What kind of hydraulic flow restrictors do I need?

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