Hydraulic ram questions

Depending where you hook it to the gate, the ram may not need to be all that long (strong short cylinders may be cheaper than long cylinders). Some counterbalancing would reduce the force needed. A reservior is needed because the piston does not hold the same amount of fluid when in as it does when out.

You should have some sort of safety switch (as on a garage door) so that the gate does not crush someone who got stuck under it as it was closing (think child falling off a bicycle). You would presumably want to close the valve and stop pumping when the gate was all the way up or down, too. This is assuming you want some sort of automatic operation - if it's fully under manual control, and you have the controls locked so that they won't be "played" with, you might be able to assume that the operator will act as the safety system. You might want flow restrictors so the gate does not close too fast. You might want a pin to hold the gate open in case of hydraulic failure (burst hose) or leakage while the gate is open.

Is money an object, or not? Overkill costs money, unless you happen upon a good surplus deal. Math is system pressure times piston area to get the force available (greater force is available for extending than for retracting the ram, as the area of the shaft is subtracted from the piston area on the inward stroke, for a double-acting cylinder - a single acting cylinder has no ability to retract itself, so gravity or another cylinder needs to do that). The force needed depends on the mass and center of gravity of the gate, where the pivot is, and where the ram attaches. Counterweighting can reduce the force needed a great deal. Length of travel is best done with a drawing, rather than by calculation.

Sure. Look at any front-end-loader - 2 sets of 2 rams operating in parallel. Just make sure that the load is evenly distributed.

Why use hydraulics? A cable might be unsafe, as they can break. But, a linear actuator (leadscrew and motor) should be at LEAST as reliable as hydraulics. I guess the idea is that the coming down of the gate can be done with a valve and restrictor. The lin actuator would need power to bring the gate down. Remember, this stuff has to be out in the weather, and that my be real hard on hydraulic systems. Check out Surplus Center in Lincoln, NE for good deals on hydraulics and maybe even linear actuators.

It just seems to me that a motor and a screw has to be more reliable than a motor, pump, cylinder, hoses and a valve, at the minimum.

Jon

Commercially available units I've seen are counterbalanced with springs. Very little effort needed to open and close. A relatively simple electric motor and gear train running off a car battery kept charged with a small solar panel. Lots of ways to do the job with hydraulics though. Some components here

Budget, I'd guess you'd need 250 for a pump, 100 for a ram, perhaps

300 more for valves, hoses, fittings, reservoir, switches etc. Might be able to cut that part a lot if you keep it simple, single acting cylinder perhaps, gravity down.

If you wanted to do something like the commercial units (counterbalanced), a cheap way would be to use a surplus Ajack H-H satellite dish mover, which would give you a very reliable motor/gear train with built in limit switches. About $50 perhaps if you could find one. Can send you a photo if you decide to go that way.

On a slightly related note, here's a link to a way-cool hydraulic project

It's a biiig tilting tower for a wind generator, but it could have been a really fancy vegetable-shooting device. :-)

Wayne

A couple of years ago I built a hydraulic scissor lift that raised a couple of thousang pounds 8 ft up. What I learned from that is that as the angle of the force of the cylinder change due to the movement you can be expending a lot of force that does not result in motion. You can't push something sideways and expect it to go up. You need to be sure that the you get the geometry right so that you're not putting 90% of your force into pulling the gate apart while the other 10% does real work.

I don't think you need to go bidirectional. Gravity will do the work on the way down. You can get a flow control check valve to slow the descent speed.

You will need a tank. There are things called power packs that combine the motor, tank, and pump.

On my system I had a real mechanical engineer calculate the sizes of rams I'd need. He told me two 4" cylinders running at 2500 psi would barely suffice. It turned out a single cylinder peaked at 1100 at the worst part of the cycle. So I'd advise against trying to calculate it. What I would do instead is build the gate and get a cylinder with a pressure guage and try different mounting points to find the best spot. Start with a too big cylinder then you can get a smaller one based on the pressure reading you get. An extra cylinder will only set you back another $100 or so, and you'll find a use for the bigger one.

Two one way rams is easy, with two way rams you need special valves or they can lock up.

All of these applications seem like they may be better served with linear actuators than hydraulics. No pump, no oil, no mess. Just a motor that turns a screw to move a rod in and out.

Check out surplus center for a selection.

On Mon, 12 Apr 2004 18:46:38 GMT, snipped-for-privacy@well.com (Philippe Habib) vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email

I agree with your point, but....

There are not very many hydraulic systems that are not in this "ineffective" state at some stage of their operation cycle, particularly when rotation is involved. You can minimise it, but usually at the cost of size of cylinders, ability to fold right down etc.

You do have to design as much as possible so that when the system is ineffective, the forces are minimal.

**************************************************** I went on a guided tour not long ago.The guide got us lost. He was a non-compass mentor.........sorry ........no I'm not.

On Mon, 12 Apr 2004 11:46:41 -0500, Jon Elson vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email

It may be simpler. And in low load situations (a counterbalanced gate) they are more cost effective AFAICS. But in exposed situations, with all that mechanical movement, I doubt that much can be more reliable than a hydro system. Your car's brakes are hydraulic rams and drivers. As are mosts steering systems.

**************************************************** I went on a guided tour not long ago.The guide got us lost. He was a non-compass mentor.........sorry ........no I'm not.

expensive/practical

At work we use some water hydraulic cylinders with ~300PSI water. You could use tap water and perhaps get 50PSI, this might not require too large of a cylinder if you counterbalance the gate. I recommend sizing the cylinder to provide plenty of force to do the job and overcome friction, but not so much that it tears things up or hurts people if it malfunctions. To actuate both ways, you want a double acting cylinder. How do you want the valve to respond? If released, it can spring to center and stop the motion (closed center) or release pressure to the cylinder and let gravity take effect (open center). Also, what about detents, do you need the valve to latch in open or closed position with lost power or lever released? Perhaps a lever operated valve that will open or close the gate only while the lever is being pushed or pulled? Or the equivalent two solenoid valve that stops the gate when power is removed from the solenoids. Just consider what could happen during a malfunction and don't use any more force than needed to do the job, hopefully not enough to hurt someone if they get hit by a malfunctioning gate.

If the gate will be large and long, lifiting it as you suggest might be quite a project. Why not consider something like an old phone booth door. If you used one on each side of the drive it would take up little room. You could actuate this with either hydraulic cylinders or linear actuators and the power needed would be a whole lot less.

On Mon, 12 Apr 2004 08:25:24 -0700, "SteveB" vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email

One big aspect of coutnerbalancing is that to lower that gate requires no power, and it can be balanced to lower very slowly and relatively safely. It can be set up take as little or as much force to open as you want, balancing safety and the need to keep the gate down.

**************************************************** I went on a guided tour not long ago.The guide got us lost. He was a non-compass mentor.........sorry ........no I'm not.

On Mon, 12 Apr 2004 23:02:44 -0700, "Roger Shoaf" vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email

All you have to do is pucker up to the nozzle and blow hard after brushing....

**************************************************** I went on a guided tour not long ago.The guide got us lost. He was a non-compass mentor.........sorry ........no I'm not.

Is the gate also going to be operated manually amd by remote control ? Al

"Al 2" wrote

Manually.

If you wanted to keep the cost down, a system could be designed to use water and just exhaust into the bushes. By using the household water supply, you eliminate the need for the pump. Cylinders can be made from plastic pipe using O-rings and non corroding parts. Automatic sprinkler system parts could be used to your advantage. Just a thought.

Ron Thompson Was On the Beautiful Mississippi Gulf Coast, Now On the Beautiful Florida Space Coast, right beside the Kennedy Space Center, USA

The ultimate result of shielding men from the effects of folly is to fill the world with fools.

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