Back to original thread...
My point was to show that we control the out put power different in Open Center systems than Closed Center systems....
and a work port flow control restrictor accordingly will do different things in the two systems
I think we can agree on that we need to DIVERT flow, when we use work port restrictors in Open Center system (constant flow)
Hydraulic power is the product of flow and pressure...
HORSEPOWER = PRESSURE(PSIG) x FLOW(GPM)/1714
metric is so much easier....power (kW)= pressure(MPa) x flow (l/sec)...:laughing:
To vary the TOTAL out put power in a constant flow system, we use the control valve to VARY THE PRESSURE (the center "valve")....as shown on my previous posts...and we might only use part of the TOTAL power for real WORK, the rest will be diverted as heat....both from DIVERTED FLOW and/or DIVERTED PRESSURE (pressure drop). Pump always tend to increase pressure so much that max flow can be maintained.....Demand for pressure is controlled by the control valve (center valve)
To vary the TOTAL out put power in a Closed Center system (constant pressure), we use the control valve (the work port "valve") to VARY THE FLOW. The pump is variable and can internally change the displacement by sensing the max allowed pressure. Pump always tend to increase flow so much that max pressure can be maintained..... Demand for flow is controlled by the work port valve
Adding an additional work port restrictor is accordingly an easy fix in a closed center system (constant pressure), because system will react like a using a normal "throttle" valve....just a restricted demand on flow......
But adding an additional work port restrictor will not work the same way in an Open Center system (constant flow).....we want to reduce speed but use a device (restrictor) that actually will increase pressure. Increased supply pressure usually means increased speed, so we have to divert A LOT of power (flow) to reduce the actuator speed....so the consequences with a work port restrictor in a constant flow system is INCREASED PRESSURE, and INCREASED POWER LOSSES (HEAT).
CONCLUSION is that if we do not allow VARIABLE RPM's (lower rpm's) on an open center system, we will get a lot of power losses.
A lot of equipment today, has hydrostatic drive (wheel travel), this works best on a constant raised rpm....maybe around 1500 rpm or so....and this will then become a conflict when using the open center hydraulic implements, like FEL, back hoe etc....which would do better operated with a variable "prime mover" (engine) EDIT:rpm's....or in other words throttle engine when there is a demand on increased flow...and lower rpm's when (let up gas pedal) when you want to "feather".... and if you do this you will save a lot of fuel, have less overheating problems and operate your implements much smoother....
