Open center system, confused...

[Borisw37]

I'm in the process of designing a system that will have a gasoline engine, pump (gear pump), two hydraulic motors and two directional valves (3 position, 4 way valve).
The goal is to be able to run either motor in either direction at the same time, one at a time, both stopped, etc... (any combination).
The only way I could figure this out is to have both valves in parallel and a pressure relief valve after the pump, dumping "unused" fluid back to tank.
Problem is that in this configuration the engine, pump and relief valve are always under max load.

How do open center systems deal with operating multiple devices at the same time (or one at at a time)?

Thank you,

Boris.

P.S. This forum has been great, I'm technically inclined but have very little knowledge of hydraulics. Have been able to gather a lot of useful info from the folks here.

 

[J_J]

Why not just split the pump flow and use a reversing motor valve for each motor. Two independent circuits, with one supply.

Surplus Center - 1/2" NPT 8-16 GPM DIVIDER VALVE

Using open center path, all valves should be in series, except when ;you split the flow, and that is like two circuit.

Should there be two valves in series, the first valve can use all the fluid and leave none for the second valve.

If the first valve is using only half of the pump flow, then both valves will use half of the pump fluid.

The first valve has priority.

 

[glastron23]

boris, just 3 questions.. 1: what are you trying to do??? 2: what HP and pump flow are you going to use?? 3: what is the budget for this project??
open center systems are good, cheap and easy to install and understand how they work.. the valve JJ talks about will work in a small system but not in a high flow/high pressure system.
If the budget can handle it the best system would be a closed type. variable displacement type pump would be great. no need for flow dividers. just use a set of good motor spools. these have several advantages over open systems.. its just the cost of the items Jim

 

[Borisw37]

@Jim,

I'm trying to build a skid-steer type vehicle / motorized wheel barrow. Walk behind, 20-24HP riding mower engine, 2 independent motors that will either drive 2 sets of wheels or tracks, TBD. If wheeled, wheels on each side will be linked together with chain and sprocket.
I also want to have auxiliary hydraulic outputs for future, if for example I want to add a log splitter attachment, etc..

 

[oldnslo]

Another option is to use a double gear pump. One pump for each drive wheel. This allows full pressure to each wheel and would be fairly simple to plumb.

Example of a double pump:Surplus Center - 0.86/0.86 CU IN PRINCE DOUBLE HYD GEAR PUMP

 

[J_J]

This is what some ZTR's use with a 20 to 22 HP engine.

Independent operation each side with reverse.

You may be able to drive the tracks using the hub already installed.

Surplus Center - ZTR LH/RH HYDRO-GEAR ZT-220O EZT TRANSAXLE ASSY

Use two pulleys on the engine one to drove the ZTR's, and one pulleys to drive a gear pump for implements.

 

[Borisw37]

J.J. Thanks for the info. I have seen those ZTR transmissions but I will not be able to "siphon" fluid from the pumps to be used with other attachments, or should I use the ZTR system and add an auxiliary pump just for attachments?

 

[J_J]

A 5 GPM pump and a 5 gal tank should be good enough. If you want to use the engine and pump as a log splitter, you can power a 10 GPM pump with a 24 HP engine.

If you use a two stage pump, you can pump about 28 GPM at low pressure and 7 GPM at 3000 psi.

If you use both pump, the ZTR pumps and the gear pump. You will limit something , be it speed or rpm on say a brush cutter.