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.

beenthere · Dec 18, 2004

Look at the site suggested and you will see that there is flow restriction in one direction but free-flow in the other. That is why the two.

adlertom · Dec 18, 2004

( Look at the site suggested and you will see that there is flow restriction in one direction but free-flow in the other. That is why the two. )

Yes, I saw that's how THOSE restrictors worked, but a simple pinhole restrictor would restrict flow by the same amount in both directions, wouldn't it?

PineRidge · Dec 18, 2004

We have used both the fixed and the adjustable restrictors. The advantage of the adjustable is that you can make immediate changes anytime that you need the cylinder to go slower or faster. With the fixed version if the cylinder moves too slow then you have to drill out the hole size a bit larger. How far do you go increasing the hole size to get the correct speed of travel on the cylinder is a hit and miss proposition but it can be done. The adjustable flow control is always easiest to use IMHO.

And one simple pinhole restrictor would restrict flow by the same amount in both directions.

JerryG · Dec 18, 2004

Yes, I saw that's how THOSE restrictors worked, but a simple pinhole restrictor would restrict flow by the same amount in both directions, wouldn't it? 
Actually cylinders go faster in one direction that they do in the other. If you use the same size of restrictor on both sides, one side will be slower than the other. If you want to use two restrictors and have the cylinder travel the same speed in both directions, one side must have a larger orifice.

RickB · Dec 19, 2004

In your example, the restrictor on the base end hose is the limiting factor regardless which direction the oil flows through it. The rod end hose restrictor is handling less oil so it is not "maxed out" in extension or retraction; cylinder speed is limited by the base end restrictor. The cylinder will react at the same speed in either direction whether or not the rod end restrictor is used. If only a rod end restrictor of the same size is used, cylinder speed will be faster.

PineRidge · Dec 19, 2004

Actually cylinders go faster in one direction that they do in the other. If you use the same size of restrictor on both sides, one side will be slower than the other. If you want to use two restrictors and have the cylinder travel the same speed in both directions, one side must have a larger orifice.


Jerry are you sure that's the case with all double acting cylinders? Our T&T system uses only one pinhole type restrictor in each cylinder and we would be hard pressed to sell any difference whether the cylinders are extending or retracting in actual speed. I really don't notice a difference although admittedly it may be ever so small.

RickB · Dec 19, 2004

Unrestricted cylinders retract faster than they extend.

Henro · Dec 19, 2004

Jerry are you sure that's the case with all double acting cylinders? 

PineRidge,

I think Jerry is correct in what he is saying.

The reason why a cylinder will move faster in the retract direction than in the extend direction is because there is more volumn on the side that does not have the cylinder rod inside it, taking up space. For a given flow to a double acting cylinder, that cylinder will retract faster than it will extend.

This is the same reason that force is less on retract than on extend. For the same pump flow, you get faster movement as a cylinder retracts, but it pulls with less force than it extends at, given equal pump pressure being applied in both cases, which is generally the case.

What Jerry was saying (what I heard anyway) was that if one would want to set something up to have equal speeds in both directions he would have to use two flow restrictors, each only working in one direction. The would be adjusted so speed would be equal in both directions.

I suppose if you just wanted to have the speed the same in both directions, and did not really care what that speed was, he could get by with a single one-way restrictor on the extend (faster) side of the cylinder.

I'm a little confused by RickB's post above. The loop through a single double acting cylinder sure looks like a series path to me. So I don't see how having a restrictor in one part of the loop would change anything over having it in another part of the loop.

Edit: Gee...I think this is the first time I hit the "post" button by accident! /forums/images/graemlins/blush.gif Guess I will just leave this as is... /forums/images/graemlins/crazy.gif /forums/images/graemlins/tongue.gif

JerryG · Dec 19, 2004

Bill,
That is exactly what I was saying....... /forums/images/graemlins/cool.gif

adlertom · Dec 19, 2004

Guys,

I'm still confused, so maybe I need to rephrase my question.

The grapple currently moves too fast in BOTH directions. There may indeed be a difference between the extension an retraction speeds, but the bottom line is that both speeds are too darn fast /forums/images/graemlins/smile.gif

So, the $64,000 question is: Will installing a SINGLE pinhole style restrictor (i.e. one that restricts flow in both directions) in only ONE of the cylinder hydraulic lines (flip a coin to choose) result in slower cylinder operation in both directions?

Thanks,

Tom