|
cropsey, il 61731 | Open center (Simple) - think of a gear pump - to gears meshing together pushing fluid through. The valves in open center systems allow flow to go through them all the time. When you use a valve it redirects the flow to the outlet. If the flow dead heads, a relief valve will open and allow flow to go through. Usually this makes a high pitch whine noise when the relief is open. Without the relief valve something would break.
Closed center - the pump is a version of the hydro pump on a combine where it controls how much it pumps (on a combine, the hydro lever controls flow and pressure usually determines flow on a closed center tractor pump). The valves in a closed center shut completely off when flow isn't needed and direct flow to the cylinder etc. when you use the valve. The pump senses the drop in pressure (or other factor) and starts pumping more fluid (takes milliseconds). When you shut the valve the pump senses the rise in pressure and shuts down. Closed centers have a relief as well in case of an over pressure situation (something broke or ?).
Older tractor used open center systems because it's simple and cheap. The drawback is fluid is always chasing through the system and that takes power and creates heat. The closed center system is more efficient. Most of the time, planters, etc. don't care which system supplies hydraulic pressure. You can get into situations where you need to reduce the flow to a fan or similar and if it's enough, the pump will see the port as closed and shut down. A lot of times fans use a bypass line to allow a little more flow and to allow the fan to coast to a stop when the hydraulic valve is closed.
| |
|
Open Center/Closed center hydraulics questions
