Choosing a hydraulic power unit (HPU) depends on the details of each job, especially the number of points on the load and the tolerance for uneven motion in vertical or horizontal planes.
For example, skidding an empty, decommissioned pressure vessel straight across a space to a doorway is a relatively simple move with a low-risk load. In contrast, transferring a precision CNC machine from a loading dock, down the hall, around a corner, then lifting it onto a platform, all while keeping it level, is far more complex.
From ensuring safety and predictable performance on the jobsite to specifying the right HPU for an efficient and cost-effective move, there’s several considerations for each job, and we’ll explore them in this guide.
HPUs Power Skidding and Lifting Systems
A hydraulic power unit consists of a motor, pump, and valves that pressurize hydraulic fluid, carry it to one or more cylinders, and actuate those cylinders to move a load. The primary types are:
- Synchronous. These use multiple, independent oil circuits that maintain equal oil flow to each move point, even if a load is unevenly distributed or encounters resistance. Ports can also be paired to increase flow and, therefore, skidding speed.
- Conventional. These have a single oil circuit, which means pressure is consistent across all lines, but flow rates may differ if the flow is split across more than one port.
Comparing Functionality and Operation
Here’s a closer look at how synchronous and conventional HPUs operate and behave in the real world, and what you can (or cannot) expect from them.
How HPUs Work Together with Hydra-Slide Equipment
Synchronous and conventional power units are central to a complete solution. Both can be used with Hydra-Slide skidding systems, turntables, climbing jacks, and alignment shoes to move loads safely and with precision.
The details of your application determine the most suitable power unit choice, and when the move is simpler, a conventional HPU is often sufficient. Synchronous units may be a better choice for complex moves that involve a variety of equipment or phases, such as hydraulic jacks for lifting followed by skidding.
How to Choose the Right Hydraulic Power Unit for the Job
Which HPU is best for your next job depends on the details and what works best in one scenario may not be suitable in another. Ask these key questions when deciding on a hydraulic power unit:
- What’s the complexity level? This includes things like movement in multiple directions or planes, lifting or lowering the load in addition to skidding, turning corners, dealing with slopes, or an offset center of gravity. Greater complexity often needs synchronous movement.
- How many push/lift points are required? This includes knowing now much load distribution varies among the points and operators’ capacity to manage it manually.
- What tolerances are involved? Tight tolerances apply to keeping loads level, aligning them in their final position, or the dimensions of the physical space you’re working in. Conventional HPUs are often well-suited to less restrictive tolerances.
- Is the load or equipment sensitive to deflection or tilt? This applies to large or small loads and moves of any distance or complexity. Sensitive loads may fare better with a synchronous HPU.
- What is the travel distance? Longer moves and directional changes compound small misalignments, which can be countered with synchronous movement.
- What’s the timeline for the job? To determine the timeline, first consider if the job requires or can tolerate a faster skidding speed. It’s a trade-off because increasing speed requires combining ports with a synchronous HPU, which limits the number of push points available.
- What is your crew’s experience with heavy lift? Are they capable of continuous monitoring and manual adjustments throughout the job? If a manager doesn’t feel confident in the crew’s experience they might opt for the safer, simpler option to keep their crew safe. Heavy reliance on manual processes with sensitive loads adds time to the job and creates more opportunities for mistakes.
- Are there specific safety considerations for the load or site? Both synchronous and conventional HPUs are designed for safe operation on the job site; however, a synchronous unit with its individual circuits offers safety advantages in some cases, like:
- Loads that are awkward or prone to shifting.
- Loads that have an offset center of gravity.
- Fragile or rigid structures and machinery.
- Live, operational plants or facilities and hazardous environments.
- Very long distances or multiple direction/elevation changes.
Real-World Skidding with a Synchronous Hydraulic Unit
Recently, Northwest Crane Service, LLC installed a 119,000 lb (54,000 kg) transformer at a live power station with a Hydra-Slide HT500 heavy track skidding system and synchronous power unit.
Keeping the crew, load, and working environment safe was the top priority. Risk factors included:
- The size and weight of the load
- Limited site access
- A live substation environment
- Energized electrical equipment near the work area and overhead
Northwest Crane Services says collaborating with Hydra-Slide was critical to the job. “The synchronous power unit allowed us to safely synchronize all movements with the [HT500] push/pull cylinders, as well as all movements of our jacks. This system allows us to complete these projects in a 100% safe manner.”
Talk to Our Team About Your Next Move
At Hydra-Slide, we love to learn about skidding and rigging challenges and engineer solutions that prioritize safety, efficiency, and precision. We are passionate about building partnerships and building reliable systems that meet our customers’ needs.
Please contact us to discuss your next heavy skidding project or to learn more about choosing the right hydraulic power unit for your application!
