Hydraulics

Maintaining a normal oil temperature in all hydraulic systems is important for successful system operation. Normal operating temperatures for hydraulic systems is 110 to 130° F (unless specified by the equipment manufacturer). At high temperatures, oxidation of the oil is accelerated. This oxidation shortens the fluid’s useful life by producing acids and sludge, which corrode metal parts. These acids and sludge clog valve orifices and cause rapid deterioration of moving components. The chemical properties of many hydraulic fluids can change dramatically by repeated heating/cooling cycles to extreme temperatures. This change or breakdown of the hydraulic media can be extremely detrimental to hydraulic components, especially pumping equipment.

Overheated hydraulics can be caused by decomposing fluid, wear, or damaged seals and bearings. Coolers can prevent overheating and extend the service life of your hydraulic system. However, smaller hydraulic systems with lower operating temperatures can often be cooled through natural convection. If natural convection is not enough, it becomes necessary to add a cooler.

Coolers are also crucial for systems with temperature requirements such as needing to stabilize the hydraulic fluid’s viscosity by keeping it at a specific temperature, or equipment with a history of hot oil problems that shortened seal life and break down the fluid. Hot fluid is always a concern with large mobile equipment, as well as commercial and industrial processing equipment. Specifying a properly sized cooler saves time, money and maintenance.

The process to select a cooler is driven by the type of system that needs to be cooled. Parameters to consider include heat load, power source, noise, operating costs, space available, environmental conditions, and more.

Actual heat generation varies throughout the machine’s cycles, as well as changing environmental factors and ambient temperatures. This can make it challenging to accurately define your cooling needs. When considering the application and sizing of coolers, the hydraulic fluid’s ideal operating temperature and the time it takes to arrive at that temperature must be used.

For new designs and retrofits, the first step in selecting the right cooler is identifying the challenges and performing the necessary calculations. Virtual design and sizing tools are available from most manufacturers to help determine the best fit for your application. Some companies provide online sizing calculators and other interactive resources that let engineers plug in specifications to get an idea of what is needed. Parker offers a comprehensive suite of online cooler sizing software. For instance, Parker offers an online cooler selector tool for each of the different types of coolers including brazed plate, shell and tube and air-oil coolers.   

To select the best air-oil coolers, you’ll need as much information about the application as possible, including, but not limited to the following:

• Oil Heat Load in BTU/Hr or HP
• Oil Flow Rate (GPM)
• Maximum Inlet Oil Temperature (°F)
• Maximum Ambient Air Temperature During Operation (°F)
• Environmental contaminants that can affect the system
• Maximum Allowable Pressure Drop Across the Cooler (PSI)

If the required heat dissipation is not known, it can be estimated assuming 20-30 percent of the installed horsepower will be converted into heat load. The most accurate way to calculate the heat load is to record the time it takes the oil to get up to temperature without a cooler in the system.

For water-oil coolers, which include Parker’s ST and OAW series coolers, you also need to know the inlet temperature and flow rate of the cooling water. Most manufacturers’ literature includes examples, steps and simplified equations to properly size coolers. For instance, Parker provides engineering specifications for their ST series water-oil coolers, such as cooling capacity, flow rate, working pressure, sizing, and connection thread in their online tools to enhance the specifying process. Once the heat-load parameters and other key influencing factors are defined, the next step is choosing an air-oil (air-cooled) or water-oil (water-cooled) cooler.

Air-oil coolers remove heat from the oil in a cooler by using the ambient air around the cooler. Air-oil coolers convect heat, which makes them ideal when no water source is available or when the preference is to remove heat from the oil by using ambient air. In air-oil coolers, hot oil passes through channels that contain turbulators to prevent laminar flow from developing in an effort to promote heat transfer from the fluid to the channel wall. The channel wall is always constructed of metals with high thermal conductivities.

The cores of air-oil coolers are constructed in two different styles: tube-and-fin or bar-and-plate construction. Tube-and-fin construction consists of round or oval tubes mechanically connected to an array of external fins. The tube-and-fin design is lightweight and offers low pressure drop across the core. The tubes in a tube-and-fin design can be susceptible to damage from pressure spikes and external debris that can be encountered in any application. Bar-and-plate construction uses compact and efficient cores that offer more cooling per cubic-inch than a tube-and-fin design. They consist of finned chambers separated by flat plates which route fluids through alternating hot and cold passages. The bar-and-plate design creates a honeycomb structure that resists vibrations and shocks. This core is usually made of aluminum and is furnace brazed in a controlled atmosphere or high vacuum. With all the bar-and-plate design characteristics that provide certain benefits over the tube-and-fin design, it can be seen that bar-and-plate coolers can offer design engineers greater system design flexibility.

Both types of air-oil coolers typically have a fan driven by a hydraulic or electric motor. Off-road or mobile equipment used in construction, forestry, or material handling typically use either a hydraulic-driven or DC electric-driven fan motors. Industrial equipment such as Hydraulic Power Units (HPU) use AC electric-driven motors to drive the fans. Cooler manufacturers offer a lot of motor configurations, voltages, and displacements to fit various applications. For instance, Parker offers a variety of air-oil coolers with AC, DC, hydraulic fluid, and engine driven fans.  

Cooler manufacturers offer a lot of motor configurations, voltages and displacements to fit various applications. For instance, Parker offers a variety of air-oil coolers with AC, DC, hydraulic fluid and engine driven fans.  Parker’s two most popular air-oil coolers are the ULDC Series (DC fan motor) and the ULAC Series (AC fan motor).

Water-oil coolers remove heat from oil by using a second fluid (typically water). For more than 50 years, shell-and-tube oil coolers have been an industry mainstay when considering water-oil coolers. However, newer designs have been developed that increase efficiency while providing an equivalent heat-transfer surface in a smaller package at a reduced cost.

Shell-and-tube (bare tube) coolers have an outer flanged shell with end bonnets appropriately sealed to each shell end. Inside, a precise pattern of tubing runs the length of the shell and terminates in the endplates. Tube ends are fastened to the endplates, which seal each end of the shell. Cool water flows through the tubes while hot oil flows around the tubes within the shell. The tubes run through several baffle plates that provide structural rigidity and create a maze through which the hot fluid must traverse. This maze created by the baffles lengthens the path the hot oil must flow through. This elongated path increases the amount of heat transfer from the hot fluid to the water by forcing the hot fluid to travel around the tubes for a longer period of time.

As mentioned above, there are shell-and-tube designs in the market now that mechanically add fins to the external surface area of the internal tubes, which increases heat transfer and efficiency. Parker does offer this type of high-efficiency “hybrid” design in the ST Cooler Series. The way the hybrid design works is that the fins add surface area and improve heat transfer, letting the overall size be smaller than standard shell-and-tube exchangers without fins on the tubes (bare-tube). However, due to the increased time the hot fluid has to traverse the interior of the cooler, the pressure drop can be higher than shell-and-tube coolers without the increased flow path created by the baffles.

Another type of water-oil cooler is the brazed-plate style. In this cooler design, heat-transfer surfaces are a series of stainless-steel plates, each stamped with a corrugated pattern for strength, efficiency, and resistance to fouling by creating turbulence in the flow of both fluids. The number and design of the plates varies depending on the desired heat-transfer capacity.

Plates are stacked with thin sheets of copper or nickel between each plate. The plate pack, endplates, and connections are then brazed in a vacuum furnace to join the plates at the edges and all contact points. This design can be used with several different types of inlet and outlet connections.

Brazed-plate coolers are compact, rugged and provide high-heat transfer capacities. They hold approximately one-eighth of the liquid volume of a thermally comparable shell-and-tube cooler. Their stainless-steel construction permits flow velocities up to 20 feet per second. Higher velocities, combined with turbulent flow, provide heat transfer at three to five times the rate of shell-and-tube coolers. A good example of the increased horsepower is Parker’s OAW Series that offers up to 275 horsepower of cooling at an entering temperature difference of 60°F, based on a 2:1 water flow. The higher heat transfer rate requires less heat-transferring surface area for a given capacity.

Due to their compact construction, brazed-plate coolers are ideal when space and size are design requirements. One drawback of using a brazed plate cooler is that there can be higher pressure drops when compared to an equivalent shell-and-tube design. In addition, tests prove brazed-plate designs handle particles up to 1-mm in diameter without issue. Filters or strainers should be used if larger particles will be encountered. Due to their construction, brazed-plate coolers require chemical, rather than mechanical, cleaning.

When properly specifying the right cooler into a hydraulic system, a system will maintain the correct working temperature, which yields numerous economic and environmental benefits, including:

• Extending the hydraulic system’s service life
• Lengthening the oil’s useful life
• Improving operating time and decreasing shutdowns
• Reducing service and repair costs
• Delivering high efficiency for continuous operation
• Resources that simplify the choice

Given the many variables involved when specifying coolers, it is always best to directly contact a cooler supplier such as Parker, with any questions you have. Manufacturers will have additional resources that you can use in the selection process, including specialized sizing software and testing equipment like wind tunnels and cooler design simulation software. Lastly, it is important to take advantage of and rely on your manufacturer’s expertise and available resources to ensure you successfully size and implement the best cooler for your application. To view Parker’s wide range of coolers, visit www.parker.com/ACD.

This article was contributed by Francis C. Gradisher Jr., product marketing manager - KleenVent & Coolers, Parker Hannifin's Accumulator and Cooler Division.

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As mobile machinery makers expand into more global markets, they are presented with the added complexity of creating unique machine configuration for local markets, while still trying to manage the additional costs and complexity resulting from these new machine variations and options. This can be as simple as changing the units from miles per hour (MPH) to kilometers per hour (KPH) and selecting the local language for the text, to complete screen changes to reflect local tastes and requirements, or unique customer interface specifications. These new features can be key to help global machine OEMs capture value in local markets.

One area that can help software teams respond to this demand, is an easy to use programming tool for the display screens. Parker’s PHD display family is designed for use in mobile machinery and offers an easy to use graphical programming tool for faster application development, including:

The WSYWIG environment helps reduce development time by showing the developer how the screens and menus look and feel during the development process, reducing the number of design iterations.

Having no hardware in the loop during screen development not only reduces the complexity of application development, but also reduces the time for each design iteration by significantly reducing the hardware download cycle in each design iteration.

Exporting the screens and menu operation to IoS, Windows or Android devices speed up the design review process by allowing a remote stakeholder to view the screen menus and operation with having any hardware or a development license. 

The included image library and the ability to easily import graphic image files helps reduce development time by allowing screen designers to focus on developing the application instead of creating graphics.

Article contributed by Kirk Lola, product manager, Electronic Controls Division, Parker Hannifin Corporation.

K&B Lumber, a one-stop shop for logging and millwork was in search of a more energy-efficient sawmill that produced higher quality lumber for furniture than a typical sawmill. For most conventional sawmills, the log moves back and forth past the saw and cuts in only one direction. As a result, the operator’s view of the log can be obstructed when it is on the far side of the saw, which can affect lumber quality.

K&B Lumber’s goal was to develop a sawmill that utilized a moving saw, which cuts lumber in both directions and provides the operator visibility to the log while it is being cut. These two features increase the production of high-quality lumber over a traditional sawmill.

K&B Lumber collaborated with Mill Innovations & Design (MID), an original equipment manufacturer of sawmill equipment, to build a sawmill featuring a 6-foot Double Cut HeadRig that was energy efficient and capable of producing furniture grade lumber.

The new HeadRig consisted of a 12” wide band saw with teeth on both edges running on 6’ diameter wheels requiring 250 horsepower (HP). The challenge was finding enough real estate to fit a 25O HP motor on a moving saw.

A second challenge was finding a carriage drive that could accurately control the 30,000 pound saw with a high number of direction changes, 4000+ in an eight hour period. 

Due to the sawmill’s space restrictions with the moving saw carriage, K&B Lumber and Mill Innovations Design chose closed-circuit hydraulics over an electric system to power the equipment.

With a hydraulic system planned, K&B Lumber and MID worked with Parker Hydraulic Pump and Power Systems (HPS) and a Parker distributor to select high-performance hydraulic components to power the sawmill’s saw and carriage drive.

For the saw’s power source, a Parker Gold Cup P14S Pump was selected, driving a Gold Cup M20R Motor stacked with a Parker F12 Series Bent Axis Motor on the back. This powerful combination allowed for additional system displacement.

Using the Gold Cup hydrostat to power the saw, provided the sawmill’s operator the ability to change speeds on the fly, which is critical for cutting different wood species efficiently.

An additional benefit of the saw’s Gold Cup system was a smooth, controlled stop while shutting down the saw voluntarily or in an emergency stop situation.

In terms of the 30,000 pound carriage drive, each direction change means decelerating and accelerating the load in a controlled manner. According to LeRoy Kuhns of K&B Lumber, the Parker F12 Series Motor on the carriage drive has close to a million direction changes and still continues to run flawlessly.

Overall, K&B Lumber has benefited by a smaller, safer sawmill. The new sawmill has also resulted in more efficient energy usage, while producing more output.

In the near future, K&B Lumber plans to enhance their hydraulic system by adding Parker’s Gold Cup - IE (Intelligence Enabled). Gold Cup - IE will monitor their Gold Cup pump to obtain longer service life, and help reduce downtime and service costs with actionable, real-time insights.

Article contributed by Dave Ebert, product manager, Parker's Hydraulic Pump and Power Systems (HPS).

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Power Take-Offs (PTOs) provide truck versatility beyond the usual function of providing transportation for materials. Power is directed from the engine to the auxiliary equipment to perform the work. With many applications for PTOs, there are many different PTO designs being developed - each design for its specific application of use. This creates many categories to assist in your search for the right PTO. Below are some of the main filtering search categories and tools that can be used to ensure the correct PTO is chosen for each application.

The variety of transmissions being used in the market today leads to multiple mounting types available for PTOs. The different mounting types can be designed around clearance concerns and assembly arrangements with the specific transmission application.

Depending on the transmission being the PTO is being applied to, there could be a couple of apertures from which to choose. The aperture is the opening on either side of the transmission which permits installation of a PTO. They can be standard or non-standard depending on the transmission manufacturer.

The number of bolts required to mount the PTO to the transmission is one way to classify the PTO. At Parker Chelsea, we have 6-Bolt, 8-Bolt, and 10-Bolt PTO designs. 

We also have rear mount, Ford, reversable and split shaft PTOs. Each one is a category that can be searched in our products tab (parker.com/Chelsea). For the difference of the split shaft PTOs themselves, it is important to note that they are attached within the vehicle’s drivetrain, behind the transmission, and they require special mounting to the chassis frame.

When looking for the right PTO, you must know the make of your transmission. It is an easy and effective way to narrow down your search results quickly. At Parker Chelsea, we use an application guide that allows you to conduct a search based on the transmission manufacturer. From there, you will find a list of transmissions that will lead to pages that show the available PTOs. In our products tab (parker.com/Chelsea), there is a filter in place to search based on the transmission manufacturer.

Chelsea PTOs can be sorted by shift type by using the category filter in the products tab (parker.com/Chelsea). The options in this filter are constant mesh, hydraulic, lever, pneumatic and wire and cable. Constant mesh applies to applications that always require live power and are engaged as long as the engine is running. All others have the ability to be engaged and disengaged.

For an example of a product series to display how a PTO can be categorized in many ways, let’s use Parker Chelsea’s 280 Series PTO. The 280 Series PTO can be found on Allison and other transmission manufacturers. It is a 10-Bolt, hydraulically-shifted PTO. If you are unsure of the information initially, you can visit the product page to learn more about the PTO series. With this information, you would be able to find the PTO series in a product search based on the mounting type under 10-Bolt. For shift type, it would fall into the hydraulic filter. Both of those search results can be filtered down on parker.com/Chelsea.

The driven equipment being used is an important aspect of your PTO selection. While classifying PTO search categories can help narrow down search results, the driven equipment as well will need to be considered when making your final decision. Some helpful information to find the right final product includes the type of driven equipment, the input horsepower required for the driven equipment and the operating speed of the driven equipment. The quick reference guide online provides what information is helpful to know.

You can find different support materials on the website to help learn more about the PTO options available for your application as well as more in-depth information of the PTOs themselves. The products tab, as mentioned, will have the different product category filters to narrow down your PTO search. On the homepage, you can find a competitor interchange tool. if you know of a competitor’s product, and you want to find the Parker Chelsea equivalent, you can learn more on the product page and find similar PTOs of Parker Chelsea. Other support materials to assist in your search can be found on the homepage as well as the support tab: brochures, catalogs, part lists and more. 

Products tab

Application guide

Competitor interchange tool

Quick reference guide

Support tab

This article was contributed by Michael Mabrouk, marketing leadership associate, Chelsea Products Division, Parker Hannifin Corporation.  

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Properly applied hydraulic cylinders provide outstanding linear-actuation performance in a wide variety of applications. But if applied improperly, a cylinder in short order may not only ruin itself but also the equipment on which it is installed.

There are fundamentally three categories of mounting styles. Both fixed and pivot styles can absorb forces on the cylinder’s centerline and typically include medium- and heavy-duty mounts for accommodating thrust or tension. The third category of fixed styles allows the entire cylinder to be supported by the mounting surface below cylinder centerline, rather than absorbing forces only along the centerline.

There are several available standardized mounts within these categories. Engineers can use this variety of mount offerings for an ever-widening number of application requirements. NFPA Tie rod cylinders, which are used in the majority of industrial systems, typically can be mounted using a variety of standard mating configurations from trunnion-style heads and caps to extended tie rod cap and/or head end styles, flange-style heads, side-lug and side-tapped styles, a range of spherical bearing configurations, and cap fixed clevis designs. Most of these mounting options are available for both single-acting and double rod cylinders.

The goal of every mounting design is to allow the mount to absorb force, stabilizing the system and optimizing performance. For rods loaded primarily in compression (push), cap end mounts are recommended; for those in tension (pull), a head end mount is preferred.

It is the amount of tension or compression that determines piston rod diameter; it is the amount of pull or push that determines the bore diameter. Other relevant factors to consider when selecting a mounting style include:

• Load

• Speed

• Cylinder motion (straight/ fixed or pivot)

Every mounting type comes with its own benefits and limitations. For example, trunnions for pivot-mounted cylinders are incompatible with self-aligning bearings where the small bearing area is positioned at a distance from the trunnions and cylinder heads. Improper use of such a configuration introduces bending forces that can overstress the trunnion pins.

Many performance expectations that at first appear to require atypical mounts can be accommodated by existing styles, sometimes with only slight modifications, facilitating replacement and reducing costs.

One key is to focus on factors that impact cylinder performance. These include the cylinder’s size and force relative to load, the working environment, mounting hardware, and options that prevent wear and improve efficiency. Manufacturers, such as Parker, generally categorize cylinders by the type of action and physical construction. They usually group linear action into these three categories, which directly impacts the mounting options:

• Single acting cylinders provide power only on the extension or "push" stroke.  A separate force, usually an internal spring, returns the piston to its orininal position in preparation for the next stroke.
• Reverse single acting cylinders are similar to single acting, but with the port on the opposite end to provide power only on the retraction or “pull” stroke.
• Double acting cylinders have dual pressure chambers and provide pneumatic power on both extension and retraction, eliminating the need for a spring.

Select the mounting style based on the cylinder’s size, force and function. All these factors are necessary because the wrong mounting or improper installation can side load the rod, which creates excessive wear on the piston, piston rod, rod bearing, and seals. With wear comes leakage, and that is how cylinders fail. 

Regardless of how well a hydraulic cylinder is designed and manufactured, it can fail if not mounted correctly. Proper mounting avoids problems like side loads that cause excessive seal and bearing wear, or even bend the rod or bind the load. 

Contact the Parker’s Cylinder Division or visit www.parker.com/cyl if you have questions regarding which mounting style is right for your application.

Article contributed by Jim Hauser, senior engineer, Parker Hannifin Corporation's Cylinder Divison

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The first hydraulic press may have been invented in the 3rd Century BC, but the fluid power universe has become a little more complicated since then. Today’s hydraulic cylinders, which essentially convert fluid pressure and flow into force and linear movement, are complex devices incorporating a wide range of individual components available in a multitude of dimensions, configurations and materials.

Although pneumatic systems are in some respects simpler, they are generally incapable of achieving the transfer of higher loads and forces. Hydraulic cylinders also have the advantage of smoother, more controllable movement as they are devoid of the spring-like action associated with the release of gaseous fluid media. As an added benefit, hydraulic systems can perform ancillary functions such as lubricating and cooling.

However, since the availability of power and media is a non-negotiable factor in fluid power system design, it should be noted that a properly designed and sized pneumatic system can achieve higher performance where a compact footprint is not required.

Specifying hydraulic cylinders is essentially a balancing act as each design factor influences one or more of the many other design considerations.

Although NFPA standards and ISO-compliant guidelines are a great starting point for hydraulic system design, many industries have guidelines of their own. Working with an engineering manufacturer experienced with all these standards can expedite the design process.

Cylinder manufacturers can offer a range of options capable of achieving the widest scope of performance requirements that increase the likelihood that standard components will meet the design criteria of an application. The major factors to consider when specifying hydraulic cylinders include:

1. Capacity: Medium-duty systems account for most of industrial applications and are typically at 1000 PSI. Standard heavy-duty hydraulic cylinders are capable of handling pressures as high as 3000 PSI, which are typically required for hydraulic presses, automotive applications and other related industrial applications.
2. Stroking distance requirements: Although custom stroke distances above 10 feet (3.05m) are possible. Pressure rating can be a concern. Rod diameter needs to be determined to handle the load.
3. Speed: Standard hydraulic cylinder seals can easily handle speeds up to 3.28 feet (1 meter) per second. The tolerance threshold for standard cushions is roughly two thirds (2/3) of that speed. Frequently, a standard low-friction seal is the better choice for higher speed applications.
4. Temperature: Hydraulic cylinder systems using standard components can be designed to meet application temperatures as hot as 500°F (260°C) and as cold as -65°F (-54°C). Applications requiring temperature extremes at either or both ends of the temperature spectrum require extensive knowledge of the interdependency of individual components to achieve the best balance of short- and long-term performance expectations.
5. Mounting styles: There are three types: a) Fixed mounts that absorb force along the centerline of a cylinder, b) Fixed mounts that do not absorb force along the centerline, and c) Pivot mounts that drive a load in a curved path.
6. Cylinder bore size: Bore size is related to operating pressure. It is the amount of push or pull force required that determines the bore size needed.
7. Piston rod size: OEM design engineers probably request customization of piston rod sizes more frequently than any other hydraulic cylinder component. Remember to always consider that push or pull is never independent of stroke length when determining rod size.
8. Cylinder configurations: For applications requiring equal force pressure on both sides of the piston, a standard double-acting cylinder configuration using pressure to extend and retract the cylinder, combined with a four-way directional control valve to direct pressure to either the head or the end cap, is almost always preferable to more customized solutions.
9. Rod ends/rod threading: Standard threads can be made in inch or metric format, customization is rarely needed or warranted due to delays, expense and the inability to readily mate with accessory components.
10. Cylinder body tube: Standard cylinder bodies are plain steel or chromed plated and will be able to handle a majority of applications. Using alloy steels, stainless steel or brass materials are prevalent in special application like a water type environment.
11. Stop tubing: Stop tubing is generally used to lengthen the distance between the rod bearing and the piston bearing in order to reduce bearing load on push-stroke cylinders when the cylinder is fully extended. Stop tubing is especially critical for horizontally mounted cylinders where it helps to restrict the extended position of the rod.
12. Seals: Experienced hydraulic system manufacturers will offer seals to meet a complete range of temperatures and fluid types and can help guide an engineer’s specification to meet precise application requirements.

Every industrial application is unique, and there are many ancillary components involved in hydraulic cylinder specification. Energy-absorbing cushions, pillow blocks, regenerative circuits, over- or under-sizing ports — all these and more contribute to optimizing the performance of hydraulic systems, depending on each application’s specific performance requirements.

As with the specification of more fundamental components, selecting appropriate ancillary components can present a specification challenge. For example, cushions are intended to retard the force of motion, but OEM engineers sometimes overlook the fact that fluids are typically not moving very fast anyway and may not require such redundancy in certain types of systems. An engineer may be tempted to take a “belt and suspenders” approach to designing push/pull systems by using cushions with spring cylinder systems, overlooking the fact that the oil needs to work its way through the cap, hoses, valves and so on. In such cases, specifying standard single action cylinders with cushions may be wiser than attempting to insert cushions into spring cylinders.

There are certainly applications for which specifying the right cylinder for the right duty require some customization either in component size, material type or configuration. However, far more often than not, partnering with an experienced hydraulic system solution manufacturer early in the design process will save the OEM engineering team time and money while ensuring the system does its assigned duties as efficiently as possible for as long as possible.

Need help determining the right cylinder for your needs? Use Parker’s easy to use cylinder quoting tool - www.quotecylinders.com.

Article contributed by Jim Hauser, senior engineer, Parker Hannifin Corporation's Cylinder Division

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