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Tuesday, February 24, 2015

One of the hardest things to do in Hydraulics is to get two or more Cylinders to move at the same time and speed.

They say that getting  two or more cylinders to move at time and same speed is one of the hardest things to do in hydraulics.
We had a call from a customer who recently purchased a 12 Volt DC hydraulic power pack from us,  he was in the final stages of completing his motor home. He installed and set up two Hydraulic cylinders to open up a hinged roof but he could not get the roof to move smoothly or evenly as the cylinders would not extended at the same time or speed.
The cylinders were exactly the same size, same bore, same stroke, same rod diameter but had only one supply in and out. Fact No 1 Hydraulic oil under pressure will always take the path of least resistance, If one of the cylinders has more load or one had tighter seals or one had a meter more hose or even one more hydraulic fitting the cylinder circuit with least resistance, least friction or least load or work to do will always move first. Even if the the 2 cylinders are physically connected to a strong a rigid frame one cylinder will always move before the other eventually causing jams or at the least creating twisting forces. As most of the work and Plumbing had been completed we recommended a Flow Divider / Combiner but these items have errors of between 10% and 5% at dividing and combining flows. These errors were considered acceptable by the client.
Last Christmas the Owner of a 12 metre Mustang Cruiser complained to us that the hydraulic cylinders lifting the floor over his boat's engine room were not lifting evenly, after investigation we discovered that the installation had Phasing Cylinders. Phasing Cylinders by design are manufactured to move at the same time and speed, BUT ONLY if they have been correctly set up and installed and only if the hydraulic seals are in perfect condition  This synchronised movement is accomplished in the following way.
As a Double acting cylinder is extended the oil on the rod side of the cylinder is displaced, if you take the displaced oil and send into another smaller bore cylinder with the same stroke designed to take all the oil displaced from the first cylinder you will get them to move at the same time and speed. Take 2 minutes to look at our You Tube Video showing what we found on strip down and how we bench tested and finally got the engine room cover to move smoothly.
Remember the boat's engine room cover has two phasing cylinders.
We lift the floor by extending both cylinders but by sending oil only into the bottom of the first Larger Cylinder.
We lower the floor by retract Both cylinders by sending oil only into the top of the second Smaller Cylinder. Our 2 min video.        .

Cheers Everyone
The Team at MHF-GC
Remember MHF-GC "Done Right Once".