Hydraulics At Work

Horses For Courses: When NOT To Use A Hydraulic Solution

One of our readers is contemplating a change from an electro-mechanical drive to hydraulic:

"We are a small manufacturing company that produces honey extracting equipment. And we are looking to make our machinery quieter. We use several linear actuators on our equipment which consist of instant reverse or gear motors and acme threaded rods. They have a lot of bearings that have a habit of making a lot of noise. It is very important to us that our machinery be reliable and fairly easy and inexpensive to maintain.

Our current systems are very reliable but somewhat complex both electrically and mechanically, making them on occasion difficult to maintain. In your opinion, would changing to hydraulics meet these objectives (quieter, reliable and simpler to maintain)?"

Errrr... if I'm honest, nope. Let's consider the noise issue first. I looked at the data sheets for four different makes of linear actuators and none of them published any sound levels. But of course, a linear actuator requires an electric motor - the noise from which depends on its type, size and how many poles it has. In the case of 3-phase, AC motors, the more poles it has (and the slower it spins) the lower the sound pressure level.

For example, typical sound pressure levels for 63 frame-size motors--which are around the size you might expect to find on the linear actuators used on this manufacturer's honey equipment, at 60 Hz are: 56 dB(A) for 2-poles, 48 dB(A) for 4-poles and 47 dB(A) for 6-poles. These figures are slightly lower for a 50 Hz AC supply. What they tell you is, if you are concerned about noise, avoid 2-pole electric motors like the plague! And this applies to both linear actuators and hydraulic power units.

Of course the hydraulic solution also requires a pump, and as you know from your own efforts to avoid industrial deafness, even a small one is noisy, at around 50 to 70 dB(A), depending on its design and operating pressure. Yes, the hydraulic power unit can be mounted a considerable distance from the actuator and/or encapsulated, which means from the operator's perspective, a hydraulic solution could largely eliminate the noise objection.

But so could pneumatics--and without the expense of food-grade oil, and the potential for oil leaks and spills, filter changes, oil sampling, etc. No solution is truly maintenance-free, and a pneumatic system isn't. But of the three: hydraulics, pneumatics and electro-mechanical, the hydraulic solution is probably the most complex from a maintenance perspective. Which brings us to the question of reliability.

The harsh reality is optimal hydraulic system reliability is all too often compromised at the outset through bad or cheap design. Oil quality, tank size, filtration, installed cooling capacity, conductor size and connector type are just a few of the corners that are all too easy to cut on the drawing board.

But even a relatively well designed (from a maintenance and reliability perspective) hydraulic system will suffer from reliability issues if left to its own devices over time. This means optimal reliability requires a certain level of knowledge (and intervention) on the part of the equipment end-user.

Considering all the of above, I would strongly suggest that it's highly unlikely that over time, a hydraulic solution in this application would be seen by bee keepers as: "reliable and fairly easy and inexpensive to maintain".

Bottom line: using hydraulics in applications where its disadvantages outweigh its advantages can be a mistake. And to discover six other costly mistakes you want to be sure to avoid when using hydraulics, get "Six Costly Mistakes Most Hydraulics Users Make... And How You Can Avoid Them!" available for FREE download here.