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The advancements in hydraulics and variable speed drives (VSD) were running in parallel for many years but on opposite sides of the fence from each other in solving paper converting industrial applications. Once the engineers on both sides met in the middle and shared their knowledge, a door opened to a new way of thinking and problem-solving. Combining VSD and hydraulics was difficult at first; the unforgiving nature of positive displacement pumps, the non-compressibility (incompressibility) of the fluids, demanded a different solution than what VSD engineers had experienced with more forgiving lower pressure centrifugal pumps. The combination of hydraulics and VSD has created a new type of system with lower noise, fewer components, and higher energy efficiencies.
Download our white paper and learn how Drive Controlled Pump (DCP) technology can make center winders the ideal winding technology for the paper converting industry.
Hydraulic systems are known for their ability to deliver significant power density in a small package. Electric motors and variable speed drives are known for their programmability and responsiveness. Dating back to the 1990s, hydraulic and drive system engineers could see the potential for combining the two technologies. Historically, the motion control industry has had limited success in combining the technologies. However, in today’s manufacturing environment, the higher cost of electrical power, the increasing global concern for the CO2 footprint and the need for quieter industrial solutions offer opportunities to reevaluate the combined technology. Today, the advancement in new Variable Frequency Drives (VFD) control algorithms, faster programmable VFDs and more efficient hydraulic pumps specifically designed for variable speed applications allows our engineers from both technologies to work together with greater opportunities for success by implementing an ideal technology known as Drive Controlled Pump technology (DCP).
Traditionally, electromechanical drive systems are used for the majority of converting line’s center winders or combined center surface winders. These drive systems use electric motors larger than the web horsepower by the factor of their buildup ratio. DCP can keep the electric motor size close to its web horsepower by eliminating the buildup factor in a winding application. This takes advantage of the continuously variable flow and pressure feature of an electronically controlled variable displacement hydraulic pump operating at variable radial speeds.
Taking advantage of electric drive and hydraulic technology yields a positive outcome in winding and unwinding techniques. DCP technology allows us to create a wide constant HP range and trade speed for torque during the buildup process while reducing the size requirements for the electric motor. Since this technology operates the hydraulic pump at a variable speed; it uses fewer and simpler hydraulic valves. DCP hydraulic systems are less complex and more efficient than traditional hydraulic systems; it operates at much lower noise and temperatures resulting in quieter and cooler surroundings.
This system is very flexible; a variable displacement motor and a fixed displacement pump can be used to achieve the same results. The following diagrams show the control schematic of a DCP winding system using a variable displacement hydraulic motor and a fixed displacement open loop pump.
The system can also be adapted to closed loopX hydraulics and unwinding applications quite easily as shown below.
Paper converting lines employ surface, center, and center/surface combination winders and each winding technique has inherent benefits and limitations. Download our white paper and learn more about how Drive Controlled Pump (DCP) technology can make center winders the ideal winding technology for the paper converting industry.
Article contributed by Rashid Aidun, application engineer, Parker Hannifin.
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Proportional valves that employ powerful, voice-coil valve technology are used in applications where higher flows from smaller valves are ideal. While the list is endless, a few of the activities in which you may need to use these particular valves are lifting, steering and suspension. For an improved operation, acting on these three tips may be in your favor.
Trapped airflow is a common problem for proportional valve systems. When it comes to pilot operated valves, it can take some time to get the air out. Some indicators of trapped airflow due to valve instability include pulsing, modulation or an unusual performance overall. Higher flows tend to help push out the trapped air behind the spool so if you can run yours at a higher flow, then it should perform well at lower flows.
The position of your valve plays a big role in operation. Be sure that the valve is not positioned at the high point of your system or in an upright orientation. This can trap the air. Keep the valve mounted horizontally so the tube is off to the side. An advantage to having the tube horizontal is that any G load acting on the valve will not tend to self-activate the valve. Some systems see about 3 to 5 G loads but can go as high as 10 G.
Ideally, the proportional valve is located below the oil reservoir with the tank port of the valve oriented upward. This keeps the oil in the valve when the system is shut down. On many systems, we have used a check valve in the tank line to help with this and have seen this help with stability in several cases.
For our proportional valves, we call out a specific PWM frequency for best results on these products. Some operators may not be following this and could be using IQAN or something similar. However, we do not have any test results for this type of system. Keep in mind that the dither frequency and amplitude are different from each manufacturer but drivers typically range anywhere from 1 kHz to 10 kHz.
To achieve the best possible operation, users should follow the manufacturer’s operation guidelines. Find out more about Parker's proportional valve offering from the Hydraulic Cartridge System Division.
Parker offers a wide range of proportional valves that employ a powerful voice-coil valve technology through its Hydraulic Cartridge Systems Division. Visit the website or consult your Hydraulic Cartridge System Division Catalog for more information.
Article contributed by Stephen Brunton, product manager, Hydraulic Cartridge Systems Division.
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The position of your valve plays a big role in its operation. Be sure that the valve is not positioned at the high point of your system or in an upright orientation. This can trap the air. Keep the valve mounted horizontally so the tube is off to the side. An advantage to having the tube horizontal is that any G load acting on the valve will not tend to self-activate the valve. Some systems see about 3 to 5 G loads but can go as high as 10 G.
Ideally, the proportional valve is located below the oil reservoir, with the tank port of the valve oriented upwards. This keeps the oil in the valve when the system is shut down. On many systems, we have used a check valve in the tank line to help with this and have seen this help with stability in several cases.
To achieve the best possible operation, users should follow the manufacturer’s valve operation guidelines. Find out more here on Parker Proportional Valves. Parker offers a wide range of proportional valves that employ a powerful voice-coil valve technology through its Hydraulic Cartridge Systems Division. Visit the web site or consult your Hydraulic Cartridge Systems catalog for more information.
This article was contributed by Stephen Brunton, product manager, Hydraulic Cartridge Systems Division.
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Inefficient energy allocation, heat generation and noise are typical concerns among facility engineers in manufacturing environments. Parker’s new variable speed drive solution, called Drive Controlled Pump (DCP), increases hydraulic power unit efficiency while maintaining high power density, precise control and performance. DCP is the pairing of electric motors, hydraulic pumps, electronic drives and software to meet the local load demands within your hydraulic system. Precisely controlled variable speed pump macros are custom configured to meet the functional requirements of each process within a complex hydraulic system.
Don’t just use the Hydraulic Power Equation to size the electric motor.
(HP = P x Q ÷ 1714)
Do compute the pump torque first, then use the motor’s base speed to compute power.
(T = Vi x P ÷ 24π)
(HP = T x N ÷ 5252). HP: Horse Power, P: Pressure PSI, Q: Flow GPM, T: Torque Ft-Lb, Vi: Pump Displacement In³/Rev, N: motor base speed (4 pole motor’s base speed = 1,800 RPM).
Don’t just use load’s flow and pressure demand to compute motor power.
Do consider the pump’s internal flow and torque losses at various speeds and pressures.
Don’t be content with power computations to maintain flow and pressure.
Do allow for the acceleration power requirement. Variable speed pump controls need reserved power to accelerate the combination of the electric motor rotor, couplings and the pump’s rotating group while under full pressure. The reserved power gets larger with the acceleration rate and rotor moment of inertia.
Ta = I x Δω / (308 x Δt), Ta: Acceleration Torque(Ft-Lb), I moment of inertia (LB-Ft2), Δω: Speed Change (RPM), Δt: Speed Change (Sec)
Don’t oversize the electric motor. Oversized motors have larger rotor inertia and require larger drives to power.
Do break down the cycle by pressure, flow and time. Compute each segment for power.
Don’t just use maximum flow and maximum pressure to compute power. You might end up with an oversized motor.
Do use the larger of the two computed horsepower values. Compare flow at maximum pressure and pressure at maximum flow.
Don’t just use the RMS value of computed power segments to size the electric motor.
Do use the RMS value, yet pay attention to peak power. Peak power should be less than 150% of the selected motor size, and its duty cycle must be within the operation parameters of the electric motor and drive.
Don’t use your standard TENV electric motor for variable speed fixed pumps.
Do use low rotor inertia motors to minimize reserve acceleration power. Open frame and force ventilated motors offer much lower rotor inertia.
Don’t exceed the induction motor’s base frequency when operating at maximum pressure.
Do exceed motor’s base frequency only when pressure drops proportional to over-speed.
Don’t operate below the minimum recommended pump speed. Operating below minimum speed damages the pump.
Do add a controlled bleed off loop to the pump’s outlet to limit its minimum speed. Also, an accumulator can allow the pump to get turned off at deadhead conditions.
Don’t accelerate/decelerate a pump too fast.
Do limit the pump speed change rate to stay above the pump’s minimum inlet pressure to avoid cavitation. Also, keep in mind rapid pump speed changes consume additional power which can lower the HPU’s efficiency.
To learn more about Drive Controlled Pump (DCP) Technology, download the white paper, Integrated Energy-Saving Hydraulic Systems Customized to Your Application Requirements here or view the on-demand presentation.
Rashid S. Aidun who draws on his electrical and fluid power background to create custom drive controlled pump solutions. Prior to joining Parker 17 years ago, he worked as an industrial manufacturing and fluid power and controls engineer for various OEMs. He has a BSME from Syracuse University.
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Given the many risks of excess heat in a hydraulic system – such as fluid decomposition, increased wear on system components, damage to seals and bearings, etc. – the need for an effective heat exchanger is often an essential consideration.
Smaller hydraulic systems with low operating temperatures may be able to rely on natural convection, but when that doesn’t provide sufficient cooling, a heat exchanger must be installed. You can also assume a heat exchanger is needed when a specific oil temperature is required to stabilize hydraulic fluid viscosity, or when equipment has a history of hot oil problems, such as shortened seal life or frequent oil breakdown.
Whether you work with large mobile equipment (for example, construction, military, forestry, and material-handling units) or commercial/industrial process machinery with hydraulic systems, hot fluid is a concern. A properly sized heat exchanger in any equipment can save time, money, repair headaches and extend system life.
To learn more about heat exchanger types and choosing the proper size for your hydraulic system, download the whitepaper.
So how do you determine which heat exchanger is best for a particular application? As with most design challenges, the answer is, it depends.
Accurately defining hydraulic cooling needs can be confusing because actual heat generation often varies as a machine goes through different cycles and because ambient temperatures or other environmental factors can affect system heat levels. When considering application and sizing of heat exchangers, the ideal operating temperature of the hydraulic fluid and the time it takes to arrive at that temperature must be used.
“There are many factors to consider and a wide range of heat exchangers, with certain benefits to each kind. The choice of a heat exchanger generally ties directly to the type of system to be cooled. That means you have to take into account vital parameters like heat load, available space, environmental conditions, power source, noise, operating costs, and so on.”
Rick Morton, business development manager, Parker Accumulator and Cooler Division.
Whether it’s a new design or a retrofit, it’s hard to pick the right heat exchanger without identifying the challenges and performing all the calculations. Fortunately, most heat exchanger manufacturers offer software to help you determine the best fit for each application. For example, we provide an online calculator (Essential Cooler Sizing Parameters) and other interactive resources where an engineer can plug in specifications to get a better idea of what exactly is needed.
Given the many variables involved, it’s not uncommon for some engineers to delay their decisions on heat exchanger specifications until after seeing how a system performs and how much heat transfer is actually needed.
When you have questions, it's often best to simply contact a heat exchanger supplier directly. Here at Parker, if a customer comes to us with questions on heat exchanger specifying, we can walk them through the process.
Before reaching out to a manufacturer for assistance, a bit of preparation will go a long way in expediting the selection process. For example, gathering the necessary information such as heat load parameters and other key influencing factors.
Article contributed by Rick Morton, business development manager, Parker Accumulator and Cooler Division.
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