Industrial Motors: How to Get More Bang for Your Buck

The recent push to make everything smart or connected has led to some interesting evolutions in manufacturing. Application and infrastructure divided the use of electromechanical and fluid power. However, with the development of high-speed controls, quick-response motors, and improved software, variable-speed electric drives are finding their way into power hydraulic pumps.

Previously these technologies were difficult to combine. Over the last few years there have been more motor-pump combinations able to provide power and responsiveness to match systems controlled by electrohydraulic valves or a variable-displacement pump. The result is not only new features and control, but also a reduction in energy consumption.

While smart fluid systems sound new, they have been around for years. What is changing is how smarter they are becoming. It was inevitable with advancing technology, or perhaps the skills gap in the fluid power community, but an intelligent innovation has been triggered by blending electromechanical with hydraulic and/or pneumatic. These new solutions tend to be easy to program and control in a turnkey product. Moving forward, these variable-drive, electromechanical hydraulic, smart, all-in-one solutions might become the new norm.

The Kyntronics Smart Hydraulic Actuator is a variable-speed electric motor driving the hydraulic pump, servo-valve, cylinder, and support components all in one assembly. All you need to provide is electrical power and I/O signals. This solution controls position, force, and speed in applications requiring 500 lb (2,225N) to more than 100,000 lb (445 kN) of force with strokes up to 120 in. (3,048 mm).

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How to Create a Linearized Math Model of a Hydraulic Motor

The most sensible way to design a motion-control system is to use the stated performance requirements as the design goals, and to do so at the very outset of the design process. The techniques are analytical in nature, so they require mathematical descriptions of all elements of the system. Only then can synthesis and simulation methods be applied to direct the design process toward the end result without undue trial-and-error techniques. This is where motion control and mathematical models complement and enhance one another.

The nature of the model is dictated as much by the intended use as it is by the nature of the device that is being modeled. Individual modelers’ beliefs and biases have been known to influence models, too. But most would agree that models fall into two broad categories: steady-state and dynamic. Both the fluid power industry and the fluid power educational community are fixated on steady-state performances, not dynamic ones. In keeping with this tradition, I, too, will begin with steady-state models. A hydraulic motor will be modeled and then analyzed through some examples of how the models can be used.

The analytical schematic of the hydraulic motor has three internal leakage paths and one internal friction-windage resistance. However, note in Fig. 1 that output is mechanical power in the form of speed and torque, while the input is hydraulic in the form of pressure and flow. Visualization is eased by imagining the real physical processes that the three leakage resistances represent in, say, a piston motor.

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High Pressure Hydraulic LNG Fuel Systems in Marine Service 

Hydraulic LNG Fuel Systems as a marine fuel has shown great potential as a clean, safe, reliable, and cost effective alternative to diesel fuel in an ever changing global environment. Perhaps the most significant of these changes has been the International Maritime Organization implementation of MARPOL Annex VI. MARPOL Annex VI was initially implemented in 2005 to lower global SOX and NOX emissions, and then revised later that year, with the revision being implemented in 2010. This revision called for further increases in global emission regulations, as well as for the development of emission control areas (ECA) in which emissions would be further regulated. To comply with these regulations, a large focus was placed on the quality and compositions of fuels used in maritime service, resulting in a plan that would reduce the current diesel fuel sulfur limits from 3.50% to just 0.50%, to be effective as of January 1, 2020. As often occurs when necessity stokes the flames of ingenuity and invention, the notion of this potentially more costly and less available lower sulfur diesel fuel inspired many to look for prospective alternatives. Eventually this resulted in a push to research and implement the use of liquefied light hydrocarbons – LNG being the most common – as marine fuels. ACD has experience with both low pressure (approximately 8 bar) port injected engines, and high pressure (approximately 300 bar) direct injected engines, the more intricate of which is the high pressure variety.

High pressure fuel gas systems vary somewhat in design from one application to another, however they typically consist of several primary components, namely the reciprocating high pressure pump, drive motor, power transmission system (such as a gearbox or belt drive), centrifugal feed pump (often referred to as a boost pump), a high pressure heat exchanger (often referred to as a vaporizer), a lubrication system of one of various forms, piping and valves, control and diagnostic electronics, and a base frame. ACD has built these systems in both single pump and dual pump configurations, depending on the level of redundancy requested by the ship owner.

Pump Selection and Operation
At the heart of the fuel gas system is the high pressure pump. To achieve output pressures in excess of 300 bar, reciprocating piston type positive displacement pumps are utilized. Selecting the appropriate pump for this application is crucial, as there are many challenging demands placed upon it. As LNG is a cryogenic fluid, the pump must be specially designed for this service, employing unique technologies, geometries, and material selections. The pump must be capable of running continuously for days or even weeks at a time. It must be of sufficient size to satisfy the relatively large (as far as reciprocating cryogenic pumps are concerned) flow rates required by an engine operating at maximum power, yet be able to turn down to comparatively small flow rates required by an engine operating at idle conditions. Finally, and perhaps most importantly, it is imperative that the pump be able to operate reliably, as the only opportunity to perform major maintenance is typically every five years in dry dock. ACD has made high pressure pumps of various sizes (ranging from just 1 liter/min to as high as 750 liter/min) and configurations for many decades, and based on the aforementioned criteria, a pump was chosen from ACD’s SLS enhanced oil recovery line. While this was not a pump initially designed specifically for maritime service, it has decades of reliable operating experience in service conditions much more severe than those now being demanded of it, making it the ideal candidate to be configured into what is now known as the MSPSL, the world’s first high pressure pump to ever supply high pressure LNG fuel to an ME-GI engine in a marine environment.

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Hydraulic Motor ‘Dry Starts’ And How To Avoid Them

I was asked recently to do a failure analysis on a hydraulic motor that was the subject of a warranty claim. The motor had failed after only 500 hours in service, some 7,000 hours short of its expected service life. Inspection revealed that the motor’s bearings had failed through inadequate lubrication, as a result of the hydraulic motor being started with insufficient oil in its case (housing).

A common misconception among maintenance personnel with limited training in hydraulics, is that because oil circulates through hydraulic components in operation, no special attention is required during installation, beyond installing the component and connecting its hoses. Nothing could be further from the truth.

After this hydraulic motor was installed, its case should have been filled with clean hydraulic oil, prior to connection of its case drain line. Starting a piston-type motor or pump without doing so, is similar to starting an internal combustion engine with no oil in the sump – premature failure is pretty much guaranteed.

Now, some of you may be thinking that the case of this motor should have filled itself with hydraulic oil through internal leakage. In most instances it will, but not before the motor or pump has been damaged! And this damage may not show itself until the component fails prematurely, hundreds or even thousands of service hours after the event.

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Hydraulic Motors Give Mexican Dam a Big Lift

A crane with a huge iron plate on its hook stands on the dam wall at Nezahualcóyotl Lake in southern Mexico. The crane operator carefully lowers it into the lake in front of a spillway gate in the dam. The water mass of the lake pushes the plate against the concrete wall as the plate slowly descends, closing the opening. The spillway gate then opens, and the water between it and the iron plate drains off. The spillway gate—which usually prevents the dam from overflowing—is now dry, so workers can now inspect the area.

Manuel Schuhmann, technical project manager at Bosch Rexroth, is enthusiastic: “It is fascinating: The plate, or the so-called stop lock, is held in place solely by the reservoir’s water pressure.” The task of the engineers is to modernize the old drives on the dam’s spillway gates.

Cautious Innovation

Built between 1958 and 1966, the 138-m-high dam, which is officially known as the Nezahualcóyotl Dam, holds back a lake with more than 10 million m3 of water and a surface area of about 110 km2. The dam protects the lowlands of the Federal State of Tabasco against yearly flooding and also contains six turbines, which generate hydroelectric power for the region.

The Comisión Federal de Electricidad (CFE) operates the dam and invests regularly in the safety and availability of all its technical equipment. Last year the Comisión decided to modernize three of the dam’s seven spillway gates, which regulate the water level of the reservoir. Each spillway had an electric motor driving two pinion gear drives via a drive shaft. The motor had been raising the 170-ton spillway gate using chains on each side ever since the dam went into operation in the 1960s.

Martín Gómez, project manager at Bosch Rexroth in Mexico, recalls the CFE’s invitation to tender for this project: “We initially proposed a solution with long-stroke hydraulic cylinders to drive the gates.” The team had already used this proven type of drive in new construction many times—such as the La Yesca Dam, also in Mexico. However, the concrete structure at the Malpaso Dam proved to be unsuitable.

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