external means of changing the cam-ring position so that pump output can be changed at will, or changed automatically using feedback. The stroking pistons shown in Figure 7 provide that capability.

    External ports allow hydraulic access to the pistons, usually with an electrohydraulic servo or proportional valve. Electrohydraulic stroking is done by closing the loop on the cam-ring position with a position transducer, most often with a linear variable differential transformer (LVDT), not shown in Figure 7. Cam-ring guides (dark green) prevent its right-left movement.

    Pressure compensation in the variable-displacement pump is easily achieved via hydraulic methods. Pressure compensation equips the pump with internal feedback that automatically reduces displacement if a threshold pressure is exceeded.

    In fact, pressure-compensation pumps can be safely deadheaded; that is, the output port can be totally blocked without damaging the pump. One way to achieve pressure compensation of the vane pump is shown in Figure 8.

    8. Pressure compensation can be achieved by connecting the stroking piston port to the outlet pressure and replacing the lower stroking piston with an adjustable bias spring.

    Here, the lower stroking piston has been replaced by a bias spring with a pre-compression adjusting screw. The upper stroking piston’s hydraulic port is connected to the outlet pressure so that the piston “senses” the outlet pressure. The bias-spring pre-compression causes an upward force on the cam ring, forcing the cam ring into the position shown when the outlet pressure is low. Under this operating condition, the pump operates like a fixed-displacement pump at max displacement and max output flow.

    As the load pressure builds, the stroking piston exerts an increasing force on the top of the cam ring. At some point, the stroking piston force exceeds the pre-compression force of the spring, which automatically decreases the displacement. Blocked port pressure and deadhead pressure mean the same thing, i.e., the pressure at the outlet port under the condition of zero output flow. It is analogous to the Thevenin voltage of an electrical generator or other voltage source.

    The preceding figures on vane pumps are not necessarily depicting actual construction practice of such machines. Instead, they show the principles of operation. For example, pressure-compensated vane pumps do not use physical stroking pistons. A less-costly method is to rotate the kidney ports slightly in the direction shaft of rotation, counter-clockwise. A tremendous force acts on the inside of the cam ring at high pressures, upwards of tens of thousands of pounds in large pumps at high pressures.

    By rotating the kidneys ever so slightly, a component of force emerges in the down direction. That force is used to act against the bias spring and force the cam ring downward in the face of high outlet pressures. Therefore, no stroking piston is needed. And eliminating the stroking piston can significantly reduce the size of the pump body. Many other practical construction details exceed the scope of this brief look at electric and hydraulic analogies and principles of operation.

    Looking for parts? Go to SourceESB.

    From hydraulicspneumatics Thursday, May 5, 2016
  • ABB Inc: Current Limiting Miniature Circuit Breakers with Ring Tongue Connections

    The breakers conform to UL 489, CSA 22.2 No. 5 and IEC/EN 60947-2 standards. They are, the company says, currently the only UL489 MCB on the market with rated current up to and including 35 A for 480Y/277 VAC, and up to 63 A for 240 VAC. The Supplemental Protection conforms to UL1077, CSA 22.2 No. 235 and EN 60947-2 standards. Both ranges are available in 1, 2, 3 and 4 pole configurations, from 0.2 A through 63 A, and feature integrated captive screws that simplify the secure connection of cables, prevent installers from loosing the connection screws, provide extra protection and save time. All markings are permanent laser markings, clearly visible from the front even when mounted in position on the DIN rail. The breakers have a true Contact Position Indicator (CPI) that indicates the actual contact position, ensuring the display of fault conditions such as contacts that may be “welded” closed due to excessive fault current. They also comply with the latest UL requirement for barriers of MCBs fitted with ring tongue terminals, and their structural material is a flexible, recyclable thermoplastic.

    >>For more information on this product, click here
     

    From automationworld Thursday, January 10, 2013
  • Hose installation

    Figure 1. Make hose assemblies long enough and routed in a manner that prevents exceeding minimum bend radius recommendations.

    Most engineering efforts focus on ways to design and manufacture products that satisfy application requirements as inexpensively as possible. But you can make a satisfactory design better by making it more reliable and easier to maintain – and without spending a lot of money. How? Simply by following simple tips and recommendations offered by manufacturers. These fundamentals concern bending, alignment, motion, and similar basic guidelines.

    Application basics

    Unlike metal tubing, hose is flexible, so it is used primarily to allow relative motion between components at either end of the hose assembly and to simplify routing and installation. It is much easier to route a hose assembly over, under, around, or through a series of obstacles than it is to bend and install a rigid tubing assembly. Furthermore, replacing a hydraulic line by fabricating a rigid tube assembly often is more costly and time consuming than making a hose assembly.

    Figure 2. To prevent excessive strain at hose-to-coupling interfaces, make hoses long enough to allow for contraction and expansion.

    Most manufacturers offer hose that can be bent to a tighter radius than that published in industry standards. Still, bending hose to a smaller radius than recommended should be avoided to avoid shortening service life. Therefore, route hose in a manners that provides ample bend radius, Figure 1.

    Because hose is flexible, you must allow for contraction and expansion when cutting the hose to length. Manufacturers state that, depending on its type, hose can elongate up to 2% when pressurized, but, more importantly, can contract as much as 4%. This length differential can strain hose reinforcement wires and eventually lead to failure, especially at the hose-to-coupling interface. Therefore, cut hoses slightly longer than needed to compensate for contraction, Figure 2.

    Figure 3. Left-hand drawing shows how hose twists because it is bent in one plane while oscillating motion bends in a second plane. Rerouting the hose eliminates multi-plane bending.

    Bend hose in one plane only to avoid twisting its wire reinforcement, which would reduce the hose’s pressure capability. Manufacturers state that twisting a high-pressure hose only 5° can reduce service life by 70%, and 7° of twist can reduce service life up to 90%. Unfortunately, hose routing usually occurs late in the design process, so it may be difficult to find an ideal path. Multi-plane bending often can be avoided by reorienting the hose, Figure 3. If this is not possible, install a hose clamp between bends, Figure 4, and provide enough length on both sides of the clamp to relieve strain on the hose’s reinforcement wires. This length depends on the hose ID, degree of bending, and helix angle of the particular hose’s reinforcing wire, so manufacturers prefer to evaluate each application individually.

    Figure 4. When multi-plane bending cannot be avoided, install a hose clamp between bends and provide enough hose length on both sides of the clamp to relax torsion and compensate for hose contraction.

    Another alternative is to use a single section of hose for each bend and install a hose-to-hose coupling and hose clamp between bends. This technique is less preferred because it not only is more costly and time consuming to perform, but increases the number of potential leak points in the hose assembly. Also, to help ensure that technicians replace and secure hose assemblies properly, include detailed instructions on hose length, use of hose clamps, and special considerations in service manuals.

    Providing protection
    Figure 5. Hose clamps can prevent abrasion by holding hose away from surfaces it would otherwise rub against.

    Hose manufacturers now offer a variety of products with abrasion-resistant covers. No wonder: manufacturers state that about 80% of hose failures are attributable to external physical damage, with abrasion cited as the major culprit. Abrasion is generated primarily by hoses repeatedly rubbing against equipment surfaces or each other.

    To help prevent abrasion, use clamps to secure hose in place and keep it from rubbing against adjacent surfaces, Figure 5. The clamp should have a snug fit around the hose to prevent movement, but not be tight enough to damage the hose by squeezing too tightly. Be sure the hose is slack on both sides of the clamp to compensate for contraction and expansion.

    Additional protection can be provided by sleeves. Metal sleeves resemble springs that protect the hose from being crushed. Fabric sleeves help keep abrasive particles away from hoses, and both types can serve the added function of nestling multiple hoses into a compact bundle.

    Some types of sleeves must be installed from one unconnected end of the hose and slid along its length. Others have a longitudinal slit to enable installing the sleeve without having to disconnect either end of the hose assembly.

    Accommodating movement
    Figure 6. Design at left provides ample hose length when cylinder is pivoted, but bends hose in too small a radius when cylinder is vertical. Increasing hose length and providing greater clearance produces much greater bend radii.

    In addition to causing twisting and abrasive wear, motion can also quickly spell doom for hoses that do not properly accommodate equipment dynamics. For example, hoses connected to a cylinder that undergoes pivoting motion, Figure 6, must be of proper length and routed to avoid becoming kinked or bent beyond their minimum bend radius.

    An item that can make a good design better is a swivel joint, sometimes called a live swivel. Unlike standard swivel fittings, which connect hydraulic lines at any fixed angular position, swivel joints accommodate relative motion between the hose and the component to which it is connected. As Figure 7 shows, swivel joints permit pivoting motion that reduces the bending transmitted to the hose assembly and can reduce the length of hose required.

    Figure 7. Swivel joints can extend hose life by reducing the amount of bending caused by relative motion between machine elements. They also aid maintenance by simplifying hose installation and replacement.

    When multiple lengths of hose lie close to each other, and substantial linear motion will occur, hose carriers keep hoses neatly nestled to prevent tangling, twisting, and rubbing against each other. Depending on which particular type is specified, carriers can also isolate the hoses inside from potentially hostile conditions outside – impact from falling objects, abrasive particles, chemicals, or intermittent high temperatures.

    Other important considerations

    Most hydraulic hose is wire reinforced, which makes it an electrical conductor. For equipment that may be used near power lines or where hose will be in close proximity to flammable solutions that could be ignited by static electricity discharged from the hose, manufacturers offer non-conductive hose.

    In other applications, static electricity sometimes may be discharged through the hose wall to surrounding surfaces. This is caused by conducting electrostatic charges from the fluid through the hose’s metal reinforcement and cover to adjacent surfaces. Consequences can include localized burning that weakens the hose or even produces pin-size holes in the hose wall. In this case, hose with a conductive tube may be called for to conduct electrostatic charges to hose end fittings rather than through the hose.

    Just as twisting can dramatically shorten hose life, so can excessive heat. Heat from external sources, such as exhaust components on mobile equipment, can quickly soften or embrittle the hose wall from the outside in. Therefore, it is important to keep hose away from external sources of heat. If this is not possible, manufacturers offer insulated protective sleeves to partially block heat transmitted to the hose.

    Figure 8. Lack of planning produces cluttered hose routing, far left, that complicates maintenance and can even reduce hose life. Well-thought-out routing and choice of end fitting configurations, near left, makes assemblies that are more reliable and easier to maintain and troubleshoot.

    However, heat from an internal source — the hydraulic fluid itself — also can reduce the service life of the hose. Pumping hydraulic fluid at a temperature of only about 18° F over the maximum recommended temperature for a hose can cut its expected life in half. What makes this problem even more serious is that machine operators often are unaware that fluid temperatures may exceed manufacturers recommendations – especially if the high temperatures occur only intermittently.

    Finally, strive for neat appearance when routing hoses, Figure 8. This not only prevents tangling, twisting, and rubbing together (which can cause abrasive wear), but aids maintenance by making it easy to remove and re-install hose assemblies and trace circuit routing.

    Use adapters sparingly because they add to the number of components in an assembly. This increases assembly time, cost, and the number of potential leak points. However, when properly applied, adapters can simplify hose assemblies that use angled fittings (such as 90° elbows) at each end. Hose-end fittings on these assemblies must be carefully oriented to prevent twisting the hose during installation. So using an angled hose coupling at one end of the hose and a straight coupling connected to an angled adapter fitting on the other eliminates the need to carefully align hose ends during assembly.

    Clean hose prevents early contamination troubles

    When cutting hose to length, either a serrated or abrasive blade is used. Serrated blades cut one- and two-wire braid and textile-reinforced hose cleanly and efficiently, but usually are not recommended for use on spiral-reinforced hose because the blades would wear quickly or become damaged. Abrasive wheels cut all types of hose efficiently, but produce abrasive debris that usually finds its way into the hose. If not flushed from the finished hose assembly, this debris holds potential for serious wear and damage to sensitive components of the hydraulic system. Skiving and crimping can also produce debris that must be removed before putting the finished hose assembly into service. Skiving involves cutting a length of the outer jacket from the hose to prepare it for accepting a hose-end coupling. Crimping squeezes the coupling onto the hose’s inner and outer surfaces, so some residual plating material could come off and find its way into the hose.

    Compared to skiving and crimping operations, storage can introduce more and a wider variety of contaminants. During storage, dirt, water, metal particles, rust, abrasive particles, and any number of other types of contaminants may migrate into a hose sitting on a shelf. It should be obvious, then, that all hose assemblies should be cleaned before being put into service. At the very least, finished hose assemblies should be cleaned with a strong blast of compressed air. Naturally, this air should be clean and dry.

    The most effective cleaning technique is high-velocity, bidirectional flushing. This floods the hose assembly with cleaning fluid until the fluid comes out of the hose as clean as when it went in. However, the cost of this equipment and the time required to flush an assembly makes it impractical for many potential applications.

    A relatively new cleaning technique offers an effective and practical alternative to these procedures by using sponge-like projectiles that are shot through hose and tubing assemblies by a blast of compressed air. Equipment for this procedure is much more affordable than that for high-velocity flushing. Perhaps more importantly, though, it cleans assemblies much more effectively than compressed air alone and in a fraction of the time it takes for high-velocity flushing.

    Once the hose assembly has been cleaned, be sure to install protective caps or plugs at both ends to prevent contamination from entering the assembly. These should not be removed until the hose assembly is being installed on the equipment.

     

    From hydraulicspneumatics Sunday, January 1, 2012