What kind of hydraulic flow restrictors do I need?

adlertom · Dec 18, 2004

I have a grapple bucket with a double acting hydraulic cylinder that opens and closes the grapple. The grapple operation is a bit too fast and I would like to slow it down somewhat.

I've read about flow restrictors and am wondering if I need one in each of the two hydraulic lines, or if putting one in just one of the lines would be sufficient. Since cylinder inflow on one line causes cylinder outflow on the other, can I accomplish my goal with just one restriction point?

Also, should I use the simple "pinhole" style restrictor(s), or do I need the one way style that only restricts flow in one direction. Of course, if I used the one way style, then I would need one in each of the lines.

Thanks,

Tom

jinman · Dec 18, 2004

( Also, should I use the simple "pinhole" style restrictor(s), or do I need the one way style that only restricts flow in one direction. Of course, if I used the one way style, then I would need one in each of the lines. )

Tom, I think you answered your own question. /forums/images/graemlins/smile.gif If you want the grapple to open and close slowly, then the single orifice type restrictor will be your choice. If you want the grapple to close slowly, but open at full speed, then a single one-way restrictor will do the job.

whoop · Dec 18, 2004

Tom, the proper way to do this is with a valve that has flow control one way and full flow the other way like this valve flow valve .
If you need control both directions you will need two valves. The valves need to be installed not as you would expect. Install it restricting the return side of the cylinder not the pressure side. In other words install the valve with the flow arrow pointing away from the cylinder port.

adlertom · Dec 18, 2004

( The valves need to be installed not as you would expect. Install it restricting the return side of the cylinder not the pressure side. In other words install the valve with the flow arrow pointing away from the cylinder port.
)

Thanks Jinman and Whoop, and welcome Whoop to TBN!

What is the reason for putting the flow restrictor in the return side? Does it have to do with lessening heat buildup?

beenthere · Dec 18, 2004

I'm real curious as to why you recommend installing so the pressure buildup is on both the hoses, and not restricted until the oil returns to the flow control which I understand you to say should be at the end of the loop?????

I have been using these same flow control valves and following the directions I received, that the valve is at the beginning of the 'flow' going to the cylinder. Please explain why you say do it 'the other way', and not as one would expect. I need to get straightened out here. Thanks.

whoop · Dec 18, 2004

Restricing the flow on the pressure side of the cylinder is ideal in applications where a load always offers a positive resistance to flow during a controlled stroke.

Restricing the flow on the return side of the cylinder is ideal for load applications in which a workload tends to pull faster than a pump's delivery would warrant

I was wrong in my thinking, a grapple would be on the pressure side not the return. I used this type of valve on an old international tractor loader, it was installed on the loader down return line, which is correct in that case.

beenthere · Dec 18, 2004

Tom
You will want two flow control valves, as Whoop said. His suggested source (Surplus Center) is the best price I am aware of, and available usually in 1/4, 3/8, 1/2" NPT sizes. I have had very good dealings with this company off and on for several years. They put out a great catalog too, and reasonable prices, IMO.
I tried the flow restrictor route, but it is hard to figure the right size 'hole' or orifice to get. If too small (slow) they can be drilled out if you have a good selection of very small drill bits or know someone who has them. SC has a selection of those too, for under $2 for the 1/4" NPT size, with a 1/32" orifice.

MMM · Dec 18, 2004

There are numerous adjustable flow control valves on ebay for near nothing that you can fine tune. Personally, I prefer to control flow ahead of control valve with adjustable press compensated flow divider.

adlertom · Dec 18, 2004

Thanks for the suggestions guys.

What I still don't understand is why a flow control restrictor in both lines would be superior to having just one in one of the lines.

Since the grapple moves with force in both directions, either line is the "supply" line, depending on whether you are opening or closing the grapple.

For example, as I close the grapple, I'm pushing fluid into the back side of the cylinder with one line, and (a different bunch of) fluid is coming out the front side of the cylinder via the other line. When I open the grapple the opposite occurs.

If I were to restrict the "outflow" side, wouldn't that slow the process down just the same as restricting the "inflow" side? The "outflow" fluid has to be pushed out of the cylinder to make room for the "inflow" fluid, right? So, restricting the outflow would slow down the inflow. Or is this not how these cylinders work?

I want to slow the grapple down in both directions, to keep it from reaching its travel limits with a "bang". I'm feathering the remote valve to avoid this, but I want to build in some slowness so I don't have to be so delicate with the control.