Hydraulic divider question

rScotty · Mar 1, 2023

etpm said:
I'm confused. I'm told I need a priority flow divider with a relief valve. So part of the flow goes to the steering and the rest goes to the FEL and 3PH. But what's the point of a priority flow divider with a relief valve if the excess flow must go directly to the tank in order for the relief to work? Then how am I supposed to power everything downstream from the priority flow divider and the power steering cylinder?
I guess I was way off in what I thought my pump put out. I have seen priority flow dividers that are 11 GPM max somewhere. I will need to buy one of those. If it will even work. I haven't seen any 8 GPM max ones.
Thanks,
Eric

To answer your question: The pressure relief valve does nothing unless the circuit is overloaded. It shouldn't be involved in the powering of anything downstream unless it is called on to prevent the system from exploding. When the relief valve kicks in, it dumps fluid directly to the tank for as long as it needs to reduce pressure to a safe level. Then the pressure-sensng spring shuts the relief valve off and the system returns to normal operation.

Once you understand your tractor's limts, you might operate the tractor for ten years and never hear the relief valve go off. They squeal.
Interesting aside: I once saw a tractor operating manual that told the operator to heat up the hydraulic fluid in cold weather by deliberately engaging the steering relief valve.

Yes, your description is accurate. that is how a priority flow divider works. It takes a flow of fluid and directs most of it to the priority circuit until that flow rate is satisfied and then directs the remainder to the secondary circuit. Normally steering would have priority and your secondary circuit would be the loader control valve.

Which leads directly to different types of divider valves. Have you thought about the difference between a priority and a proportional divider? Which one does Yanmar use in their OEM equipment?

Check your planned hydraulic scheme to make sure that there are no surprises. For example if you regulate the pressure to the steering to something around 1000 psi, will that also lower your pressure in the FEL?
More sophisticated tractors often use a second hydraulic pump dedicated to steering - partly to overcome that problem.

11 gpm is a common number for valves. Should be close enough.
rScotty

A lifetime of experience has taught me that no matter how much study I put into a design, once I build it I can immediately see how to make it better. For my own projects it is more efficient to build it, try it, and then modify it.