Variable Flow Open Center Delivers Constant Efficiency

You may know that properly maintaining a hydraulic pump will ensure maximum efficiency and prevent damage, but did you know that it is especially critical to regularly monitor inlet conditions? Poor inlet conditions can result in cavitation—the second leading cause of pump failure.

 

What is cavitation and how can you prevent it?

While it’s common for people to think of a pump’s inlet as sucking in oil, in reality, it is atmospheric pressure doing the work. In essence, the weight of the atmosphere pushes the oil out of the reservoir and into a region of lower pressure—the inlet. Once the oil is forced from the reservoir and through the inlet, it then moves the volume of liquid into a region of decreasing volume to create flow. For this process to begin, there must be minimum pressure at the inlet of a hydraulic pump, as shown in the diagram below.

As you can see, the inlet of a pump plays a large role in how well it operates. Unfortunately, those designing and maintaining pump systems can become so focused on downstream flow that they overlook proper inlet maintenance. This can result in degradation of inlet function and serious problems such as cavitation.

Cavitation occurs when the absolute pressure on the inlet side of the pump is too low and air is drawn out of the solution, creating bubbles in the oil. As these bubbles get pushed around to the high-pressure outlet side of the pump, they collapse. This creates localized shock waves that blow bits of material out of the pump. It can also result in excessive heat and reduced lubrication that leads to friction and wear over time.

Cavitation can cause pump failure and it can damage other components of your system, which is why it is critical to examine the condition of the pump's inlet on a regular basis.

Analyzing inlet conditions on steady-state and variable-flow pumps

PSI versus PSIA. What’s the difference? PSI, or pounds per square inch, is a unit of measurement for pressure used in the United States. PSIA describes the absolute pressure in psi, including the pressure of the atmosphere. Absolute pressure is also referred to as total pressure. 

Maintaining steady-state hydraulic pumps

There are two areas you should monitor to maintain minimum inlet pressure on steady-state pumps:

1. The energy it takes to lift oil through the suction line (including pressure drop due to flow). We refer to this action as Phase 1 pressure, because it represents the amount of energy it takes to accelerate the fluid through the pumps internal pathways and keep the pump full. 

1. The minimum absolute pressure the pump must have in order to avoid damage.  This is known as the Net Positive Suction Head, or NPSH. 

In order for a pump to function, atmospheric pressure must be greater than Phase 1 pressure + NPSH. Every pump has its own specifications regarding acceptable minimum/maximum inlet pressure, but we can use the example below to illustrate how to calculate it.

To begin, assume that you are maintaining an 18 GPM hydraulic pump. The NPSH is equal to 12 PSIA with standard hydraulic oil and 1800 RPM per manufacturer’s specifications.

As you can see in the diagram above, the inlet line is 1.38” in diameter x 18.1” long with a 12.1” lift using standard petroleum-based fluid. 

 

Each foot of oil lift requires approx. = 0.4 PSI. Fluid velocity is 3.8 feet per second. A typical lookup table shows there will be a 0.05 PSI drop due to the flow through the pipe. 

 

Total loss of the inlet line during steady state is 0.4 PSI + 0.05 PSI, or 0.45 PSI. 14.7 – 0.45 = 14.25 PSI. Because this final number—14.25 PSI—is greater than the NPSH of 12 PSIA, you can rest assured the system is functioning well.

 

Maintaining variable-flow hydraulic pumps

If we apply the same numbers to a variable-volume pump, the result will be less acceptable. Here’s why: Imagine the pump is not in demand and is therefore being held off stroke, meaning there is no flow. When the pump is suddenly needed, it will come on stroke, requiring the column of oil in the suction line to accelerate. This sudden change in demand requires the pump pressure to accelerate from static to a pressure that is strong enough to move the oil and prevent cavitation.

Let’s look back at our model, applying revised numbers.

Assume the pump strokes on in 70 milliseconds (msec). The volume of liquid that has to accelerate is 1.5in^2 x 18.1” = 27.1 cubic inch (cu. in.). Note: Since the entire column of oil in the pipe has to accelerate, we used a measurement of 18.1” instead of 12.1”.

To calculate the weight of oil in the inlet line, we multiply the volume (27.1 cu. in.) by specific weight (0.0314 lbs./cu. in.), equaling 0.85 lbs. Fg (gravity force) = 0.85 lbs.

Fa = mass x acceleration 

a = v/t = 3.8/0.07 = 54.3ft/sec^2

Fa = (0.85/32.2) x 54.3 = 1.4 lbs.

Ft = 0.85lbs + 1.4 lbs. = 2.25 lbs.

The available force in the pipe from the atmosphere (Fluid power (Fp)) = 14.7 PSIA x 1.5 sq. in. = 22.05 lbs.

Net force = 22.05 lbs. – 2.25 lbs. = 19.8lbs.

NPSH = 19.8 lbs./1.5 in.^2 = 13.2 PSIA 

These calculations reveal that the system is fine, because the pump requires a minimum 12 PSIA at its inlet to operate effectively. However, if this system was installed at 2,300 feet above sea level (13.4 PSIA), the pump would cavitate whenever it came on stroke.

           13.4 PSIA x 1.5sq in = 20.1lbs

            20.1 lbs. – 2.25 lbs. = 17.85 lbs.

            17.85 lbs./1.5 in.^2 = 11.9 PSIA, which is lower than the minimum 12 PSIA required.

The above example assumes no losses due to other plumbing, however, it is not uncommon to see elbow fittings on pump ports, which could add to losses in the inlet line.

 

Other design considerations

In addition to maintaining good inlet conditions, any small leak on the inlet will entrain air, which is also bad for the pump. Small leaks will cause a pump to lose prime whenever the system is shut off, which means it will start dry and run dry until prime is re-established. For this reason, it is never a good idea to install hydraulic pumps above the fluid level. Rather, hydraulic systems designs should ensure that the pump inlet is flooded, i.e. the oil level is above the pump inlet. A ball valve can be used to isolate the pump from the reservoir in case it needs service, and a limit switch can be used on the ball valve to prevent the system from running if the ball valve isn’t fully open. 

 

For more information on hydraulic inlet maintenance or other topics, email us. Your pump will thank you.

This article contributed by Tim Beck, manager - system design and application, Parker Hannifin Corporation Hydraulic Pump and Power Systems Division.

 

 

 

 

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Benefits of Compact Closed-Circuit Pumps for Mobile Hydraulic Applications

Doing more with less is a common theme in business and the pump market for medium-duty applications is no exception. With the overall hydraulic system size becoming increasingly smaller and smaller, mobile, medium-duty end-users in industries such as oil & gas, construction, agriculture, transportation and material handling industries are in search of a flexible, high-performance compact pump.

With two hydraulic pump loop options, open circuit or closed circuit, a closed circuit loop saves valuable system space by offering continuous fluid flow without the need for additional parts. In comparison, an open circuit loop typically requires a larger reservoir and as a result, increases the system’s footprint. To fulfill the market’s need for smaller hydraulic components, Parker recently introduced the PC3 Compact Closed Circuit Pump. This article explores three primary benefits of the PC3 pumps:

1. Compact size

On trend with hydraulic mobile systems decreasing in size, each system component has to do more in order to save valuable system space. PC3 is a solution for this market trend with a closed-circuit design, resulting in fewer components than an open circuit hydraulic pump. In addition to the closed-circuit design, it also offers a built-in bypass valve and hot oil shuttle valve eliminating the need for third-party components, conserving valuable system space.

2. System efficiency and streamlined performance

To achieve greater system efficiency and streamlined performance, PC3 includes a variety of features, such as:

- A hydraulic pressure override to ensure that the prime mover is not loaded in excess

- A built-in hot oil valve to increase operational efficiency and reduce system complexity

- Cross port reliefs to prevent system overload by limiting the maximum pressure in your system

 

Each of these features ensure system performance and efficiently deliver the exact power required for each unique application.    

3. Flexibility

Finally, Parker’s PC3 offers the hydraulic pump market flexibility through various product features and sizes to use in a wide variety of applications.

PC3’s modular and interchangeable controls include options for a manual servo, hydraulic proportional and electric proportional controls, providing end-users with further customizations.

In addition, the product line offers ten standard displacements options: 7, 11, 18, 20, 25, 30, 35, 40, 45, 52 and in three different frame sizes to help customer choose the best option for their medium-duty applications ranging from turf care to transportation.

Resources

When designing hydraulic systems for mobile equipment, getting the right pump is crucial.  Resources are available to help ensure the right selection is made—use an online configurator for assistance in selecting the best compact closed-circuit pump for the application. Full system supplier such as Parker can also assist with overall system designs that optimize all of the components to work together. For more information, contact us.

 

Article contributed by Justin Wheeler, product manager, Hydraulic Pump and Power Systems Division
 

 

 

 

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Bain’s projections show that the Internet of Things (IoT) market will grow to $520 billion in 2021. Specific to the construction market, 6.8 million connected heavy construction machines will be shipped between 2018 and 2025. Although no one in the industry has a crystal ball, it is predicted that the future of mobile IoT will be driven by machine learning and 5G networks to power further data collection and analysis, enable autonomous equipment operation and overall innovation in the field.

Technology that can remotely analyze millions of points of data in real time, make decisions and report on the data as necessary will enable machine intelligence to begin moving from the cloud to the machine itself. For instance, a recent case study by Parker’s Mobile IoT team illustrates how an OEM was able to improve their time-to-service, hydraulics-related efficiencies and customer loyalty with the use real time diagnostics and over the air programming. This is by contrast to the current method of telematics systems sending limited data to a server based on thresholds and events. 

    The IoT landscape in construction

The basis of competition is changing for OEMs, and it's important for organizations to monitor the basic assumptions of competition to redefine the space going forward. For the longest time, the industry was based on driving machines through engine power, however, electrification is changing how an OEM manufactures off-road equipment. Electrification, as well as remote monitoring, positively impacts the priorities during the engineering process such as the safety element. Furthermore, off-road machines have been operated by people for decades but with the development of robotics and other autonomous capabilities, those assumptions are changing. Electrification reduces the safety concerns centered around hydraulic and autonomous machines can eliminate the human safety factor during operation. 

Semi-remotely operated or semi-autonomously operated equipment opens up a host of possibilities in terms of machine design. But when you understand how connected machines will be sold or distributed, OEMs are not only looking at selling products but at offering services that can be remotely monitored, controlled or operated. This opens us up to a whole host of things in terms of business models. As part of Parker’s Tech Tuesday video series, Parker’s Business Unit Manager for Mobile IoT discusses the trend of IoT for off-road equipment and how the business model is evolving.

 

The challenges of autonomous machines in off-road industry

Although the push towards autonomous equipment follows in the path of the automotive industry, the challenges for autonomous machines in areas such as construction and agriculture differ from automotive. The environments these machines operate in lack lane lines, signage, sidewalks and other indicators that automotive vision systems rely on to guide cars. The additional “appendages” of booms and buckets must also be taken into account for their operation. In sectors like mining, autonomous equipment is highly attractive. It can take hours to properly ventilate an area after blasting to make it safe for operators to enter. Removing humans from that equation will increase productivity and safety in operation.

It will take time for this technological evolution for the off-road industry to occur, though, due to the uncontrolled environments in which off-road equipment is typically used. More advanced Artificial Intelligence (AI) will be required than what is currently available. The future of mobile IoT lies in building the fully connected environment where all elements of the contractor’s job are seamlessly integrated. 

  Applying artificial intelligence

With AI, users can learn patterns that lead to failures or how to operate the equipment to maximize its useful life, offering trade-offs between performance and longevity.

According to the Association of Equipment Manufacturers (AEM), AI will empower construction teams to handle critical tasks but there are challenges that must be overcome in order to achieve widespread adoption, including fear among workers of AI taking away their jobs, cultural resistance to new technologies and security. These are challenges that OEMs, suppliers and AI partners are already addressing in order to move their industries forward.

Embedded IoT systems rely on cellular communication technology. As 5G networks are being rolled out, it’s clear that they will change the way that data is transmitted via IoT systems. With the coming of 5G, telematics companies have spearheaded the development of Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) communications capabilities. This sophisticated level of machine-to-machine (M2M) communication will be critical to autonomous vehicle operations. It would very difficult to implement to implement autonomous today given so few data points going to the cloud. Data being sent to the cloud today is limited, simply because of the cost to not only send it, but to store it, process it and then drive decisions with it. The promise of 5G is the ability to send a lot more data with less latency, which will enable more real-time operations such as streaming video and the other necessary functions for autonomous mobile equipment.

Transformation of job responsibilities

In the future off-road machine operations will change from being hydraulic driven to more electrical driven, to more software driven. That means that our industry, not only in designing machines but also building, and servicing, and maintaining the machines is going to have to migrate to a having talent that is capable of operating in that software digital space. That's why you see a lot of companies in our space starting to hire more and more software engineers.. The addition of an IoT solution is positively impacting job responsibilities by increasing efficiencies at the same time IT job titles within OEMs are becoming more and more necessary to support IoT, electrification and the development of autonomous operated equipment.

 

Holistic approach to adopting digital technologies

The introduction of digital technologies in the off-road equipment industry is here. Therefore, organizations need to consider the following technology roadmap:

• Hire experienced professionals with IT skills
• Create strategies for effective deployment
• Allocate appropriate budgets
• Generate analytics to gain insights into the various industry trends
• Educate employees and customers about the positive impact

  Stay competitive with smart networking

Digital disruption has already made multiple industries more competitive. Similar situations will be faced by the off-road equipment industry when digital technologies become more broadly leveraged.  Traditional operational and service-related tasks need to be executed faster and more efficiently, and mobile IoT solutions can help.

 

Article contributed by Clint Quanstrom, IoT general manager, Motion Systems Group, Parker Hannifin Corporation.

 

 

 

 

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