In Hydraulics they say that getting two or more cylinders to move at the same time and at the same speed is one of the hardest things to do.
We had a call from a customer who recently purchased a full hydraulic kit including a 12 Volt DC hydraulic power pack with push button pendant control as well as hydraulic cylinders or rams,
do it yourself D.I.Y High-Pressure Hydraulic Hoses and Hose Fittings, he was in the final stages of completing his Hydraulic Motor Home Canopy.
He installed and set up two Hydraulic cylinders to open up a hinged frame for a canvas canopy on the motor home but he could not get the canopy to move smoothly or evenly as the cylinders would not be extended at the same time or speed.
The cylinders were exactly the same size, same bore, same stroke, same rod diameter and had a single in and out supply split with Tee fittings to supply both cylinders.
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 like those on a skip bin track or compactor 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 on the hydraulic motor home canopy had been completed we recommended a Cartridge type Hydraulic Flow Divider / Combiner, these items have errors of between 5% and 15% at dividing and combining hydraulic oil flows. These errors were considered acceptable by the client.
|A Cartridge Flow Divider will divide a single hydraulic flow|
into 2 almost identical flows. It will also works in reverse to combine
2 divided flows into one combined flow.
If more accuracy is required to move hydraulic cylinders in unison then we would recommend a Gear Flow Divider, this type of flow divider uses two or more accurately machined gears to mechanically split or combine flow, an error of 5% or less is achievable all be it at a little more cost compared to a cartridge style flow divider.
The Most accurate way to move two or more cylinders at the same time is with specially manufactured Phasing Cylinders.
Last Christmas the Owner of a 12-metre Mustang Cruiser pleasure boat 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 synchronized 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.
Remember the boat’s engine room cover has two phasing cylinders.
From the team at Mobile Hose Fixers & Hydraulics
Hydraulic Hose Repairs and a whole lot more.