The Forestry Forum

Anyone know much about sizing hydraulic adjustable flow controls?  I see flow controls capable of between 8 and 30 GPM.  My system is 3-4gpm.  Does it matter if I use a flow control rated at 16gpm, or should I choose one closer to my system's flow rate?  I ask because I am unsure if the flow control's adjustable flow is proportional to it's orifice diameter or simply the incoming flow to the valve.  My thinking is that is I use a large flow control, I will have less of an adjustable range, but I'm not sure!  Thoughts?

The rating of the valve is for maximum flow, you can shut the flow completely off. So you won't loose anything (other than a few bucks) using an oversized flow control.

Not sure of your application but a flow control restricts flow in one direction only and a needle valve restricts flow in both directions.

With the bigger one you will probably need to reduce the connection
fittings.

Thanks guys.  I'm controlling the feed speed of my mill.  I understand flow is controlled only in one direction. 

I'm concerned about the fine-tune adjustability of the flow.  Most descriptions of one-way adjustable flow control valves suggest "flow is proportional to orifice diameter", and I would assume the orifice diameter of a given valve increases as the GPM rating increases.  So for example given my fixed flow of 4 gpm, an 8 gpm flow control set at 50% open would pass 4 gpm, and a flow control with 16 gpm set at 25% would pass 4 gpm.  So what I'm thinking is I will have less of a range of adjustability with the 16 gpm (0-25%) vs the 8 gpm (0-50%).  And less adjustability would mean less control over the carriage feed speed.

Am I just babbling or making sense?  I'm no hydraulics expert by any stretch!!

I would use the same size as your valve and hoses. You want needle control for feed and full flow for gig back. I used a 1/2" valve for my feed, or what ever is close for metric. Frank C.

Flow control valves are most accurate at the high end of their range.

Avoid the pressure-compensated type unless you expect to see a wide variation in pressure while you are sawing.