Most economical way to open/close ball valves.

I'm building a prototype that has a 2 ball valve subassembly. It works like a water lock but with cold gas.1 1/2 dia id with about 75 in lbs (6.25 ft lb) to rotate. So we are looking at 90 deg rotation. Also it would be nice to be able to use just one mechanical source to be cheaper, but I'm starting to think that two actuators would be less complicated. Right now I have a gear mounted on the valve stub of each cvalve, and a drive gear with 90 degrees of teeth to do the turning. But now I'm thinking that maybe I've complicated the thing too much. When the drive gear leaves the valve gear, there is some jolt. And that will not be good long run...and may lead to a possible gear mis-timing. How about some linkage on the valve shaft and some kind of linear actuator? If the lengths and sizes are picked out correctly, it would not need any limit switches and could just bottom out on the actuator. What do you think?

 

Do the valves need to operate simultaneously? What's the motive force to drive them, air, electric, hydraulic? How fast and how often?

I've used air cylinders to operate 90° rotation valves, simple to size the length of the arm on the valve shaft to the stroke of the cylinder so you get exactly 90° rotation.

 

In what basis you have chosen 90 degree rotational valves is there any formula for that?

 

The valve (from a catalog) I wanted to use had 90° rotation.

 

Sorry, I wasw out of touch for a week. No air supply, so it has to be electric. They are not sync'ed. They act as a lock. one closes to lock and one opens to dump with a small time delay. The medium is -70c gas. with product.

 

Ball Valve Actuation

I believe there are commercially available worm drive actuators that utilize either a DC or AC motor to rotate with enclosed limits to shut down motor at end of stroke for each direction.

A quick google search came up with this one
http://www.automation4less.com/store/proddetail.asp?prod=S1000F-12ISO-024AC/DC

There are a number of solutions that can be filtered down to just a few with some simple questions:
1. Space available what fits.
2. Operating temperature range does the actuator need to be thermally isolated from the valve.
3. Available power. Is high voltage AC OK? or should it be low voltages dc or ac for human safety?
4. Time to close, and Time to open.

A long lever arm and a ball screw drive might isolate the cold stem from the actuation mechanism.
Some fluids are damaging to the ball seats when high flow is allowed to flow for some time.
I.E as the ball closes or opens the area for fluid flow changes rapidly and near closure the velocity is often much increased. If the fluid erodes seals or edge of ball then the time to close or open becomes a concern so that the damaging condition is at minimum exposure time.
Sometimes the difference between 1 sec and 180 sec to close is a major maintenance head ache. I think most actuators are designed in the 60 to 180 sec range or longer.

Dave

 

The valves are not in the fluid, but in a gas environ...on the inside and -20 C on the outside. The actuators will be room temp. I'm with you on the linear actuators, but 60 seconds sounds like a long time. That would be relative to the linera motion used to operate the valve. I think no more that 4 to 7 inches with little torque will do the trick. I think DC is avail.Why use high voltage AC? Better and less expensive actuators? Enclosed system so no problem with AC, unless you want "HIGH VOLTAGE"
The product is solid, and should clear the valve seat ok.

 

My intent was to get you thinking about pertinent questions the valve actuator must operate within.
I know you mentioned the fluid in this case is a gas and presumably is no erosive in nature to the material in the ball valve. You mentioned the outside of the valve body is -20C but contend the actuator is at room temperature.
Again there is either a heater in the actuator or it is remote from the valve body as far as heat conduction is concerned.

The time to operate the valve is a design spec you decide on then find the actuator capable of meeting that spec.
By discussing the actuation with suppliers in that business you may learn your needs are not easily met or they may offer many choices. Either way you will get a bit more education on how different companies approach the problem and their respective attributes.

The motor wattage goes down with the longer time to move the through the 90 degree stroke which makes the actuator less expensive. If the process your opening and closing fluid flow in has no time dependency and the materials are compatible then a longer time will cut costs.

Note: Those actuators that are designed to be battery powered will have a slower spec because they want to use less wattage. Again a method to learn about actuators by asking questions of a vendor who sells them.

Finally the question of design voltage you want is a matter of choice you spec. High voltage AC such as anything above 40v has safety considerations to take into account in it;s wiring. Below that not so important.

The higher the voltage the smaller the motor for the same wattage related to the current drop for the same winding resistance. More hp per cubic inch of motor.

Typically the motor voltage will inversely impact the costs of both the control and motor for the same reason less copper needed per watt of work done. Increase voltage will drop price provided the wattage is above some minimum say 50 watts which your actuators are probably above.

As always, it is important to understand your task ask questions why to little or too much matters of some parameter. and discuss with people selling similar devices to learn what spec;s are important before designing your own or buying one .

Good luck
Dave

 

Let's get back to generalities here. I'm basically rotating a couple of independant ball valves 90 degrees, back and forth. Forget where the valves are, and what environment they are in. I either rotate the valves with rotational device or use an arm on the valve stem and use linear motion to rotate the arm. The actuators will be at room temp and the drive will enter the valve operating volume. Forget if the valves will work or not, not my problem, for now. My problem is reliability and cost. Trickery can get me to use one actuator or motor to operate both valves, as they are back to back about 5 inches apart. I've alreadyhave the gearset made and operating by hand. It is not foolproof because if the valves back lash or spring back disengagement then I may get gear lock down the road. Right mow it looks like it will work at ambient. Who knows what lurks at operating temp. So right now I'm entertaining using a linear actuator to rotate the drive gear that will rotate the valve stem mounted gears. At about 5-7 inches (depending on the linkage) the job can be done. Actuators have various power requirements and supply various torque. From what I'm hearing is that low voltage is slow and more costly. I already have 120vac and I'm not sure what the other power sources will be available in the electronic area. So, the other consideration is controlling the actuator vs controlling a rotational motor. The actuator may have dead stops at each end or built in sensors etc. that could be utilized. Blah, blah...

So, is it in the general opinion that lineral actuators are most likely the better option cost wise and operational wise? If so, then I will dig in and pick out something once I get all the peripheral information of the other things going on.


Edit: On Ebay, 12 or 24 vdc 6" linear actuator (automotive part I guess) 12 mm per second , built in clutch for override safety. 225lb lift .........................$58.00. Who said these were slow? that is 12.5 seconds for 6". Perfect.

I'm hopeful that we have 12 or 24 vdc available.

 

90 degree rotation that sounds strange. Cause I have never tried at this position. Can you tell me which catalog you have used? For guidance and further proceedings.