Banishing boom bounce with the CMA valve
07 October 2016
Picture a construction site. Concrete needs to be delivered to the formwork, which may be overhead or underground, close to the concrete mixer or on the opposite side of the job site.
Before concrete boom trucks were available, concrete was mixed and then moved, in wheelbarrows or buckets, to the formwork. Capable of pumping high volumes of concrete, with long booms, these trucks allow concrete to be delivered directly where it is needed, greatly improving productivity.
Pushing concrete at any volume, though, is difficult. Concrete is very heavy and difficult, if not impossible to pump evenly. Concrete is pumped through the boom by a pump with two pistons. One piston pushes and advances a chunk of concrete. After a very discrete pause, the other piston pushes and advances the chunk again. Concrete moving in bursts causes oscillation, and by the time the oscillation reaches the end of the boom, it causes the boom to move up and down – or bounce – several meters in each direction.
When the boom is bouncing, the hose located at the end of the boom – which is used to direct the flow of the concrete – swings around freely. This causes two problems. First, there is a safety concern that the hose may whip around and hit someone. Second, if a hose is freely swinging about, so is the concrete being pumped through that hose, making it very difficult to place effectively.
Traditionally, this bounce is managed in two ways. A team of workers on the ground hold several ropes that are attached to the hose at the end of the boom, helping keep the hose from moving too much. To help reduce bounce, concrete is pumped much more slowly – the slower the concrete moves, the less the boom bounces. But, the slower the concrete moves, the less productivity on the job.
The problem is an issue of physics. When the uneven concrete pumping puts shock on the boom structure, which is not completely rigid, it flexes and moves. Another, bigger contributor to the issue is the cylinders which hold the booms out in the extended positions. The oil in the cylinders compresses with the movement, and as the oil compresses more, the boom moves more. While hydraulic solutions cannot fix the flex in the steel beams of the boom, the majority of boom-end oscillation is a result of oil compression, so Eaton's engineers sought a solution.
A smart valve solution
Eaton's CMA Advanced Mobile Valve features independent metering, on-board sensors and on-board electronics that allow implementation of control algorithms not previously possible. The flexibility of the valve enables new ways of solving problems, such as the bouncing concrete boom.
Looking to stabilise the cylinder position – and thus the entire boom structure – Eaton developed a system that includes a CMA mobile valve in place of the traditional mobile valve, as well as pressure sensors, counterbalance valves and an HFX controller, utilising the Pro-FX Technology platform.
The CMA valve, which is CAN-enabled with electronics and sensors, enables Eaton to solve challenging problems by implementing advanced control algorithms directly on the valve. It also offers independent metering, which allows the valve to control the work ports separately. One spool holds the load, while the other spool implements a unique algorithm to stabilise the cylinder – and thus hold the boom in place.
Testing the algorithm
To test the system, Eaton gathered data on what the oscillations looked like and then reproduced the oscillations digitally. Working with simulations of complete machines, engineers tested the algorithms virtually before implementing on a test machine.
The testing then moved to the lab, where two cylinders were set up – one to impose oscillation on the other. Using the CMA valve, counterbalance valve, pressure sensors and HFX controllers, the algorithm was implemented on the second, oscillating cylinder, resulting in a 70 percent reduction in movement of the second cylinder. The system was then installed on a test machine so that the motion of the boom could be observed.
In a customer trial, the boom bounce algorithm reduced cylinder movement by 73 percent, which noticeably reduced the bounce at the end of the boom.
Boom bounce is a challenge that has been dogging hydraulics engineers for years. The control made possible by the CMA valve is previously unseen in the industry and implementation could go far beyond concrete boom trucks. Any application with a long boom, from a telehandler to a fire truck, could benefit from the reduced movement made possible by the CMA valve and the boom bounce algorithm.
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