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914Wilhelm
10-24-2011, 01:09 AM
I am going to build a device that uses a hydraulic cylinder that will move about 3/4". I want to feed a constant 2500 # of force at 25liters/minute to the device. The cylinder will be double acting so that when it reaches the end of it's stroke, it will automatically reverse and travel till it reaches the end of the opposite stoke. I want this to keep cycling back and forth till I turn off the feed line. Based on the volume of flow and the diameter of the cylinder I think it will run 30 to sixty strokes a minute. Is anyone familiar with a valve designed to do this or seen a mechanism to cause this type of action on a reliable basis? Thanks for your input.

Wilhelm

darryl
10-24-2011, 01:19 AM
I have not seen one, but I also have a similar application. I wanted to run a small pump (was thinking power steering pump) from an ac motor, then run the apparatus back and forth with the fluid. My concern was with the overlap while the valve was switching. I didn't want the fluid pressure to have a momentary peak everytime the valve switched, and on the other hand I didn't want it to become unloaded momentarily either. Before I shelved the project for the time being, I was thinking that a 'water hammer' reducer might become a part of the system.

macona
10-24-2011, 02:36 AM
The only way to do it is with limit stitches and electric valves.

darryl, what you are looking for is called a hydraulic accumulator.

Black Forest
10-24-2011, 03:34 AM
You don't say what the bore is on the cylinder. Stroke is 3/4" correct? How many cylces do you want to have per minute and for what length of time is it to normally run?

There are cylinders with built in limit switches. Especially for that small of a cylinder. Your electric vlave manifold will have a relief valve to avoid the spiking.

More info please!

Weston Bye
10-24-2011, 05:27 AM
Follow the design of the Westinghouse steam powered air compressor.

http://www.nelsonslocomotive.com/Heisler/Brakes/DesCompressor/DesCompressorI/DesCompressorI.htm

A shuttle valve was directly shifted at the ends of the cylinder strokes.

Boostinjdm
10-24-2011, 06:00 AM
does it have to be hydraulic? Why not a mechanical set up like old steam locomotives. Big wheel, short connecting rod and an electric motor to run it.

Black Forest
10-24-2011, 06:31 AM
Another thing we need to know. Does the speed of extend need to match retract speed?

garagemark
10-24-2011, 06:43 AM
Sixty strokes a minute is really a lot of fluid moving. Could this thing be spring return? If so, just copy and tweak any automotive brake system. If not, well, it does get a bit more complicated.

What kind of force does it need?

Rustybolt
10-24-2011, 09:54 AM
There are proportional hydraulic valves-think Moog Hydrapoint- but they are complicated and hugely expensive.
Like others have said, it is probably cheaper to do it mechanically or with air.

Toolguy
10-24-2011, 10:01 AM
I have a system like that on my surface grinder. There is a lever on the valve that is moved by an adjustable stop on the table. Every time the table goes by, the stop shifts the lever to the other side. It is simply a mechanical means of shifting the valve back and forth.

914Wilhelm
10-24-2011, 10:13 AM
I'm going to be running a 5" or 6" diameter hydraulic cylinder through a repetive 3/4" stroke. At 2500# of fluid pressure this will be about 50000 pounds at the end of the cylinder. This will be to run a small jaw crusher to reduce up to 4" rock to gravel. I suspect I cold use a two position valve and have a lever flop the valve fully to its opposite position when the cylinder reaches full travel limit. Just need to figure out the valve type terminology. I think this must be similar to how hydraulic concrete pumps work.

MaxHeadRoom
10-24-2011, 11:26 AM
There are proximity switches for end of stroke on Hyd cylinders, they are a bit more expensive than the pneumatic variety that can sense anywhere on the stroke due to the cylinder being aluminum.
But if you want end of stroke detection these would work, Baluff are one manuf.
They could operate a simple relay flip flop circuit which would alternate the two solenoid coils on a double acting valve.
Max.

cucvzuz
10-26-2011, 08:45 PM
This can be done hydraulicly, you want a cartridge valve. I believe you want a logic element valve. call www.hydraforce.com or www.sunhydraulics.com they will have what you need. they are relatively low priced.

you will need a relief valve in the system, and a cooler would be nice and quite a bit of oil at least 1 gal for every gpm flow, 2 would be better.

KEJR
10-26-2011, 09:12 PM
There are proximity switches for end of stroke on Hyd cylinders, they are a bit more expensive than the pneumatic variety that can sense anywhere on the stroke due to the cylinder being aluminum.
But if you want end of stroke detection these would work, Baluff are one manuf.
They could operate a simple relay flip flop circuit which would alternate the two solenoid coils on a double acting valve.
Max.

You can do this with a dual solenoid valve that doesn't return to center when power is unapplied. Then you wire your end stroke limit switches such that when it gets to the end of stroke the other solenoid fires and it oscillates. Obviously your switches need to be rated to throw the solenoids or use a relay in between.

If you don't need super precision I'd jsut use two flow controls to control extend and retract speeds.

I've not done this with Hydraulics, but with pneumatics but the concepts should be the same. Obviously these hydraulics are alot more dangerous!

KEJR

Chris S.
10-26-2011, 09:47 PM
Is there any particular reason you're taking this tac instead of traditional rock crushing methods?

914Wilhelm
10-27-2011, 12:23 AM
I'm looking at this approach because I want to build a crusher bucket like: http://www.youtube.com/watch?v=HJgbBl8aqpk&feature=youtube_gdata_player
I could build a traditional jaw crusher using a gas engine to turn a heavy flywheel but the problem is its stationary. I'm trying to decrease material handling cause I'm getting old. By building a crusher bucket I hope to be able to scoop material and at the same time tap into the tractors hydraulics to power it. Why do I want to crush rock? Unfortunately I live on a rock pile. I just built this unit http://www.youtube.com/watch?v=NuDQj7X2XLw&feature=youtube_gdata_player & http://www.youtube.com/watch?v=CkRm3DHYFYw&feature=youtube_gdata_player to extract dirt out of my rocks so we can have soil for the garden, lawn, etc. I am using the big rocks for fill. It's a lot easier to grade soil than riprap. I've made about 100 yards of soil in the past 2 months. Excuse the video goofiness, I hadn't seen my sister for a while and we were havin fun.

becksmachine
10-27-2011, 12:58 AM
One thing to keep in mind here, crushing rocks is going to be a whole different animal than crushing bricks and mortar.

I doubt that the crusher in the video would do anything but scratch the harder granites or basalt.

Dave

Chris S.
10-27-2011, 02:09 PM
One thing to keep in mind here, crushing rocks is going to be a whole different animal than crushing bricks and mortar.

I doubt that the crusher in the video would do anything but scratch the harder granites or basalt.

Dave

You sure hit that nail on the head. 1963 found me in Thailand as a Quarryman with the 809Th Engr Bn near the Cambodian border. One of my duties was running a portable 72 ton per hour rock crusher. It was trailered as two separate sections, the primary and secondary crusher. The primary crusher had a reciprocating, vertically ribbed, jaw. This jaw didn't simply open and close. The motion was more akin to how a human chews. We crushed a sh*t load of granite, so we were constantly building up the ribs with weld bead. A conveyor belt carried the aggregate to the secondary crusher. This unit had horizontally oriented ribbed twin rollers. From there the rock was sifted through screens and the one's that didn't make it through the screen were conveyed back to the rollers again. The secondary separated the rock into "base coarse" for road bed base and finer rock that we trucked to the asphalt plant.

This was one hell of a dirty job and deafening! The rock dust covered the entire area like fresh snow. All of us where required to be proficient with all the equipment in the quarry and we all loved being on the demo team. The 4th of July and new years eve couldn't hold a candle to it! :D

boslab
10-27-2011, 05:19 PM
all the buckets i've seen dont have electronics like limits on the bucket, they wont last very long!, assuming you have a machine piped for hammer around 3 tons you can get a small bucket, the throughput is about 8oo lbs/hr, these run on the hammer cercuit, double acting reciprocating cylynder, assume its an off the shelf unit as only flow and return present, foot on pedal and the loose jaw rocked about 1 1/4 inches, curved ridge jaw similar to a stuativant jaw crusher, took granites ok but lots of flying bits!, the jaws are like^^^^ in profile , ridge to vally so you get a 3 point bite, eats brick and concrete nicely and the loose jaw can wind in to about 3/8" but not recomended for a single pass,
you can also valve it like this
http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Industrial%20Automation%20control/pdf/L-28(SM)%20(IA&C)%20((EE)NPTEL).pdf
mark
[still making my riddle bucket!]